Oxidation Communications 35, No 2, 245–256 (2012) Autooxidation of fuel in liquid phase
Storage Period Potential of Premium Near Zero Sulphur Gasoline and the Effect of Anhydrous Bioethanol Addition I. Sharafutdinova, R. Dinkova*, D. Stratieva, K. Kirilova, I. Shishkovaa, P. Petkovb, N. Rudnevc Lukoil Neftochim Bourgas JLC, 8104 Bourgas, Bulgaria E-mail:
[email protected] b ‘Prof. Asen Zlatarov’ University, 8104 Bourgas, Bulgaria c Ufa State Petroleum Technical University, Ufa, Russia a
ABSTRACT The storage period potential of near zero sulphur gasoline and its blend with 5% v/v bioethanol is determined as 8 and 7 months, respectively, and is expressed by the rate of natural antioxidants decrease. A special care should be taken about the hydrotreated gasoline fractions as the removing of some heteroatoms containing hydrocarbons worsens the oxidation stability of the fuel. Keywords: chemical stability, natural and synthetic antioxidants, storage period potential. AIMS AND BACKGROUND The modern European unleaded automotive petrol is an additive product, which consists of a base (crude oil derived fractions), components (bioethanol, synthetic, etc.) and synthesised additives1. The base is a blend of mandatory hydrotreated gasoline fractions, corresponding to the stringent environmental regulations. Oxidation stability of gasoline is a very important property related to normal engine operation. This property is a function of base and components quality, and also natural and synthetic antioxidants concentration. Some authors2–6 studying the petroleum part have found that the presence of cyclic alkenes and dienes determines the gasoline as susceptible to oxidation. Other authors7,8 announce that some of the natural antioxidants are removed during hydrotreatment and thus a deterioration of oxidation stability is obtained. There are also investigations on gasoline/ethanol blends chemical stability2,9,10. Most of the researchers, however, describe chemical stability of gasoline with the increase of *
For correspondence.
245
final oxidation products (acids, gums, sludge, etc.) that are formed in an accelerated oxidation test at elevated temperatures or in extended storage11. The storage period potential of Euro IV gasoline is determined in other publications12,13 but a gap in literature exists about the same parameter value of next generation (Euro V) gasoline containing bioethanol. EXPERIMENTAL Materials. For the aim of this study, 4 conventional near zero sulphur (NZS) components, produced in Lukoil Neftochim Bourgas refinery (LNHB) during processing Russian export blend crude oil (REBCO) were considered. Physicochemical properties and gas chromatographic hydrocarbon composition of the LNHB gasoline pool constituents are presented in Table 1. Fluid catalytic cracking hydrotreated gasoline (FCCHTG), reformate, alkylate and hydrotreated straight run naphtha (HTSRN) were blended for the production of the mineral part of the fuel in the following proportion: 50% v/v FCCHTG, 30% v/v reformate, 10% v/v alkylate and 10% v/v HTSRN. Anhydrous ethanol of biological origin, with properties summarised in Table 2, was blended as a renewable component to the conventional gasoline base, described above. The bioethanol, produced according to the requirements of EN 15376, was of high purity (over 99.5% m/m) but as can be seen in Table 2, the concentration was 98.1% m/m due to the presence of denaturing agents (denatonium benzoate and mainly methyl ethyl ketone) with total concentration of 1.43% m/m. For determination of storage period potential (SP) a compound with strong antioxidative property – 2,6-bis(1,1dimethylethyl)-4-methylphenol (BHT) was used. Table 1. Physicochemical properties and GC composition of REBCO-derived gasoline components
Property 1 Density at 15 оС RON MON Sulphur content Distillation IBP 5% (v/v) evaporates at 10% (v/v) evaporates at 20% (v/v) evaporates at 30% (v/v) evaporates at 40% (v/v) evaporates at 50% (v/v) evaporates at 70% (v/v) evaporates at 90% (v/v) evaporates at
Units 2 kg/m3 mg/kg о С
FCCHTG 3 734.9 93.3 81.8 12.20 31.2 46.7 51.1 58 65.7 75.8 89.2 123.1 166.5
Reformate 4 805.2 100 88.9 0.10 31.9 57.6 71.6 96.1 114.9 126.4 135.1 151 172.4
Alkylate 5 702.1 96.3 92.7 1.00 34.5 66.9 79.5 94.7 101.1 104.4 106.4 110.1 121.1
HTSRN 6 672.5 68.8 67.3 0.23 34.9 47.2 48.8 51.1 53.5 56.5 59.7 68.8 82 to be continued
246
Continuation of Table 1
1 95% (v/v) evaporates at FBP GC composition n-Alkanes C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 Total n-alkanes iso-Alkanes C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 Total iso-alkanes Alkenes C4 C5 C6 C7 C8 C9 C10 C11 Total alkenes
2 % m/m
3 180.7 196.9
0.32 1.43 1.17 1.02 0.56 0.35 0.19 0.1 0.07 5.21 0.05 6.49 7.82 4.79 4.04 1.68 1.33 0.18 0.11 26.49 1.52 12.32 6.26 3.65 0.41 0.08 24.24
4 188.3 210.1 0.28 1.97 2.46 1.5 1.24 0.5 0.12 0.02 8.09 1.09 2.93 3.5 4.59 2.39 0.42 0.04 14.96 0.04 0.15 0.02 0.21
5 148.1 183.6
5.83
5.83
9.2 6.04 5.54 64.94 1.29 2.43 4.68 94.12
0.00
6 90.4 103 0.49 12.83 11.68 5.62 1.17 0.82 0.53 0.4 0.11 0.01 33.66 0.05 12.16 14.97 8.95 2.18 1.21 0.63 0.22 0.17 0.03 40.57 0.03 0.01 0.04 0.34 0.05 0.06 0.53 to be continued
247
Continuation of Table 1
1 Cycloalkanes C5 C6 C7 C8 C9 C10 C11 Total cycloalkanes Arenes C6 C7 C8 C9 C10 C11 Total arenes Unknown Total
2
3 0.76 2.13 2.94 0.96 0.72 0.23 7.74 2.37 4.98 8.64 7.48 6.1 0.96 30.53 5.79 100
4 0.21 0.28 0.19 0.09 0.04 0.81 1.69 10.65 24.31 20.1 16.13 1.76 74.64 1.29 100
5
0.00
0.00 0.05 100
6 1.8 9.03 6.6 1.25 1.01 0.21 0.09 19.99 1.11 1.12 0.39 0.42 0.69 3.73 1.52 100
Table 2. Physicochemical properties of the anhydrous ethyl alcohol of biological origin
Property Appearance Density at 15оС Ethanol content Methanol content Water content Sulphur content Involatile material content Acidity (as acetic acid)
Units visual inspection kg/m3 % m/m % m/m % m/m mg/kg mg/100 ml % m/m
Value clear and bright 794.1 98.1 0.01 0.02 5.0 1.0 0.0023
Methods and procedures. The crude derived gasoline, bioethanol and bioethanol/gasoline blends were characterised by analysing their densities as is described in EN ISO 3675. Antiknock properties of conventional gasoline and its bioblends were determined by EN ISO 5164 and EN ISO 5163. The distillation profile was obtained according to EN ISO 3405 and the sulphur content in petroleum fractions and their blends with bioethanol was measured as is described in EN ISO 20846 and the sulphur content in anhydrous ethanol – according to EN 15485. The volatility (Rvp) of the blends was evaluated by the results from EN 13016-1 and oxygen content was measured according to EN 1601. The biocomponent was also characterised via ethanol and methanol content determination according to EN 15721, water content – EN 15489, involatile 248
material content – EN 15691 and acidity – EN 15491. The gas chromatographic quantification of hydrocarbon type content in gasoline components was performed by 5890 series GC equipped with a flame ionisation detector (FID) (Agilent Technologies, Inc., USA). A fused-silica capillary column PONA (50 m length, 199 μm i.d., film thickness 0.5 μm) was used. Hydrogen was used as a carrier gas at a constant flow rate of 1.0 ml/min. Injection volume was 0.2 µl and split ratio 1:100. The other terms of hydrocarbon type determination are described in ASTM D 5134. In order to determine the influence of gasoline composition over its stability EN ISO 7536 was used for evaluating the induction period (IP). The NZS gasoline fractions and bioethanol were used for the production of 4 blends containing 0, 2, 5 and 10% v/v bioethanol. The properties of the 4 blends are given in Table 3. For the ageing study 2 blends were selected – the one with the worst oxidative stability (the lowest IP) and the base gasoline with 0% bioethanol with the aim to evaluate the effect of bioethanol over blends stability. The 2 blends were stored in LNHB laboratory in dark glass containers with free access to atmospheric air for period of 4 months. Table 3. Physicochemical properties of bioethanol/gasoline blends
Property Bioethanol content RON MON Distillation Е70 Е100 Е150 FBP Distillation residue Vapour pressure Oxygen content
Units % v/v % v/v % v/v % v/v o C o C kPa % m/m
Added bioethanol to mineral gasoline base 0 2 5 10 93.6 94.1 95.1 96.4 83.1 83.6 84.2 85.2 24.4 26.3 32.7 41.5 46.4 46.8 48.4 52.4 80.9 81.3 81.9 82.6 205.8 205.8 204.3 203.2 1.1 1.1 1 1.1 52.2 57.1 58.5 58.4 98%, Fluka), tetrabutyl o-titaniate (Ti(OBu)4, 95%, Fluka), tetrabutylammonium hydroxide (TBAOH, 40 wt.% water solution, Aldrich), and isopropyl alcohol (analytical grade, P.O.Ch. Gliwice). The TS-2 catalyst was obtained by the method of Reddy et al.9 XRD pattern of the obtained TS-2 catalyst confirms the crystalline structure of the catalyst (MEL) and is the same as in the literature10–12. Figure 1 shows the XRD pattern of the obtained TS-2 catalyst. The content of titanium determined by XRF expressed for TiO2 was 0.40 wt.%. The IR spectrum of the catalyst shows the adsorption band at 960 cm–1, while its UVvis. spectrum exhibits a band at 220 nm, which confirms the inclusion of titanium into the crystalline structure of silica. No additional bands were observed in UV-vis. spectrum thus extra-framework titanium was not present in the sample of TS-2 catalyst (Fig. 2).
258
5
10
15
20
25
30
35 40 ș GHJUHH
45
50
55
60
65
70
Fig. 1. XRD pattern of the obtained TS-2 catalyst
200
250
300
350
400
(nm)
Fig. 2. UV-vis. spectrum of the obtained TS-2 catalyst
The morphology of TS-2 catalyst was established on the basis of the SEM micrograph showing uniform crystals of about 2 μm long and 0.3 μm wide. Epoxidation procedure and analytical methods. The epoxidation of 1B3O was carried out in a glass reactor equipped with a reflux, dropping funnel and a thermometer. Into the reactor the substrates were introduced in the following order: TS-2 catalyst, 1B3O, methanol, while hydrogen peroxide was dropped in after stabilisation of the reaction temperature. The products of epoxidation process were identified with the help of a GC-MS analyser (Hewlett Packard 6890 equipped with a mass detector, HP 5973 and a capillary column, HP 5MS, 30 m × 250 mm × 0.25 mm). The products were quantitatively analysed by gas chromatography, on a Focus apparatus with a flame-ionisation detector (FID) and a capillary column Quadrex (30 m × 250 μm × 0.25 μm). The unreacted hydrogen peroxide was determined iodometrically13. After performing the mass balance for each of the synthesis, there were determined the main functions characterising the process such as the selectivity of transformation 259
to 1,2EB3O in relation to 1B3O consumed, yield of 1,2EB3O in relation to 1B3O introduced in reactor, the conversion of 1B3O and the selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed. These functions were calculated from the following equations: S1,2EB3O/1B3O =
Y1,2EB3O/1B3O =
C1B3O =
Sorg.comp./H2O2 =
mol of 1,2EB3O obtained mol of 1B3O consumed mol of 1,2EB3O obtained mol of 1B3O taken mol of 1,2EB3O obtained mol of 1B3O taken mol of org. comp. obtained mol of H2O2 consumed
× 100;
× 100;
× 100;
× 100.
RESULTS Epoxidation of 1B3O over titanium-silicalite TS-2 by 30 wt.% hydrogen peroxide in methanol as a solvent leads to 1,2-epoxy-3-butanol as the main product. In this process depending on the conditions also by-products are formed. The main by-products of this process are: 1,2,3-butanetriol, bis(3-methyl-1-propene) ether and 3-(3-methyl1-propene)-3-methyl-1,2-epoxypropane ether. All by-products which can be formed by changing technological parameters are shown in the Scheme. In this work are presented the results of the investigations performed to determine the influence of the technological parameters on the epoxidation of 1B3O. The optimisation of the technological parameters was performed according to rotatableuniform design14–16. An experimental design and the calculations were performed by applying a computer software Cadex:Esdet 2.2. The plan was realised for 5 input variables x1–x5 (technological parameters), where x1 – temperature 10–60oC, x2 – the 1B3O to H2O2 molar ratio 0.5–5.0, x3 – methanol concentration 5–90 wt.%, x4 – TS-2 concentration 0.5–8.0 wt.%, and x5 – reaction time 30–420 min. The total number of the systems of design (experiments) amounted to 32, including 16 in the plan nucleus, 10 in the stars points, with 6 in the plan centre. The real values of input variables x1–x5 were recalculated into the normalised values (dimensionless) according to the following equation: Xk = [2α (xk – xk min. )/(xk max. – xk min. )] – α
for Xk ∈ [–α, α], where Xk – normalised input variable, k = 1,..., i; i – the number of input variables (5); α – star arm (α = 2); xk – real input variable, k = 1,..., i; xk max. – maxi260
mum value of the real input variable, k = 1,..., i; xk min. – minimum value of the real input variable, k = 1,..., i. Scheme Main and side products of the epoxidation of 1-butene-3-ol over titanium-silicalite TS-2 catalyst H2O2 TS-2 –H2O
H 2O 2 CH3OH –H2O CH2=CH-CH-CH3 OH 1-butene-3-ol (1B3O)
H2O
CH2-CH-CH-CH3 O OH 1,2-epoxy-3-butanol
CH2-CH-CH-CH3 OH OH OH
1,2,3 -butanetriol
CH3OH
CH2-CH-CH-CH3
CH3OCH3O OCH3 1,2,3-trimethoxybutane
CH2-CH-CH-CH3 O
–H2O
OCH3
1,2-epoxy-3-methoxybutane H 2O 2 –H2O
CH2=CH-CH-O-CH-CH-CH2 CH3
O
CH3
3-(3-methyl-1-propene)-3-methyl-1,2-epoxypropane ether –H2O
CH2=CH-CH-O-CH-CH=CH2 CH3
CH3
bis(3-methyl-1-propene) ether +H2O2 –H2O
CH3-CH-CH-CH2-O-CH-CH=CH2 OH OH CH3 4-(3-methyl-1-propene)-butane-2,3-diol ether
+H2O2 –H2O
CH2-CH-CH-O-CH-CH-CH2 O
CH3
CH3
O
bis(3-methyl-1,2-epoxypropane) ether +H2O
CH3-CH-CH-CH2O-CH2-CH-CH-CH3 OH OH OH OH bis(2,3-dihydroxybutane) ether
+H2O2
CH2-CH-CH-O-CH-CH-CH3 O
CH3
OH OH
3-(2,3-dihydroxybutane)-3-methyl-1,2-epoxypropane ether
261
An universal experimental design with the values of normalised input variables in the dimensionless range [–2, 2] was achieved as a result of the normalisation operation. The real and normalised input variables at the levels resulting from the experimental design are shown in Table 1. Table 1. Levels of the examined factors
Level
Basic Higher Lower Star higher Star lower
Coded factor Temperature Molar ratio Methanol (oC) 1B3O/H2O2 concentration (wt. %) Xi x1 x2 x3 0 1 –1 2 –2
35 47 22 60 10
2.4 3.9 1.6 5.0 0.5
47 69 26 90 5
TS-2 concentration (wt. %)
Reaction time (min)
x4
x5
4.250 6.125 2.375 8.000 0.500
225.0 322.5 127.5 420.0 30.0
x1, x2, x3, x4, x5 – independent factors.
The response functions characterising the epoxidation process of 1B3O with H2O2 over the TS-2 catalyst were assumed as follows: z1 – selectivity of transformation to 1,2EB3O in relation to 1B3O consumed (S1,2EB3O/1B3O); z2 – yield of 1,2EB3O in relation to 1B3O introduced in reactor (Y1,2EB3O/1B3O); z3 – conversion of 1B3O (C1B3O); z4 – selectivity of transformation to organic compounds in relation to H2O2 consumed (Sorg. comp./H2O2). The design matrix of the experimental design and experimentally determined values of the response functions z1–z4 are shown in Table 2. The influence of normalised independent factors (X1÷X5) of the epoxidation on the values of the response functions, such as selectivities and conversions, was presented as a polynomial of the 2nd order: Z = Z(Xk) = b0 + b1 X1 + ... + bi Xi + b11 X12 + ... + bii Xi2 + b12 X1 X2 + ... + bi–1,i Xi–1 Xi.
for Xk ∈[–2, 2], where bi – normalised coefficient of the approximation function; Nb – the number of polynomial coefficients; Nb = 0.5 (i + 1) (i + 2), i – the number of the input variables Xk ; k =1,2,...,i. In order to obtain the response function containing the real coefficients and the real input variables xk (technological parameters), the normalised input variables Xk were recalculated into the real values using the following relationships: X1 = 0.08(x1 – 10) – 2, X2 = 0.89(x2 – 0.5) – 2, X3 = 0.05(x3 – 5) – 2, X4 = 0.53(x4 – 0.5) – 2, X5 = 0.01(x5– 30) – 2.
262
Table 2. Design matrix and experimental results
No
X1
X2
X3
X4
X5
z1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
–1 1 1 1 1 –1 –1 –1 1 –1 –1 –1 –1 1 1 1 –2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0
–1 –1 –1 –1 1 1 1 1 –1 –1 –1 –1 1 1 1 1 0 0 –2 2 0 0 0 0 0 0 0 0 0 0 0 0
–1 1 –1 –1 –1 1 –1 –1 1 –1 1 1 1 –1 1 1 0 0 0 0 –2 2 0 0 0 0 0 0 0 0 0 0
–1 –1 –1 1 –1 –1 –1 1 1 1 1 –1 1 1 1 –1 0 0 0 0 0 0 –2 2 0 0 0 0 0 0 0 0
–1 –1 1 –1 –1 –1 1 –1 1 1 –1 1 1 1 –1 1 0 0 0 0 0 0 0 0 –2 2 0 0 0 0 0 0
100 83 98 92 100 52 100 31 71 80 67 89 54 34 71 79 79 48 85 29 86 85 100 48 54 54 50 49 49 46 52 49
z2 z3 (mol.%) 60 60 58 70 60 61 50 54 25 25 23 45 25 25 25 81 60 84 56 70 57 85 59 66 25 47 25 74 23 33 22 28 36 45 73 73 79 93 20 68 9 11 31 37 18 18 35 74 35 64 36 68 36 72 36 73 36 73 36 78 34 67 35 72
z4 100 100 100 84 100 100 100 100 100 94 100 100 100 100 100 100 100 100 40 100 27 92 52 100 100 100 100 100 100 100 100 100
The coefficients of the regression function for the normalised input variables (technological parameters) were determined by the least squares method with the application of matrix calculations (Table 3). After the determination of function approximating the experimental results, a verification of an adequacy of this function was performed basing on the Fisher–Snedecor test by a comparison to the critical value of F(α) taken from the tables presented in Ref. 17. The relative errors of the approximation and the correlation coefficient R for the respective functions were calculated. In 263
Table 3 are also given the values of: S2repeat. – variance of inaccuracy; frepeat. – freedom degrees number of variance of inaccuracy; S2adeq. – variance of adequacy; fadeq. – freedom degrees number of variance of adequacy; R – coefficient of multiple correlation; ∆zmax. – the maximum error of approximation. All the calculations were carried out for the significance level α = 0.05. Table 3. Coefficients of the regression equation and results of statistic analysis
Coefficients b00 b01 b02 b03 b04 b05 b11 b12 b13 b14 b15 b22 b23 b24 b25 b33 b34 b35 b44 b45 b55 S2repeat. frepeat. S2adeq. fadeq. R Δzmax.
Z1 48.47 –0.29* –11.29 –2.96 –12.7 0.38* 4.28 2.44 1.81 1.06* –8.56 2.66 3.19 –5.06 1.06* 9.78 7.56 1.94 6.91 –3.31 1.91 3.77 5 91.11 10 0.97 17.02
Z2 34.92 2.79 –16.04 1.88 0.96 0.54 5.33 0.06* 0.32* –0.19* 0.69 4.08 –0.94 1.06 –0.56 –3.3 1.06 –0.06* –1.67 0.69 0.58 0.70 5 85.36 10 0.95 14.66
Z3 71.41 0.25* –10.08 2.5 10.83 0.42* –2.28 –1.63* –0.38* –1.63* 8 3.09 –7 4.75 –1.38* –11.03 –4.25 –1.13* –5.53 2.63 –0.53* 12.30 5 119.7 10 0.95 16.77
Z4 95.95 –0.42 5.92 6.33 3.08 0.42 4.05 0.63 0.63 –0.63 1.38 –3.45 –1.38 1.38 –0.63 –6.08 1.38 –0.63 –1.95 0.63 4.05 0.00 5 528.9 10 0.69 31.97
* Essential coefficient.
The mathematical optimisation of the obtained regression equations has been performed with the application of the methods: Hooke-Jeeves and Gauss-Seidel. Similar values of the maxima were obtained in each of the methods. The highest values of the response functions and corresponding to them values of the technological parameters are summarised in Table 4.
264
Table 4. Parameters determining maximum values of the response functions
Values of the functions Temperature Molar ratio 1B3O/H2O2 Methanol concentration TS-2 concentration Reaction time
Unit (mol.%) (oC) – (wt.%) (wt.%) (min)
Functions S1,2EB3O/1B3O Y1,2EB3O/1B3O C1B3O 100 100 100 16 58 47 0.7 0.6 0.6 38 64 56 7.6 5.8 4.1 208 399 414
Sorg.comp./H2O2 100 59 4.6 58 6.4 412
The technological parameters determining the maximum values of functions: S1,2EB3O/1B3O, Y1,2EB3O/1B3O, C1B3O and Sorg.comp./H2O2 (all reach 100 mol.%) are slightly close to one another. These parameters comprise: temperature 16–59oC, the 1B3O/H2O2 molar ratio 0.6–0.7 (only for the Sorg.comp./H2O2 the molar ratio of reagents amounts to 4.6), methanol concentration 38–58 wt.%, TS-2 concentration 4.1–7.6 wt.% and reaction time 208–414 min. The functions Y1,2EB3O/1B3O, C1B3O and Sorg.comp./H2O2 achieve maximum (100 mol.%) at higher temperatures (47–59oC) than the function S1,2EB3O/1B3O (16oC). The first function achieves maximum at lower methanol concentration (38 wt.%) and at higher TS-2 concentration (7.6 wt%), whereas the other functions achieve 100 mol.% at the highest methanol concentrations (56–64 wt.%) and at the lowest TS-2 catalyst concentrations (4.1–6.4 wt.%). Moreover, the 1st function needs the shortest reaction time (208 min) in comparison to the other 3 functions (399–412 min). In order to determine definitely which values of the parameters are the optimum parameters for the whole epoxidation process, the analysis of each function should be performed. For this purpose the courses of function variations during the changes of 2 technological parameters were plotted, maintaining the other ones constant. The constant parameters determined the maximum of a given function. The most important function in the determination of the optimum process parameters was S1,2EB3O/1B3O. Influence of the technological parameters on the selectivity of transformation to 1,2EB3O in relation to 1B3O consumed. The influence of changes of 2 selected technological parameters of the process on selectivity of transformation to 1,2EB3O in relation to 1B3O consumed (z1), at the optimum values of remaining independent variables (factors) allowed obtaining the maximum of the function, was shown in Figs 3–6. Figure 3 shows that not only for the temperature of 16oC and the molar ratio of 1B3O/H2O2 = 0.7 but also for other values of these technological parameters very high values of the S1,2EB3O/1B3O can be achieved. Practically, in the whole range of the process temperatures (10–60oC) and for the molar ratio of reagents 0.5–0.7 this function achieves values close to 100 mol.%. From a technological point of view, the most beneficial is carrying out the epoxidation process at ambient temperature (20oC), because the reaction mixture does not need cooling as well as heating. However, the most beneficial molar ratio of reagents seems to be the equimolecular molar 265
ratio. Studies with an excess of hydrogen peroxide can cause the formation of soluble complexes of hydrogen peroxide with titanium incorporated in the structure of the catalyst. Consequently, it causes the deactivation of the catalyst18–20. Furthermore, the using of the excess of hydrogen peroxide in relation to organic raw materials causes an increase in an ineffective decomposition of hydrogen peroxide to water and oxygen, which is a disadvantageous phenomenon in the process. Figure 3 also shows that at constant temperature the increase in molar ratio of 1B3O/H2O2 causes the decrease in epoxide selectivity. The decrease in the value of this function is caused by etherification reactions of 1B3O and formation of bis(3-methyl-1-propene) ether. At temperature about 22–33oC and for a molar ratio of 1B3O/H2O2 = 5:1, bis(3-methyl1-propene) ether is the only product. On the other hand, at constant value of the molar ratio of 1B3O/H2O2, e.g. 2.5, the increase in temperature causes, firstly, decrease in the epoxide selectivity from 65 to about 52 mol.% (at temperatures 30–40oC), and further increase to 70 mol.%.
Fig. 3. Influence of temperature and the 1B3O/H2O2 molar ratio on the selectivity of transformation to 1,2EB3O in relation to 1B3O consumed, constant parameters: methanol concentration 38 wt.%, TS-2 concentration 7.6 wt.%, reaction time 208 min
Figure 4 shows that for the temperature of 20oC (and also for the higher temperatures) the most beneficial methanol concentrations amount to 22–64 wt.%. In this range of methanol concentrations the highest selectivity of transformation to epoxide can be achieved. The increase in methanol concentration above 64 wt.% facilitates the etherification of –OH group in 1,2EB3O (1,2-epoxy-3-methoxybutane is formed) and etherification of 1,2,3-butanetriol to 1,2,3-trimethoxybutane. Thus, the concentration of methanol 64 wt.% can be named the border methanol concentration for the epoxidation 1B3O to 1,2EB3O. 266
Fig. 4. Influence of temperature and methanol concentration on the selectivity of transformation to 1,2EB3O in relation to 1B3O consumed, constant parameters: molar ratio 1B3O/H2O2=0.7:1, TS-2 concentration 7.6 wt.%, reaction time 208 min
On the other hand, the methanol concentrations below 22 wt.% are probably too low to produce enough amount of 5-member active compounds in active centres of catalyst (Ti atoms). These active compounds are crucial for the effective course of epoxidation process21: (CH3OH) OSi
SiO Ti CH3
O
O
O H
At lower methanol concentrations (below 22 wt.%) the reaction of etherification of epoxide with 1B3O is intensified and 3-(3-methyl-1-propene)-3-methyl-1,2-epoxypropane ether is formed with selectivity 11 mol.% and also hydration of epoxide takes place and 1,2,3-butanetriol with selectivity above 40 mol.% is formed. Figure 4 also shows that at constant value of the methanol concentration, e.g. 80 wt.%, the increase in temperature causes first increase in the epoxide selectivity from 60 to about 80 mol.% (at temperatures 32–42oC) and next decrease to 60 mol.%. Figure 5 shows that at the temperature of 20oC it is not necessary to work with very high catalyst TS-2 concentrations as it results from the mathematical optimisation (7.6 wt.%). The TS-2 catalyst concentrations in the range of 0.5–3.8 wt.% allow achieving the highest values of the selectivity of transformation to epoxide. The epoxidation of 267
1B3O at highest catalyst concentrations can increase ineffective decomposition of hydrogen peroxide to water and oxygen. Figure 5 shows also that for temperatures above 20oC only catalyst concentrations in the range 0.5–2.2 wt.% are needed.
Fig. 5. Influence of temperature and TS-2 concentration on the selectivity of transformation to 1,2EB3O in relation to 1B3O consumed, constant parameters: molar ratio 1B3O/H2O2=0.7:1, methanol concentration 38 wt.%, reaction time 208 min
At constant value of the temperature (e.g. 40oC) the increase in catalyst concentration, firstly decreases the epoxide selectivity from 95 to about 85 mol.% (at TS-2 concentration 3.5–6.5 wt.%), and next increases to 95 mol.%. Figure 6 shows that already at temperature of 20oC and for the reaction time of 30 min the selectivity of transformation to epoxide achieves 100 mol.%. The prolongation of the reaction time does not change the value of this function. Similar results are obtained for the temperature of 30oC. For the higher temperatures and the reaction time above 200 min, the decrease in the values of the selectivity of transformation to epoxide is visible. It is connected with the secondary reactions, such as etherification, hydration, solvolysis and polymerisation. Figure 6 also shows that at the same reaction time (e.g. 260 min) the selectivity to epoxide, first decreases from 100 to about 85 mol.% (for temperatures 45–50oC), and next increases slightly to 90 mol.%.
268
Fig. 6. Influence of temperature and reaction time on the selectivity of transformation to 1,2EB3O in relation to 1B3O consumed, constant parameters: molar ratio 1B3O/H2O2=0.7:1, methanol concentration 38 wt.%, TS-2 concentration 7.6 wt.%
Influence of the technological parameters on the yield 1,2EB3O in relation to 1B3O introduced in reactor. The dependence of yield of 1,2EB3O in relation to 1B3O introduced in reactor (z2) on the 2 selected technological parameters of the process at the optimum values of the remain independent variables allowed obtaining the maximum of the function, was shown in Figs 7–10. In the case of this function the base of choosing the optimal parameters will be the optimum parameters established after analysing of the layer drawings for selectivity of transformation to 1,2EB3O. Figure 7 shows that high yield of 1,2EB3O (about 80 mol.%) can be achieved not only at the temperature of 58oC and at the molar ratio of reagents amounts to 0.6 but also at the temperature of 20oC and for the equimolecular rate of reagents (optimum 2 parameters for selectivity of transformation to epoxide). Figure 8 shows that at temperature of 20oC and in the range of methanol concentrations 22–64 wt.% also high value of the yield of 1,2EB3O can be obtained (about 80 mol.%). Thus, it is not necessary to use the temperature of 58oC in the process of epoxidation.
269
Fig. 7. Influence of temperature and molar ratio 1B3O/H2O2 on the yield of 1,2EB3O in relation to 1B3O introduced in reactor, constant parameters: methanol concentration 64 wt.%, TS-2 concentration 5.8 wt.%, reaction time 399 min
Fig. 8. Influence of temperature and methanol concentration on the yield of 1,2EB3O in relation to 1B3O introduced in reactor, constant parameters: molar ratio 1B3O/H2O2=0.6:1, TS-2 concentration 58 wt.%, reaction time 399 min
Figure 9 shows that at temperature of 20oC and in the whole range of the TS-2 catalyst concentrations, high yield of 1,2EB3O can be achieved (above 80 mol.%). However, the most beneficial is to work in the range of TS-2 catalyst concentrations 2.5–7.0 wt.%. 270
Fig. 9. Influence of temperature and TS-2 concentration on the yield of 1,2EB3O in relation to 1B3O introduced in reactor, constant parameters: molar ratio 1B3O/H2O2=0.6:1, methanol concentration 64 wt.%, reaction time 399 min
Figure 10 presents that it is beneficial to carry out the epoxidation process at the temperature of 20oC and for the whole range of reaction time, because the yield of 1,2EB3O achieves values above 85 mol.%.
Fig. 10. Influence of temperature and reaction time on the yield of 1,2EB3O in relation to 1B3O introduced in reactor, constant parameters: molar ratio 1B3O/H2O2= 0.6:1, methanol concentration 64 wt.%, TS-2 concentration 5.8 wt.%
271
Influence of the technological parameters on the 1B3O conversion. The influence of changes in the 2 selected technological parameters of the process on the conversion of 1B3O (z3) at the optimum values of remaining independent variables allowed obtaining the maximum of the function and is shown in Figs 11–13. Similarly, as previously, also in the case of this function the base of choosing the optimal parameters will be the optimum parameters established after analysing of the layer drawings for selectivity of transformation to 1,2EB3O. Figure 11 shows that at the temperature of 20oC and for the equimolecular molar ratio of reagents is possible to achieve the conversion of 1B3O about 80 mol.%. The increase in temperature to 30oC increases the 1B3O conversion to 90 mol.%, and for the temperatures above 35oC there is possible to obtain the maximum conversion of this organic raw material. But taking into account the parameters established for the function of selectivity of transformation to 1,2EB3O as optimum, the temperature of 20oC should be taken as optimum for the conversion of 1B3O.
Fig. 11. Influence of temperature and 1B3O/H2O2 molar ratio on the 1B3O conversion, constant parameters: methanol concentration 56 wt.%, TS-2 concentration 4.1 wt. %, reaction time 414 min
Figure 12 presents that at the temperature of 20oC and for the methanol concentrations in the range of 50–70 wt.% the highest values of the 1B3O conversion can be achieved. For the methanol concentrations below 50 wt.%, conversion of 1B3O amounts, respectively, to: 75 mol.% (methanol concentration 40 wt.%), 60 mol.% (methanol concentration 30 wt.%), 40 mol.% (methanol concentration 20 wt.%) and 15 mol.% (methanol concentration 10 wt.%).
272
Fig. 12. Influence of temperature and methanol concentration on the 1B3O conversion, constant parameters: molar ratio 1B3O/H2O2=0.6:1, TS-2 concentration 4.1 wt.%, reaction time 414 min
Figure 13 shows that at the temperature of 20oC and for the TS-2 catalyst concentrations in the range of 3.5–6.2 wt.%, the conversion of 1B3O achieves the value of 85 mol.%.
Fig. 13. Influence of temperature and TS-2 concentration on the 1B3O conversion, constant parameters: molar ratio 1B3O/H2O2=0.6:1, methanol concentration 56 wt.%, reaction time 414 min
273
The dependence temperature–reaction time shows that at studied conditions and practical for the whole range of temperatures and reaction time, the conversion of 1B3O achieves high values (about 90 mol.%). Influence of the technological parameters on the selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed. Also for the selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed the base of choosing the optimum parameters will be the optimum parameters, established after analysing of the layer drawings for selectivity of transformation to 1,2EB3O. Figure 14 shows that almost in the whole range of the investigated temperatures and molar ratio of reagents the highest selectivity transformation to organic compounds can be achieved. The layer drawings for dependences: temperature–methanol concentration, temperature–TS-2 concentration and temperature–reaction time, looks similarly as the dependency mentioned above.
Fig. 14. Influence of temperature and molar ratio 1B3O/H2O2 on the selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed, constant parameters: methanol concentration 58 wt.%, TS-2 concentration 6.4 wt.%, reaction time 412 min
CONCLUSIONS The comparison of the optimum parameters established for the selectivity of transformation to 1,2EB3O in relation to 1B3O consumed with the results for the following functions: yield of 1,2EB3O, conversion of 1B3O and selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed, shows that shared parameters for these 4 functions can be found. Thus, as the most beneficial technologi274
cal parameters for the whole 1B3O epoxidation process can be taken: temperature 20oC, molar ratio of 1B3O/H2O2 = 1:1, methanol concentration 50–64 wt.%, TS-2 catalyst concentration 3.5–3.8 wt.% and reaction time 30–420 min. The comparison between the results presented in this article with the results achieved earlier22 (by the method of one-variable) points very high similarity in the established, the most beneficial technological parameters (temperature 20oC, molar ratio of 1B3O/H2O2 = 1:1, methanol concentration 80 wt.%, TS-2 catalyst concentration 5 wt.% and reaction time 300 min). But the mathematical method of establishing the optimum parameters seems to be a better method, because it allows taking into account at the same time a few functions describing the process. It allows selecting such optimum parameters of the function in order to achieve simultaneously, if it is possible, high values of all functions describing the process. It shortens the time of studies and reduces the cost of syntheses (mainly the cost of raw materials and energy). On the other hand, not for all processes so high compliance can be achieved. We also compared the optimum parameters presented in this work with our previous studies, made by the method of one-variable, for the process of 1B3O epoxidation over TS-2 catalyst, but at the autogenic pressure in autoclave23. The most beneficial parameters for this process are as follows: temperature 20oC, molar ratio of 1B3O/ H2O2 = 1:1, methanol concentration 80 wt.%, TS-2 catalyst concentration 5 wt.% and reaction time 120 min. The comparison shows that these most beneficial parameters are very close to established by the method of one-variable and by mathematical method process design, but for the process epoxidation at the atmospheric pressure. For this pressure process of epoxidation the considerable reduction in the reaction time can be only observed. But taking into account the cost of pressure equipment the method at the atmospheric pressure seems to be the most beneficial. REFERENCES 1. S. T. OYAMA : Mechanisms in Homogenous and Heterogenous Epoxidation Catalysis. Elsevier, Amsterdam, 2008. 2. P. TUNDO, A. PEROSA, F. ZECCHINI: Methods and Reagents for Green Chemistry. John Wiley&Sons, Hoboken, New Jersey, 2007. 3. R. XU, W. PANG, J. YU, Q. HUO, J. CHEN: Chemistry of Zeolites and Related Porous Materials. John Wiley&Sons, Singapore, 2007. 4. A. de LUCAS, L. RODRIGUEZ, P. SANCHEZ: Synthesis of TS-2 in the System SiO2–TiO2–H2O2– TBAOH. Influence of the Synthesis Variables. Appl. Catal. A: General, 180, 375 (1999). 5. G. T. KOKOTAILO, P. CHU, S. L. LAWTON, W. M. MEIER: Structure of Synthetic Zeolite ZSM-5. Nature, 275, 119 (1978). 6. M. VALLURI, R. M. HINDUPUR, P. BIJOY, G. LABADIE, M. A. AVERY: Total Synthesis of Epothilone B. Org. Lett., 3 (23), 3607 (2001). 7. R. M. HINDUPUR, B. PANICKER, M. VALLURI, M. A. AVERY: Total Synthesis of Epothilone A. Tetrahed. Lett., 42, 7341 (2001). 8. J. WAJZBERG, A. WROBLEWSKA: The New Method of 1,2-epoxy-3-butanol Production over Titanium Silicalite Catalysts. Pol. J. Chem. Technol., 2 (9), 49 (2007).
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9. J. S. REDDY, R. KUMAR, P. RATNASAMY: Titanium Silicalite-2: Synthesis, Characterization and Catalytic Properties. Appl. Catal., 58, L1 (1990). 10. A. TUEL, Y. B. TAARIT: Synthesis of Titanium Silicalite-1 Using Hexapropyl-1,6-hexanediammonium Ions as Templating Agent. Zeolites, 14, 272 (1994). 11. A. V. RAMASWAMY, S. SIVASANKER, P. RATNASAMY: Selective Oxidation Reactions over Metallosilicate Molecular Sieves: A Comparison of Titanium and Vanadium Silicates with MEL Structure. Micropor. Mat., 2, 451 (1994). 12. M. A. UGUINA, D. P. SERRANO, G. OVEJERO, R. van GRIEKEN, M. CAMACHO: TS-2 Synthesis from Wetness-impregnated SiO2-TiO2 Xerogels. Zeolites, 18, 368 (1997). 13. W. F. BRILL: The Origin of Epoxides in the Liquid Phase Oxidation of Olefins with Molecular Oxygen. J. Am. Chem. Soc., 85, 141 (1963). 14. D. C. MONTGOMERY: Design and Analysis of Experiments. Wiley, New York, 1976. 15. S. L. ACHNAZAROVA, V. V. KAFAROV: Optimization of Experiments in Chemistry and Chemical Technology. Scientific-Technical Publishers, Warsaw, 1982. 16. Z. POLANSKI: Experiments Planning in Technique. Scientific-Technical Publishers, Warsaw, 1984 (in Polish). 17. R. ZIELINSKI: Statistical Tables. Scientific Publishers, Warsaw, 1992 (in Polish). 18. L. J. DAVIES, P. McMORN, D. BETHELL, P. C. BULMAN PAGE, F. KING, F. E. HANCOCK, G. J. HUTCHINGS: By-product Formation Causes Leaching of Ti from the Redox Molecular Sieve TS-1. Chem. Commun., 1807 (2000). 19. L. J. DAVIES, P. McMORN, D, BETHELL, P. C. BULMAN PAGE, F. KING, F. E. HANCOCK, G. J. HUTCHINGS: Effect of Preparation Method on Leaching Ti from the Redox Molecular Sieve TS-1. Phys. Chem. Chem. Phys., 3, 632 (2001). 20. L. J. DAVIES, P. McMORN, D. BETHELL, P. C. BULMAN PAGE, F. KING, F. E. HANCOCK, G. J. HUTCHINGS: Epoxidation of Crotyl Alcohol Using Ti-containing Heterogeneous Catalysts: Comments on the Loss of Ti By Leaching. J. Catal., 198, 319 (2001). 21. W. ADAM, A. CORMA, T. I. REDDY, M. RENZ: Diastereoselective Catalytic Epoxidation of Chiral Allylic Alcohols by the TS-1 and Ti-β-zeolites: Evidence for a Hydrogen-bonded, Peroxy-type Loaded Complex as Oxidizing Species. J. Org. Chem., 62, 3631 (1997). 22. A. WROBLEWSKA, J. WAJZBERG, A. FAJDEK, E. MILCHERT: Influence of Technological Parameters on the Epoxidation of 1-butene-3-ol over Titanium Silicalite TS-2 Catalyst. J. Chem. Technol. Biotechnol., 84, 1344 (2009). 23. A. WROBLEWSKA, J. WAJZBERG, E. MILCHERT: Epoxidation of 1-butene-3-ol with Hydrogen Peroxide under Autogenic and Atmospheric Pressure. J. Adv. Oxid. Technol., 10 (2), 316 (2007). Received 10 September 2011 Revised 17 October 2011
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Oxidation Communications 35, No 2, 277–292 (2012) Epoxidation of organic alcohols
Epoxidation of Methallyl Alcohol to 2-Methylglycidol over Ti-MWW Catalyst under Atmospheric Pressure A. Fajdeka, A. Wroblewskaa*, E. Milcherta, J. Ziebrob Institute of Organic Chemical Technology, West Pomeranian University of Technology, Szczecin, 10 Pulaskiego Street, Pl 70-322 Szczecin, Poland E-mail:
[email protected] b Institute of Inorganic Chemical Technology, West Pomeranian University of Technology, Szczecin,10 PulaskiegoStreet, Pl 70-322 Szczecin, Poland a
ABSTRACT The influence of the technological parameters on the course of the epoxidation of methallyl alcohol (MAA) with 30 wt.% hydrogen peroxide over titanium silicalite catalyst Ti-MWW has been investigated. Experiments were performed under atmospheric pressure, and in the presence of methanol as a solvent. The effect of the parameters such as: temperature (20–60°C), molar ratio of methallyl alcohol to hydrogen peroxide (1:1–5:1), methanol content (5–90 wt.%), catalyst content (0–5.0 wt.%) in reaction mixture, reaction time (5–300 min) and intensity of stirring (0–500 rpm) was determined. The course of the process was described by the following functions: the selectivity of transformation to 2-methylglycidol (2MG) in relation to methallyl alcohol consumed, conversion of methallyl alcohol and selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed. Keywords: 2-methylglycidol, epoxidation, Ti-MWW, hydrogen peroxide. AIMS AND BACKGROUND The successes of the liquid-phase oxidation catalyst TS-1 have encouraged the researchers to synthesise other titanium silicalites with different zeolite structures. A novel zeolite with MWW topology, having an unique and unusual crystalline structure, is expected to serve as such a candidate for preparing Ti-containing catalysts that are both highly stable and accessible1. The MWW structure is constructed from a lamellar precursor undergoing dehydroxylation upon calcinations between the layered sheets. Besides 2-dimensional sinusoidal channels of 10-member rings (MR) run*
For correspondence.
277
ning throughout the structure parallel to the ab-plane, the MWW structure contains an independent channel system which is comprised of large supercages 0.7 × 0.7 × 1.8 nm. The supercages turn to be pocket or cup moieties 0.7 × 0.7 nm at the crystal exterior. This may provide potential opportunities for a wide variety of applications in petrochemical and fine chemicals manufacture2. For the catalytic epoxidation of olefins, organic peroxides and hydrogen peroxide are being used as single oxygen donors. Although organic peroxides are generally much more active as oxidants than hydrogen peroxide, they are more expensive and the active oxygen content is rather low. Hydrogen peroxide, with respect to active oxygen content (47%) and the nature of by-products (only water), seems to be the oxidant of choice in catalytic liquid-phase epoxidations. However, the inherent coproduction of water poses some serious difficulties. Most transition metal catalysts are very sensitive to water, which causes them to leach their active metal. In case the catalyst is stable, water has a serious retarding effect on the epoxidation reaction, making the search for new environmentally friendly, effective epoxidation catalysts a challenging one3. 2-Methylglycidol finds various applications, especially in the synthesis of biologically active compounds, exhibiting antitumor and anti-HIV-1 activities4,5. Moreover, 2-methylglycidol finds applications in the synthesis of active compounds, such as aziridines, oxazolines and oxazolidines, which are intermediate for the preparation of α-methyl-α-amino-acids applied for synthesis of enzyme inhibitors, drugs and cosmetics6,7. 2-Methylglycidol is also used in the preparation of various natural products and their analogues (Vitamin D3, several choline and acetylcholine analogues)8. 2-Methylglycidol has also importance in the synthesis of a novel immunomodulator ((+)-conagenin), which fulfills an important role in therapy of diseases, such as cancer9. The structure of 2-methylglycidol is present in AK-toxins which are host-specific toxins produced by Alternaria altenata Japanese pear pathotype; this discovery led to the production of synthetic AK-toxins. The structure of 2-methylglycidol was also found in azinomycins-antitumor antibiotics10. Moreover, 2-methylglycidol is used for the synthesis of (1S)-(–)-frontalin which is sex attractant discharged by insects (beetles and woodworms) and adult male Asian elephants. 2-Methylglycidol has also importance in the production of polymers, which are used for the manufacture of quick drying varnishes, drawing inks, printer adhesives and another adhesive materials, and the other group of 2-methylglycidol applications includes the surface active agents which are applied in the production of shampoo, detergents for washing, toothpaste and cosmetics11. The aim of this work was to determine the best parameters of the epoxidation of methallyl alcohol to corresponding epoxide over Ti-MWW catalyst. The main functions describing the process were: selectivity of transformation to 2-methylglycidol in relation to methallyl alcohol consumed, conversion of methallyl alcohol, and selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed. 278
EXPERIMENTAL Preparation of Ti-MWW catalyst and its characteristics. The Ti-MWW catalyst was prepared according to the method described by Wu et al.12 The detailed characteristics of the catalyst are presented in our previous work13. Determination of the specific surface area by the BET method was carried out on an ASAP 2010 Micrometrics apparatus, with nitrogen adsorption. Before starting the BET measurements the samples were degassed at 150°C for 24 h under reduced pressure. The adsorption expressed as cm3 of nitrogen per g of the Ti-MWW catalyst (standard temperature 298.15 K, pressure 101.3 kPa) as a function of relative pressure is presented in Fig. 1. It can be seen from this figure that the catalyst after crystallisation adsorbs only on the external surface of crystallites. After the calcinations and template removal, the adsorption proceeds on the internal space of crystallites. From the course of adsorption and desorption curves results that the crystallites mainly have a microporous character, but the mesopores are also present. This is confirmed by a hysteresis loop which is visible in Fig. 1b. The measurements of the specific surface area by the BET method also confirm the morphology of crystallites (Table 1). The surface area after the calcination is almost 2 orders of magnitude higher than before calcination. The area of micropores calculated by the t-plot method for sample before the calcination gives the negative result, whereas after the calcination this area amounts 200, what constitutes 77.6% of the entire surface area. Hence, the catalyst after the calcination has appropriately developed surface area and can be used in the epoxidation process.
Fig. 1. The Ti-MWW catalyst adsorption and desorption isotherm: after the crystallisation (a) and after bathing with 2M HNO3 and calcinations (b)
279
Table 1. Characteristic values of Ti-MWW catalyst (after crystallisation and after washing with 2M HNO3 and calcination)
Ti-MWW catalyst
After crystallisation After washing with 2M HNO3 and calcination
BET SSA Langmuir SSA t-plot micro- Average pore (m2/g) (m2/g) pore SSA diameter BJH (nm) (m2/g) 2.98 4.32 – 5.57 257.83 341.74 200.15 2.59
BET SSA – specific surface area BET method; t-plot micropore SSA – specific surface area of micropore t-plot method.
Reactants used in the epoxidation of methallyl alcohol. In the process of the epoxidation of methallyl alcohol the following reactants were used: methallyl alcohol – MAA (98%, Fluka), Ti-MWW titanium silicalite catalyst (prepared in the Institute of Organic Chemical Technology, West Pomeranian University of Technology, Szczecin), hydrogen peroxide (30 wt.% water solution, analytically pure POCh Gliwice) and methanol (analytically pure, POCh Gliwice). Epoxidation of methallyl alcohol. The epoxidation was performed under atmospheric pressure in a glass reactor with reflux condenser, thermometer and mechanic stirrer. The determined amounts of reactants were introduced into the reactor in the following sequence: Ti-MWW catalyst, methallyl alcohol, methanol (solvent) and 30 wt.% hydrogen peroxide. The process was carried out for a specified period of time. After the process was completed, a post-reaction mixture was weighed and analysed. Determination of the composition of post-reaction mixtures. In order to make mass balances of the syntheses performed, the following analyses were made: unreacted hydrogen peroxide was iodometrically determined14, the products and the unreacted methallyl alcohol were determined by gas chromatography. The chromatographic analyses were performed on a FOCUS apparatus equipped with a flame-ionisation detector (FID), using a capillary column Quadrex 30 m×250 μm×0.25 μm packed with methylsiloxane modified with phenyl groups. The parameters of chromatographic separation were as follows: helium pressure 50 kPa, sensitivity 10, temperature of the sample chamber 150˚C, detector temperature 250˚C. The thermostat temperature was programmed in the following way: isothermally 50˚C for 3 min, followed by an increase at the rate 10˚C/min to 250˚C, isothermally 250˚C for 5 min, cooling to 60˚C. After calculation of the mass balance for each synthesis, the main functions describing the process were determined, i.e. the selectivity of transformation to 2-methylglycidol in relation to methallyl alcohol consumed, the conversion of methallyl alcohol, the selectivity of transformation to organic compounds in relation
280
to hydrogen peroxide consumed. These functions were calculated according to the following formula: – the selectivity of transformation to 2-methylglycidol (2MG), in relation to methallyl alcohol (MAA) consumed (S2MG/MAA): S2MG/MAA =
amount of 2MG obtained (mol) amount of MAA consumed (mol)
× 100%;
– the conversion of methallyl alcohol (CMAA): CMAA =
amount of MAA consumed (mol) initial amount of MAA (mol)
× 100%;
– the selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed (Sorg/H2O2): Sorg/H2O2=
amount of org. comp. obtained (mol) amount of H2O2 consumed (mol)
× 100%.
RESULTS Epoxidation of methallyl alcohol over titanium silicalite catalyst Ti-MWW by a 30 wt.% water solution of hydrogen peroxide in methanol as a solvent leads to 2-methylglycidol as the main product. The by-products of this process are: 2-methylglycerol, 2-methylacroleine, bis(methallyl) ether and polymers of 2-methylglycidol and methallyl alcohol (Fig. 2). Influence of temperature. The influence of temperature in the range of 20–60˚C on the course of methallyl alcohol epoxidation over Ti-MWW catalyst was studied. The initial parameters of the epoxidation were as follows: molar ratio of MAA/H2O2 = 1:1, methanol content (solvent) 40 wt.%, Ti-MWW content 2 wt.%, reaction time 3 h and intensity of stirring 500 rpm. The values of conversion of methallyl alcohol increases in the examined range of temperatures from 9 mol.% (20°C) to 24 mol.% (60°C) (Fig. 3). This increase in the conversion is mainly associated with the formation of 2-methylacroleine in the oxidation reaction of methallyl alcohol. Moreover, this is also a result of creating of another by-products, which are formed by using methallyl alcohol, especially bis(methylglycidyl) ether and 2-methylacroleine (Table 2).
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CH3
CH3 H2O 2 , Ti-MWW -H2O
H 2C
H2 C
C
OH
H2O
H 2C
O
H2 C
C
OH
OH
OH
2-methylglycerol
2-methylglycidol O 1/2 O2
H 2C
C
H2 C
C
C
H2C
-H2O
CH3
H
CH3 2-methylacroleine
OH
methallyl alcohol
CH3 H2C
CH3 H2 C
C
OH
,
H 2C
H2 C
C
OH
O
-H2O CH3 H2 C
C
CH3 H2 C
O
H2 C
CH2
C
bis(methallyl) ether CH3
O 2HC
H2 C
C
O
H2 C
CH2
C
CH3 methylallyl-methylglycidyl ether
O 2HC
H2 C
C
O
O
H2 C
C
CH3
CH2
CH3 bis(methylglycidyl) ether
CH3 H2 C
CH3 +
C CH2OH
n
poly(methallyl alcohol)
H2 C
C
O
CH2OH
m
poly(methylglycidol)
Fig. 2. Reaction products of the epoxidation of methallyl alcohol with 30 wt.% hydrogen peroxide over the Ti-MWW titanium-silicalite catalyst
Fig. 3. Influence of temperature on the methallyl alcohol epoxidation over Ti-MWW catalyst: ■ – conversion of methallyl alcohol; ♦ – selectivity of transformation to 2-methylglycidol in relation to methallyl alcohol consumed; – selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed
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Table 2. Influence of temperature on the selectivity of transformation to by-products in the epoxidation of MAA over Ti-MWW catalyst
Temperature (˚C)
20 30 40 50 60
Selectivity of transformation to by-products in the epoxidation of MAA 2-methyl bis(methallyl) methallyl- 2-methylacro- bis(methyl glycerol ether methylglyleine glycidyl) ether 2MGL BMAE cidyl ether 2MACR BMGE MAMGE S2MGL/MAA SBMAE/MAA SMAMGE/MAA S2MACR/MAA SBMGE/MAA (mol.%) (mol.%) (mol.%) (mol.%) (mol.%) 0 0 3 3 4
5 5 1 2 2
19 18 11 8 7
41 51 54 57 61
8 13 17 17 16
The selectivity of transformation to 2MG in relation to MAA consumed achieves the highest value (26 mol.%) at the temperature of 20°C. With increasing of temperature to 30–60oC the function decreases to average value of 12 mol.%. This is the result of by-products forming, which are formed by using methallyl alcohol, especially bis(methylglycidyl) ether (BMGE), 2-methylacroleine (2MACR) and 2-methylglycerol (2MGL, Table 2). The analysis of the composition indicates also a slight decrease an amount of methallyl-methylglycidyl ether (MAMGE, Table 2). In the temperature range of 30–60°C, the selectivity of transformation to the sum of by-products is constant and amounts to 86–88 mol.%. 2-Methylacroleine constitutes the largest fraction among the by-products. In the range of increasing conversion of methallyl alcohol, i.e. from 12 to 24 mol.%, the selectivity of transformation to 2methylacroleine increases from 51 to 61 mol.%, at a constant selectivity of transformation to 2-methylglycerol. Under these conditions the oxidation of methallyl alcohol to 2-methylacroleine proceeds more readily than its epoxidation to 2-methylglycidol. Thus, 2-methylacroleine is the main product of the epoxidation process. The selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed increases in the studied range of temperature from 3 mol.% at 20˚C to 7 mol.% at 60˚C. This function depends on the amount of forming organic compounds, mainly 2-methylacroleine. Hence, the optimum temperature of the MAA epoxidation is 20oC. At this temperature the selectivity of transformation to 2-methylglycidol is the highest. However, it should be noted that at this temperature the conversion of methallyl alcohol and the selectivity of transformation to organic compounds in relation to H2O2 consumed are lower. Influence of molar ratio of MAA/H2O2. The influence of the molar ratio of MAA/H2O2 on the course of epoxidation was examined in the range from 1:1 to 5:1 and at temperature of 20˚C, while the other starting parameters were unchanged. The conversion of MAA (Fig. 4) decreases from 14 to 7 mol.% with the increase of the molar 283
ratio of MAA/H2O2 from 1:1 to 5:1. The reason for the decrease in conversion is the significant excess of MAA. The molecules react with each other only in the small amounts forming bis(methallyl) ether. In the first order methallyl alcohol undergoes epoxidation to 2-methylglycidol or oxidation to 2-methylacroleine (MACR). The selectivity of transformations to BMAE is enhanced by the increase in the MAA/H2O2 molar ratio. As a consequence of this the selectivity of transformation to MAMGE and BMGE is also increased. These compounds are prevailing in the product, simultaneously at the constant selectivity of transformation to 2-methylacroleine S2MACR/MAA= 36 mol.% and 2-methylglycidol S2GL//MAA= 4 mol.% at the molar ratio MAA/H2O2> 3:1. At the equimolecular ratio of reagents, the main reaction product is 2-methylacroleine S2MACR/MAA= 50 mol.%. A significant amount of 2-methylglycidol S2GL//MAA= 13 mol.%, is also formed at this molar ratio, whereas this amount decreases to 3 mol.% after enhancing the molar ratio to 5: 1. Besides it can be concluded that the increase in molar ratio of MAA/H2O2 causes the decrease of the values of the selectivity of 2-methylglycidol from 26 mol.% at 1:1 MAA/H2O2 molar ratio to 17 mol.% at 5:1 MAA/H2O2 molar ratio. The selectivity is almost constant and amounts about 3−5 mol.% within the range of the molar ratios of MAA/H2O2 from 3:1 to 5:1. The selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed increases in the range of molar ratio of reagents 1:1−4:1 from about 4 to 9 mol.%, and at a 5:1 molar ratio the values of this function decrease to 6 mol.%. It indicates that the amounts of 2 methylacroleine, 2-methylglycidol, 2-methylglycerin and other organic compounds are decreasing (Table 3). The amount of H2O2 reacted is constant, and its conversion is 97−99 mol.%, independently of molar ratio of MAA/H2O2. Thus, the molar ratio of MAA/H2O2 = 1:1 is the optimum for the process of MAA epoxidation. At this molar ratio the selectivity of transformation to 2MG amounts to 13 mol.%, the selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed equals 4 mol.%, the conversion of methallyl alcohol is 14 mol.% and the conversion of hydrogen peroxide is above 97 mol.%. The experiments at molar ratios of MAA/H2O2 > [PCC]), the plot of lg[PCC] against time was linear indicating first order dependence of the rate on PCC. The observed rate constant k was not affected by the change in PCC initial concentration (Table 1).
363
Table 1. Variation of rate with PCC, glycine, perchloric acid concentrations, DMF:H2O and temperature
[PCC] ×103 [Glycine] ×102 (mol dm–3) (mol dm–3) 2.5 2.0 2.25 2.0 2.0 2.0 1.75 2.0 1.5 2.0 1.0 2.0 2.0 1.2 2.0 1.43 2.0 1.6 2.0 2.0 2.0 2.4 2.0 2.8 2.0 3.66 2.0 5.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0
[H+]×10 (mol dm–3) 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 1 2.5 3.0 3.5 5.0 7.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0
Temp. (K) 313 313 313 313 313 313 313 313 313 313 313 313 313 313 313 313 313 313 313 313 298 303 308 313 318 323 313 313 313 313 313 313
DMF: H2O (%) 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 60:40 55:45 50:50 40:60 30:70
kobs × 105 (s–1) 31.34 30.15 31.25 30.71 31.25 31.25 18.53 21.75 25.25 31.25 36.77 43.18 55.65 65.25 11.20 28.28 31.09 43.37 66.40 102.09 11.51 15.04 21.41 30.39 40.61 54.37 31.25 23.30 12.25 6.91 4.60 2.10
Activation parameters: Ea = 52.37 kJ mol–1 ; ΔH* = 49.767 kJ mol–1; ΔS* = –96.2 J K–1 mol–1; ΔF* = 79.87 kJ mol–1
Effect of substrate. At constant PCC concentration, [H+] and temperature, the reaction rate increased with an increase in the concentration of glycine from 1.2 × 10–2 to 5.0 × 10–2 mol/dm3 (Table 1). The plot of lgkobs versus lg [glycine] (Fig. 1) was linear with positive slope of 0.89 indicating first order dependence of the rate on [glycine]. 364
The plot of 1/kobs versus 1/[glycine] (Fig. 2) is a straight line with positive intercept, which indicates that the Michaelis–Menten type kinetics is followed with respect to glycine. Although the intercept value is very small, it indicates formation of a complex which may be highly reactive so concentration will be very small at any time. A similar phenomenon has been observed in the oxidation of α-amino acid by Cr(VI) (Refs 10 and 11). 2
5 + lg k
1.8 1.6 1.4 1.2 0
0.2
0.4
0.6
0.8
2 + lg [glycine]
Fig. 1. Variation of rate with glycine concentration 0.06
0.05
0.04
1/k obs
0.03
0.02
0.01
0 0
0.2
0.4
0.6
0.8
1
1/[glycine]
Fig. 2. 1/kobs versus 1/[glycine]
Effect of ionic strength. The effect of ionic strength was studied by varying sodium sulphate concentration. The ionic strength in the reaction medium was varied from 1.0 to 11.0 × 10–3 mol dm–3 (Table 2) at constant concentration of glycine, PCC, HClO4 and with other conditions remaining constant. It has been observed that there was no 365
significant effect of ionic strength on the rate. This indicates that the reaction may be between an ion and a neutral molecule or between neutral molecules12. Table 2. Variation of rate with sodium sulphate concentration at 313 K [Glycine] = 2.0 ×10–2 mol dm–3; [HClO4] = 0.3 mol dm–3; [PCC] = 2.0 ×10–3 mol dm–3; DMF = 70% (v/v)
[Na2SO4] × 103 (mol dm–3)
1.0
3.0
5.0
7.0
11.0
kobs × 10 (s )
31.25
31.34
30.70
30.01
30.70
5
–1
Effect of solvent composition. It was observed that the change in solvent composition by varying DMF (% v/v) in the reaction mixture, keeping other conditions remaining constant, affected significantly the reaction rate. The rate of reaction increased with an increase in volume percentage of DMF (Table 1). Many theories have been put forward to give a quantitative explanation13,14 for the effect of dielectric constant (D) of the medium on the kinetics of liquid phase reactions. For the limiting case of a zero angle of approach between 2 dipoles or ion–dipole system, Amis15 had shown that in the linear plot of lgkobs versus 1/D a positive slope indicates a positive ion–dipole reaction, while a negative one indicates the involvement of two dipoles or a negative ion–dipole reaction. In the present investigation a plot of lgkobs versus 1/D (Fig. 3) gives a straight line with a positive slope, clearly supporting that there is an involvement of positive ion–dipole in the rate-determining step. 1.8 1.6 1.4 1.2
5 + lg kobs
1 0.8 0.6 0.4 0.2 0 0.125
0.13
0.135
0.14
0.145
0.15
0.155
0.16
1/D × 10
Fig. 3. Variation of rate with solvent composition of glycine
Effect of temperature. The rate constant of the reaction was found to increase with an increase in temperature (Table 1). The energy of activation was obtained by the plot of lg k versus 1/T (Fig. 4), from which the activation parameters were calculated 366
(Table 1). The entropy of activation is negative as expected for bimolecular reaction. The negative value also suggests the formation of a cyclic intermediate from non-cyclic reactants in the rate-determining step16. The complex formation is proved by the plot of inverse of rate constant against inverse of substrate concentration [glycine]. It has been pointed out17 that if entropy of activation is negative and small the reaction will be slow. 2
5 + lg k obs
1.8 1.6 1.4 1.2 1 3.05
3.1
3.15
3.2
3.25
3.3
3.35
3.4
1/T × 103 (K–1)
Fig. 4. Variation of rate with temperature
Effect of acrylonitrile. Involvement of radical mechanism is ruled out, as there is neither any decrease in rate in the presence of stabiliser free acrylonitrile nor milky appearance under kinetic conditions. The rate of reaction dose not change on addition of pyridine indicating thereby, the stability of PCC, i.e. PCC is not hydrolysed under the conditions under study. Effect of perchloric acid. At fixed concentration of glycine and PCC and with other conditions remaining constant, the rate was found to increase with an increase in the perchloric acid concentration (Table 1). A plot of lgkobs versus lg [HClO4] (Fig. 5) is a straight line with a positive slope ≈1 (1.16). This shows that reaction is of first order with respect to the hydrogen ion concentration. 2.5
5 + lg k obs
2
1.5
1 0
0.2
0.4 0.6 1 + lg [H +]
0.8
1
Fig. 5. Variation of rate with perchloric acid concentration
367
Under the present experimental conditions, the concentration of anion form will be very low and hence the possible species may be either the cation form of glycine or zwitterion. With cation as the active species, the rate law predicts a second order dependence of the rate on [H+], which is contrary to experimental results. Protonated glycine is not involved in the reaction sequence and the zwitterion is the active species in this reaction. An amino acid is known to exist in the following equilibria: H
H R
+
+ H
-NH 2
C
R
_ H+
COOH [amino acid]
+
C
NH 3
COOH [cation] +
_
+ H H
H
+
-NH 2
C
R
_
+ H _
COO [anion]
+
H
R
+
H
+
C
NH 3 _
COO [zwitterion]
The acid catalysis may well be attributed to a protonation of PCC (equation (2)) to yield a stronger oxidant and an electrophile both with the protonated and unprotonated forms being reactive. The formation of a protonated species of PCC has been also reported18–20.
PyHOCrO2Cl + H+
PyHOCr+(OH)OCl
(2)
Mechanism. On the basis of the above experimental results, a suitable mechanism is given below: –
+
Cr
O
O PyH O
Cl
368
[PCC]
–
O PyH
+
H
+
k
O
Cr
+
+
(A)
OH
Cl [protonated PCC]
–
O PyH
H H
C
NH 3
COO
+
+
Cr
O
+
+
OH
Cl
–
[glycine]
k1
[complex[C]]
k –1
(B)
[protonated PCC] slow
[complex[C]] ––––→ HCHO + HN4+ + CO2 + Cr(IV)
Cr(VI) + Cr(IV) ––––→ 2Cr(V)
k′
fast
[PCC]
(C) (D)
fast
2 Cr(V) + 2HCH(NH2)COOH + 2H2O ––––→ + 2HCHO + 2CO2 + 2NH4+ + 2Cr(III) + 2H+ (E) [PCC] [glycine]
The overall reaction may be represented as follows: 2Cr(VI) + 3HCH(NH2)COOH + 3H2O → 3HCHO + 2Cr(III) + 3NH4+ + 3CO2 + 3H+ (F)
On the basis of the above mechanism the rate law can be expressed as by the following expression: –d[PCC]/dt = [PCC] [glycine] [H+]
CONCLUSIONS The study on the oxidation of glycine by pyridinium chlorochromate in DMF–water medium in the presence of perchloric acid reveals that the neutral amino acid takes part in the reaction, and the protonated amino acid is not involved in the reaction. The reaction was carried out at different temperatures. In the temperature range of 298–323 K, the Arrhenius equation is valid. The thermodynamic parameters indicate that the reaction is entropy-controlled. The overall mechanistic sequence described here is consistent with the product analysis and kinetic and mechanistic data. ACKNOWLEDGeMENT One of the authors, Munna Lal Meena, is thankful to the University Grants Commission, New Delhi, for financial assistance.
369
REFERENCES 1. A. KOTHARI, S. KOTHARI, K. K. BANERJI: Kinetics and Mechanism of Oxidation of Alcohols by Butyltriphenylphosphonium Dichromate. Indian J. Chem., 447, 2039 (2005). 2. A. BHANDARI, P. K. SHARMA, K. K. BANERJI: Kinetics and Mechanism of the Oxidative Regeneration of Carbonyl Compounds by Pyridinium Chlorochromate. Indian J. Chem., 40A, 470 (2001). 3. H. RAM, R. S. SINDAL, P. K. SHARMA: Cyclic Voltammetric Studies of Cadmium (II) in Presence of Glycine. J. Indian Chem. Soc., 69, 607 (1992). 4. V. SHARMA, P. K. SHARMA, K. K. BANERJI: Kinetics and Mechanism of the Oxidation of Methionine by Pyridinium Chlorochromate. J. Indian Chem. Soc., 74 (8), 607 (1997). 5. V. SHARMA, P. K. SHARMA, K. K. BANERJI: Kinetics and Mechanism of Oxidation of Methionine by Pyridinium Bromochromate. Indian J. Chem., 36A, 418 (1997). 6. S. VARSHANEY, S. KOTHARI, K. K. BANERJI: Kinetics and Mechanism of the Oxidation of Oxalic and Formic Acids by Pyridinium Chlorochromate J. Chem. Res., 356, 2901 (1992). 7. G. L. AGARWAL, S. TIWARI: Kinetics and Mechanism of the Oxidation of d-Mannose with Pyridinium Chlorochromate. J. Reaction Kinet. & Catalysis Letters, 49 (2), 361 (1993). 8. K. K. ADARI, A. NOWDURI, P. VANI: Kinetics and Mechanism of Oxidation of L-cysteine by Corey’s Reagent. J. Trans. Metal Chem., 31 (6), 745 (2006). 9. E. J. CORE, W. T. SUGGS: Pyridinium Chlorochromate. An Efficient Reagent for Oxidation of Primary and Secondary Alcohols to Carbonyl Compounds. Tetrahedron Lett., 31, 2647 (1975). 10. B. L. HIRAN, V. JOSHI, J. CHOUDHARY, N. SHORGAR, P. VERMA: Studies on Oxidation of Tyrosine by Pyridinium Bromochromate in Acetic Acid –Water Mixture. Int. J. Chem. Sci., 2 (2), 164 (2004). 11. S. T. NANDIBEWOOR, P. N. NAIK, S. A. CHIMITADAR: A Kinetic and Mechanistic Study of the Oxidation of Tyrosine by Chromium (VI) in Aqueous Perchloric Acid Medium. Transition Metal Chem., 33, 405 (2008). 12. S. KABILAN, K. GANAPATHY: Kinetics of Oxidation of Some ortho-, meta-, and para-substituted S-phenylmercaptoacetic Acids by N-chloro-3-methyl-2,6-diphenyl piperidin-4-one in Buffered Ethanol–Water. Int. J. Chem. Kinet., 21 (6), 423 (1989). 13. E. S. AMIS: Solvent Effects on Reaction Rates and Mechanisms. Academic Press, New York, 1966. 14. S. G. ENTELIS, R. P. TIGER: Reaction in Liquid Phase. Wiley, New York, 1976. 15. E. S. AMIS: Coulomb’s Law and the Quantitative Interpretation of Reaction Rates. J. Chem. Educ., 30, 351 (1953). 16. K. MEHLA, S. KOTHARI, K. K. BANERJI: Kinetics and Mechanism of the Oxidation of Substituted Benzaldehydes by Benzyltrimethyl Ammonium Tribromide. Indian J. Chem., 41B, 832 (2002). 17. S. GLASSTONE, K. J. LAIDLER, H. EYRING: Theory of Rate Process. Chapters III and IV, Megraw-Hill, New York, 1941. 18. M. SETH, A. MATHUR, K. K. BANERJI: Kinetics and Mechanism of Oxidation of Phosphinic, Phenylphosphinic, and Phosphonic Acids by Pyridinium Chlorochromate. Bull. Chem. Soc. Jpn., 63, 3640 (1990). 19. V. SHARMA, P. K. SHARMA, K. K. BANERJI: Kinetics and Mechanism of the Oxidation of Methionine by Pyridinium Chlorochromate. J. Indian Chem. Soc., 74 (8), 607 (1997). 20. K. K. BANARJEE, R. KUMBHAT, V. SHARMA: Kinetics and Mechanism of the Oxidation of Oxalic and Formic Acid by Quinolinium Bromochromate. J. Indian Chem. Soc., 81, 745 (2004). Received 12 April 2010 Revised 25 May 2010
370
Oxidation Communications 35, No 2, 371–377 (2012) Oxidation of organic acids in the presence of cerium/thallium chlorides
Comparative Kinetic and Mechanistic Study of Oxidation of Heterocyclic Acid Hydrazides by Thallium(III) in Acidic Medium S. Varale*, V. S. Varale, N. P. Hilage Department of Chemistry, Shivaji University, 416 004 Kolhapur, Maharashtra State, India E-mail:
[email protected] ABSTRACT The study on the kinetics and mechanism of oxidation of heterocyclic acid hydrazides by thallium(III) in acidic medium is carried out iodometrically by keeping ionic strength of reaction mixture constant. The reaction proceeds through formation of complex with reactants, which decomposes in subsequent steps to give product. The increase in [H+] and [Cl–] decreases the rate of the reaction. The thermodynamic parameters were also determined and a mechanism was predicted. Keywords: kinetics, thallium(III), oxidation. AIMS AND BACKGROUND Hydrazides are pharmaceutically important compounds used as antitubercular1 and antibacterial2,3 agents, some of them have been reported to possess anti-inflammatory4 and diuretic5 activities. Interest in the use of thallium(III) in the oxidation of organic compounds has increased only recently and research in this regard has not been extensive. The thallium(III) oxidations of several other aliphatic, aryl aliphatic and cyclic ketones have been examined6.The oxidation of phenol by thallium(III) acetate in aqueous acetic acid leads to formation of dione as a major product7. It is clear that little information is available regarding the oxidation of heterocyclic hydrazides by thallium(III). Hence, the present work deals with the kinetics and mechanism of oxidation of heterocyclic acid hydrazides by thallium(III) in acidic medium.
*
For correspondence.
371
EXPERIMENTAL Thallium(III) solution was prepared by dissolving Tl2O3 (ACROS) in 1.0 mol dm–3 HCl and the concentration was ascertained by iodometric titration. The heterocyclic acid hydrazides were prepared by reported procedure8 and characterised by determining their melting points. Stock solutions of heterocyclic acid hydrazides were prepared in 50% v/v, 1,4-dioxane. Ionic strength was kept constant. The reactions were carried out in 50% v/v 1–4 dioxane (s.d.fine.chem) under pseudo-first order conditions keeping concentration of hydrazide in large excess over that of the oxidant. The solutions containing the reactants and all other constituents were thermally equilibrated separately, mixed and the reaction mixture was analysed for unreacted thallium(III) iodometrically by titrating against standard thiosulphate. The pseudo-first order rate constants were determined from the slopes of linear lg[Tl(III)] versus time plots. The results were reproducible up to ± 5%. Kinetic runs were followed to about 3 half-lives of the reactions. Under the experimental condition oxidation of 1,4-dioxan did not occur. End product analysis. For identification of products the reaction was carried out by using aqueous solution of hydrazide, thallium(III), HCl and HClO4. The flask containing reaction mixture was kept in thermostated water bath maintained at 50oC for 24 h to complete the reaction, the residue obtained after filtration was analysed for acid as follows: (i) The presence of carboxylic acid group was detected by testing with bicarbonate; (ii) The formation of acid was confirmed by IR and its melting point. RCONHNH2 + 2Tl(III) + H2O → R–COOH + N2 + 4H+ + 2Tl(I)
(1)
RESULTS AND DISCUSSION The reaction occurs rapidly in perchloric acid medium, but in the presence of hydrochloric acid the rate is measurable. Therefore, the reaction was carried out in a mixture of both the acids. The effect of reactants on the reaction was studied at constant [HCl] and [HClO4] of 0.1 mol dm–3 each and ionic strength of 0.6 mol dm–3. Concentration of oxidant was varied from 6.4 ×10–4 to 6.4 × 10–3 mol dm–3 keeping [hydrazide] constant at 1×10–1 mol dm–3. Since the pseudo-first order rate constants were fairly constant (0.94 ± 0.1 × 10–4 s–1 for PAH at 25oC, 1.30 ± 0.1 × 10–4 s–1 for NAH at 25oC and 8.3 ± 0.1 × 10–4 s–1 for ISNAH at 25oC), the order with respect to [oxidant] is unity. The effect of [hydrazide] was studied between the concentration range from 1×10–2 to 1×10–1 mol dm–3 keeping the [oxidant] constant at 3.0 ×10–3 mol dm–3. The pseudo-first order rate constants increase with increase in concentration and the order with respect to hydrazide is found to be fractional.
372
To study the effect of [H+] and [Cl–], [oxidant], [hydrazide] and ionic strength were kept as 3.0×10–3, 1×10–1 and 0.6 mol dm–3, respectively. To vary [H+] and [Cl–], HClO4 and NaCl were used. Increase in [H+] from 0.13 to 0.60 mol dm–3 decreases k ×10–4 (s–1) from 6.20 to 0.045 for PAH at 25oC, 8.40 to 0.063 for NAH at 25oC and from 10.87 to 0.12 for ISNAH at 25oC. Increase in [Cl–] from 0.13 to 0.60 mol dm–3 decreases k ×10–4 (s–1) from 1.78 to 0.045 for PAH at 25oC, 1.90 to 0.056 for NAH at 25oC and from 2.04 to 0.076 for ISNAH at 25oC. The relative permittivity was varied by changing the 1,4-dioxane content from 5 to 40% v/v. The rate was found to decrease with decrease in relative permittivity. Added acrylonitrile in the concentration range from 0.5 to 2.5 vol.%, by keeping concentrations of oxidant, reductant, perchloric acid, hydrochloric acid and ionic strength fixed, did not produce any precipitate due to polymerisation of the added acrylonitrile, indicating absence of free radicals. Since there is no formation of free radicals in the reaction, the reaction proceeds with 2-electron transfer step. The order in thallium(III) was found to be unity and the order in hydrazide was found to be fractional. Such a fractional order in substrate concentration is due to the prior complex formation equilibrium between the reactants. Scheme 1
Tl(III) + hydrazide
Kc
complex
k1
complex –––→ Tl(I) + intermediate fast
Tl(III) + intermediate –––→ Tl(I) + products
The Michealis–Menten plots of 1/kobs versus 1/[hydrazide] were linear with an intercept in support of the complex formation. Therefore, in agreement with the results obtained the mechanism of the reaction can be represented as in Scheme 1. Equation (2) gives the rate according to Scheme 1. Since, total [Tl(III)] exists in the form of free [Tl(III)] and the complex (equation (3)) therefore, the [Tl(III)] free is given by equation (5). The overall rate law is now expressed by equation (6) and the pseudofirst order rate constant kobs – by equation (7). rate = k1 [complex] = k1Kc [hydrazide]free [Tl(III)]free
(2)
[Tl(III)]total = [Tl(III)]free + [complex]
(3)
[Tl(III)]total = [Tl(III)]free + Kc[hydrazide] [Tl(III)]free
(4)
[Tl(III)]free = [Tl(III)]total/(1 + Kc [hydrazide])
(5)
rate = k1Kc [hydrazide] [Tl(III)]free
(6)
kobs = k1Kc [hydrazide]/(1 + Kc [hydrazide])
(7)
373
Rate law (7) is verified by plotting 1/kobs against 1/[hydrazide] at 4 different temperatures and from the slopes and intercepts of these plots the values of k1 and Kc were calculated (Table 1). Table 1. Values of Kc and K1 [HCl] = 0.1 mol dm–3, [HClO4] = 0.1 mol dm–3; [Tl(III)] = 3.0 × 10–3 mol dm–3, I = 0.6 mol dm–3
Temperature Kc k × 104 o 3 –1 ( C) (dm mol ) (s–1) PAH 15 09.85 1.00 20 12.12 1.25 25 15.41 1.47 30 17.50 2.00
Kc k × 104 –1 (dm mol ) (s–1) NAH 30.30 0.90 30.50 1.19 30.20 1.78 30.40 2.63 3
Kc k × 104 –1 (dm mol ) (s–1) ISNAH 6.17 10.00 7.52 14.30 8.10 20.00 9.70 33.34 3
The effect of hydrogen and chloride ion concentrations on the reaction is due to the protonation of hydrazides9 and different chloro-complexes10 of thallium(III) present in the solution. in acid medium according to equation (8). Hydrazides are known to be protonated, therefore, total [hydrazide] can be expressed by equation (9) and thereby the fact that there was no effect of free [hydrazide] by equation (11). Since the rates of reaction decreases as the [H+] increases, free hydrazide is the active species, this is in support of ionic strength on the reactions indicating that one of the reactant is neutral. RCONHNH2 + H+
KH
RCONHNH3+
(8)
[hydrazide]total = [hydrazide]free + [hydrazide]protonated
(9)
[hydrazide]total = [hydrazide]free + KH [hydrazide]free
(10)
[hydrazide]free = [hydrazide]total /(1+ KH [H ])
(11)
+
Thallium(III) forms strong complexes with chloride ions of the formula TlCln3–n where n is the number of chlorides complexes with thallium(III) as represented in equilibria (12)–(15). The values of the respective stability constants11 are as follows: K1 = 1.38 × 108, K2 = 3.98 × 1013, K3 = 6.02 × 1015 and K4 = 1.0 × 1018 dm3 mol–1. T13+ + C1– TlCl2+ + Cl– TlCl2+ + Cl– TlCl3 + Cl–
K1
K2 K3 K4
TlCl2+
(12)
TlCl2+
(13)
TlCl3+
(14)
TlCl4+
(15)
All the thallium(III) will exist as TlCl2+ and its concentration can be expressed by equation (16). The [TlCl2]+free can now be given by equation (18), where β1 = K3/K2 = 151 and β2 = K4/K3 = 166, further, using equations (17) and (18), the concentrations of [TlCl2]+free, TlCl3 and TlCl4– were calculated at different chloride ion concentrations and compared with the change in rate constant as the chloride ion concentration varied. 374
[Tl(III)]total = [TlCl2+]total = [TlCl2+]free + [TlCl3] + [TlCl4]
(16)
[TlCl2+]total = [TlCl2+]free (1+β1[Cl–] + β2[Cl–]2)
(17)
[T1Cl2+]free = [TlCl2+]total / (1 + β1[Cl–] + β2[Cl–]2)
(18)
The concentration both of [TlCl2+] free and TlCl3 parallel the values of rate constants as [Cl–] changes, but the order [Cl–] is 1.5, which makes [TlCl2+] free as the only active species. Scheme 2
TlC12+ + hydrazide
Kc
complex
k1
complex –––→ RCONNH + TlC12– + H+ fast
RCONNH+H2O+TlC12+ –––→ RCOOH+N2+2H+ + TlC12–
where R is C5H4N for heterocyclic acid hydrazides. The mechanism considering TlCl2+ of oxidant and free hydrazide of the substrate as the active species can now be represented by Scheme 2 with the respective rate law and the expression for the pseudo-first order rate constants by equations (19) and (20). The rate law (20) was verified by plotting 1/kobs against 1/[hydrazide] and 1/kobs against [H+] which were found to be linear. From the slopes and intercepts of these plots the values of Kc and KH were determined. The values of Kc are given in Table 1 and those of KH were found to be 13 and 16 dm3 mol–1 for heterocyclic acid hydrazides, respectively. rate =
kobs =
k1Kc [hydrazide]total [T1C12+]total (1+Kc [hydrazide]) (1+KH[H+]) (l+β1[Cl–]+β2 [Cl–]2) k1KC [hydrazide]total (1+Kc [hydrazide]) (1+KH[H+]) (1+β1[Cl–]+β2[Cl–]2)
;
(19)
.
(20)
The electrophilic character of TlCl2+ among the thallium(III) chlorocomplexes is highest thus making it the reactive species. The detailed mechanism involves electrophilic substitution on the nitrogen of the hydrazide with the formation of N–Tl bond, which decomposes in the subsequent step with direct 2-electron transfer from hydrazide to thallium to give an intermediate followed by fast steps (Scheme 3). Such N–Tl bond formation has been postulated during thallium(III) oxidation of nitrogen-containing compounds12. The activation parameters with respect to slow step, k1, ∆H* (kJ mol–1), ∆G* (kJ mol–1) and ∆S* (J K–1 mol–1) were found to be 31.73, 90.30 and –196.52 for picolinic acid hydrazide (PAH), 21.77, 78.11 and –189.06 for nicotinic acid hydrazide (NAH) and 59.74,90.49 and –103.19 for isonicotinic acid hydrazide (ISNAH), respectively. 375
Considerable decrease in the entropy of activation is due to formation of more ordered transition state as shown in Scheme 3. The mechanism involves neutral hydrazide as the active substrate, thus the reaction is unaffected by the change in the ionic strength. The increase in 1,4-dioxane content in the reaction medium decreases; such an effect of the solvent on the rate is due to the stabilisation of the complex formed between reactants13 in a medium of low relative permittivity. Scheme 3 +
O R
C
H N
H N
H
+
TlCl2
+
R
O
H
H
C
N
N
H
R
O
H
H
C
N
N
Tl
Cl
H
Tl
Cl
Cl
Cl
– –TlCl 2
complex
–H
+
O R
C
H
+
+
RCOOH
O
C
O
R
+
H
+
2H +
+
– TlCl2
+ TlCl2
H
N
O
H
N
H
R – alkyl group for acid hydrazides
376
H
N
H
+ H
N
–
C
H
N2
N
: OH 2
O R
N
–
N +
H
N
H
CONCLUSIONs As we go from isonicotinic acid hydrazide to picolinic acid hydrazide steric hinderence increases and hence rate decreases. ACKNOWLeDGEMENT The authors are thankful to Prof. G. S. Gokavi for his keen interest and help during the course of work and to the UGC, New Delhi, for financial assistance. REFERENCES 1. W. WERNER: Aromaticity and Antiaromaticity: What Role Do Ionic Configurations Play in Delocalization and Induction of Magnetic Properties? J. Org. Chem., 18, 1333 (1953). 2. A. L. MADZHOYAN: Handbook of Chemistry. Arm. Khim. Zh., 19, 793 (1966). 3. A. WINTERSTEIN, H. HEGEDUS, B. FUST, E. BOHNI, A. STUDER: Inhibition of [3H] GABA Binding to Postsynaptic Receptors in Human Cerebellar Synaptic Membranes by Carboxyl and Amino Derivatives of GABA , Helv. Chem. Acta, 39, 229 (1956). 4. R. Pfister, A.Soilman, Ch. Hammers: W. SwissPal, 42, 132 (1967); Chem. Abstract., 68, 49283 (1968). 5. F. JUCKER, A. L. NOMANN: Helv Chim Acta, 45, 2316 (1962). 6. P. S. RADHAKRISHNAMURTHI, S. N. PATIL: Kinetics and Mechanism of Oxidation of Oximes. J. Chem., 17A, 97 (1979). 7. P. S. RADHAKRISHNAMURTHI, S. N. PATIL: Kinetics and Mechanism of Oxidation of Ketones. J. Chem., 16A, 139 (1978). 8. A. I. VOGEL: Textbook of Practical Organic Chemistry. 4th ed. ELBS & Longman Group, 1975, p. 1125. 9. R. C. WEAST: Handbook of Chemistry and Physics. 50th ed. CRC, 1970. 10. (a) K. KAZO, T. HIRAKAZO, K. HISASHI, T. ZENZO: Chem. Pharm. Bull., 11, 797 (1963); (b) P. V KRISHNARAO, M. S FRANK, A. K RAMAIH: Kinetics of Oxidation of Phenylacetic Acid Hydrazide by Vanadium(V). React. Kinet. Catal. Lett., 9, 159 (1978); (c) P. V. KRISHNARAO, M. S. FRANK, A. K. RAMAIH: Hexacyanoferrate(III) Oxidation of n-valeric and Isovaleric Acid Hydrazides in Perchloric Acid. Indian J. Chem., 16A, 418 (1978); (d) A. K. RAMAIH, M. S. FRANK, G. BABURAO, P. V. KRISHNARAO: Hexacyanoferrate(III) Oxidation of n-valeric and Isovaleric Acid Hydrazides in Perchloric Acid. Indian J. Chem., 18A, 416 (1979). 11. A. G. LEE: The Chemistry of Thallium. Elsevier, London, 1971, p. 48. 12. (a) A. McKILLOP, J. D. HUNT, R. D. NAYLOR, E. C. TAYLOR: Manganese Triacetate Mediated Regeneration of Carbonyl Compounds from Oximes. J. Am. Chem., 93, 4918 (1971); (b) R. N. BUTTLER, G. J. MORRIS, A. M. O’DONOHUE: J. Chem. Res. (s) Soc., 61 (1981). 13. E. S. AMIS: Solvent Effects on Reaction Rates and Mechanisms. Academic Press, New York, 1966. 14. A. S .VARALE, N. P. HILAGE: Kinetics and Mechanism of Oxidation Reactions by Thallium (III) in Acidic Medium. Oxid. Commun., 31, 537 (2008). 15. A. S. VARALE, N. P. HILAGE: Oxidation of p-toluic Acid Hydrazide by Thallium(III) in Acidic Medium. Asian J. of Chemistry, 21, 1265 (2009). 16. A. S. VARALE, N. P. HILAGE: Comparative Kinetic and Mechanistic study of Oxidation of Benzoic and p-nitro Benzoic Acid Hydrazide by Thallium(III) in Acidic Medium. Oriental J. of Chemistry, 24, 545 (2008). Received 23 March 2009 Revised 26 April 2009
377
Oxidation Communications 35, No 2, 378–388 (2012) Oxidation of organic acids in the presence of cerium/thallium chlorides
Kinetics and Mechanism of Silver(I)-catalysed Oxidation of Valine by Cerium(IV) in Acid Perchlorate Medium M. B. Yadava, V. Devrab, A. Ranic* P. G. Department of Chemistry, Govt. College Kota, 324 001 Kota, India P. G. Department of Chemistry, Govt. J. D. B. Girls College, 324 001 Kota, India c Department of Pure and Applied Chemistry, Kota University, 324 005 Kota, India E-mail:
[email protected] a
b
ABSTRACT The kinetics of the silver(I)-catalysed oxidation of valine with cerium(IV) has been studied in perchloric acid medium. An usual decrease in rate with increasing concentration of cerium(IV) is observed and the detailed quantitative analysis of this behaviour is presented on the basis of dimerisation of cerium(IV). The reaction exhibits fractional dependence on valine and that has been accounted for the formation of an adduct with silver(I). A plausible reaction mechanism is given and the rate law is derived: k=
k1K1[VH+][H+] ([H+] + Kh)(1 + K1[VH+])
,
where the observed k is second order rate constant. Keywords: valine, cerium(IV), silver(I), perchloric acid. AIMS AND BACKGROUND Amino acids act not only as the building blocks in protein synthesis but they also play a significant role in metabolism. The specific metabolic role of amino acid includes the biosynthesis of polypeptides, proteins and synthesis of nucleotides1. The oxidation of amino acids is of interest as the oxidation products differ for different oxidants2,3. L-valine is an essential amino acid classified as non-polar. It forms active sites of enzymes and helps in maintaining their proper conformation by keeping them in proper ionic states. So oxidation of L-valine may help in understanding some aspects of enzyme kinetics. *
For correspondence.
378
The kinetics of oxidation of several amino acids by a number of oxidants have been reported. Aqueous solutions of amino acids have been oxidised by Mn(III) (Ref. 4), Fe(CN)63– (Ref. 5), chloramine-T (Ref. 6), N-bromobenzenesulphonamide7, peroxo monosulphate8, Mn(VII) (Ref. 9), pyridinium bromochromate10, peroxydisulphate11, etc. both in acid and alkaline media. Very few reports are available on the kinetics of oxidation of valine by Ce(IV) (Ref. 12), diperiodatoargentate13, and polymer-supported Cu(II) (Ref. 14). In view of this, we have taken up systematic kinetic study of the oxidation of neutral amino acid namely valine by Ce(IV) in HClO4 medium. Regarding the oxidation products, various types of reaction models have been suggested. There are studies where a group of workers indicate formation of aldehydes15 through the hydrolysis of an imine intermediate whereas the other group reports further oxidation of the imine to nitrile16. A third group reports neither aldehydes nor nitriles, instead α-keto acids are formed17. Ce(IV) is a powerful oxidising agent in acidic medium with the reduction potential in HClO4 to be 1.75 V. The oxidising potentialities of Ce(IV) in H2SO4 medium18 have conclusively been established as sulphato species. Nevertheless, the oxidant has scantly been employed in perchloric acid medium probably owing to the presence of dimers and polymers of Ce(IV)(Ref. 19). Although the concentration of such dimers and polymers is significantly less, their contribution to the overall rate of reaction can not be neglected in higher concentrations of Ce(IV). The role of Ag(I) as a catalyst is discussed in the studies of Adinarayana and Sethuram20. Metal ions act as catalysts by one of these different paths21 such as formation of complexes with reactants or oxidation of the substrate itself or through the formation of free radicals. In order to understand the active species of oxidant and catalyst, and to propose the appropriate mechanism, the title reaction is investigated in details. An understanding of mechanism allows chemistry to be interpreted and hence understood and predicted. EXPERIMENTAL The kinetic studies of oxidation of valine by Ce(IV) in perchloric acid medium has been studied by monitoring Ce(IV). The cerric perchlorate solution was prepared by dissolving cerric ammonium nitrate (B. D. H. AnalaR) in perchloric acid (E. Merck) and the solution was standardised by titrating aliquot of the test solution against standard ferrous ammonium sulphate (E. Merck) solution employing ferroin as an indicator. Since the solubility of valine in water is low, the solution was therefore prepared in the presence of 0.5 mol dm–3 perchloric acid for the higher amino acid concentration. All other reagents were of AnalaR or G. R. Merck quality. Doubly distilled water was employed throughout the study. The titration was always done in the presence of H2SO4 to obtain clear and stable colour change at the end point. The reactions were carried out in stoppered Erlenmeyer flasks immersed in a water bath thermostated at 50 ± 0.1oC. All the components of the reaction mixture except Ce(IV) were taken in the flasks and then allowed to obtain the bath temperature. The 379
reaction was initiated by adding the known volume of temperature pre-equilibrated ceric perchlorate solution. The kinetics were monitored by estimating Ce(IV) in an aliquot (5 cm3) withdrawn at different intervals of time by titrating against ferrous ammonium sulphate solution employing ferroin indicator. Initial rates were measured employing plane mirror method22. Pseudo-first order plots were constructed wherever reaction conditions permitted. Triplicate rate measurements were reproducible to within ± 1%. Stoichiometry. Since most of the reaction kinetics were studied under pseudo-first order conditions, where amino acid was in excess over Ce(IV). Such reactions were allowed to occur in a thermostated water bath at 50 ± 0.1oC for 24 h. When Ce(IV) was completely utilised, the solutions were concentrated and tested for the presence both of nitrile and aldehyde, the products usually reported in the oxidation of amino acids. Nitrile tests were negative and qualitative tests of aldehyde were positive. Further 2,4-dinitrophenyl hydrazone derivative of aldehyde was not obtained. Since ammonia is formed in the reaction, its interaction with aldehyde may yield an adduct to check the formation of hydrazone derivative in the acid medium.Therefore, the stoichiometry of the reaction with positive test of an aldehyde can be represented by the following equation: H2O
R–CH–NH3+COOH + 2Ce(IV) –––→ RCHO + NH4+ + CO2 + 2Ce(III) + 2H+ (1)
R = (CH3)2CH–. The liberated CO2 was detected by the lime water test. RESULTS Cerium(IV) dependence. The concentration of cerium(IV) was varied from 5.9×10–4 to 4.7×10–3 mol dm–3 at different concentrations of valine, viz 2.0×10–2, 3.0×10–2 and 4.0×10–2 mol dm–3, respectively, at [H+] = 0.5 mol dm–3, Ag(I) = 1.0×10–3 and temperature 50oC. The first order rate constants decrease with increasing concentration of cerium(IV). Valine dependence. The concentration of valine was varied from 1.0×10–2 to 7.0×10–2 mol dm–3 at fixed concentration of [H+] =0.5 mol dm–3, Ag(I) = 1.0×10–3 mol dm–3 and Ce(IV) = 9.0×10–4 mol dm–3 at 3 temperatures, viz. 45, 50 and 55oC, respectively. The rate of reaction initially increases and then tends towards a limiting value with further increasing concentration of valine (Table 1). Hydrogen ion dependence. Hydrogen ion concentration was varied from 0.5 to 2.5 mol dm–3 employing perchloric acid at different concentrations of valine, viz. 3.0×10–2, 4.0×10–2 and 5.0×10–2 mol dm–3, respectively, at Ce(IV) = 9.0×10–4 mol dm–3 and Ag(I) = 1.0×10–3 mol dm–3 at 50oC. First order rate constants initially increases and then tends towards a limiting value with further increasing concentration of hydrogen ion. 380
Table 1. Observed rate constant for the reaction of valine and cerium(IV) in HClO4 medium [Ce(IV)] = 9.0×10–4 mol dm–3; [Ag(I)] = 1.0×10–3 mol dm–3; [H+] = 0.5 mol dm–3
[Val] ×102 (mol dm–3) 1.0 2.0 3.0 4.0 5.0 6.0 7.0
k′×105 (s–1) 50oC 3.9 6.4 8.2 9.1 9.8 10.1 10.7
45 C 3.0 5.0 6.8 7.8 8.5 8.9 9.3 o
55oC 4.9 7.5 9.3 10.2 10.6 11.1 11.7
Effect of ionic strength. The effect of ionic strength on the rate of reaction was studied employing sodium perchlorate at fixed concentration of [Ce(IV)] = 9.0 × 10–4 mol dm–3, [Val] = 3.0 ×10–2 mol dm–3, [Ag(I)] = 1.0 × 10–3 mol dm–3 and [H+] = 0.5 mol dm–3 at 50◦C. The rate of reaction increases with increase in the ionic strength. Silver(I) dependence. Ag(I) concentration was varied from 5.0 × 10–4 to 2.0 × 10–3 mol dm–3 at constant concentration of [Ce(IV)] = 9.0 × 10–4 mol dm–3, [Val] = 3.0 × 10–2 mol dm–3 and [H+] = 0.5 mol dm–3 at 50oC. A plot of (k′) versus [Ag(I)] yields a straight line passing through the origin indicating order with respect to silver(I) to be one (Table 2). Table 2. Rate constants k′ and k at different Ag(I) concentration
[Ag(I)] ×103 (mol dm–3) 0.5 0.75 1.0 1.25 1.50 1.75 2.0
k′× 105 (s–1) 4.1 6.2 8.22 10.3 12.4 14.4 16.4
k ×102 (dm3 mol–1 s–1) 8.20 8.26 8.22 8.24 8.26 8.22 8.20
DISCUSSION The oxidations of organic and inorganic substrate by cerium(IV) in HClO4 medium proceed much faster than the reaction in sulphato medium23. However, cerium(IV) in perchloric acid medium does not indicate complex formation although Ce4+, Ce(OH)3+, (Ce–O–Ce)6+ and (HOCe–O–CeOH)4+ species of cerium(IV) are well established24. Cerium(IV) in acid perchlorate medium exists predominantly in the monomeric form such as Ce4+ and its hydrolysed forms, [Ce(OH)3+] and [Ce(OH)22+] apart from the dimeric and polymeric forms25. The polymeric species are significantly less than 381
the dimeric species in acidic solutions of moderate cerium(IV) concentration. Presence both of dimeric and polymeric forms of cerium(IV) with the monomer in the larger concentrations can not be ruled out. Since the first order rate constant decreases with increasing concentration of cerium(IV), such a behaviour accounts for the involvement of dimeric and polymeric forms of cerium(IV). The plot of 1/k′ versus [Ce4+] yields a straight line with non-zero intercept. Had polymeric species in appreciable concentration, the experimental points would have deviated from such a linear relationship. Thus the dimer of cerium(IV) appears to be primary cause of decrease in rate with increasing concentration of cerium(IV) (Ref. 26). In acid solutions, amino acids tend to exist predominantly as the protonated species according to the following equilibrium27. Further, the amino acids are known to exist in zwitterion form in equilibrium with anionic and cationic forms depending upon the pH of the solution. –H+ –H+
RCHNH3+COOH
RCHNH3+COO–
+H+ +H+
RCHNH2COO–
(2)
cation zwitterion anion
where R=(CH3)2CH. The rate of reaction increases with increasing silver(I) concentration conforming to a first order dependence with respect to silver(I). However, the order with respect to amino acid changes from unity to zero. Such an amino acid dependence can be ascribed to complexation either with Ce(IV) or Ag(I). Amino acids are reported to form an adduct with Ag(I) owing to availability of electron pair on oxygen atom28, therefore, an adduct between Ag(I) and valine is initially formed that on further interaction with Ce(IV) yields another adduct of higher valent silver as is confirmed spectrophotometrically by the addition of 2,2′-bipyridyl in the reaction mixture that yielded a brown orange coloured Ag(II)-bipy complex with its characteristic absorption maximum at 454 nm (Ref. 29). Furthermore, the adduct formation between Ce4+ and valine was ruled out on the basis that the absorbance of Ce4+ did not change even for 100-fold excess of valine added in the cerium(IV) solution. Thus Ag(I)-valine adducts are responsible for fractional dependence of amino acid. Considering these facts along with experimental results and the complex hydrogen ion dependence, a reaction mechanism consisting of steps (3) to (7) can be proposed: Ce4+ + H2O
Kh
CeOH3+ + H+
(3)
K1
Ag(I) + H3H+–(CH3)2CHCHCOOH [H3N+–(CH3)2CHCHCOOHAg(I)] (4) [adduct]
382
k1
[adduct] + Ce4+ ––––→ [adduct]+ + Ce3+
(5)
fast
[adduct]+ ––––→ H3N+(CH3)2CHCH–COO• + Ag(I) + H+
(6)
H2O
H3N+(CH3)2CHCH–COO• ––––→ NH3 + (CH3)2CHCHO + CO2 + H+ fast
(7)
The proposed mechanism leads to the following rate law:
–d[Ce(IV)]/dt = k1K1[Ce(IV)][VH+][Ag(I)].
(8)
Since the concentration of Ce(IV) is governed by equation (3), this free equilibrium concentration of Ce(IV) in terms of gross analytical concentration will be given by the following equation: [Ce(IV)][H+]
Ce(IV) =
[H+] + Kh
.
(9)
Similarly [VH+] is the free equilibrium concentration of amino acid and thus the conc. of Ag(I) which is also equilibrium concentration is governed by equation (10). Ag(I) =
[Ag(I)][VH+] . 1 + K1[VH+]
(10)
Substituting Ce(IV) and Ag(I) from equations (9) and (10), respectively, in equation (8), equation (11) is obtained: –
d[Ce(IV)] dt
=
k1K1[Ce(IV)][VH+][H+][Ag(I)] ([H+] + Kh)(1 + K1[VH+])
.
(11)
At constant hydrogen ion concentration and maintaining in pseudo-first order conditions, rate equation (11) reduced to equation (12): k′ =
k1K1[VH+][H+][Ag(I)] ([H+] + Kh)(1 + K1[VH+])
,
(12)
where k′ is the first order rate constant (Table 2). Since the order with respect to silver(I) is one, this equation (12) is further reduced to equation (13): k=
k1K1[VH+][H+] ([H+] + Kh)(1 + K1[VH+])
,
(13)
where k is second order rate constant. A plot of 1/k versus [VH+]–1 was made from equation (13) at constant hydrogen ion concentration that yielded a straight line with non-zero intercept (Fig. 1). The ratio of intercept and slope of the line yielded the values of K1 to be 25.9, 32.5, 43.8 at 45, 50 and 55oC, respectively. The value of K1 obtained in the title reaction in comparison to K1 = 20 for the Ce(IV)–glycerol complex30 at 50◦C, K1 = 18 and 29 for 383
Ce(IV)-cis-1,2-cyclohexanediol and Ce(IV)-trans-1,2-cyclohexanediol31 complexes, respectively, indicates complexation in HClO4 medium. 35
25 20 15 10
k
–1
–3
(mol dm s)
30
5 0
0
50
100
150
[VH+]–1 (dm3 mol–1)
Fig. 1. Plot of k–1 versus [VH+]–1 Ce(IV) = 9.0 ×10–4 mol dm–3; [Ag(I)] = 1.0 ×10–3 mol dm–3; [H+] = 0.5 mol dm–3; temperature: ♦ – 45oC; ■ – 50oC; ▲ – 55oC
The activation energy of the reaction was calculated from the plot between lg k1 and 1/T as 23.2 kJ mol–1, and the enthalpy of the reaction determined from the plot between lg K1 and 1/T was found to be 10.66 kJ mol–1. These values when calculated by thermodynamic equation are also found in accordance to the graphical values. A plot 1/k versus 1/[H+] was made on the basis of equation (13) at 3 different concentrations of valine that yielded a straight line with non-zero intercept (Fig. 2). With a plot of intercept versus 1/[VH+], we get again a straight line with non-zero intercept (Fig. 3). The ratio of intercept and slope of the line yielded the value of K1 to be 32.6 in agreement with the value of K1 obtained in case of amino acid variation. 14 12
8 6
k
–1
–3
(mol dm s)
10
4 2 0
0
0.5
1 1.5 [H+]–1 (dm3 mol–1)
2
2.5
Fig. 2. Plot of k–1 versus [H+]–1 Ce(IV) = 9.0 ×10–4 mol dm–3; [Ag(I)] = 1.0 ×10–3 mol dm–3; temperature 50oC; [Val] = 3.0 ×10–2 mol dm–3 (♦); 4.0 ×10–2 mol dm–3 (■); 5.0 ×10–2 mol dm–3 (▲)
384
intercept
1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0
0
10
20
30
40
[VH+]–1 (dm3 mol–1)
Fig. 3. Plot of intercept versus [VH+]–1
The electron transfer from valine to cerium(IV) in the presence of Ag(I) can be envisaged from the following Scheme. Scheme
As per the transfer of electron from the substrate to the oxidant is concerned, the detailed reaction events can be given as in the Scheme. The hydrocarbons of amino acid does not undergo any chemical reaction owing to the highly reactive functional groups. However, there are 2 distinct possibilities of the intermediate imine undergoing reactions to the final products, either reacting with water or by an interaction of imine with the oxidising species. Since the acid catalysis has been observed in the title reaction, the hydrolysis of imine is the most predominant path. The colour reaction32 for the presence of nitrile in the reaction mixture was done by adding hydroxylamine 385
and ferric chloride, this test, however, confirmed its absence and ruled out any further interaction of the imine with Ce(IV). Thus the hydrolytic decomposition of imine rather than interaction of Ce(IV) becomes important reaction event yielding aldehyde to be the oxidation product of the amino acid. CONCLUSIONS The oxidation of amino acid is interesting due to their biological importance. Amino acid plays significant role in a number of metabolic reactions.The kinetic study of the oxidation of amino acid is interesting as oxidation products are different with different oxidants. In this study, we used L-valine, which is essential amino acid classified as non-polar. The kinetics of Ag(I)-catalysed oxidation of valine with Ce(IV) has been studied in perchloric acid medium. The pseudo-first order rate constant decreases with increasing concentration of Ce(IV), this behaviour is presented on the basis of dimerisation of Ce(IV). The reaction exhibits fractional dependence with respect to valine and that has been accounted for the formation of an adduct with Ag(I). The mode of electron transfer has been indicated through an adduct between Ag(I) and valine via oxygen atom of carboxyl group rather than amino group. The rate of reaction increases with increasing Ag(I) concentration conforming to a first order dependence with respect to Ag(I). Considering these experimental results and complex hydrogen ion dependence, a reaction mechanism is given and rate law is derived: k=
k1K1[VH+][H+] ([H+] + Kh)(1 + K1[VH+])
.
The stoichiometry of the reaction on the basis of positive test of aldehyde can be represented as follows: R–CH–NH3+COOH + 2Ce(IV) → RCHO + NH4+ + CO2 + 2Ce(III) + 2H+
R = (CH3)2CH—. ACKNOWLEDGEMENT Sincere thanks to Prof. P. D. Sharma, University of Raj, Jaipur, for his help and suggestions. REFERENCES 1. G. C. BARRETT: Amino Acids, Peptides and Proteins. Royal Society of Chem., 29 (1998). 2. D. LALOO, M. M. MAHANTI: Kinetics of Oxidation of Amino Acids by Alkaline Hexacyano ferrate(III). J. Chem. Soc. Dalton Trans., 311 (1990). 3. K. B. REDDY, B. SETHURAM, T. N. RAO: Ind. J. Chem., 20A, 395 (1981).
386
4. H. ILOUKHANI, H. BAHRAMI: Kinetic Studies and Mechanism on the Permanganic Oxidation of L-glutamine in Strong Acid Medium in the Presence and Absence of Silver(I). Int. J. Chem. Kinet., 31, 95 (1999). 5. T. P. JOSE, S. T. NANDIBEWOOR, S. M. TUWAR: Osmium(VIII) Catalyzed Oxidation of a Sulfur Containing Amino Acid – A Kinetics and Mechanistic Approach. J. of Sulphur Chem., 27, 1 (2006). 6. N. GROVER, N. KAMBO, S. K. UPADHYAY: Kinetics and Mechanism of Pd(II) Catalysed Oxidation of Some α-aminoacids by Chloramine-T in Perchloric Acid. Ind. J. Chem., 41A, 2482 (2002). 7. PUTTUSWAMY, N. VAZ: Kinetics of Oxidation of Acidic Amino Acids by Sodium N-bromobenzenesulphonamide in Acid Medium. A Mechanistic Approach. Proc. Ind. Acad. Sci. (Chem. Sci.), 113 (4), 325 (2001). 8. R. S. KANNAN, D. EASWARAMOORTHY, K. VIJAYA, M. S. RAMACHANDRAN: Autocatalytic Oxidation of β-alanine by Peroxomonosulfate in the Presence of Copper(II). Int. J. Chem. Kinet., 40 (1), 44 (2007). 9. H. ILOUKHANIl, S. R. EKVAN, A. A. RAFATI: Oxidation of L-phenyl Alanine by Mn(VII) in Concentrated H2SO4 Medium. Physics and Chem. of Liquids, 41 (1), 25 (2003). 10. N. ANNAPURNA, A. K. KUMAR, P. VANI, G. NAGESWARA RAO: Kinetics of Oxidation of L-cystine by Pyridinium Bromochromate. Ind. Chem. Soc., 85, 542 (2008). 11. G. CHANDRA, S. N. SRIVASTAVA: Kinetics And Mechanism of the Silver(I) Ion Catalysed Oxidation of α-alanine by Peroxydisulphate. J. of Inorganic and Nuclear Chemistry, 34 (1), 197 (1972). 12. K. K. ADARI, A. NOWDURI, V. PARWATANENI: Kinetics and Mechanism of Oxidation of Lcystine by Ce(IV) in Sulphuric Acid Medium. Acta Chim. Slov., 55, 425 (2008). 13. V. C. SEREGAR, C. V. HIREMATH, S. T. NANDIBEWOOR: Mechanism of Oxidation of L-proline by Aqueous Alkaline Diperiodatoargentate (III): Decarboxylation and Dehydration, J. of Physical Chemistry, 220, 5 (2006). 14. V. B. VALODKAR, G. L. TEMBE, M. RAVINDRANATHAN, R. N. RAM, H. S. RAMA: Catalytic Oxidation by Polymer Supported Cu(II)-L-valine Complexes. J. of Molecular Catalysis, A. Chemical, 208 (1–2), 21 (2004). 15. T. GOWDA, R. V. RAO: Ind. J. Chem., 24A, 1021 (1985). 16. M. S. RAMACHANDRAN, T. S. VIVEKANANDAM: Kinetics of Oxidation of Amino Acids by Chloramine-T. A Reinvestigation on the Oxidation of Alanine, 2-aminobutyric Acid, Valine, Serine, and Threonine. Bull. Chem. Soc. Jpn., 60, 3397 (1987). 17. R. C. ACHARYA, N. K. SARAN, S.R.RAO, M. N. DAS: Kinetics and Mechanism of Osmium(VIII)catalysed Hexacyanoferrate(III) Oxidation of Amino Acids in Alkaline Medium. Int. J. Chem. Kinet., 14, 143 (1982). 18. G. MILLAZZO, S. CAROLL, V. K. SHARMA: Tables of Standard Potentials. John Wiley and Sons, New York, 1978; W. LATIMER: Oxidation Potentials. 2nd ed. Prentice-Hall, Englewood Cliffs, NJ, 1952. 19. T. J. HARDWICK, E. ROBERTSON: Ionic Species in Ceric Perclorate Solution. Canad. J. Chem., 29, 818 (1951). 20. M. ADINARAYANA, B. SETHURAM, T. NAVANEETH RAO: Kinetics of Oxidation of Some Amino Acids by Ce (IV) in Sulphuric Acid Medium in the Presence and Absence of Ag (I). J. Indian Chem. Soc., 53, 877 (1976). 21. M. G. RAM REDDY, B. SETHURAM, T. N. RAO: Effect of Cu(II) on Kinetics and Mechanism of Silver(I) Catalyzed Oxidation of Some Amino Acids by Peroxydisulfate Ion in Aqueous Medium. Ind. J. Chem., 16A (7), 591 (1978). 22. M. LATSHAW: Notes. Tangentimeter. J. Amer. Chem. Soc., 47, 793 (1925). 23. S. B. HANNA, S. A. SARAC: Metal-ion Oxidative Decarboxylations. 9. Reaction of Benzilic Acid with Cerium(IV) in Acidic Perchlorate and Sulfate Media. J. Org. Chem., 42 (12), 2063 ( 1977).
387
24. W. H. RICHARDSON: Oxidation in Organic Chemistry (Ed. K. B. Wiberg). Academic Press, New York, Ch. 4, 1965; T. J. KEMP: Comprehensive Chemical Kinetics (Eds C. H. Bamford, C. F. H. Tipper). Elsevier, 7, 274 (1972); Z. AMZAD, McAULEY: J. Chem. Soc. Dalton Trans.,1, 252 (1974). 25. T. J. HARDWICK, E. ROBERTSON: Ionic Species in Ceric Perclorate Solution. Canad. J. Chem., 29, 818 (1951). 26. V. DEVRA, S. AGARWAL, P. D. SHARMA: Kinetics and Mechanism of Silver(I) Catalysed Oxidation of Alanine by Cerium(IV). Oxid. Commun., 17, 245 (1994). 27. A. E. MARTELL, R. M. SMITH: Critical Stability Constants. Vol. I. Plenum Press, New York, 1974. 28. V. DEVRA: Kinetics and Mechanism of Silver(I) Catalysed Oxidation of Alanine by Cerium(IV) in Perchloric Acid. J. Ind. Chem. Soc., 82, 290 (2005). 29. I. SHARMA, V. DEVRA, D. GUPTA, C. M. GANGWAL, P. D. SHARMA: Kinetics and Mechanism of Electron Transfer Reactions in Aqueous Solutions: Silver(I) Catalyzed Oxidation of Aspartic Acid by Cerium (IV) in Acid Perchlorate Medium. John Wiley & Sons, Inc., 1995. 30. G. G. GUILBAULT, W. H. McCURDY: Mechanism and Kinetics of the Oxidation Glycerol by Cerium(IV) in Perchloric and Sulfuric Acids. J. Phys. Chem., 67, 283 (1963). 31. M. B. YADAV, V. DEVRA, A. RANI: Kinetics and Mechanism of Silver(I) Catalysed Oxidation of Lysine by Cerium(IV) in Acid Perchlorate Medium. J. Ind. Chem. Soc., 86 (2009). 32. S. SOLAWAY, A.LIPSCHITY: Colorimetric Test for Amides and Nitriles. Anal. Chem., 24 (5), 898 (1952). Received 17 April 2009 Revised 23 August 2009
388
Oxidation Communications 35, No 2, 389–393 (2012) Oxidation reactions in the presence of heterogeneous catalysts
An Improved Method for Oxidation of Oximes with Potassium Permanganate Adsorbed on Graphite Reagent under Viscous Conditions Li-Yun Zhua, Chen Huangb, Chenxiao Shic, Fang Lina, Changhe Zhanga,e, Ji-Dong Loud* College of Life Sciences, China Jiliang University, Hangzhou, 310 018 Zhejiang, China E-mail:
[email protected] b China Pharmaceutical University, Nanjing, 210 009 Jiangsu, China c School of Environmental and Chemical Engineering, Shanghai University, 200 444 Shanghai, China d Centre for the Research and Technology of Agro-environmental and Biological Sciences (CITAB)/Department of Biology and Environment, Universidade de Trásos-Montes e Alto Douro (UTAD), Apartado 1013, 5001-801 Vila Real, Portugal e Sirnaomics Inc., 401 Professional Drive, Gaithersburg, MD 20879, USA a
ABSTRACT An improved procedure for oxidative cleavage of oximes to the corresponding aldehydes and ketones with potassium permanganate adsorbed on graphite reagent under viscous conditions at room temperature in yields between 80 and 97% is described. The main advantage of the present procedure is that under viscous conditions the oxidation of the solid substrates can be carried out as a mild process with high efficiency. Keywords: aldehydes, ketones, oxidation, oximes, potassium permanganate, graphite, viscous conditions. AIMS AND BACKGROUND Oximes have great potential as intermediates and have been widely applied for the protection of carbonyl groups in organic synthesis. Oximes can be easily obtained from the corresponding carbonyl compounds. However, only a limited number of methods are available for the conversion of oximes to their parent carbonyl compounds under mild reaction conditions. Therefore, the development of convenient and efficient pro*
For correspondence.
389
cedures for the selective cleavage of oxime derivatives to afford carbonyl compounds continues to be a significant aspect of organic chemistry. As we know the solid-supported reagents have been extensively used to carry out a range of reactions with the advantages of short reaction time, high conversion, and selectivity. In most cases, solid-supported reagents have been found superior to the non-supported reagents1. However, there are limited examples for the use of potassium permanganate on solid supports for oxidative cleavage of oximes to their corresponding parent carbonyl compounds, such as potassium permanganate-manganese(II) sulphate2, potassium permanganate-manganese dioxide2, potassium permanganate-wet silica gel3, potassium permanganate-alumina4,5, potassium permanganate-montmorillonite K-10 (Ref. 6), potassium permanganate-zeolite7, potassium permanganate-graphite8, and potassium permanganate-kieselguhr9. In addition, a considerable attention has been paid to the solvent-free reactions in organic synthesis. Solvent-free reactions are of interest not only from ecological point of view, but in many cases also offer considerable synthetic advantages in terms of yield, selectivity, simplicity of the procedure, and operation at room temperature. These factors are especially important in industry. Of the potassium permanganate on solid supports for oxidative cleavage of oximes indicated above, 4 of them are carried out under solvent-free conditions2–4,6, and the rest are under heterogeneous conditions5,7–9. In general, under solvent-free reactions it may not satisfied for the reaction between solid substrates and solid reagents, for example oximes that are in highly crystalline state and potassium permanganatebased reagents, to carry out at room temperature because both of molecules are in crystal forms, so that these reactions are normally carried out at temperature near or over the melting point of the substrate or with other technologies, for example, pestle with mortar. Although all reported methods have received good results, introduction of new methods or reagents is still fraught with experimental challenges, especially in search of environmentally friendly, inexpensive, versatile, and selective oxidation reagents. EXPERIMENTAL Oxidative cleavage of benzophenone oxime to benzophenone. Typical procedure. Benzophenone oxime (197 mg, 1 mmol) was dissolved in dichloromethane (0.25 ml) to form a viscous liquid, and then potassium permanganate-graphite reagent (1840 mg, 2 mmol of potassium permanganate)10 was added. The mixture was shaken mechanically at room temperature. The progress of the reaction was monitored by TLC using hexane:ethyl acetate (7:3) as eluent. After 30 min the reaction mixture was washed with dichloromethane (3 × 10 ml). The combined filtrates were evaporated to give crude product, which was purified by preparative TLC with hexane:ethyl acetate (7:3) to afford benzophenone (175 mg, 97%).
390
RESULTS AND DISCUSSION In continuation of our previous investigations on reactions between solid substrates and solid-supported reagents under viscous conditions11–17, we now report a highly efficient procedure for the oxidation of oximes (1) to the corresponding aldehydes and ketones (2) using potassium permanganate supported on graphite that we described previously10 under viscous conditions at room temperature (Scheme), which can overcome the problems existing in the common solvent-free reactions, i. e. the difficulty for the solid molecular collision to react.
N
Scheme
OH
R1
KMnO 4 – graphite
O
viscous conditions, RT
R2
R1
(1)
R2 (2)
In the present procedure, a 1 to 2 molar ratio of the substrate to potassium permanganate supported on graphite is employed. After the solid substrate is dissolved with a minimum amount of dichloromethane to form a viscous liquid, the oxidant is added in one portion. The mixture is shaken magnetically at room temperature until TLC analysis indicates a completed reaction. The residue is washed, and the product is then purified by preparative TLC. The oxidised products are all known compounds and identified by spectroscopic comparison with authentic samples. Our results are listed in the Table. Table. Oxidative cleavage of oximes to their corresponding carbonyl compounds with potassium permanganate adsorbed on graphite reagent under viscous conditions
Entry
Oxime
1
2 N
OH
1
Producta 4
97
OH
2
O
30
N
Yieldb (%) 5
O
30
N
3
Time (min) 3
OH
86 O
60
86 to be continued
391
Continuation of the Table
1 4
5
2 N
N
3
4
OH
5
O
60 OH
N
60
O
80
CHO
OH
6
82
30 N
CHO
OH
7
90
30 OCH3
N
OCH3
CHO
OH
8
9
86
30
N OH
92
CHO
60
82
All products were identified by comparison of their physical and spectral data with those of authentic samples; b yield of isolated pure product. a
The main advantages of the present procedure are that under viscous conditions the oxidation of the solid substrates can be carried out in high efficiency with mild process, and due to the reaction using a very minimum amount of solvents, combustion, toxicity, and environmental pollution of the solvents are reduced. Furthermore, graphite provides a particular reaction environment capable of enhancing the reaction selectivity and reactivity. Also because of using a non-toxic and inexpensive reagent, potassium permanganate, it makes the reaction process convenient, economic, and environmentally benign. CONCLUSIONS An improved procedure for oxidative cleavage of oximes to the corresponding aldehydes and ketones with potassium permanganate adsorbed on graphite reagent under viscous conditions at room temperature is described. The main advantage of the present 392
procedure is that under viscous conditions the oxidation of the solid substrates can be carried out as a mild process with high efficiency. REFERENCES 1. K. SMITH (Ed.): Solid Supports and Catalysts in Organic Synthesis. Prentice Hall, New York, 1992. 2. A. SHAABANI, S. NADERI, A. RAHMATI, Z. BADRI, M. DARVISHI, D. G. LEE: Cleavage of Oximes, Semicarbazones, and Phenylhydrazones with Supported Potassium Permanganate. Synthesis, 3023 (2005). 3. A. R. HAJIPOUR, A. E. RUOHO: Wet Silica-supported permanganate: A Mild and Inexpensive Reagent for Highly Enantiomeric Purity Conversion of Alpha-Sulfinyl Oximes and Alpha-Sulfinyl Hydrazones to Alpha-Keto Sulfoxides. J. Iranian Chem. Soc., 1, 159 (2004). 4. G. H. IMANZADEH, A. R. HAJIPOUR, S. E. MALLAKPOUR: Solid State Cleavage of Oximes with Potassium Permanganate Supported on Alumina. Synth. Commun., 33, 735 (2003). 5. W. CHRISMAN, M. J. BLANKINSHIP, B. TAYLOR, C. E. HARRIS: Selective Deoximation Using Alumina Supported Potassium Permanganate. Tetrahedron Lett., 42, 4775 (2001). 6. I. MOHAMMADPOOR-BALTORK, M. M. KHODAEI, A. R. HAJIPOUR, E. ASLANI: A Facile, Mild, and Environmentally Benign Procedure for the Cleavage of Carbon–Nitrogen Double Bonds Using KMnO4 in the Presence of Montmorillonite K-10 under Solvent-free Conditions. Monatsh. Chem., 134, 539 (2003). 7. V. K. JADHAV, P. P. WADGAONKAR, P. L. JOSHI, M. M. SALUNKHE: Oxidation of Oximes to Ketones with Zeolite Supported Permanganate. Synth. Commun., 29, 1989 (1999). 8. Y. F. ZHOU, F. LIN, X. L. LU, C. ZHANG, Q. WANG, X. ZOU, J. D. LOU: Oxidation of Oximes with Potassium Permanganate Adsorbed on Graphite Reagent under Heterogeneous Conditions. Oxid. Commun., 35 (91), 72 (2012). 9. J. D. LOU, F. LIN, L. HUANG, X. ZOU: A Mild and Environmentally Benign Procedure for the Oxidative Cleavage of Oximes with Potassium Permanganate Supported on Kieselguhr, Synth. React. Inorg. Metal Org. Nano-Metal Chem., (2012), in press. 10. J. D. LOU, G, Q. WANG, L. LI, L. ZHU: Oxidation of Alcohols Catalyzed by a New Potassium Permanganate Adsorbed on Graphite Reagent. Synth. React. Inorg. Metal Org. Nano-Metal Chem., 35, 281(2005). 11. J. D. LOU, X. L. LU, A. J. MARROGI, F. LI, C. GAO, X. YU: A First Example for a Reaction under Viscous Conditions: Oxidation of Solid Benzoins with Manganese Dioxide. Monatsh. Chem., 139, 609 (2008). 12. J. D. LOU, C. ZHANG, G. WANG, C, GAO: Oxidation of Benzoins to Benzils with Chromium Trioxide Supported on Kieselguhr under Viscous Conditions. Synth. React. Inorg. Metal Org. NanoMetal Chem., 39, 6 (2009). 13. J. D. LOU, Y. MA, N. VATANIAN, Q. WANG, C. ZHANG: Selective Oxidation of Benzoins with Potassium Dichromate under Viscous Conditions. Synth. React. Inorg. Metal Org. Nano-Metal Chem., 40, 160 (2010). 14. J. D. LOU, Y. MA, N. VATANIAN, Q. WANG, C. ZHANG: Selective Oxidation of Benzoins with Chromic Acid Supported on Aluminum Silicate under Viscous Conditions. Synth. React. Inorg. Metal Org. Nano-Metal Chem., 40, 495 (2010). 15. L. HUANG, Q. WANG, Y. MA, J. D. LOU, C. ZHANG: Oxidation of Benzoins to Benzils with Chromium Trioxide under Viscous Conditions. Synth. Commun., 41, 1059 (2011). 16. J. D. LOU, Y. MA, J. GE, C. ZHANG, Q. WANG, X. ZOU: Oxidation of Benzoins to Benzils with Sodium Dichromate under Viscous Conditions. Oxid. Commun., 34, 53 (2011). 17. J. D. LOU, F. LIN, Q. WANG, C. ZHANG, Y. MA: Selective Oxidation of Benzoins with Chromic Acid Supported on Silica Gel under Viscous Conditions. Oxid. Commun., 34, 616 (2011). Received 26 February 2012 Revised 24 March 2012
393
Oxidation Communications 35, No 2, 394–398 (2012) Oxidation reactions in the presence of heterogeneous catalysts
Oxidative Conversion of Oximes to Their Parent Carbonyl Compounds with Potassium Permanganate Adsorbed on Silica Gel under Heterogeneous Conditions Li-Yun Zhua, Chen Huangb, Chenxiao Shic, Fang Lina, Changhe Zhangd, Ji-Dong Loua,e* College of Life Sciences, China Jiliang University, Hangzhou 310 018, Zhejiang, China E-mail:
[email protected] b China Pharmaceutical University, Nanjing, 210 009 Jiangsu, China c School of Environmental and Chemical Engineering, Shanghai University, 200 444 Shanghai, China d Centre for the Research and Technology of Agro-environmental and Biological Sciences (CITAB)/Department of Biology and Environment, Universidade de Trásos-Montes e Alto Douro (UTAD), Apartado 1013, 5001-801 Vila Real, Portugal e Sirnaomics Inc., 401 Professional Drive, Gaithersburg, MD 20879, USA a
ABSTRACT A convenient oxidative procedure for the regeneration of aldehydes and ketones from the corresponding oximes using economically and environmentally-benign reagent, potassium permanganate supported on silica gel, under heterogeneous conditions at room temperature in the yield between 80 and 96% is described. Keywords: aldehydes, ketones, oxidation, oximes, potassium permanganate, silica gel. AIMS AND BACKGROUND Oximes are widely used for the protection of carbonyl groups, for the purification and characterisation of carbonyl compounds, as well as for the preparation of amides by the Beckmann re-arrangement. Because oximes can be prepared from non-carbonyl compounds, such as the Barton reaction, their conversion to carbonyl functionality is important from a synthetic point of view. Therefore, the development of mild and efficient procedures for the selective cleavage of derivatives containing a carbon–ni*
For correspondence.
394
trogen double bond like oximes to afford carbonyl compounds continues to be a significant aspect of organic synthesis1,2. An important procedure for the regeneration of the corresponding carbonyl compounds from the oximes is oxidative cleavage reaction, and for this transformation several potassium permanganate or potassium permanganate-based reagents have been reported as oxidants, such as potassium permanganate-manganese(II) sulpphate3, potassium permanganate-manganese dioxide3, potassium permanganate-wet silica gel4, potassium permanganate-montmorillonite K-10 (Ref. 5), potassium permanganatealumina6,7, potassium permanganate-zeolite8, and potassium permanganate-graphite9. Three of them are carried out under heterogeneous conditions7–9 and the rest are performed under solvent-free conditions3–6, all of which have achieved good results. EXPERIMENTAL Oxidative cleavage of benzophenone oxime to benzophenone. Typical procedure. The potassium permanganate-silica gel10 (1450 mg) was placed in a flask together with dichloromethane (30 ml) and the mixture was magnetically stirred. A solution of benzophenone oxime (197 mg, 1 mmol) in dichloromethane (5 ml) was added, and after 1 h at room temperature (RT) the solid was filtered and washed with dichloromethane (3 × 5 ml). The combined filtrates were evaporated to give crude product, which was purified by preparative TLC with hexane:ethyl acetate (7:3) to afford 174 mg (96%) benzophenone. RESULTS AND DISCUSSION We have described that potassium permanganate supported on silica gel is an efficient reagent for the oxidation of alcohols under heterogeneous conditions10 and under solvent-free conditions11. Since potassium permanganate is a relatively environmental friendly and inexpensive reagent, we are interested in extending this supported reagent to oxidise other functional groups. Therefore, based on our previous works10,11, we report here an efficient procedure for the oxidation of oximes (1) to the corresponding aldehydes and ketones (2) using potassium permanganate supported on silica gel under heterogeneous conditions at room temperature (Scheme), which offers a simple and efficient oxidation method for the regeneration of carbonyl compounds from the corresponding oximes. Since the present method avoids the use of toxic reagents such as hexavalent chromium derivatives, it may be carried out on a large scale. Furthermore, to use solid supports has become popular due to their characteristic properties such as enhanced selectivity and reactivity, milder reaction conditions, and straightforward work-up procedure12.
395
N
Scheme
OH
R1
KMnO 4 – silica gel
O
CH2 Cl2 , R T
R2
R1
(1)
R2 (2)
In the present experiments, the mixture of oximes and potassium permanganate supported on silica gel is stirred in dichloromethane at room temperature, and a 1 to 2 molar ratio of the substrate to the oxidant is employed. The progress of the reaction is monitored with TLC, and the corresponding aldehydes and ketones are purified by preparative TLC in good yields. The oxidised products are all known compounds and are identified by spectroscopic comparison with authentic samples. Our results are listed in the Table. Table. Oxidative cleavage of oximes to their corresponding carbonyl compounds with potassium permanganate supported on silica gel under heterogeneous conditions
Entry
Oxime
1
2 N
96 O
1
N
86
OH
3
O
1.5
N
N
82
OH
O
1.5 OH
N
Yieldb (%) 5
O
OH
2
6
4
1
N
5
Producta
OH
1
4
Time (h) 3
2
80 O
78
CHO
OH
1
92 to be continued
396
Continuation of the Table
1
2 N
3
OH
7
4
5
CHO
1 OCH3
N
OCH3
CHO
OH
8
9
90
1.5
N OH
90
CHO
2
86
All products were identified by comparison of their physical and spectral data with those of authentic samples; b yield of isolated pure product. a
CONCLUSIONS A convenient oxidative procedure for the regeneration of aldehydes and ketones from the corresponding oximes using economically and environmentally-benign reagent, potassium permanganate supported on silica gel, is described. The present method has advantages such as mild reaction conditions, short reaction times, and high yields of the products and is an extension of our previous work as well. REFERENCES 1. A. CORSARO, U. CHIACCHIO, V. PISTARA: Regeneration of Carbonyl Compounds from the Corresponding Oximes. Synthesis, 1903 (2001). 2. A. CORSARO, M. A. CHIACCHIO, V. PISTARA: Regeneration of Carbonyl Compounds from the Corresponding Oximes: An Update Until to 2008. Curr. Org. Chem., 13, 482 (2009). 3. A. SHAABANI, S. NADERI, A. RAHMATI, Z. BADRI, M. DARVISHI, D. G. LEE: Cleavage of Oximes, Semicarbazones, and Phenylhydrazones with Supported Potassium Permanganate. Synthesis, 3023 (2005). 4. A. R. HAJIPOUR, A. E. RUOHO: Wet Silica-supported Permanganate: A Mild and Inexpensive Reagent for Highly Enantiomeric Purity Conversion of Alpha-sulfinyl Oximes and Alpha-sulfinyl Hydrazones to Alpha-keto Sulfoxides. J. Iranian Chem. Soc., 1, 159 (2004). 5. I. MOHAMMADPOOR-BALTORK, M. M. KHODAEI, A. R. HAJIPOUR, E. ASLANI: A Facile, Mild, and Environmentally Benign Procedure for the Cleavage of Carbon–Nitrogen Double Bonds Using KMnO4 in the Presence of Montmorillonite K-10 under Solvent-free Conditions. Monatsh. Chem., 134, 539 (2003). 6. G. H. IMANZADEH, A. R. HAJIPOUR, S. E. MALLAKPOUR: Solid State Cleavage of Oximes with Potassium Permanganate Supported on Alumina. Synth. Commun., 33, 735 (2003).
397
7. W. CHRISMAN, M. J. BLANKINSHIP, B. TAYLOR, C. E. HARRIS: Selective Deoximation Using Alumina Supported Potassium Permanganate. Tetrahedron Lett., 42, 4775 (2001). 8. V. K. JADHAV, P. P. WADGAONKAR, P. L. JOSHI, M. M. SALUNKHE: Oxidation of Oximes to Ketones with Zeolite Supported Permanganate. Synth. Commun., 29, 1989 (1999). 9. Y. F. ZHOU, F. LIN, X. L. LU, C. ZHANG, Q. WANG, X. ZOU, J. D. LOU: Oxidation of Oximes with Potassium Permanganate Adsorbed on Graphite under Heterogeneous Conditions. Oxid. Commun., 35 (1), 72 (2012). 10. L. WANG, J. D. LOU, L. ZHU: Oxidation of Alcohols with a New Potassium Permanganate Adsorbed on Silica Gel Reagent. Oxid. Commun., 27, 906 (2004). 11. J. D. LOU, L. PAN, L. LI, F. LI, C. GAO: Selective Oxidation of Alcohols with Potassium Permanganate Adsorbed on Silica Gel under Solvent-free Conditions. Synth. React. Inorg. Metal Org. Nano-Metal Chem., 36, 729 (2006). 12. K. SMITH (Ed.): Solid Supports and Catalysts in Organic Synthesis. Prentice Hall, New York, 1992. Received 12 February 2012 Revised 20 March 2012
398
Oxidation Communications 35, No 2, 399–403 (2012) Oxidation reactions in the presence of heterogeneous catalysts
An Improved Deoximation with Chromic Acid Supported on Silica Gel under Viscous Conditions Li-Yun Zhua, Chen Huangb, Chenxiao Shic, Fang Lina, Changhe Zhangd, Ji-Dong Loua,e* College of Life Sciences, China Jiliang University, Hangzhou 310 018, Zhejiang, China E-mail:
[email protected] b China Pharmaceutical University, Nanjing, 210 009 Jiangsu, China c School of Environmental and Chemical Engineering, Shanghai University, 200 444 Shanghai, China d Centre for the Research and Technology of Agro-environmental and Biological Sciences (CITAB)/Department of Biology and Environment, Universidade de Trásos-Montes e Alto Douro (UTAD), Apartado 1013, 5001-801 Vila Real, Portugal e Sirnaomics Inc., 401 Professional Drive, Gaithersburg, MD 20879, USA a
ABSTRACT An improved method for oxidative cleavage of oximes to their parent aldehydes and ketones with chromic acid supported on silica gel reagent under viscous conditions at room temperature in the yield between 82 and 96% is described. The present procedure can overcome the problems existed in the solvent-free reactions of the difficulty for the solid molecular collision to react. Furthermore, there is no need of microwave irritations. Keywords: carbonyl compounds, chromium trioxide, deoximation, oximes, silica gel. AIMS AND BACKGROUND Oxime derivatives of carbonyl compounds, such as aldehydes and ketones, are highly crystalline and are widely used for the characterisation and purification of carbonyl compounds. Aldehydes and ketones protected as oximes can be later removed to expose the original carbonyl functional group in the synthesis of complex organic molecules. The regeneration of carbonyl compounds from the corresponding oximes under mild conditions is important and of considerable interest. In addition, oximes *
For correspondence.
399
can be prepared from non-carbonyl compounds, so that their deoximation provides an alternative pathway to produce aldehydes and ketones. So far, the cleavage of these derivatives to the parent carbonyl compounds has been extensively investigated1,2. EXPERIMENTAL Oxidative cleavage of benzophenone oxime to benzophenone. Typical procedure. Benzophenone oxime (197 mg, 1 mmol) was dissolved in dichloromethane (0.2 ml) to form a viscous liquid, and then chromic acid supported on silica gel reagent3 (502 mg, 1.5 mmol) was added. The mixture was shaken mechanically at room temperature. After 3 h the reaction mixture was washed with dichloromethane (3 × 10 ml). The combined filtrates were evaporated to give crude product, which was purified by preparative TLC with hexane:ethyl acetate (7:3) to afford benzophenone (162 mg, 90%). RESULTS AND DISCUSSION One of the most important procedures for the deoximation is the oxidative cleavage of corresponding oximes with chromium(VI) compounds4, especially using chromic acid-based reagents. Khadilkar and co-workers reported chromic acid supported on silica gel as oxidative reagent for the deoximation of oximes under heterogeneous conditions5 and under solvent-free conditions assisted with microwave irritations6, respectively. Till now the use of solid supports in organic synthesis has become popular due to their characteristic properties such as enhanced selectivity and reactivity, straightforward work-up procedure, milder reaction conditions, and associated ease of manipulation. In addition, solvent-free reactions are not only of interest from ecological point of view, but in many cases also offer considerable synthetic advantages in terms of yield, selectivity, simplicity of the procedure, and operation at room temperature. Unfortunately, under solvent-free conditions, in general it is difficult to perform the reaction between solid substrates and solid reagents, like oximes and chromium (VI)based oxidants at room temperature, because both of molecules are in crystal forms, so that such reactions are normally carried out at temperature near or over the substrate melting point either by heating or other technologies in advance in order to dissolve the solid substrates into the liquid forms thus increasing the reaction rate. In continuation of previous investigations on the reaction under viscous conditions7–13 we report here an improved procedure for the oxidative cleavage of oximes (1) into the corresponding aldehydes and ketones (2) using chromic acid supported on silica gel reagent under viscous conditions at room temperature (Scheme), which can overcome the problems existing in the solvent-free reactions, i. e. the difficulty for the solid molecular collision to react. The present procedure offers a simple and highly-efficient oxidation method for the regeneration of carbonyl compounds from the corresponding oximes. The results are shown in the Table, the oxidised products 400
are all known compounds and are identified by spectroscopic comparison with authentic samples.
N
Scheme
OH
R1
O
CrO 3 – silica gel viscous conditions, RT
R2
R1
(1)
R2 (2)
Table. Oxidative cleavage of oximes to their corresponding carbonyl compounds with chromic acid supported on silica gel reagent under viscous conditions
Entry
Oxime
1
2 N
4
90
OH
2
O
3
N
82
OH
3
O
4
N
N
86
OH
O
4 OH
N
4
82 O
3 N
95 CHO
OH
7
4 OCH3
80
CHO
OH
6
Yieldb (%) 5
O
3
N
5
Producta
OH
1
4
Time (h) 3
96 OCH3
to be continued
401
Continuation of the Table
1
2 N
3
OH
8
9
4
5
CHO
3
N OH
90
CHO
3.5
90
All products were identified by comparison of their physical and spectral data with those of authentic samples; b yield of isolated pure product. a
Comparing with reported methods for the deoximation of oximes under heterogeneous conditions5 and under solvent-free conditions with microwave irritation6 using chromic acid supported on silica gel reagent, the main advantages of the present procedure are that under viscous conditions the oxidation of the solid substrates can be carried out very efficiently with mild process, and due to the reaction using a minimum amount of solvents, combustion, toxicity, and environmental pollution of the solvents are strongly reduced. Furthermore, according to the current procedure there is no need of microwave irritation. Therefore, the benefits of the present procedure are over those of the oxidation methods reported previously5,6. CONCLUSIONS In conclusion, an efficient and improved method for oxidative cleavage of oximes to the corresponding aldehydes and ketones using chromic acid supported on silica gel reagent under viscous conditions at room temperature is described. The present procedure can overcome the problems existing in the common solvent-free reactions due to the difficulty for the solid molecular collision to react. Furthermore, there is no need of microwave irritation. REFERENCES 1. T. W. GREENE, P. G. M. WUTS: Protective Groups in Organic Synthesis. 3rd ed. Wiley, New York, 1999. 2. N. D. CHERONIS, J. B. ENTRIKIN: Identification of Organic Compounds. Interscience, New York, 1963. 3. J. D. LOU, Y. A. WU: A Convenient Synthesis of α,β-unsaturated Aldehydes via the Oxidation of Corresponding Alcohols with Chromic Acid Adsorbed on Silica Gel as Oxidant. Chemistry and Industry (London), 531 (1987). 4. Y. F. ZHOU, F. LIN, X. L. LU, C. ZHANG, Q. WANG, X. N. ZOU, J. D. LOU: Oxidation of Oximes with Chromium Trioxide in Dimethyl Sulphoxide under Homogeneous Conditions. Oxid. Commun., 35 (1), 45 (2012) and references cited therein.
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5. P. M. BENDALE, B. M. KHADILKAR: Silica Gel Supported Chromium Trioxide: An Efficient Reagent for Oxidative Cleavage of Oximes to Carbonyl Compounds under Mild Condition. Synth. Commun., 30, 665 (2000). 6. P. M. BENDALE, B. M. KHADILKAR: Microwave Promoted Regeneration of Carbonyl Compounds from Oximes Using Silica Supported Chromium Trioxide. Tetrahedron Lett., 39, 5867 (1998). 7. J. D. LOU, X. L. LU, A. J. MARROGI, F. LI, C. L. GAO, X. YU: A First Example for a Reaction under Viscous Conditions: Oxidation of Solid Benzoins with Manganese Dioxide. Monatsh. Chem., 139, 609 (2008). 8. J. D. LOU, C. ZHANG, G. WANG, C. GAO: Oxidation of Benzoins to Benzils with Chromium Trioxide Supported on Kieselguhr under Viscous Conditions. Synth. React. Inorg. Metal Org. NanoMetal Chem., 39, 6 (2009). 9. J. D. LOU, Y. MA, N. VATANIAN, Q. WANG, C. ZHANG: Selective Oxidation of Benzoins with Potassium Dichromate under Viscous Conditions. Synth. React. Inorg. Metal Org. Nano-Metal Chem., 40, 160 (2010). 10. J. D. LOU, Y. MA, N. VATANIAN, Q. WANG, C. ZHANG: Selective Oxidation of Benzoins with Chromic Acid Supported on Aluminum Silicate under Viscous Conditions. Synth. React. Inorg. Metal Org. Nano-Metal Chem., 40, 495 (2010). 11. L. H. HUANG, Q. WANG, Y. MA, J. D. LOU, C. ZHANG: Oxidation of Benzoins to Benzils with Chromium Trioxide under Viscous Conditions. Synth. Commun., 41, 1059 (2011). 12. J. D. LOU, Y. MA, J. GE, C. ZHANG, Q. WANG, X. ZOU: Oxidation of Benzoins to Benzils with Sodium Dichromate under Viscous Conditions. Oxid. Commun., 34 (1), 53–58 (2011). 13. J. D. LOU, F. LIN, Q. WANG, C. ZHANG, Y. MA: Selective Oxidation of Benzoins with Chromic Acid Supported on Silica Gel under Viscous Conditions. Oxid. Commun., 34 (3), 616 (2011). Received 19 January 2012 Revised 16 March 2012
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Oxidation Communications 35, No 2, 404–412 (2012) Antioxidant, antibacterial, antagonists activity in biological systems
Comparative Study on the Antioxidant Activity and Polyphenol Content of Some Salvia Species (Salvia L.) N. Gougoulias Department of Plant Production, Technological Educational Institute of Larissa, Larissa, Greece E-mail:
[email protected] ABSTRACT Мethanol extracts of 4 Salvia species: Salvia officinalis, Salvia sclarea, Salvia tribola and Salvia pomifera, grown in the experimental field of TEI – Larissa, Greece were studied. The leaves mass of the plants was analysed in regard to antiradical activity with DPPH• and ABTS•+ and the ferric reducing antioxidant power using the FRAP reagent. The total content of polyphenols (TP), nonflavonoid (NFP) and flavonoid (FP) phenols as well as that of total flavanols (F-3-ols) was measured. It was found that the DPPH activity in the studied herbs varies from 6.20 tо 8.34 μmol Trolox/g dry weight (dw), АBTS – from 13.12 tо 16.32 μmol Trolox/g dw, and FRAP – from 2.66 tо 3.53 μmol Trolox/g dw. The content of ТР, NTP FP and F-3-ols in the investigated samples depends on the species type and their average content is 11.80, 8.54, 3.33 mg GAE/g dw and 95.5 mg СЕ/g dw. The relation ‘dose–effect’ between the amount of TP and IC50 determined by DPPH, ABTS and FRAP is different for the various species. The results are discussed and compared with those reported by other authors. Keywords: Salvia, DPPH, ABTS, FRAP, polyphenols, phenolic fractions, IC50. AIMS AND BACKGROUND In recent years the evidences for the damaging effect of active oxygen- and nitrogencontaining free radicals (ROS, RNS) on various biomolecules in the cells of anaerobic organisms have increased essentially. They largely contribute to pathological disturbances, leading to inflammation processes, atherosclerosis, cardio-vascular, diabetic nervous-pathological and other diseases of the human organism1. This provokes an enhanced interest towards natural biologically active substances in the food, called antioxidants and to the studies on the plant sources of substances neutralising and scavenging the free radicals2–5. Today the studies of these compounds are expanding intensively in view of their practical use in foodstuff, pharmaceutical cosmetic and perfumery industry6. Among these plants Salvia species are distinguished by numerous 404
biologically active and pharmacological effects with antioxidant, anti-inflammatory, antimicrobial, antivirus and other activity. It is noted in literature that most of the antioxidant activity of the plants, including that of Salvia is closely related with the presence of various in structure and biological effect polyphenols, some of which are abundant in the separate types7–10. Garden sage belongs to the genus Salvia L. (Lamiaceae family), which has nearly 900 species throughout the world. The Mediterranean climate and high atmospheric humidity of the air in Greece favour the growth of many essential and medicinal plants including those of the Salvia genus. Greece is one of the countries with wide multivariant distribution of this genus and some of these species are called ‘Greek’ or ‘Cretan’ Salvia. The literature survey reveals that there are few comparative studies on the relation between antioxidant activity and polyphenol fractions in methanol extracts of different Salvia species Most of the studies in literature are focused on Salvia officinalis (garden sage), since it is used as a reference plant because of its well-known and widely documented antioxidant properties10 ,11. The aims of this research were: (a) to compare the antiradical activity (DPPH•, АBTS•+) and ferric reducing antioxidant power (FRAP) of methanol extracts of 4 Salvia species; (b) to determine the amount of total phenolics (ТР) of 4 Salvia, and the content of polyphenol fractions – nonflavonoid (NFP), flavonoid (FP), total flavanols (F-3-ols), and (c) to compare their antioxidant activity by estimating IC50 of the studied extracts. EXPERIMENTAL Plant material. The plant material consisted of the leaf mass of 4 species: Salvia officinalis L., known as garden sage (Sage), Salvia sclarea L., Salvia triloba L. (Greek Salvia) and Salvia pomifera L. (Cretan Salvia). The leaves were collected in the summer of 2010. The plants were grown in the experimental field of TEI – Patra, Greece. The leaves were dark-dried, at room temperature, finely ground and kept at 4oC in dark until tested. The water content of the samples was determined by the classical method by drying at 102oC. Preparation of the methanol extracts. 500 mg of the finely ground sample were 2fold treated by 20 ml 80% aqueous methanol. At the 1st treatment the samples was incubated for 24 h in the extragent at stirring and the 2nd one – continued for 2 h at stirring at ambient temperature. The extract was gathered after centrifugation or filtration and the volume was made up to 50 ml with aqueous methanol. DETERMINATION OF ANTIOXIDANT ACTIVITY
DPPH• assay. The antiradical activity of the methanol extracts was determined on the basis of the method of Brand-Williams12, using the stable free radical 2,2′-diphenyl1-pycrylhydrazyl (DPPH•), as a reagent. The activity was expressed in μmol DPPH/g
405
dry weight, as well as in mg/g dry matter and μmol Trolox (synthetic vitamin Е)/g dry weight. ABTS assay. The activity was determined by bleaching the coulour of the stable free cation ABTS•+ (2,2-аzinobis-(3-ethylbenzothiazolin-6-sulphonic acid ) using the method of Re et al.13, and expressed in μmol Trolox (TAEC)/g dry weight. Ferric reducing antioxidant power assay (with FRAP reagent). The ferric reducing antioxidant power (FRAP) was evaluated according to the method of Benzie et al.14 and was expressed as µmol FRAP reagent/g dry weight. The activity was also presented as aTrolox equivalent (TEAC) and scorbic acid equivalent (AAE) in μmol/ g dry weight. DETERMINATION OF POLYPheNOLS
Total polyphenols (TP). Total polyphenols (TP) contents were determined with the Folin-Ciocalteu (F.-C.) reagent according to the method of Singleton and Rossi15 using the microvariant proposed by Badenschneider et al.16, and were expressed as gallic acid equivalent (GAE) in mg/g fresh and dry weight. Nonflavonoid phenols (NFP). They were determined with the F.-C. reagent after the removal of flavonoid phenols (FP) with formaldehyde according to the method of Kramling17. NFP content was expressed as gallic acid equivalent (GAE) in mg/g fresh and dry weight. Flavonoid phenols (FP). Flavanoid phenols were determined as a difference between the content of total phenols (TP) and nonflavonoid phenols (NFP). Their amount was evaluated as gallic acid equivalent in mg/g fresh and dry weight, Total flavanols (F-3-ols). The determination of the content of total flavanols (catechins and procyanidins) were performed using р-dimethylaminocinnamaldehyde (p-DMACA) reagent after the method of Li et al.18 and was presented as catechin equivalent (CE), in μg/g fresh and dry weight. The inhibition coefficient (IC50), represents 50% reduction in the colour intensity of the radicals DPPH and ABTS by the total phenols (mg/g) in the studied extracts after plotting the depencence of the TP content on the bleaching of DPPH• and ABTS•+ solutions. The percentage of inhibition was calculated by the following equation: % inhibition = ((E0 – Ex)/E0) × 100,
where Е0 is the extinction of the radical solution before the reaction, and Ех – after antioxidant addition19. Data were reported as mean arithmetic for at least 3 replications. The statistical analysis of the results was performed by well-accepted methods with the help of program estimating the mean±SD.
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RESULTS AND DISCUSSION The antiradical activity of the extract from the studied Salvia species determined by the DPPH• assay are given in Table 1.The radical-scavenging activity (RSA), expressed as μmol DPPH/g dw varies from 18.62 to 25.58. The methanol extract of S. officinalis leaves has the highest activity, and that of S. tribola – the lowest, and the difference amounts to 80% (р0.05). The antiradical activity of the extracts expressed as Trolox equivalent (TEAC) shows also that S. officinalis and S. pomifera has the highest activity. The inhibition coefficient (IC50) varies from 12.51 tо 17.20 μg total phenols (ТР), in 1 g of dry weight. The antiradical efficiency (АЕ) of the Salvia species extracts represents the reciprocal value of the inhibition coefficient (1/IC50) and varies from 7.99 × 10–2 tо 5.12 × 10–2 μg ТР/g dw. Considering the values of the antiradical efficiency the extracts of the investigated Salvia species follow the order: S. pomifera >= S. officinalis > S. sclarea > S. tribola. Table 1. Antiradical activity ( DPPH•) of Salvia leaves extracts
No Species 1 2 3 4
Salvia officinalis L. Salvia sclarea L. Salvia tribola L. Sаlvia pomifera L.
DPPH• (μmol/g dw) 25.58±0.31 21.18±0.37 18.62±0.24 25.46±0.40
TEAC (μmol/g dw) 8.34±0.12 7.16±0.18 6.20±0.21 8.21±0.24
IC50 (μg TP/ml) 12.79 15.91 17.20 13.11
The antiradical activity of the methanol extracts determined by the free radical action assay (ABTS•+), expressed as Trolox equivalents varies from 13.12 tо 16.32 μmol Trolox/g dw (Table 2). The extracts from the leaves of S. tribola manifests the highest antiradical activity (16.32 μmol Trolox/g dw), and those of S. officinalis – the lowest (13.12 μmol Trolox/d dw). The inhibition coefficients IC50 and the corresponding antiradical efficiency (АЕ) with respect to the reaction of phenol compounds in the leaves of the methanol extracts of the studied Salvia species vary from 2.58 tо 4.12 μmol TP/ml and from 23.38 × 10–2 tо 38.80 × 10–2 mol TP/ml. Regarding the АЕ the phenol compounds of the studied species are arranged in the following sequence: S. tribola > S. sclarea > S. pomifera > S. officinalis. Table 2. Antiradical activity (ABTS•+) of methanol extracts from Salvia leaves
No
Species
1 2 3 4
Salvia officinalis L. Salvia sclarea L. Salvia tribola L. Sаlvia pomifera L.
1/ IC50 (μmol TP/g dw) 23.38 × 10–2 26.70 × 10–2 38.80 × 10–2 24.31 × 10–2
TEAC (μmol/g dw) 14.40±0.23 15.93±0.18 16.32±0.14 13.12±0.19
IC50 (μg TP/ml dw) 4.20±0.05 3.78±0.03 2.58±0.04 4.12±0.03
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The antioxidant activity of the 4 Salvia species was also assayed by applying the method using the FRAP reagent, which shows the ferric reducing power antioxidant power of the methanol extracts (Table 3). According to Gohari et al.20, tthe method is characterised by by high sensitivity and provides possibility for estimation of specific reducing properties of medicinal plants extracts. The ferric reducing power of the studied extracts varies from 6.35 tо 9.05 μmol FRAP, from 2.66 tо 3.53 μmol Тrolox, and from 3.30 tо 4.56 μmol ascorbic acid in 1 g dw. The leaves of S. pomifera demonstrate the highest ferric reducing power – 9.05 μmol FRAP, 3.53 μmol Trolox and 4.56 μmol EAA g dw, and the lowest is displayed by the leaves of S. sclarea – 6.35 μmol FRAP, 2.66 μmol TEAC and 3.3 μmol EAA/g dw. Table 3. Ferric reducing antioxidant power of methanol extracts from Salvia leaves
No Species 1 2 3 4
Salvia officinalis L. Salvia sclarea L. Salvia tribola L. Sаlvia pomifera L.
FRAP (μmol/g dw) 7.30±0.09 6.35±0.08 8.32±0.11 9.05±0.14
TEAC (μmol/g dw) 2.97±0.03 2.66±0.04 3.30±0.06 3.53±0.04
EAA (μmol/g dw) 3.75 3.30 4.22 4.56
The higher antiradical and ferric reducing power of the methanol extracts is related to the content and the various types of the phenol compounds which are contained in the various species of the Lamiaceae family9,21,22. The TP content in the studied samples ranges from 10.78 tо 12.51 mg/g dw in gallic acid equivalent (GAE) (Table 4). The leaves of S. pomifera and S. officinalis are distinguished by the highest amount of TP – 12.51 and 12.30 mg/g dw, and those of S. sclarea – by the lowest (10.78 mg/g). However, the highest content of TP, expressed per fresh weight was found in the leaves of S. officinalis (3.80 mg/g), and the lowest – in S. рomifera (2.75 mg/g). Comparing these results with those of other authors9,10, who have studied a larger number of Salvia species, the variations in the TP content in the studied 4 species are not significant and reach 15% (р < 0.02). Polyphenols and their structural diversity besides the type depend on a number of ecological and geographical factors which affect the antioxidant and pharmacological properties9,23–27. Table 4. Content of total phenols (ТР) in extracts from Salvia leaves
No
Species
1 2 3 4
Salvia officinalis L. Salvia sclarea L. Salvia tribola L. Sаlvia pomifera L.
Gallic acid equivalent (GAE) mg/g fw mg/g dw 3.80 ± 0.07 12.30 ± 0.15 3.02 ± 0.05 10.78 ± 0.11 3.60 ± 0.08 11.70 ± 0.13 2.75 ± 0.04 12.51 ± 0.13
It was found that among the polyphenol fractions the flavonoid (FP) phenols are dominant in the 4 Salvia species (Table 5). The highest FP was observed in the 408
leaves of S. pomerata and the lowest – in the leaves of S. tribola, 9.42 and 7.70 mg/g dw, respectively. Regarding the FP content the studied species form 2 groups: the 1st one includes S. рomifera and S. оfficinalis with total content of 9.36 mg GAE/g , and the 2nd one – S. sclarea and S. tribola with 7.75 mg GAE/g dw. The difference is statistically significant (р < 0.05). Table 5. Content of flavonoid phenols (FP) in extracts from Salvia leaves
No
Species
1 2 3 4
Salvia officinalis L. Salvia sclarea L. Salvia tribola L. Sаlvia pomifera L.
Gallic acid equivalent (GAE) mg/g fw mg/g dw 2.88 9.29 ± 0.12 2.16 7.70 ± 0.09 2.08 7.79 ± 014 2.06 9.42 ± 0.11
The nonflavonoid phenols (NFP) in the 4 Salvia species amount to 1/3 of the TP content, and vary from 3.08 tо 3.71 mg gallic acid/g dw (Table 6). The S. tribola extracts have the highest NFP content and the extracts of S. sclarea and S. pomifera – the lowest (p < 0.05). Table 6. Content of nonflavonoid phenols (NFP) in extracts from Salvia leaves
No
Species
1 2 3 4
Salvia officinalis L. Salvia sclarea L. Salvia tribola L. Sаlvia pomifera L.
Gallic acid equivalent (GAE) mg/g fw mg/g dw 1.06 3.43 ± 0.05 0.86 3.08 ± 0.04 0.96 3.71 ± 0.03 0.68 3.09 ± 0.04
The contents of total flavanols (catechins, proanthocyanidins) determined with the help of p-DMACA reagent are lower in comparison with TP, FP and NTP, i. e. from 85 tо 108 μg catechin/g dw (Table 7). The differences in the amounts of F-3-ols in the studied Salvia species are statistically insignificant. Table 7. Content of total flavanols (F-3-ols) in extracts of Salvia leaves
No
Species
1 2 3 4
Salvia officinalis L. Salvia sclarea L. Salvia tribola L. Sаlvia pomifera L.
Catechin equivalent (CE) μg/g fw μg/g dw 30.3 98 ± 1.2 25.8 92 ± 1.5 22.1 85 ± 1.8 23.5 107 ± 1.4
The analysis of the results for the antiradical activity determined by DPPH and ABTS, and the ferric reducing power of the methanol extracts of the studied 4 Salvia species supports the conclusions of many authors for the existence of significant 409
differences in the antioxidant activity of the various Salvia species. Kamatou9 , investigating 17 Salvia species from South Africa established that IC50 determined by DPPH varies from 1.61 tо over 100 μg/ml, and that assayed with ABTS – from 11.48 tо 49.94 μmol/ml. The content of TP is also very different in these species ranging from 45.56 tо 211.78 mg GAE/g dw. Similar differences in the antioxidant properties of the various Salvia species have been reported by other authors8,10,28–30. The results obtained for the antioxidant and ferric reducing potential of the methanol extracts of the studied Salvia species point to a different free radical scavenging activity. This shows that the free radicals and the reducing agent react via different pathways with the phenol compounds. According to some authors, the reason for this phenomenon is the great diversity and the different ratio of the phenol and individual compounds in the different Salvia species8,9. Our results for the content of TP, FP, NFP and F-3-ols demonstrate also that their ratio varies in the leaves of the studied species: ТР:FP is ranging from 1.32 tо 1.50; ТР : NTP – from 3.18 tо 4.00; FP : NFP – from 2.02 tо 3.02. Using different techniques many researchers have established that the various Salvia species are rich in flavonoid phenols and in different phenolic acids (rosmarinic acid, caffeic acid, ferulic acid, etc.). These compounds are strong antioxidants and depending on their content the radical scavenging activity and ferric reducing power vary8,9,22,23,31. The results of the studies confirm the findings of many authors that the leaves mass of the Salvia species are rich in antioxidants, and particularly the species Salvia officinalis, Salvia sclarea, Salvia tribola and Salvia pomifera can be proper sources and raw materials for the preparation of antioxidants for food and medical purposes as well as for preparations for the biological agriculture32. CONSLUSIONS The results from the 3 assay methods (DPPH, ABTS and FRAP) revealed that the methanol extracts of 4 Salvia species (S. officinalis, S. sclarea, S. tribola and S. pomifera) exhibited high antiradical and ferric reducing activity. The studied species are rich in total phenols (on average 11.80 mg GAE/g dw), of flavonoid phenols (on average 8.54 GAE/g dw), nonflavonoid phenols (on average 3.33 mg GAE/g dw) and lower amount of total flavanols (on average 95.5 μg СЕ/g dw). The high antiradical capacity and ferric reducing power of the phenol compounds of the studied Salvia species correspond with the data reported by other authors on other Salvia species in countries and regions of the Mediterranean basin. REFEReNCES 1. B. Halliwell, J. M. C. Gutteridge: Free Radicals in Biology and Medicine. 2nd ed. Clarendon Press, Oxford, 1989, 1–21. 2. F. Shahidi: Natural Antioxidants: Chemistry, Health Effects and Applications (Ed. F. Shahidi). AOCS Press, Champaign Illinois, 1997. 3. B. J. F. Hudson: Food Antioxidants (Ed. B. Hudson). Elsevier Applied Science, London, 1990.
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4. L. Parsker, M. Hiramatsu, T. Yoshikawa: Antioxidant. Food Supplements in Human Health (Eds L. Packer, M. Hiramatsu, T. Yoshikawa). Academic Press, 1999. 5. L. BRAVO: Polyphenols: Chemistry, Dietary Sources, Metabolism and Nutritional Significance. Nutrition Reviews, 56 (11), 317 (1998). 6. J. Pokorny, N. Yanashlieva, M. Gordon: Antioxidants in Food. CSC Press, England, 2001 7. M. R. MOEIN, S. MOEIN, S. AHMADIZADEH: Radical Scavenging and Reducing Power of Salvia mirzayanii Subfractions. Molecules, 13, 2804 (2008). 8. B. NICKAVER, M. KAMALINEJAD, H. IZADPANAH: In vitro Free Radical Scavenging Activity of Five Salvia Species. Pak. J. Pharm.Sci., 20 (4), 291 (2007). 9. G. P. P. KAMATOU: Indegenus Salvia Species and Investigation of Their Pharmacological Activity and Phytochemistry. Ph. D. Tessis, Johannesburg, 2006. 10. M. TOSUN, S. ERCISLI, M. SENGUL, H. OSER, T. POLAT, E. OZTURK: Antioxidant Properties and Total Polyphenolic Content of Eight Salvia Species from Turkey. Biol. Res., 42, 175 (2009). 11. G. ОBOH, T. HENLE: Antioxidant and Inhibitory Effects of Aqueous Extracts of Salvia officinalis Leaves on Pro-antioxidant Induced Lipid Peroxidation in Brain and Liver in vitro. J. Med. Food, 12 (1), 77 (2009). 12. W. Brand-Williams, M. E. Cuvellier, C. Berset: Use of Free Radical Method to Evaluate Antioxidant Activity. Lebensm. Wiss. Technol., 28, 25 (1995). 13. R. RE, N. Pellegrini, A. Proteggente, A. Pannala, C. Min Yang, C. Rice-Evans: Antioxidant Activity Applying an Improved ABTS Radical Cation Decolorization Assay. Free Radical Biology and Medicine, 26 (9/10), 1231 (1999). 14. F. F. Benzie, J. J. Strain: Ferric Reducing (Antioxidant Power Assay). Methods in Enzymology, 299, 15 (1999); F. F. Benzie, J. J. Strain: Red Wines. J. Agric. Food Chem., 48, 220 (2000). 15. V. L. Singleton, S. A. Rossi: Colorimetry of Total Phenolics with Phosphomolibdic-phosphotungestic Acid Reagents. J. Enol. Viticult., 16, 144 (1965). 16. B. BADENSCHNEIDER, D. LUTHRIA, A. L. WATERHOUSE, P. WINTERHALTER: Antioxidants in White Wine ( cv. Riesling ): 1. Comparison of Different Testing Methods for Antioxidant Activity. Vitis, 38 (3), 127 (1999). 17. T. E. Kramling, V. L. Singleton: An Estimate of the Nonflavonoids Phenolics in Wines. Am. J. Enol. Vitic., 20, 86 (1969). 18. Y.-G. Li, G. Tanner, P. Lakin: The DMACA–HCL Protocol and the Threshold Proantocyanidin Content for Bloat Safety in Forage Legumes. J. Sci. Food Agric., 70, 89 (1996). 19. G. C. YEN, P. D. DUH: Scavenging Effect of Methanolic Extracts of Peanut Huills on Free Radical and Active-oxygen Species. J. Agric. Food Chem., 42, 629 (1994). 20. A. R. GOHARI, H. HAJIMEHDIPOOR, S. SAEIDIA, Y. AJANI, A. HADJIAKHOONDI: Antioxidant Activity of Some Medical Plant Species Using FRAP Assay. J. Med. Plants, 10 (37), 54 (2011). 21. K. K. KODJE, V. K. JAJDALE, S. S. DUDHE, G. PHANIKUMAR, R. S. BADERE: Antioxidant Property and Phenolic Compounds of Few Important Plants from Trans-Himalayan Regions of North India. J. Herb. Med. and Toxicology, 4 (2), 145 (2010). 22. M. A. ESMAEILI, M. R. KANANI, A. SONBOLI: Sallvia reuterana Extract Prevents Formation of Advanced Glycation and Products: An in vitro Study. Iranien J. Pharm. Sci., 6 (1), 33 (2010). 23. M. ATANASOVA, S. GEORGIEVA: Comparative Polyphenol Composition and Antioxidant Capacity of the Bulgarian Plants (Dry Herbs). EJEAFChe, 9 (9), 1514 (2010). 24. М. CIOROI, D. DIMITRIU: Studies of Total Polyphenols Content and Antioxidant Activity of Aqueous Extracts from Selected Lamiaceae Species. Ann. Uni. Dunarea de Jos Galati, Romania, Fascicle – Food Technology, 34 (1), 42 (2009). 25. G. MILIAUSKAS, P. R. VENSKUTONIS, A. WAN BEEK: Screening of Radical Scavenging Activity of Medical and Aromatic Plant Extracts. Food Chem., 85, 231 (2004).
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26. F. N. HABIBVASH, M. A. RAJAMAND, R. HEIDRI, S. H. SARGHEIN, M. H. RICANI: Study of Some Salvia (Lamiaceae) Species Native to West Azarbeijan Considering Their Phenolic Compounds. Pakistan J. of Nutrition, 6 (5), 443 (2007). 27. B. TEPE, M. SOKMEN, H. A. AKPULAT, A. SOKMEN: Screening of Antioxidant Potentias of Six Salvia Species from Turkey. Food Chemistry, 95, 200 (2006). 28. D. BARCEVIC, T. BARTOL: Pharmacology. 11. The Biological/Pharmacological Activity of Salvia Genus. Copiryght OPA, part of the Gordon and Breach publishing group, 2000, 143–184. 29. E. A. ADEWUSI, N. MOODELY, V. STEENKAMP: Antioxidant and Acetylcholinesterase Inhibitory Activity of Selected Southern African Medicinal Plants. South African J. of Botany (SAJB), doi:10.1016/j.sajb,.2010.12.009, 2011. 30. L. KUZMA, D. KALEMBA, M. ROZALSKI, B. ROZALSKA, M. WIECKOWSKA-SZAKIEL, U. KRAJIEWSKA, H. WYSOKINSKA: Chemical Composition and Biological Activity of Essential Oil from Salvia slarea Plant Regenerated in vitro. Moleculs, 14, 1438 (2009). 31. G. JNICSAK, I. MATHE, M. MIKLOSSY-VERI, G. BLUNDEN: Comparative Studies of the Rosmarinic Acid and Caffeic Acid Contents of Lamiaceae Species. Biochemical Systematic and Ecology, 27, 733 (1999). 32. S. DAGOSTIN, T. FORMOLO, O. GIOVANNINI, I. PERTOT: Salvia officinalis Extract Can Protect Grapevine againts Plasmopora viticola. Plant Dis., 94, 575 (2010). Received 8 August 2011 Revised 27 October 2011
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Oxidation Communications 35, No 2, 413–422 (2012) Antioxidant, antibacterial, antagonists activity in biological systems
Protein Carbonyl Content as the Most General and Well-used Biomarker of Severe Oxidative Stress A. Hacisevkia*, B. Babaa, A. Gonenca, S. Aslanb Department of Biochemistry, Faculty of Pharmacy, Gazi University, 06 330 EtilerAnkara, Turkey E-mail:
[email protected] b Department of Surgery, Ankara Oncology Educational and Research Hospital, Ankara, Turkey a
ABSTRACT Oxidative damage to macromolecules is thought to be an important etiologic factor in the development of several diseases including cancer. The aim of our study was to evaluate the protein and lipid oxidation in patients with gastrointestinal cancers and to investigate the relationship between protein and lipid oxidation, and gastrointestinal cancers. In our study, we included 108 gastrointestinal cancer patients and 35 healthy volunteers. Patients were divided into 3 groups: the 1st group included patients who had pancreas cancer, the 2nd group – patients who had colorectal cancer,and the 3rd group – patients who had liver and esophagus cancer. We investigated changes in serum protein carbonyl (PCO) and plasma nitrotyrosine (NT) levels, as an indicator of protein oxidation and peroxynitrite formation, malondialdehyde (MDA) and tumor necrosis factor α (TNF-α) levels in gastrointestinal cancer (GIC) patients and compare with healthy control groups. Malondialdehyde, a lipid peroxidation marker, was measured by the thiobarbituric acid method. PCO, TNF-α and NT levels were measured by using kits. The levels of MDA, PCO, TNFα and NT were significantly higher in patients with gastrointestinal cancer compared to those of control group (p 6PE is satisfied and hence they can be said to have a good predictive power. Conclusions From the results and discussion made above, it may be concluded that: (1) Of all the indices used the surface tension St is most appropriate for modelling based on multiparametric regression analysis. (2) Smaller groups should be used in future modelling. Cl HN
(3) The group
O N
at R2 position favours the inhibitory activity.
HN
(4) The group
O
at R2 position should be avoided.
REFERENCES 1. R. J. Gillespie, S. J. Bamford, S. Gaur, A. M. Jordan, J. Lerpiniere, H. L. Mansell, G. C. Stratton: Antagonists of the Human A2a Receptor. Part 5. Highly Bio-available Pyrimidine4-carboxamides. Bioorganic and Medicinal Chemistry Letters, 19, 2664 (2009). 2. ACD – Lab Software for Calculating the Referred Physiochemical Parameters. Chem Sketch www. acdlabs.com/acdlabs-rss-feed.xml 3. Dragon Software for Calculation of Topological Indices: www.disatunimib.it. 4. A. K. Srivastava, M. Jaiswal, Archana, A. Srivastava: QSAR Modelling of Selective CC Chemokine Receptor 3 (CCR3) Antagonists Using Physicochemical Parameters. Oxid. Commun., 32, 55 (2009). 5. A. K. Srivastava, A. Srivastava, Archana, M. Jaiswal: Role of Physicochemical Parameters in Quantitative Structure–Activity Relationship Based Modeling of CYP26A1 Inhibitory Activity. J. Indian Chem. Soc., 85, 721 (2008). 6. A. K. Srivastava, Archana, M. Jaiswal: Quantitative Structure–Activity Relationship Studies of ρ-Arylthiocinnamides as Antagonists of Biochemical ICAM- 1/ LFA-1 Interaction in Relation to Antiinflammatory Activity. Oxid. Commun., 31, 44 (2008).
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7. A. K. Srivastava, M. Jaiswal, Archana: QSAR Studies on Indole Substituted Potent Human Histamine H4 Antagonists: Role of Physicochemical and Statistical Parameters. J. Saudi Chem. Soc., 12, 221 (2008). 8. A. K. Srivastava, Archana, M. Jaiswal: Exploring QSAR of Selective PDE4 Inhibitors as 8-substituted Analogues of 3-(3-cyclopentyloxy-4-methoxy-benzyl)-8-isopropyl Adenine. J. Saudi Chem. Soc., 12, 227 (2008). 9. A. K. Srivastava, Archana, M. Jaiswal, A. Srivastava: QSAR Modelling of Selective CC Chemokine Receptor 3 (CCR3) Antagonists Using Physicochemical Parameters. Oxid. Commun., 32, 55 (2009). 10. J. Singh, V. K. Dubey, V. K. Agarwal, P. V. Khadikar: QSAR Study on Octanol–Water Partitioning: Dominting Role of Equalised Electronegativity. Oxid. Commun., 31 (1), 27 (2008). 11. J. Singh, V. K. Agarwal, S. Singh, P. V. Khadikar: Use of Topological as well as Quantum Chemical Parameters in Modelling Antimalarial Activity of 2,4-diamino-6-quinazoline Sulphonamides. Oxid. Commun., 31 (1), 17 (2008). 12. M. V. Diudea: QSPR/QSAR Studies for Molecular Descriptors. Nova Science, Huntingclon, New York, 2000. 13. L. POGLIANI: Structural Property Relationships of Amine Acids and Some Peptides. Amino Acids, 6, 141 (1994). 14. L. Pogliani: Modeling with Special Descriptors Derived from a Medium Size Set of Connectivity Indices. J. Phys. Chem., 100, 18065 (1996). 15. R. D. Carmer III, J. D. Bunce, D. E. Patterson, I. E. Frank: Cross-validation, Bootstrapping, and Partial Least Squares Compared with Multiple Regression on Conventional QSAR Studies. Quant. Struct. Act. Relat., 7, 18 (1988). 16. S. Chatterjee , A. S. Hadi, B. Price: Regression Analysis by Example. 3rd ed. Wiley VCH, New York, 2000. Received 10 February 2010 Revised 3 April 2010
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Oxidation Communications 35, No 2, 438–451 (2012) Thermal degradation and stabilisation of polymeric materials
Thermal and Combustion Behaviour of PP/MWCNT Composites G. E. Zaikova*, S. M. Lomakina, E. V. Kuvardinab, L. A. Novokshonovab, N. G. Shilkinab, R. Kozlowskic N. M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygin Street, 119 334 Moscow, Russia E-mail:
[email protected] b N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygin Street, 119 991 Moscow, Russia c Institute of Natural Fibres, 71b Wojska Polskiego Street, 60 630 Poznan, Poland a
ABSTRACT Studies of thermal and fire-resistant properties of the polypropylene/multi-walled carbon nanotube composites (PP/MWCNT) prepared by means of melt intercalation are discussed. The sets of the data acquired with the aid of non-isothermal TG experiments have been treated by the model kinetic analysis. The thermal-oxidative degradation behaviour of PP/MWCNT and stabilising effect caused by addition of MWCNT has been investigated by means of TGA and EPR spectroscopy. The results of cone calorimetric tests lead to the conclusion that char formation plays a key role in the mechanism of flame retardation for nanocomposites. This could be explained by the specific antioxidant properties and high thermal conductivity of MWCNT which determine high-performance carbonisation during thermal degradation process. Comparative analysis of the flammability characteristics for PP-clay/MWCNT nanocomposites was provided in order to emphasise the specific behaviour of the nanocomposites under high-temperature tests. Keywords: polypropylene, thermal degradation, combustion, kinetic analysis, TG, TGA, ESR spectroscopy, cone calorimetric test, antioxidants, thermal conductivity. AIMS AND BACKGROUND At present time the great attention is given to the study of properties of polymeric nanocomposites produced on the basis of well-known thermoplastics (polypropyl*
For correspondence.
438
ene (PP), polyethylene (PE), polystyrene (PS), poly(methylmethacrylate (PMMA), polycarbonates, polyamides) and carbon nanotubes (CN). CNs are considered to have the wide set of important properties like thermal stability, reduced combustibility, electroconductivity, etc.1–7 Thermoplastic polymer nanocomposites are generally produced with the use of melting technique1–12. Development of synthetic methods and the thermal characteristics study of PP/ multi-walled carbon nanotube (MWCNT) nanocomposites were taken as an objective in this paper. A number of papers pointed at synthesis and research of thermal properties of nanocomposites (atactic polypropylene (aPP)/MWCNT) were reported10–12. It is remarkable that PP/MWCNT composites with minor level of nanocarbon content (1–5 wt.%) were determined to obtain an increase in thermal and thermal-oxidative stability in the majority of these publications. Thermal stability of aPP and aPP/MWCNT nanocomposites with the various concentrations of MWCNT was studied in the paper10. It was shown that thermal degradation processes are similar for aPP and aPP/MWCNT nanocomposites and initial degradation temperatures are the same. However, the maximum mass loss rate temperature of PP/MWCNT nanocomposites with 1 and 5 wt.% of MWCNT raised by 40–70°C as compared with pristine aPP. Kashiwagi et al. published the results of study of thermal and combustion properties of PP/MWCNT nanocomposites11,12. A significant decrease of maximum heatrelease rate was detected during combustion research with use of cone calorimeter. A formation of char network structure during the combustion process was considered to be the main reason of combustibility decrease. The carbonisation influence upon combustibility of polymeric nanocomposites was widely presented in literature10–13. Notably, Kashiwagi et al.11,12 were the first to hypothesise that abnormal dependence of maximum heat-release rate upon MWCNT concentration is closely related with thermal conductivity growth of PP/MWCNT nanocomposites during high-temperature pyrolysis and combustion. EXPERIMENTAL Materials. Isotactic polypropylene (melting flow index = 0.7 g/10 min) was used as a polymer matrix in this paper. Multi-walled carbon nanotubes (MWCNT) (purchased from Shenzhen Nanotechnologies Co. Ltd.) were used as a carbon-containing nanofillers. This product contains low amount of amorphous carbon (less than 0.3 wt.%) and could be produced with different size characteristics – different length and different diameter and therefore different diameter to length ratio. Size characteristics for 3 MWCNT used in this paper are given in Table 1. Sizes and structure of initial MWCNT were additionally estimated by SEM (Fig. 1). Table 1. Properties of MWCNT
439
Designation
D (nm)
L (μm)
MWCNT (K1) MWCNT (K2) MWCNT (K3)
C=O of carbonyl group), 1604, 1535–1511 cm–1 (C=N) and 1373–1357 cm–1 (N−H, C−N). In the 1H NMR spectra one can observe multiple signals with chemical shifts at 1.75–2.07 ppm related to the 15 protons in adamantyl groups, in the weakest field of the 1H NMR spectra is shown that the proton at the unsaturated carbon atom gives 3 resonance signals in the form of a wide singlet. In the 1H NMR spectra of the synthesised azomethins (Fig. 1) one can observe singlet signal with chemical shift 8.04 ppm for the protons in the NH groups and the resonance signal with chemical shift 8.52 ppm for the proton of the azomethine group HC=N. The resonance signal with chemical shift 3.01 ppm is assigned to protons of N(CH3)2 (III compound) . In the 1H NMR spectra one can observe also quartet signals with chemical shifts in the 461
range 6.67–7.61 ppm for protons in phenyl groups, also resonance signals with chemical shifts in the range 9.88–10.87 ppm for the protons of HO-groups. In the 13C NMR spectra one can observe a signal with 4 chemical shifts within the range 27.6–40.7 ppm typical for adamantyl group. In the 13C NMR spectra we also observe chemical shifts within the range 160.31–172.60 ppm and the chemical shifts within the range 110.41–159.33 ppm related to carbon atom of C=O groups and carbon atom of phenyl group, correspondingly. 13 C NMR spectral analysis of the synthesised compounds was made as well. 4 sections are clearly distinguished in the spectrum: (i) Resonance signal of sp3 hybridised carbon atoms (=CH2, ≡CH groups of adamantane) with chemical shift 0–40 ppm; (ii) Resonance signals with chemical shift – 40–50 ppm of the carbon atom of methyl groups bound with electrically negative element; (iii) Resonance signal of sp2 hybridised carbon atoms of aromatic nucleus, and (iv) Resonance signal related to carbon atoms of the carbonyl groups (Table 1) (Refs 16 and 17). Mass-spectrometric method gives significant information for establishing the structure of the synthesised compounds. In particular, this method allows determining values of molecular masses (M+), while mass values (m/z) of fragmentary ions formed as a result of cleavage of molecular ion clearly show the order of cleavage of atoms or groups of atoms. The mass-spectrogram data for the synthesised azomethins (for example, Ms m/z 314 (M+,4.8, 255 (40), 180 (12), 135 (100), 105 (27), 77 (18) – compound IV) show that the masses of molecular (M+) and fragmental ions correspond with obtained structures of mentioned above compounds Electronic structure and complex-forming capacity of initial ligands were studied using semi-empirical quantum-chemical method AM1 (Austn Model 1) (CS MOPAC (Chem 3D Ultra-version 8.03)). Power and geometrical characteristics, effective charges on atoms and electron occupation of atomic orbital (electronic density) were determined (Tables 2–7). Table 2. Relative charges and electronically density on the atoms in compound II benzaldehydeadamantoylhydrazone
Atom, i 1 C1 C2 C3 C4 C5 C6 C7 C8 C9
Relative charge, qi 2 –0.057107 –0.151028 –0.099041 –0.151232 –0.101033 –0.144070 –0.143182 –0.151055 –0.149775
Electronic density, qi (d) 3 4.0571 4.1510 4.0990 4.1512 4.1010 4.1441 4.1432 4.1511 4.1498
Atom, i 4 H23 H24 H25 H26 H27 H28 H29 H30 H31
Relative charge, qi 5 0.086037 0.090760 0.081184 0.083797 0.093275 0.108483 0.084429 0.087674 0.106152
Electronic density, qi (d) 6 0.9140 0.9092 0.9188 0.9162 0.9067 0.8915 0.9156 0.9123 0.8938 to be continued
462
Continuation of Table 2
1 C10 C11 O12 N13 N14 C15 C16 C17 C18 C19 C20 C21 H22
2 –0.101055 0.298916 –0.355295 –0.315839 –0.058157 –0.057711 –0.090905 –0.079603 –0.134203 –0.122547 –0.139128 –0.112389 0.081651
3 4.1011 3.7011 6.3553 5.3158 5.0582 4.0577 4.0909 4.0796 4.1342 4.1225 4.1391 4.1124 0.9183
4 H32 H33 H34 H35 H36 H37 H38 H39 H40 H41 H42 H43
5 0.081559 0.083639 0.081572 0.086234 0.093301 0.246457 0.159347 0.154388 0.133685 0.129615 0.130326 0.131873
6 0.9184 0.9164 0.9184 0.9138 0.9067 0.7535 0.8407 0.8456 0.8663 0.8704 0.8697 0.8681
Table 3. Electron occupation of the orbitals in the atoms of compound II benzaldehydeadamantoylhydrazone
Atom O12 N13
2s 1.91546 1.48926
2px 1.11301 1.10715
2py 1.86931 1.00147
2pz 1.45751 1.71795
Table 4. Relative charges and electronical density on the atoms in compound III: 4-dimethylamino benzaldehydeadamantoylhydrazone
Atom, i Relative charge, Electronic qi density, qi (d) 1 2 3 C1 –0.057304 4.0573 C2 –0.150719 4.1507 C3 –0.099080 4.0991 C4 –0.151132 4.1511 C5 –0.100942 4.1009 C6 –0.144102 4.1441 C7 –0.143255 4.1433 C8 –0.150886 4.1509 C9 –0.149676 4.1497 C10 –0.101113 4.1011 C11 0.300749 3.6993 O12 –0.357779 6.3578 N13 –0.316683 5.3167 N14 –0.063519 5.0635 C15 –0.045319 4.0453 C16 –0.130050 4.1301
Atom, i 4 H27 H28 H29 H30 H31 H32 H33 H34 H35 H36 H37 H38 H39 H40 H41 H42
Relative charge, qi 5 0.090132 0.080779 0.083243 0.092632 0.108193 0.083973 0.088542 0.107413 0.081540 0.082911 0.080906 0.086244 0.093330 0.244874 0.156109 0.156681
Electronic density, qi (d) 6 0.9099 0.9192 0.9168 0.9074 0.8918 0.9160 0.9115 0.8926 0.9185 0.9171 0.9191 0.9138 0.9067 0.7551 0.8439 0.8433 to be continued
463
Continuation of Table 4
1 C17 C18 C19 C20 C21 N22 C23 C24 H25 H26
2 –0.056046 –0.174723 0.072916 –0.195247 –0.082310 –0.247934 –0.099723 –0.096510 0.080743 0.086587
3 4.0560 4.1747 3.9271 4.1952 4.0823 5.2479 4.0997 4.0965 0.9193 0.9134
4 H43 H44 H45 H46 H47 H48 H49 H50 H51
5 0.136952 0.131550 0.129939 0.089986 0.084522 0.053323 0.083461 0.088774 0.057048
6 0.8630 0.8685 0.8701 0.9100 0.9155 0.9467 0.9165 0.9112 0.9430
Table 5. Electron occupation of the orbitals in the atoms of compound III: 4-dimethylaminobenzal dehydeadamantoylhydrazone
Atom O12 N13 N22
2s 1.91538 1.48939 1.52343
2px 1.11148 1.10730 1.03460
2py 1.87005 1.00162 1.66458
2pz 1.46087 1.71838 1.02532
Table 6. Relative charges and electronical density on the atoms in compound IV: 2,4- dihydroxybenzaldehydeadamantoylhydrazone
Atom, i
Relative charge, qi
Electronic density, qi (d)
Atom, i
Relative charge, qi
Electronic density, qi (d)
1 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 O12 N13 N14 C15 C16 C17 C18
2 –0.057074 –0.151109 –0.099029 –0.151220 –0.100990 –0.143852 –0.143079 –0.150923 –0.149631 –0.101195 0.301548 –0.367069 –0.315532 –0.058028 –0.028559 –0.154963 –0.018753 –0.194474
3 4.0571 4.1511 4.0990 4.1512 4.1010 4.1439 4.1431 4.1509 4.1496 4.1012 3.6985 6.3671 5.3155 5.0580 4.0286 4.1550 4.0188 4.1945
4 H24 H25 H26 H27 H28 H29 H30 H31 H32 H33 H34 H35 H36 H37 H38 H39 H40 H41
5 0.081709 0.086495 0.090524 0.081273 0.083318 0.092998 0.108189 0.084399 0.086549 0.106754 0.081091 0.083246 0.081189 0.086328 0.092734 0.247735 0.160669 0.167054
6 0.9183 0.9135 0.9095 0.9187 0.9167 0.9070 0.8918 0.9156 0.9135 0.8932 0.9189 0.9168 0.9188 0.9137 0.9073 0.7523 0.8393 0.8329
464
to be continued
Continuation of Table 6
1 C19 C20 C21 O22 O23
2 0.124353 –0.310972 0.134033 –0.247015 –0.246929
3 3.8756 4.3110 3.8660 6.2470 6.2469
4 H42 H43 H44 H45
5 0.156007 0.135141 0.217940 0.219122
6 0.8440 0.8649 0.7821 0.7809
Table 7. Electron occupation of the orbitals in the atoms of compound IV: 2,4-dihydroxybenzaldehydeadamantoylhydrazone
Atom O12 N13 O22 O23
2s 1.91548 1.48458 1.86221 1.86235
2px 1.11072 1.10805 1.40948 1.34561
2py 1.87127 1.00129 1.78825 1.75314
2pz 1.46960 1.72162 1.18708 1.28583
Calculations showed that molecules of ligand contain potentially electron-donor atoms – O and N, and that is why they are able to form coordination compounds with d-metals. In the molecule of compound II, benzaldehydeadamantoylhydrazone (Scheme 1, Fig. 1) bond lengths of carbon atom C11 with neighbour atoms and bond angles (∠C1–C11–O12=120.1o, ∠C1–C11–N13=118.6o and ∠O12–C11–N13=121.4o) point mainly to sp2 hybrid state. As seen from values of bond angles of oxygen atom O12 it seems to be in sp2 hybrid state. According to the values of bond angles, nitrogen atom N13 (∠C11–N13–N14=128.9o, ∠C11–N13– H40=117.0o, ∠ N14–N13– H40=110.0o) seems to be in sp2 hybrid state. Analysis of the values of relative charge on atoms in the molecule of the same compound (Table 2) shows that O12 (q12 = −0.355295) and N13 (q13 = −0.315839) represent potential donors of electrons18–20. Electron occupation of atom orbitals (Table 3) shows that one of the electron pairs of oxygen atom is located on 2s orbital (electron occupation 1.91546 (O12)) (Refs 18–20). It has capacity to form σ-bond with metal atom by donor-acceptor mechanism. N13 atom is unable to form σ-bond with metal atom by donor-acceptor mechanism, as the electron pair is located on non-hybridised 2pz orbital (electron occupation 1.71795). In the molecule of compound III, 4-dimethylaminobenzaldehydeadamantoylhydrazone (Scheme 1, Fig. 2) bond lengths of carbon atom C11 with neighbour atoms and bond angles (∠C1–C11–O12=120.1o, ∠C1–C11–N13=118.6o and ∠O12–C11–N13=121.4o) point to its main sp2 hybridisation state. As the values of bond angles show, the oxygen atom O12 is in sp2 hybridisation state. According to the values of bond angles, nitrogen atom N13 (∠C11–N13–N14=128.9o, ∠C11–N13–H40=117.0o, ∠ N14–N13–H40=110.0o) seems to be in sp2 hybrid state. Analysis of the values of relative charge on atoms in the molecule shows that O12 (q12 = −0.357779), N13 (q13 = −0.316683) and N22(q22 = −0.247934) (Table 4) are potentially electron- donor atoms. Electron occupation of 465
atom orbitals shows that one of the electron pairs of oxygen atom is located on 2s orbital [electron occupation 1.91538 (O12), and one of the electron pairs of N22 atom is on 2py orbital (electron occupation 1.66458 (N22)) (Table 5). They are able to form σ-bond with metal atom by donor-acceptor mechanism. N13 atom is unable to form σ-bond with metal atom by donor-acceptor mechanism as the electrons pair is located on 2pz orbital left without hybridisation (electron occupation 1.71838).
Fig. 1. 3D model of benzaldehydeadamantoylhydrazone
Fig. 2. 3D model of 4-dimethylaminobenzaldehydeadamantoylhydrazone
Thus the molecule of compound III contains 2 potentially electron-donor atoms – O12 and N22. Due to this it represents a bidentate ligand and is capable of forming coordination compounds with d-metals in the form of 9-member cycle, though due to forming of bonds of non-real length M→O and M→N(CH3)2 it is more likely 466
forming of 5-member cyclic coordination compound, being proven by the fact that in the IR spectrum of the corresponding coordination compound absorption band of C–N bond of N(CH3)2 group (1357 cm–1, Table 1) remains unchanged, though the frequency corresponding to absorption band of HC=N bond somehow decreases (for the ligand – 1535.6 cm–1, Table 1; for coordination compound – 1519.5 cm–1, Table 8). Table 8. Infrared spectral data of the coordination compounds of synthesised hydrazide–hydrazones with Cu(II), Fe(II) and some their physical properties (L = II, III, IV, Scheme 1)
No
Compound
Colour
Decom. Infrared spectral data, ν (cm–1) starting temp., in air (oC) 320 3220 (NH); 2900,2846, (CH,Ad); 1643 (C=O); 1643 (C=N); 1550, 1357 (C–N) 1172 (C–H val.); 1018 (C–C); 948, 817 (C–H bul); 725(OCN); 678, 578 (amid MN + MO); 400 (MO)
5
Fe(LIII)2SO4•4H2O yellowish
6
Cu(LIII)2Cl2 •2H2O greenish-yellow
285
3200(NH),1590(C=O);1650(C=N); 1457(CH2),1373 (CH3);1311(C–N);1172 (C–H val.);1018 (C–C); 948, 817(C–H bul); 725(OCN); 678, 578 (amid); 400 (MO)
7
Cu(LII) 2Cl2 •2H2O light yellow
270
3309(NH),1650,1604 (C=O);1 645 (C=N); 527 (CN+H+O); 457(CH2), 1373, 1311 (CH3); 1249(C–N); 1180, 1103 (C–H val.); 972, 941, 856(C–H bul); 1056(C– C),725 (OCN); 694, 609 (CNM+MNN); 516(MN+MO); 400 (MO)
8
Cu(LIV)2Cl2 •2H2O black
260
3162(NH), 1652 (C=N);1596, 1535 (C=O);1457 (CH2); 1373,1303 (CH3); 1234(C–N); 1172(C–H val.); 979, 941, 848 (C–H bul); 1072(C–C), 725 (OCN); 664, 609 (CNM + MNN); 524(MN + MO)
9
Fe(LIV)2SO4•4H2O dark green
310
3232(NH), 1619(C=N);1558 (C=O); 1457 (CH2); 1373 (CH3); 1234 (C–N); 1180(C– H val.); 979, 848 (C–H bul); 725(OCN); 663, 540 (amid); 501,470 (MN + MO)
Analysis of the values of relative charges on atoms in the molecule of IV compound (Scheme 1, Table 6) shows that atoms O12 (q12 = −0.367069) N13 (q13 = −0.315532), O22 (q22 = −0.247015) and O23 (q23 = −0.246929) seem to be potentially electron-donor atoms. Electron occupation of atom orbitals (Table 7) shows that one of pairs of oxygen atoms is located on 2s orbital (electron occupation 1.91548 (O12), 1.86221 (O22) and 1.86235 (O23)). They are able to form σ-bond with metal atom by 467
donor-acceptor mechanism. As in the mentioned above cases N13 atom is unable to form σ-bond with metal atom by donor-acceptor mechanism as the electron couple is on the 2pz orbital left without hybridisation (electron occupation 1.72162) (Refs 15, 18–20).
Fig. 3. 3D model of 2,4- dihydroxybenzaldehydeadamantoylhydrazone
Thus, the molecule contains 3 potentially electron-donor atoms O12, O22 and O23. In all 3 mentioned above cases (compounds II–IV) in spite of the relatively small value of the charge on N14 atom the coordination of this atom to d-metal ion is possible on account of its n-electrons. We elaborated the conditions for the synthesis of coordination compounds based on the above-mentioned ligands (Cu(II) and Fe(II)). Organic ligand dissolved in the obtained compounds represents fine crystalline substances of different colours. The structure of the obtained substances was established using methods of elemental analysis, infrared spectroscopy and thermogravimetric analysis21. Analysis of inrfared spectra of the synthesised coordination compounds and adamantane-containing ligands has shown that the molecule of organic ligand is coordinated to the central metal atoms by means of oxygen atom of carbonyl group and N-atom of the azomethine. Spectral data of complex compounds is presented in Table 8. Hydrazide–hydrazone H atom in complexes with ligands of Schiff-base type tends to migrate towards azomethine atom N–H….O to form intramolecular hydrogen bond, which absorption band is 3445–3449 cm–1. Coordination with oxygen atoms of ligands and corresponding M(II) ions is well expressed in infrared spectra. Accordingly, a new absorption band 400 cm–1∼524 cm–1 emerges. A strong coordination bond is formed between N atom of C=N group of ligands of free Schiff-base type and M(II) ions forming corresponding absorption band (C=N, IV – 1643 cm–1, V – 1650 cm–1, VI – 1645 cm–1, VII – 1652 cm–1, 1619 (C=N) (Refs 11 and 12). 468
Indeed, in IR spectra of the obtained coordination compounds the decrease as compared with free ligand of absorption band corresponding with valence oscillations of carbonyl group (∆ν (C=O) ≈30–40 cm–1) points that the organic ligand is coordinated to the central metal atom by means of oxygen atom of carbonyl group M←O=C and, on the other hand, by n-electrons of N atom. Complex compounds were synthesised in aqueous solution of ethanol CuCl2⋅2H2O with corresponding ligands LII, LIII, LIV at molar ratio 1:1, 1:2. Mainly formation of bi(ligand) complexes takes place, though FeSO4⋅7H2O LIII, LIV forms with the same ligand bi(ligand)bi(aqua) complexes. Molar electric conductivity of coordination compound with copper (II) and iron (II) in DMFA changes within the range of 76–88 S cm2 mol–1 (Table 9), which corresponds with 1:1 type electrolyte (69–90 S cm2 mol–1 lit.)9. This fact also confirmed the content (%) of d-metals in complex compounds (Table 9). Table 9. Content of metal in the coordination compounds and their molar electroconductivity
No
Compound
λM, S (cm2 mol–1)
V VI VII VIII IX
Fe(LIII)2SO4• 4H2O Cu(LIII)2Cl2•2H2O Cu(LII)2Cl2•2H2O Cu(LIV)2Cl2• 2H2O Fe(LIV)2SO4• 4H2O
87.5 85.2 76.4 79.7 84.3
Metal content (%) found/calculated 11.30 / 11.45 10.50 / 10.76 11.65 / 11.82 9.48 / 9.55 11.35 / 11.64
*λM determined in dimethylformamide,1 mmol dm–3 solution, 25oC. Table 10. Antibacterial activity of complex compounds (V–IX)
Compound
Concentration (g/l)
II
0.01 0.1 0.01 0.1 0.01 0.1 0.01 0.1 0.01 0.1 0.01 0.1 0.01 0.1 0.01 0.1
III IV V VI VII VIII IX
Test cultures and zones of degradation (mm) Esherichia coli Pectobacterium Xanthomonas aroideac campestris – – – 0.1 – 0.1 – – 0.2 – 0.1 – – – – – 0.5 – 0.1 – 0.5 0.5 – 0.5 0.3 0.5 0.5 0.5 1 1.2 0.3 – – 1.0 – – 0.5 – 0.5 1.0 – 0.5 0.1 – 0.5 0.5 – 0.5
469
Temperature intervals of thermolysis and stability of the obtained compounds were established using the method of thermal analysis. Thermogravimetric analysis of coordination compounds V–IX has shown that thermolysis of obtained compounds is a complex process. After losing water molecules gradual cleavage of molecules of organic ligand takes place. Oxide or salt of corresponding d-metal is a final product of thermolysis. Curves of thermolysis of coordination compound IX (Table 8, Fig. 4) show that decrease in mass of the sample starts in temperature interval 100–111oC. The endothermic effect at 200–210oC is presumably connected with cleavage of water molecules from the inner sphere of the coordination compound, as comparatively small change on mass takes place in the same interval. It should be noted that similar endothermic effect does not take place on the DTA curve of the copper complex.
Fig. 4. TGA-DTG curves of complex IX (Fe(LIII)2 SO4⋅4H2O)
Sharp change in mass is observed at 325–400oC that makes 33% of total mass. At the same temperature range exothermal effect is observed (µνs/mg=−8.9). In this range interaction of FeSO4 with organic ligand or products of its decomposition is responsible for the exothermal effect. We have established that mixture of the ligand and FeSO4 at 300–350oC interact to emit SO2. This once more confirms that reduction of SO4 ions with organic compounds takes place, and the ligand in complex with iron starts to decompose from 325oC. Processes proceeding above 400oC are connected with interaction of products of pyrolysis, which proceeds by a complex mechanism. In the range of 300–400oC also sulphation of aromatic nucleus of the ligand with SO2 and SO3 is possible. It is seen from the curves of thermal analysis of compound VIII (Table 8, Fig. 5) that dehydration of the complex Cu(LIV)2Cl2⋅2H2O starts at 100oC (for comparison CuCl2⋅2H2O undergoes dehydration at 100oC). Together with dehydration of the complex its structure improves, as a result of which a small exothermal effect is observed 470
in the range of 100–200oC. At 250–300oC sharp decline in mass takes place, being caused by cleavage of organic ligand.
Fig. 5. TGA-DTG curves of complex VIII (Cu (LIV)2 Cl2⋅2H2O)
Further drop in mass is connected with reduction of chlorides, copper oxide or base chlorides and deepening of pyrolysis process, which implies removal of volatile products from the system. Above 350oC mainly condensation of organic products takes place and there is possibility of reduction of CuO to copper. It should also be noted that 80% of exothermal effect is caused by processes proceeding up to 300oC and are removed from the reaction zone. Curves of thermal analysis of the complex VI (Table 8, Fig. 6) show that the complex compound starts to decompose at 110oC. Here too small endothermal effect is observed, pointing to splitting of crystallisation water (for comparison CuCl2⋅2H2O decomposes at 110oC).
Fig. 6. TGA-DTG curves of complex VI (Cu (LIII)2 Cl2⋅2H2O)
471
Decrease in mass observed in the range of 200–250oC makes 10% of the total mass. Within 250–275oC interval thermal effect is not evident on the curve. From 275 up to 375oC sharp decline in mass (60% of total mass) takes place that may be caused by thermal dissociation of the complex. In the same range endothermal effect is observed. Roentgenogram of the complex compounds (attachment, Fig.7) confirmed formation of one-phase system.
Fig. 7. Roentgenogram of compound IX
Based on the data of the mentioned above analysis, also considering the potential formation of relatively stable 5-member metal-containing chelate cycles, are presented below more possible structures of the obtained coordination compounds. Scheme 2 HC C
O
HN
N
N
NH
O
C
,
M
CH
where M = Cu; ligand – compound II H2O
H3C H3C
N
C
O
HN
N
N
N
NH
O
C
M
HC
where M = Fe; ligand – compound III
472
CH
H2O
CH3 CH3
,
CH
H3C H3C
C
O
HN
N
N
N
NH
O
C
CH3 CH3
,
M
HC
N
where M = Cu; ligand – compound III
HO H2 O
O
C
CH
OH
N
NH
O
C
M HN
N HC
HO
,
H2O
OH
where M = Fe; ligand – compound IV
HO CH
O
C
OH
N
NH
O
C
M HN HO
N
,
HC OH
where M = Cu; ligand – compound IV STUDY ON THE BIOLOGICAL ACTIVITY OF COMPLEX COMPOUNDS SYNTHESISED ON THE BASIS OF ADAMANTANE-CONTAINING HYDRAZIDE–HYDRAZONE LIGANDS
In order to study expected biological activity of admantane-containing ligands virtual screening was carried out using the internet-system program – PASS C@T, which allows high-precision prediction of possible biological activity of the compound. Prognosis is made on the basis of structural formulas of the compounds (http://www. ibmc.msk.ru/pass). Using microbiological method antibacterial activity of synthesised adamantanecontaining compounds and complex compounds obtained on their basis against some phytopathogenic test microorganisms was studied experimentally. In vitro antibacterial investigation of alcohol solutions of ligands of the type of Schiff base obtained on the basis of adamantane-1-carboxylic acid and correspond473
ing complex compounds at concentrations of 0.001 and 0.1 g/l was carried out on 4 bacteria: Agrobacterium tumefaciens, Escherichia coli, Pectobacterium aroideae, Xanthomonas campestris using the method of filter paper and agar. Concentration of test-solutions was 0.01–0.1 g/l. Results of testing have shown that the synthesised compound possessed selective bactericidal properties towards the above-mentioned bacteria − they manifest toxicity and with different activity suppress growth and development of cultures under study. Bactericidal properties of adamantane-containing hydrazide–hydrazones are expressed weaker than in corresponding complex compounds18,19. The results of experiments indicate that the studied compounds have different effect on test objects. The studied compounds were effective against Escherichia coli, Pectobacterium aroideae, and Xanthomonas campestris, while Agrobacterium tumefaciens was stable against them. Proceeding from the above-mentioned we can conclude that the studied ligands and complex compounds are characterised by selective bactericidal activity and they can be applied against coli bacillus E. coli and diseases caused by phytopathogenic bacteria. CONCLUSIONS • Adamantane-containing hydrazide–hydrazone novel ligands with antimicrobial and antiviral activity were synthesised and studied. • Using the data of IR, NMR and mass-spectra the structure of the obtained ligands was established. By quantum-chemical calculations the complex-forming capacity of the obtained ligands was established. By interaction of salts of some transition metals − MCl2•nH2O, MSO4•nH2O (M = Cu, n=2; M = Fe, n=7) with adamantinecontaining hydrazide–hydrazones the new coordination compounds were synthesised and studied. • Based on the data of IR and elemental analysis (metal content), also based on the data of molar electric conductivity and thermal analysis the structures of the coordination compounds were determined. • The initial ligands and the obtained coordination compounds were tested for their antibacterial activity. It was established that both ligands and the obtained coordination compounds have selective activity towards various microorganisms. REFERENCES 1. I. S. MOROZOV, V. I. PETROV, S. A. SERGEEVA: Pharmacology of Adamantane. The Volgograd Medical Academy, Volgograd, 2001, p. 320. 2. F. SZTARICSKAI, I. PELYVAS, Z. DINYA, L. SZILAGYL: Synthese und virushemmende in vitroWirkung neuerer 1-substituierter Adamantanderivate. Pharmazie, 30 (9), 571 (1975). 3. G. I. DANILENKO, E. A. SHABLOVSKAYA, L. A. ANTONOVA, S. V. GUZHOVA, I. A. LOBANOVA, A. P. DIACHENKO, A. I. PANASIUK: Synthesis and Protective Action of Derivatives of Phenyladamantane toward Rabies Virus. Chim.-Farm. J., 2, 28 (1998).
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4. G. I. DANILENKO, S. I. RYBALKO, Yu. N. MAKSIMOV, V. F. BAKLAN, S. V. GUZHOVA: Hydrazide of Adamantan-1-norbornan-2-carboxylic acid as HIV Inhibitors. Chim. Farm. Zh., 1, 24 (2000). 5. N. G. ARTSIMOVICH, T. S. GALUSHIN, T. A. FADEEVA: Adamantane – Drugs of XXI Century. Int. J. Immunorehabilitation, 2 (1), 54 (2000). 6. V. Y. KOVTUN, V. M. PLAKHOTNIK: Using Adamantancarbonylic Acids for Modification of Drugs Properties and Biologically Active Compounds. Him. Farm. Zh., 8, 931 (1987). 7. S. O. PODUNAVAC-KUZMANOVIC, V. M. LEOVAC, N. U. PERISIC-JANJIC, J. ROGAN, J. BALAZ: Complexes of Cobalt(II), Zinc(II) and Copper(II) with Some Newly Synthesized Benzimidazole Derivatives and Their Antibacterial Activity. J. Serb. Chem. Soc., 64, 381 (1999). 8. S. O. PODUNAVAC-KUZMANOVIC, V. M. LEOVAC, G. S. CETKOVIC, S. L. MARKOV: Synthesis, Physico-chemical Characterization and Biological Activity of Copper(II) and Nickel(II) Complexes with 1-benzoyl-2-methylbenzimidazole Derivatives. Acta Periodica Technologica, 33, 151 (2002). 9. W. J. GEARY: The Use of Conductivity Measurements in Inorganic Solvents for the Characterization of Coordination Compounds. Coord. Chem. Rev., 7, 81 (1971). 10. V. Kh. ARALI, V. K. REVANKAR, V. B. MAHALE, P. J. KULKARNI: Cobalt(II), Nickel(II) and Copper(II) with 2-substitited Benzimidazole Complexes. Transition Met. Chem., 19, 57 (1994). 11. K. NAKAMOTO: Inrfared and Raman Spectra of Inorganic and Cordination Compounds. Wiley, New York, 1986, p. 324. 12. R. H. HOLM, M. O’CONNOR: The Stereochemistry of Bis-chelate Metal(II) Complexes. Prog. Inorg. Chem., 14, 241 (1971). 13. R. H. HOLM, G. W. EVERT, A. CHAKRAVORTY: Metal Complexes of Schiff Bases and β-ketoamines. Prog. Inorg. Chem., 7, 83 (1966). 14. M. KATO, Y. MUTO: Factors Affecting the Magnetic Properties of Dimeric Copper(II) Complexes. Coord. Chem. Rev., 92, 45 (1988). 15. H. M. GUO, G. L. ZHAO, Y. Y. YU: Synthesis, Characterization, Crystal Structures and Antibacterial Activities of Transition Metal(II) Complexes with a Schiff Base Derived from o-vanillin and p-toluidine. Chinese J. Inorg. Chem., 24, 1393 (2008). 16. E. BREITMEIER, W. VOELTER: 13C NMR Spectroskopy. Verlag Chemie, Weinheim, N. J., 1996. 17. E. PRETSCH, J. SEIBL, W. SIMON: Strukturaufklarung organischer Verbindunger. Verlag, Berlin, Heidelberg, N.J., 1986. 18. YU-YE YU, HUI-DUO XIAN, JIAN-FENG LIU, GUO-LIANG ZHAO: Synthesis, Characterization, Crystal Structure and Antibacterial Activities of Transition Metal(II) Complexes of the Schiff Base 2-[(4-methylphenylimino)methyl]-6-methoxyphenol. Molecules, 14, 1747 (2009). 19. R. H. HOLM, G. W. EVERT, A. CHAKRAVORTY: Metal Complexes of Schiff Bases and β-ketoamines. Prog. Inorg. Chem., 7, 83 (1966). 20. S. J. COLES, M. B. HURSTHOUSE, D. G. KELLY, A. J. TONER, N. M. WALKER: Halide Tita nium(IV) Schiff Base Complexes; Fluoride and Bromide Derivatives and Evidence for a New Seven-coordinate Chloride Intermediate. J. Chem. Soc., Dalton Trans., 3489 (1998). 21. Y. Y. YU, G. L. ZHAO, Y. H. WEN: Syntheses, Characterizations, Crystal Structures and Antibacterial Activities of Two Zinc(II) Complexes with a Schiff Base Derived from o-vanillin and p-toluidine. Chinese J. Struct. Chem., 26, 1395 (2007). Received 12 May 2010 Revised 4 June 2010
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Oxidation Communications 35, No 2, 476–481 (2012) Synthesis of bioactive compounds, oxidation catalysts and spherical nanoparticles
Nano-gold Supported Nickel Manganese Oxide: Synthesis, Characterisation and Evaluation as Oxidation Catalyst M. Rafiq H. Siddiqui*, I. Warad, S. F. Adil, R. M. Mahfouz, Abdullah Al-Arifi Department of Chemistry, College of Science, King Saud University, P.O. 2455, 11 451 Riyadh, Kingdom of Saudi Arabia E-mail:
[email protected] ABSTRACT Gold nanoparticles supported on nickel manganese mixed oxide were synthesised by co-precipitation method. The catalytic properties of these materials were investigated for the oxidation of benzyl alcohol using molecular oxygen as an oxidant. It was observed that the calcination temperature and the size of the particle play an important role in the process. Keywords: gold nanoparticles, nickel manganese mixed oxides, oxidation, benzyl alcohol. AIMS AND BACKGROUND Aromatic aldehydes play an important role in the synthesis of materials of fine chemicals such as fragrances or flavourings agents that are obtained either by catalytic hydrogenation of carboxylic acids into corresponding aldehydes1–3 or by the oxidation of alcohols into corresponding aldehydes4,5. The hydrogenation of acids to aldehydes is an energy-consuming process and not very selective. Nevertheless, selective oxidation of alcohols to aldehydes can be environmentally friendly as this can be achieved by using molecular oxygen or hydrogen peroxide as an oxidant. Among the plethora of oxidation catalysts, manganese complexes have been extensively used for oxidation reactions such as epoxidation of olefins6–10, oxygenation of saturated11 and oxidation of aromatic hydrocarbons12, as well as oxidation of alcohols13–15 by peroxides and other reagents16–18. They have been combined with different elements and have been tried as catalyst for oxidation of alcohols such as *
For correspondence.
476
Co, Cr, Fe, Mg and Ni. Nickel-modified manganese oxide has been reported for the oxidation of methanol in fuel cells19. The present investigation deals with gold catalysts supported on nickel-manganese oxide and its evaluation for selective oxidation of benzyl alcohol to benzaldehyde. EXPERIMENTAL Preparation of gold supported on nickel manganese oxide. 95 ml of 0.2 M solutions of nickel nitrate and manganese nitrate were mixed in a round bottomed flask, to it were added 10 ml of 0.2 M solution of HAuCl4 solution. The resulting solution was heated to 80oC, while stirring using a mechanical stirrer and 1 M solution of NaHCO3 was added drop wise until the solution attained a pH = 9. The solution was continuously stirred at the same temperature for about 3 h and then left on stirring overnight at room temperature. The solution was filtered using a Buchner funnel under vacuum and dried at 70oC overnight. The product obtained was characterised using SEM, TEM and EDAX. The resulting powder was then calcined at different temperatures and was evaluated for its oxidation activity using benzyl alcohol as starting material. Catalyst testing. In a typical reaction run, 300 mg of catalyst were loaded in a glass flask pre-charged with 0.2 ml (2 mmol) benzyl alcohol with 10 ml toluene as a solvent; the mixture was then heated to 100oC with vigorous stirring. Oxygen was bubbled at a flow rate of 20 ml min–1 into the mixture once the reaction temperature was attained. After reaction, the solid catalyst was separated by centrifugation and the liquid samples were analysed by gas chromatography to evaluate the conversion of the desired product by (GC, 7890A) Agilent Technologies Inc., equipped with a flame ionisation detector (FID) and a 19019S-001 HP-PONA capillary column. Catalyst characterisation. Scanning electron microscopy (SEM) and elemental analysis (energy dispersive X-ray analysis: EDAX) were carried out using Jeol SEM model JSM 6360A (Japan) in order to determine the morphology of nanoparticles. Transmission electron microscopy (TEM) was carried out using Jeol TEM model JEM-1101 (Japan) to determine the shape and size of nanoparticles. Powder X-ray diffraction studies were carried out using an Altima IV Rigaku, X-ray diffractometer. RESULTS AND DISCUSSION Catalyst characterisation. The synthesised catalyst was characterised by electron microscopy to evaluate the morphology and particle size of the catalyst. The scanning electron microscopy (Figs 1–3) shows that the particles obtained are well defined and are spherical in shape. There is no effect of calcinations temperature on the catalyst morphology, except of slight increase in the size of particles with increasing calcination temperature. The TEM images show that the particles size of the gold is below 10 nm and they are uniformly dispersed on the nickel manganese oxide support and the support also is in nanometer range (Fig. 4). The powder X-ray diffraction pattern 477
shows the crystalline nature of the catalysts and is compared with the known oxide phases. The broad peaks in the XRD pattern further confirm the nanoparticles nature of these catalysts, which was confirmed by calculation of crystallite size using the Scherrer equation. The particles sizes were found to be 10.8, 7.2, and 2.2 nm for the catalyst calcined at 300, 400, and 500°C, respectively (Fig. 5).
Fig. 1. SEM of the catalyst calcined at 300°C
Fig. 2. SEM of the catalyst calcined at 400°C
Fig. 3. SEM of the catalyst calcined at 500°C
478
Fig. 4. TEM of the catalyst calcined at 300°C
Fig. 5. XRD pattern of the catalyst at different temperatures
Fig. 6. Oxidation of benzyl alcohol using catalysts calcined at different temperatures depicting the kinetics of the reaction
Catalytic properties. To investigate the catalytic oxidation properties of the prepared catalysts the oxidation of benzyl alcohol was carried out in the presence of the synthesised catalyst using toluene as a solvent. The reaction was carried out at 100°C, while passing O2 gas as a source of molecular oxygen. It was observed that there is a 479
decrease conversion of benzyl alcohol to benzaldehyde as the calcination temperature of the catalyst is increased. In order to confirm the role of gold acting as a promoter to the catalytic process, a reaction was carried out using Ni–Mn oxide without gold as a catalyst and it was observed that the conversion to the desired product falls drastically to 48% when compared to 100% conversion obtained by using the catalyst with gold calcined at 300°C. A conversion of 73 and 76% was observed for the catalyst calcined at 400 and 500°C, respectively. CONCLUSIONS Nanogold-supported nickel manganese oxide showed high activity and stability for the oxidation of benzyl alcohol using molecular oxygen as a source of oxygen. A synergistic effect between calcination temperatures and the chemical kinetics of the reaction was observed, and it was confirmed that calcination temperature plays an important role forming an active and durable catalyst. It can be assumed that this catalyst can be further used for the evaluation of its oxidative property for the synthesis of other important aromatic and aliphatic aldehydes. ACKNOWLEDGEMENT Research funding from SABIC, through Research Center, Science College, King Saud University, Saudi Arabia, is gratefully acknowledged. REFERENCES 1. T. YOKOYAMA, T. SETOYAMA, N. FUJITA, M. NAKAJIMA, T. MAKI, K. FUJITA: Novel Direct Hydrogenation Process of Aromatic Carboxylic Acids to the Corresponding Aldehydes with Zirconia Catalyst. Applied Catalysis A: General, 88, 149 (1992). 2. Y. SAKATA, C. A. TOL-KOUTSTAAL, V. PONEC: Selectivity Problems in the Catalytic Deoxygenation of Benzoic Acid. J. of Catalysis, 169, 13 (1997). 3. Y. SAKATA, V. PONEC: Reduction of Benzoic Acid on CeO2 and the Effect of Additives. Applied Catalysis A: General, 166, 173 (1998). 4. K. YAMAGUCHI, N. MIZUNO: Supported Ruthenium Catalyst for the Heterogeneous Oxidation of Alcohols with Molecular Oxygen. Angewandte Chemie International Edition, 41, 4538 (2002). 5. A. TASHIRO, A. MITSUISHI, R. IRIE, T. KATSUKI: (NO)Ru(salen)-catalyzed Aerobic Oxidation of o-hydroxybenzyl Alcohol Derivatives. SYNLETT, 12, 1868 (2003). 6. A. L. ANELLI, S. BANFI, F. LEGRAMANDI, F. MONTANARI, G. POZZI, S. QUICI: Tailed MnIIItetraarylporphyrins Bearing an Axial Ligand and/or a Carboxylic Group: Self-consistent Catalysts for H2O2 or NaOCl Alkene Epoxidation. J. Chem. Soc. Perkin Transactions, 1, 1345 (1993). 7. P.-P. KNOPS-GERRITS, D. E. de VOS, P. A. JACOBS: Oxidation Catalysis with Semi-inorganic Zeolite-based Mn Catalysts. J. Mol. Catalysis A: Chemical, 117, 57 (1997). 8. R.-M. WANG, C.-J. HAO, Y.-P. WANG, S.-B. LI: Amino Acid Schiff Base Complex Catalyst for Effective Oxidation of Olefins with Molecular Oxygen. J. Mol. Catalysis A: Chemical, 147, 173 (1999). 9. R.-M. WANG, H.-X. FENG, Y.-F. HE, C.-G. XIA, J.-S. SUO, Y.-P. WANG: Preparation and Catalysis of NaY-encapsulated Mn(III) Schiff-base Complex in Presence of Molecular Oxygen. J. Mol. Catalysis A: Chemical, 151, 253 (2000).
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10. A. BERKESSEL, M. FRAUENKRON, A. SCHWENKREIS, A. STEINMETZ: Pentacoordinated Manganese Complexes as Biomimetic Catalysts for Asymmetric Epoxidations with Hydrogen Peroxide. J. Mol. Catalysis A: Chemical, 117, 339 (1997). 11. R. JIN, C. S. CHO, L. H. JIANG, S. C. SHIM: Mechanistic Aspects of the Hydrogenation of Some Unsaturated Mono- and Diacids and Their Methyl Esters. J. Mol. Catalysis A: Chemical, 116, 342 (1997). 12. R. R. L. MARTINS, M. G. P. NEVES, A. J. D. SILVESTRE, A. M. S. SILVA, J. A. S. CAVALEIRO: Oxidation of Aromatic Monoterpenes with Hydrogen Peroxide Catalysed by Mn(III) Porphyrin Complexes. J. Mol. Catalysis A: Chemical, 137, 41 (1999). 13. C. ZONDERVAN, R. HAGE, B. L. FERINGA: Selective Catalytic Oxidation of Benzyl Alcohols to Benzaldehydes with a Dinuclear Manganese(IV) Complex. Chem. Commun., 419 (1997). 14. R. RUIZ, A. AUKAULOO, Y. JOURNAUX, I. FERNÁNDEZ, J. R. PEDRO, A. L. ROSELLÓ, B. CERVERA, B. I. CASTRO, M. C. MUNOZ: Manganese(IV) Oxamato-catalyzed Oxidation of Secondary Alcohols to Ketones by Dioxygen and Pivalaldehyde. Chem. Commun., 989 (1998). 15. A. BERKESSEL, C. A. SKLORZ: Mn-trimethyltriazacyclononane/ascorbic Acid: A Remarkably Efficient Catalyst for the Epoxidation of Olefins and the Oxidation of Alcohols with Hydrogen Peroxide. Tetrahedron Letters, 40, 7965 (1999). 16. M. A. LOCKWOOD, K. WANG, J. M. MAYER: Oxidation of Toluene by [(phen)2Mn(μO)2Mn(phen)2]4+ via Initial Hydride Abstraction. J. Am. Chem. Soc., 121, 11894 (1999). 17. C. P. HORWITZ, Y. CIRINGH, S. T. WEINTRAUB: Formation Pathway of a Mn(IV),Mn(IV) bis(μoxo) Dimer that Incorporates Alkali and Alkaline Earth Cations and Electron Transfer Properties of the Dimer. Inorganica Chimica Acta, 294, 133 (1999). 18. U. B. CHOUNDHURY, S. BANERJEE, R. BANERJEE: Kinetics and Mechanism of Hydrazine Oxidation by an Oxo-bridged Tetramanganese(IV) Complex in Weakly Acidic Media. J. Chem. Soc. Dalton Transactions, 589 (2000). 19. P. V. SAMANT, J. B. FERNANDES: Nickel-modified Manganese Oxide as an Active Electrocatalyst for Oxidation of Methanol in Fuel Cells. J. of Power Sources, 79, 114 (1999). Received 15 December 2011 Revised 20 January 2011
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Oxidation Communications 35, No 2, 482–490 (2012) Synthesis of bioactive compounds, oxidation catalysts and spherical nanoparticles
Synthesis of Shuttle-like Zinc Oxide Nanoparticles by Microwave Heating Hanmin Yang*, Leilei Guo, Xianmian Wu, Haowen Liu, Jinlin Li Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, South-Central University for Nationalities, 430 074 Wuhan, China E-mail:
[email protected] ABSTRACT Shuttle-like ZnO nanoparticles were synthesised for the first time by hydrolysis of zinc acetate dihydrate in the presence of polyvinylpyrrolidone (PVP) by microwave heating. The as-prepared ZnO nanoparticles were characterised by transmission electron microscopy(TEM) and X-ray powder diffraction(XRD). The factors affecting the morphology of ZnO nanoparticles were investigated. Due to the rapid and homogeneous heating with microwave, the morphology of the as-synthesised ZnO nanoparticles changed slightly with the increasing concentration of zinc salt. An appropriate amount of PVP is necessary for the formation of well-defined and uniform ZnO. It is worth noting that there is significant difference between preparing zinc oxide nanoparticles by microwave heating and water-bath heating. Microwave heating appears to be particularly effective as a means of accelerating the reaction among the raw materials and leading to the growth and crystallisation of ZnO. Keywords: shuttle-like, zinc oxide nanoparticles, microwave heating, synthesis. AIMS AND BACKGROUND Nanocrystalline semiconductor particles have attracted much attention in recent years because of their special properties such as a large surface-to-volume ratio, increased activity, special electronic properties and unique optical properties as compared to those of the bulk materials1,2. As an oxides of transition metals, ZnO is an important semiconductor due to its wide and direct fundamental band gap energy of 3.37 eV with large excitation binding energy (60 mV) and high mechanical and thermal stability. Various methods have been employed to synthesise ZnO nanoparticles such as the vapour-phase transport process3–5, chemical vapour deposition6, arc discharge7, *
For correspondence.
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laser ablation8, solution9,10, and a template-based method11,12. A variety of well-defined ZnO nanostructures such as nanowires (or nanorods)13–15, nanobelts (nanoribbons)16,17, comb-like nanowires array18, nanoneedles arrays19, and nanorings20 have been successfully synthesised. Microwave irradiation as a fast, simple, uniform and energy-efficient heating method has been widely used in chemistry since 1986 (Refs 21 and 22). In recent years, microwave-assisted synthesis has been widely used in the preparation of nanosized materials23–32. It has been verified that microwave irradiation is an effective method for the synthesis of small and homogeneous metal nanoparticles dispersion. The applications of microwave in the preparation of ZnO nanoparticles have been reported in recent years. Fabrication of ZnO nanoneedle arrays by direct microwave irradiation was reported33. Despite much efforts on the synthesis of the zinc oxide nanoparticles by microwave heating, little work is focused on the effect of the systhesis conditions on the morphology of ZnO nanoparticles. In this work, microwave heating was employed to synthesise unreported shuttle-like ZnO nanoparticles by hydrolysis of zinc acetate dihydrate in the presence of polyvinylpyrrolidone (PVP) in distilled water solution. Furthermore, the effect of the synthesis conditions on the morphology of ZnO nanoparticles by microwave heating, such as the choice of solvent, the concentration of zinc salt, the use of PVP and the method of heating were examined. EXPERIMENTAL Materials. Zinc acetate dihydrate from Guoyao Chemical Reagent Co. Ltd., China, was used as a starting material. Polyvinylpyrrolidone (average molecular weight, MW = 30 000) was purchased from Acros and other chemicals were purchased from local suppliers. All reagents were of analytical grade purity and were used as received. Deionised water was used throughout. All the glass wares and magnetic bars were soaked in aqua regia for a few days, then repeatedly washed with deionised water and dried in an oven before use. Synthesis of the ZnO nanoparticles. In a typical synthesis, 0.044 g of zinc acetate dihydrate were dissolved in 20 ml distilled water (0.01 mol/l) under stirring in a 50ml round-bottom flask. After dissolution, 0.2 ml hydrazine hydrate (0.2 mol/l) were introduced. The resulting solution was transferred to a modified domestic microwave oven (Galanze WD900Y ) operated at 2.45 GHz which is connected to a refluxing system and heated for 5 min with 50% of output power. During this time the refluxing system is working continuously. The resulting zinc oxide colloid was centrifuged and washed with ethanol not less than 3 times for further characterisation. The as-prepared ZnO nanoparticles using other solvents(ethanol, ethylene glycol) were synthesised similarly as in the water.
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Characterisation. Transmission electron microscopy (TEM) measurements were conducted on a FEI Tecnai G220 instrument. The sample for TEM observation was prepared by placing a drop of the colloidal dispersion onto a copper grid coated with a perforated carbon film, followed by evaporating the solvent at ambient temperature. Typically, the TEM micrographs of each sample were taken at multiple, random locations in the sample to ensure that the images reported are representative. X-ray powder diffraction (XRD) was performed on a Bruker D8 X-ray diffractometer employing CuKα radiation with 40 kV and 50 mA. The sample for XRD measurement was prepared as follows: the ZnO nanoparticles were washed with ethanol and subjected to centrifugation. After centrifugation, the precipitates were coated on a glass plate, and dried by infrared lamp carefully prior to XPS measurement. RESULTS AND DISCUSSION Figure 1 shows the XRD pattern of a typical sample of as-synthesised ZnO nanoparticles. From the XRD pattern, 3 peaks at 2θ = 31.7°, 34.4°, 36.2°, corresponding to the (100), (002), (101) lattice planes for ZnO according to the JCPDS file No 36-1451 were observed. No other diffraction peaks were detected, indicating that the particles were pure ZnO. In general, the width of XRD peaks is related to the crystallite size and strain effects. In this case, the peak is broader than that of well crystallised ZnO, attributed to the small size.
Fig. 1. XRD pattern of shuttle-like nano-ZnO nanoparticles
Effect of different solvents. Kanade et al.34 found that the polarity and saturated vapour pressure of solvents affected the ZnO morphology under thermal conditions. In order to explore the effect of solvent on the morphology of shuttle-like ZnO nanoparticles, the experiments were performed with different solvents by microwave heating. Figure 2 presents the TEM micrographs of ZnO nanoparticles synthesised in ethanol, distilled water, and ethylene glycol (EG). TEM pictures showed the agglomerated rod-like and shuttle-like morphology of ZnO in medium of ethanol and distilled water, whereas in 484
EG medium, the ZnO particles were spherical aggregates of very small nanoparticles, which shows that the solvent plays a key role in controlling the morphology of zinc oxide nanocrystalline35. A possible reason may be that the crystals were dispersed more homogeneously in water than in ethanol and the growth of crystal nuclei is subjected to less confinement in boiling droplet of solvent. When a solvent with higher saturated vapour pressure such as ethanol is used as a reaction medium, the aggregation of the nuclei is not intense due to the lower boiling point of the solvent, which results in rod-like particle morphology in ethanol. EG acts as a surfactant to efficiently stabilise the particles at high temperature, which contributes to the formation of monodispersed and small size ZnO crystals, and the size of the ZnO nanoparticles is smaller in EG than in water and ethanol medium. These observations lead us to conclusion that the selection of the solvent is a key factor for obtaining shuttle-like ZnO nanocrystals.
Fig. 2. Morphology of ZnO synthesised in different solvents: ethanol (a), distilled water (b) and ethylene glycol (c)
Shape-control of ZnO nanoparticles by using PVP. The effect of PVP on the morphology of ZnO was investigated while keeping the other conditions unchanged. As shown in Fig. 3, it is clear that the particle morphology has been changed by adding PVP as a capping agent using ethanol as the solvent, and the particle has better dispersion and more homogeneity than without PVP (Fig. 3a, b). But in water medium, the impact of the PVP on the morphology is not too obvious from Fig. 3c, d one can see that PVP makes the particle sizes becoming smaller, and with better dispersion.
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Fig. 3. ZnO particles synthesised without PVP in ethanol (a), with PVP in ethanol (b), without PVP in water (c), with PVP in water (d)
In the formation of water-soluble zinc oxide nanoparticles, stabilising agent, PVP, was adsorbed on the surface of ZnO nanoparticles preventing their aggregation. It is well established that the formation of PVP-stabilised colloidal metal oxide nanoparticles goes through 2 processes: hydrolytic decomposition and condensation36,37. In the present work, the zinc acetate species are first hydrolysed to the corresponding hydroxide, followed by condensation of the hydroxide to form the metal oxide clusters. Microwave heating accelerates the rate of the hydrolysis of metal salts and the subsequent condensation, which makes the influence of PVP on the size of nanoparticle products more obvious. Therefore, an appropriate amount of PVP was necessary for the formation of small and dispersive shuttle-like zinc oxide nanoparticles. Comparison of 2 kinds of heating methods. In addition, the difference of heating methods was investigated while keeping the other conditions unchanged. Figure 4 shows that microwave heating and water-bath heating greatly influence the morphology of ZnO nanoparticles. Microwave heating offers many advantages over water-bath heating, including rapid heating to crystallisation temperature, homogeneous nucleation, and fast supersaturation by the rapid dissolution of precipitated hydroxides, which leads to lower crystallisation temperatures and shorter crystallisation times38. Many investigators argued that the reaction rate increase in response to microwave heating was caused by the superheating of solvents beyond their normal boiling points39,40. In the current case, the microwave may accelerate the hydrolysis of Zn(NO3)2·2H2O, which is presumably helpful to the nucleation and growth of ZnO nanocrystals. The experimental phenomena support the above hypothesis: in the same conditions, the 486
total consumption of time takes only 5 min using microwave heating whereas almost 2 h were necessary using water-bath heating. This shows that microwave heating can significantly shorten the reaction time. Furthermore, the rapid heating to hydrothermal temperature accelerates interparticle collisions and effective fusion at the point of collision. It is suggested that the microwave causes fusion of the adjacent particles and attachment of primary particles on the outer layers of the ZnO nanostructures, which are the intermediate products between the initial nanoparticles and final nanostuctures41. In our work, microwave plays an important role and is found to be necessary for the synthesis of ZnO with the shuttle-like morphology.
Fig. 4. ZnO particles synthesised by microwave heating in ethanol (a), water-bath heating in ethanol (b), microwave heating in water (c) and water-bath heating in water (d)
Influence of ZnO precursor concentration. Based on the hydrolysis of zinc acetate, the size of ZnO nanoparticles is thought to be dependent on the concentration of zinc acetate. The effect of the initial concentration of zinc acetate on the particle size of shuttle-like ZnO colloids prepared by microwave heating was investigated. Figure 5 shows the representative TEM images of ZnO nanoparticles prepared by microwave heating when the concentration of zinc acetate changed from 0.01 to 0.0025 mol/l while hydrazine hydrate concentration is kept constant. As seen in Fig. 5, the particles are all shuttle-like and the effect on particle size and uniform dispersion is not significant. A possible explanation may be that the hydrolysis product of zinc hydroxide is amphoteric, it grows in size and forms gels following the mechanism similar to silica 487
in that the product of the reaction is easy to precipitation, the generation of the initial ZnO particles become smaller when the zinc precursor concentration decreases, but the reunion happens quickly. Furthermore, the microwave irradiation provides an uniform environment for nucleation. Hence the concentration of zinc acetate had a little effect on the size of the ZnO nanoparticles prepared by microwave heating.
Fig. 5. Morphology of ZnO particles synthesised at different zinc precursor concentrations: 0.01 mol/l (a), 0.005 mol/l (b) and 0.0025 mol/l (c)
CONCLUSIONS In summary, the shuttle-like ZnO nanoparticles can be synthesised by hydrolytic decomposition of the zinc acetate in the presence of PVP by microwave heating. The morphology of the as-prepared ZnO nanoparticles changed slightly with the shift of the initial concentration of zinc acetate. The solvents, PVP and the method of heating influence the morphology of ZnO signifantly. The results indicate that microwave is necessary for the synthesis of ZnO with shuttle-like morphology. ACKNOWLEDGEMENTS This research was supported by the Special Fund for Basic Scientific Research of Central College, South-central University for Nationalities (Grant No ZZY10004). REFERENCES 1. A. HENGLEIN: Small-particle Research: Physiochemical Properties of Extremely Small Colloidal Metal and Semicondutor Particles. J. Chem. Rev., 89, 1861 (1989). 2. A. AGFELDT, M. GRATZEL: Light-induced Redox Reactions in Nanocrystalline Systems. J. Chem. Rev., 95, 49 (1995). 3. Y. WU, P. YANG: Germanium Nanowire Growth via Simple Vapor Transport. Chem. Mater., 12, 605 (2000). 4. C. C. CHEN, C. C. YEH: Large-scale Catalytic Synthesis of Crystalline Gallium Nitride Nanowires. J. Adv. Mater., 12, 738 (2000). 5. Z. G. BAI, D. P. YU, H. Z. ZHANG, Y. DING, X. Z. GAI, Q. L. HANG, G. C. XIONG, S. Q. FENG: Nano-scale GeO2 Wires Synthesized by Physical Evaporation. Chem. Phys. Lett., 303, 311 (1999).
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6. M. YAZAWA, M. KOGUCHI, A. MUTO, M. OZAWA, K. HIRUMA: Characterization of Recombination Processes in Multiple Narrow Asymmetric Coupled Quantum Wells Based on the Dependence of Photoluminescence on Laser Intensity. Appl. Phys. Lett., 61, 2051 (1992). 7. Y. C. CHOI, W. S. KIM, Y. S. PARK, S. M. LEE, D. J. BAE, Y. H. LEE, G. S. PARK, W. B. CHOI, N. S. LEE, J. M. KIM: Catalytic Growth of β-Ga2O3 Nanowires by Arc Discharge. Adv. Mater., 12, 746 (2000). 8. (a) X. F. DUAN, C. M. LEIBER: General Synthesis Of Compound Semiconductor Nanowires. Adv. Mater., 12, 298 (2000); (b) A. M. MORALES, C. M. LIEBER: A Laser Ablation Method for the Synthesis of Crystalline Semiconductor Nanowires. Science, 279, 208 (1998). 9. T. J. TRENTLER, K. M. HICKMAN, S. C. GOEL, A. M. VIANO, P. C. GIBBONS, W. E. BUHRO: Solution–Liquid–Solid Growth of Crystalline III–V Semiconductors: An Analogy to Vapor–Liquid–Solid Growth. Science, 270, 1791 (1995). 10. J. D. HOLMES, K. P. JOHNSTON, R. C. DOTY, B. A. KORGEL: Control of Thickness and Orientation of Solution-grown Silica on Nanowires. Science, 287, 1471 (2000). 11. (a) M. H. HUANG, A. CHOUDREY, P. YANG: Ag Nanowire Formation within Mesoporous Silica. Chem. Commun.,12, 1603 (2000); (b) J. ZHU, S. FAN: Nanostructure of GaN and SiC Nanowires Based on Carbon Nanotubes. J. Mater. Res., 14, 1175 (1999). 12. Y. LI, G. W. MENG, L. D. ZHANG, F. PHILLIPP: Ordered Semiconductor ZnO Nanowire Arrays and Their Photoluminescence Properties. Appl. Phys. Lett., 76, 2011 (2000). 13. J. C. JOHNSON, H. J. CHOI, K. R. KNUSTEN, R. D. SCHALLER, P. YANG, R. J. SAYKALLY: Single Gallium Nitride Nanowire Lasers. Nat. Mater., 1, 106 (2002). 14. J. C. JOHNSON, H. YAN, R. D. SCHALLER, L. H. HABER, R. J. SAYKALLY, P. YANG: Single Nanowire Laser. Phys. Chem. B, 105, 11387 (2001). 15. (a) M. HUANG, S. MAO, H. FEICK, H. YAN, Y. WU, H. KING, E. WEBER, R. RUSSO, P. YANG: Room-temperature Ultraviolet Nanowire Nanolasers. Science, 292, 1897 (2001); (b) M. H. HUANG, Y. WU, H. FEICK, N. TRAN, E. WEBER, P. YANG: Catalytic Growth of Zinc Oxide Nanowires by Vapor Transport. Adv. Mater., 12, 113 (2001). 16. Z. W. PAN, Z. R. DAI, Z. L. WANG: Nanobelts of Semiconducting Oxides. Science, 291, 1947 (2001). 17. P. YANG, H. YAN, S. MAO, R. RUSSO, J. JOHNSON, R. SAYKALLY, N. MORRIS, J. PHAM, R. HE, H. J. CHOI: Controlled Growth of ZnO Nanowires and Their Optical Properties. Adv. Funct. Mater., 12, 323 (2002). 18. H. YAN, R. HE, J. JOHNSON, M. LAW, R. J. SAYKALLY, P. YANG: Dendrite Nanowire UV Laser Array. J. Am. Chem. Soc., 125, 4728 (2003). 19. (a) W. I. PARK, D. H. KIM, S. W. JUNG, G. C. YI: Metalorganic Vapor-phase Epitaxial Growth of Vertically Well-aligned ZnO Nanorods. J. Appl. Phys. Lett., 80, 4232 (2002); (b) W. I. PARK, G. C. YI, M. KIM, S. J . PENNYCOOK: ZnO Nanoneedles Grown Vertically on Si Substrates by Non-catalytic Vapor-phase Epitaxy. Adv. Mater., 14, 1841 (2002). 20. X. Y. KONG, Y. DING, R. YANG, Z. L. WANG: Single-crystal Nanorings Formed by Epitaxial Self-coiling of Polar-nanobelts. Science, 303, 1348 (2004). 21. R. GEDYE, F. SMITH, K. WESTAWAY, H. ALI, L. BALDISERA, L. LABERGE, J. ROUSELL: The Use of Microwave Ovens for Rapid Organic Synthesis. J. Tetrahedron Lett., 27, 279 (1986). 22. X. XU, W. YANG, J. LIU, L. LIN: Synthesis of a High-permeance NaA Zeolite Membrane by Microwave Heating. Adv. Mater., 12, 195 (2000). 23. W. YU, W. TU, H. LIU: Synthesis of Nanoscale Platinum Colloids by Microwave Dielectric Heating. Langmuir, 15, 6 (1999). 24. W. TU, H. LIU: Rapid Synthesis of Nanoscale Colloidal Metal Clusters by Microwave Irradiation. J. Mater. Chem., 10, 2207 (2000). 25. W. TU, H. LIU: Continuous Synthesis of Colloidal Metal Nanoclusters by Microwave Irradiation. Chem. Mater., 12, 564 (2000).
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26. T. C. DEIVARAJ, W. CHEN, J. Y. LEE: Preparation of PtNi Nanoparticles for the Electrocatalytic Oxidation of Methanol. J. Mater. Chem., 13, 2555 (2003). 27. F. K. LIU, Y. C. CHANG, F. H. KO, T. C. CHU: Microwave Rapid Heating for the Synthesis of Gold Nanorods. Mater. Lett., 58, 373 (2004). 28. Y. J. ZHU, X. L. HU: Microwave-assisted Polythiol Reduction Method: A New Solid–Liquid Route to Fast Preparation of Silver Nanowires. J. Mater. Lett., 58, 1517 (2004). 29. B. HE, J. J. TAN, K. Y. LIEW, H. LIU: Synthesis of Size Controlled Ag Nanoparticles. J. Mol. Catal. A: Chem., 221, 121 (2004). 30. Y. CHEN, B. HE, H. LIU: Preparation and Characterization of Palladium Colloidal Nanoparticles by Thermal Decomposition of Palladium Acetate with Microware Irradiation. J. J. Mater. Sci. Technol., 21 (2), 187 (2005). 31. M. TSUJI, M. HASHIMOTO, Y. NISHIZAWA, M. KUBOKAWA, T. TSUJI: Microwave-assisted Synthesis of Metallic Nanostructures in Solution. Chem. Eur. J., 11, 440 (2005). 32. Y. LUO: A simple Microwave-based Route for Size-controlled Preparation of Colloidal Pt Nanoparticles. Mater. Lett., 61, 1873 (2007). 33. SEUNGHO CHO, DAE-SEOB SHIM, SEUNG-HO JUNG, EUGENE OH, BO RAM LEE, KUNHONG LEE: Fabrication of ZnO Nanoneedle Arrays by Direct Microwave Irradiation. Materials Letters, 63, 739 (2009). 34. K. G. KANADE, B. B. KALE, R. C. AIYER, B. K. DAS: Effect of Solvents on the Synthesis of Nano-size Zinc Oxide and Its Properties. Materials Research Bull., 3, 590 (2006). 35. J. ZHANG, L. SUN, J. YIN, H. SU, C. LIAO, C. YAN: Control of ZnO Morphology via a Simple Solution Route. Chem. Mater., 14, 4172 (2002). 36. M. T. REETZ, M. G. KOCH: Water-soluble Colloidal Adams Catalyst: Preparation and Use in Catalysis. J. Am. Chem. Soc., 121, 7933 (1999). 37. B. HE, Y. HA, H. LIU, K. WANG, K. Y. LIEW: Size Control Synthesis of Polymer-stabilized Watersoluble Platinum Oxide Nanoparticles. J. Colloid Interf. Sci., 308, 105 (2007). 38. S. KOMARNENI: Environmentally Benign Microwave Hydrothermal Processing for Synthesis of Ceramic Powders. In: Proc. of the International Symposium on Environmental Issues of Ceramics (Eds H. Yanagida, M. Yoshimura). Ceramic Society of Japan, Tokyo, 1995, 199–206. 39. D. R. BAGHURST, D. M. P. MINGOS: Superheating Effects Associated with Microwave Dielectric Heating. J. Chem. Soc. Chem. Commun., 674 (1992). 40. F. CHEMAT, E. ESVELD: Microwave Super-heated Boiling of Organic Liquids: Origin, Effect and Application. Chem. Eng. Technol., 24, 735 (2001). 41. J. F. HUANG, C. K. XIA, L. Y. CAO, X. R. ZENG: Facile Microwave Hydrothermal Synthesis of Zinc Oxide One-dimensional Nanostructure with Three-dimensional Morphology. Materials Science and Engineering B, 150, 187 (2008). Received 3 May 2010 Revised 22 June 2010
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Oxidation Communications 35, No 2, 491–496 (2012) Technological aspects of oxidation processes
Borozar-PII Boronaluminising Paste for Steels Treatment Z. Zakhariev*, I. Stambolova, M. Marinov, C. Perchemliev Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Bl. 11, 1113 Sofia, Bulgaria E-mail:
[email protected] ABSTRACT Boronaluminising (simultaneous boronising and aluminising) of carbon and alloyed steel by the Bulgarian paste Borozar-PII has been carried out. The phase composition and microstructure of the layers obtained, as well as the oxidation stability have been studied. The boronaluminising diffusion layer has a very high hardness (23 500 MPa), which is higher than the hardness of a single-component layer. This feature of the boronaluminising layer provides for the high wear-resistance of the treated surfaces. The wear resistance of the layers significantly exceeds that which can be obtained by conventional thermochemical treatment processes, e.g. carbonising, nitriding, etc. The oxidation stability of the complex diffusion layers obtained by boronaluminisiation with Borozar-PII is much higher than those of the layers obtained by boronised with the German paste Ekabor-P. Keywords: steels, boronising, oxidation stability, microhardness. AIMS AND BACKGROUND Before the appearance of the pastes, boronising proceeded in powders placed in closed containers with subsequent 2-step heating (thermochemical and hardening) of the boronised details. Thus, the process required more efforts and was more expensive than similar processes of thermochemical treatment such as nitration and cementation. Boronising with pastes during the hardening of steel is a new process resulting in a surface layer with a high wear resistance, minimum time and cost losses being needed1. The technology is very simple: a coat of the paste is applied to the working surfaces of machine tools and parts. Additional procedures, staff and equipment are not required. *
For correspondence.
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Boronaluminising (boronising and subsequent aluminising) of steels with powder mixtures is used for obtaining a surface diffusion layer with an enhanced wear-resistance (due to the penetration of boron into the layer) and a higher stability (as a result of metallisation) with respect to oxidation and corrosion2. The complex (simultaneous) boronaluminising of steels by pastes has not been sufficiently investigated. The purpose of the present paper was to achieve simultaneous boronaluminising of carbon and alloyed steel using a modified commercially available paste (Borozar)3 and to investigate the oxidation and corrosion stability of the layers obtained in comparison with one-component layer resulting from boronising. EXPERIMENTAL The samples were 2 types of steels: carbon steel C45 and alloy steel C55NiCrMoV (C – 0.55%, Ni – 1.5%, Cr – 0.7%, Mn – 0.7%) with D = 10 and H = 10 mm. The samples were cleaned with acetone and dried in air. The thermochemical treatment was carried out using a Borozar-PII paste containing boron carbide, sodium hexafluoroaluminate, aluminium oxide and dextrine glue3. The Borozar-PII paste was prepared by mixing the powder and the hardener and was applied in a 3–5-mm layer on the samples. After drying of the samples in air the paste coat was covered by charcoal to prevent oxidation. The single-component boronising was performed with Ekabor paste of the German company BorTec GmbH of argon – according to the recommendation of the producer4. The thermochemical treatment of the samples after drying proceeded in a conventional furnace under air (for Borozar-PII) and argon (for Ekabor-P) at 930oC for 4–6 h. After that, the steel samples were ground and polished with a Planopol 2 (Struers) apparatus with silicon carbide abrasive paper. The thickness of the deposited layers was investigated with a Neofot-21 (Zeiss) metallographic microscope. The microhardness was determined with a micro-indenter on the metallographic microscope using an indentation load of 50–100 N. The phase composition of the diffusion layers was investigated by XRD analysis on a Philips PW 1050 diffractometer (CuKα radiation). The structure of the samples was studied by SEM+EDX (scanning electron microscopy + energy dispersive analysis) with Jeol JSM-6390. The oxidation stability was tested in a crucible furnace at a temperature of 850oC. This temperature was chosen so as to exceed the admissible temperature (800oC) for single-component boride layers5,6. In time intervals of 4 h the samples were taken out of the furnace and placed for tempering in a desiccator. The change in weight of the oxidised samples was determined by an analytical balance with an accuracy 0.0001. Comparative studies of the acid resistance of layers deposited on the steel samples were performed in solutions of 10% H2SO4 on the basis of the samples weight loss. 492
The corrosion rate was calculated according to the following equation: Kw = G0 – G1/F, mg/cm2,
where G0 is the initial weight of the sample; G1 – its weight after corrosion, and F – the surface area of the sample. RESULTS AND DISCUSSION As a result of the thermochemical treatment, a boronaluminised diffusion layer with a characteristic microstructure is formed on the treated surfaces of the steels which consists of 2 zones (Figs 1 and 2).The inner zone possesses ‘needle-like’ structure, which is characteristics for one-component boronising of the steel and contains boride phases. The outer zone contains phases composed mainly of aluminium and oxygen (‘white spots’) on the small photographs in Figs 1 and 2 obtained by characteristic radiation. The thickness, phase composition and microhardness of the layers depend on the type of treated steel, as well as temperature and duration of the boronising and boronaluminising processes (Table 1).
Fig. 1. Microstructure of a boronaluminised layer on a C45 sample using Borozar-PII paste
493
Fig. 2. Microstructure of a boronaluminised layer on a 55NiCrMoV sample using Borozar-PII paste Table 1. Physicochemical characteristic of the boronaluminised steels
Steel grade (DIN) C45 Borozar 56NiCrMoV (Borozar) C45 (Ekabor) 56NiCrMoV (Ekabor)
Temperature/duration of treatment (oC/h) 930/4–6
Layer Phase comthickness position (μm) 240–300
930/4
77–82
930/4 930/4
155–165 95–100
(Fe,Al)2B γ-Al2O3 γ-Al2O3 FeB Fe2B Fe2B
Chemical composition (%) Fe 55 3 41.5
Al O 0.3 14 58 8 44
B 40 42.9
Microhardness (MPa) 23500 19500 20500 18220
The boronaluminising diffusion layer has a very high hardness (23 500 MPa), which is higher than the hardness of a single-component layer (see Table 1). This feature of the boronaluminising layer provides for the high wear-resistance of the treated surfaces. The hardness of the boronaluminised layer, i.e. its wear-resistance, significantly exceeds that which can be obtained by conventional thermochemical treatment processes, e.g. carbonising, nitriding, etc. (Table 2). Table 2. Microhardness of treated steels (MPa)
High speed steel Cemented steel 7500
494
7700–8270
Nitrided steel 12000
Boronaluminised Boronaluminised steel C45 steel 56NiCrMoV 21500–23500 18000–19500
The application of the Borozar-PII paste effects increases the oxidation resistance of steel tools at 800 to 1000°C which is much more than the conventional boronising paste – Ekabor-P (Refs 4,7 and 8) (Fig. 3). 1
weight loss × 10–3 (g/cm3)
120
2
100 80
3
60 40 20 0
0
1
2
3
4
5
6 7 time (h)
8
9
10
11
12
Fig. 3. Oxidation resistance of steel 55NiCrMoV at 850oC 1 – uncoated steel; 2 – after boronising with Ekabor-P; 3 – after boronaluminising with Borozar-PII
Another advantage of boron metallising is the fact that it allows the use of lowalloy and cheaper steel for the manufacturing of parts and tools, with high surface hardness and high corrosion-resistance. For instance, boronaluminising substantially improves the acid-corrosion-resistance of plain steel. Figure 4 illustrates the complete dissolving of the plain steel in 10% sulphuric acid as a result of boronmetallising. As it seen from the figure the corrosion resistance of layers obtained by boronaluminising with paste Borozar-PII and paste Ekabor is almost the same as that of the alloy corrosion steel. This permits replacement of high cost corrosion steels with conventional carbon steels, boronised or boronaluminised by Borozar-PII and Ekabor-P pastes. 20 18
weight loss (mg/cm2 )
16
2
1
14 12 10 8 6
3 4 5
4 2 0
0
5
10
15 time (h)
20
25
Fig. 4. Acid corrosion resistance in 10% H2SO4 of a boronaluminising layer on C45 steel 1 – uncoated steel; 2 – boronising with BKB-2 (Ukraine); 3 – boronising with alloy corrosion steel (X18H9T, BDS); 4 – boronaluminising with Borozar-PII paste; 5 – boronising with Ekabor-P paste (Germany)
495
CONCLUSIONS The boronaluminising of carbon and alloyed steels with Bulgarian Borozar-PII paste leads to a formation of complex boronaluminised diffusion layer on the steels. These boronaluminised diffusion layers exceed significantly in hardness and oxidation stability the samples treated with paste Ekabor-P. The paste Borozar-PII is suitable for treatment of steel machine tools and parts of large dimensions, e.g. metal hot stamps, hammering press matrices, guides, rolls for wiredrawing, steel pulleys, steel belt conveyor rolls, ploughshares, tracks, extruder screws and other similar machine parts subjected to wear and oxidation (corrosion). REFERENCES 1. D. C. LOU, M. I. ONSOIEN, O. M. AKSELSEN, J. BERGETT: Self-protective Boronizing Paste for Surface Treatment of Steel and Cast Iron. In: 3rd Intern. Surface Engineering Congress, publ. by ASM International Society, Orlando, USA, August 2–4, 2004, p. 120. 2. L. S. LYUKHOVICH, L. G. VOROSHNIN, G. G. PANICH, E. D. SCHERBAKOV: Multicomponent Diffusion Coatings. Nauka i technika, Minsk, 1974 (in Russian). 3. R. PETROVA, Z. ZAKHARIEV: Structure of Boraluminized Layers on Steels. Bulg. Chem. Commun., 26, 82 (1993). 4. BorTec GmbH, Catalog Munih,Germany, 2000. 5. W. STULMANN: Boriren Stahl. VDT-Zeitschrift, 102 (24), 1161 (1960). 6. L. S. LYUKHNOVICH, L. G. VOROSHNIN, G. G. PANICH: Distribution of the Alloying Elements Boron and Carbon with the Depth of the Boronizing Layers on Medium-carbon Steel. MiTom, 5, 74 (1969). 7. C. MERIC, S. SHIN, B. BACKIR, N. S. KOKSAL: Investigation of Boronizing Effect on the Abrasive Wear Behaviour in Cast Iron. Materials and Design, 27, 751 (2006). 8. O. OZBEK, H. AKBULUT, S. ZEYTIN, C. BINDAL, A. HIKMET: The Characterization of Borided 99.5% Purity Nickel. Surf. Coat. Technol., 126, 166 (2000). Received 23 April 2009 Revised 10 June 2009
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Oxidation Communications 35, No 2, 497–502 (2012) Technological aspects of oxidation processes
Oxidation Stability of Layers Obtained by Boronaluminising of Steels Z. Zakhariev*, I. Stambolova, M. Marinov Institute of General and Inorganic Chemistry, Acad. G. Bonchev Strreet, Bl. 11, 1113 Sofia, Bulgaria E-mail:
[email protected] ABSTRACT The oxidation stability of layers obtained by boronaluminised of carbon steels C3 (C – 0.30%, Si – 0.20%, Mn – 0.50%, Cr – 0.25% and Ni – 0.25%) and tool steel 55NiCrMoV6 (C – 0.50%, Si – 0.20%, Mn – 0.60%, Cr – 0.70%, Ni – 1.6%, V – 0.2% and Mo – 0.20%) has been investigated. The thermochemical treatment of the samples is performed with a Borozar boronaluminised paste at 950oC. The oxidation stability is studied by measuring the change in weight of steel samples at 850oC. The structure and EDS elemental analysis of the layers have been investigated by a scanning electron microscope Jeol 733. The results obtained have revealed that the layers produced by boronaluminised considerably exceed in oxidation stability the 1-component boride layer and the 2-component boron-chromium and boron-zirconium layers. It is established that addition of 30 and 50 wt.% Al powder ensures the highest oxidation stability of the steels investigated. Keywords: steels, boronaluminised, oxidation stability. AIMS AND BACKGROUND The thermochemical boroaluminising process is used for obtaining a surface diffusion layer with an enhanced wear-resistance (as a result of boronising) and higher oxidation stability (due to the aluminising). The investigation1 on boronaluminised of steels has shown impossibility of combining the positive properties of layers obtained by boronising and aluminising separately, i.e. a high wear-resistance along with high oxidation stability. The layer with a low aluminium content exhibits only a negligible increase in oxidation stability in comparison with a layer resulting from boronising alone, whereas in cases when *
For correspondence.
497
the complex layers consist mainly of aluminide phases, the oxidation stability is high on account of the wear-resistance of the layer obtained by aluminising only. Simultaneous diffusion saturation of steels with boron and aluminium is very difficult due to the occurrence of a series of parallel processes during the formation of the active boron and aluminium atoms. This happens in the saturating medium during the adsorption of the atoms on the surface, the reactions at the phase boundary and the diffusion on the adsorbed atoms into the steel. Owing to the foregoing many authors recommend a 2-stage boronaluminised2,3 which is unfavourable both from technological and economic viewpoints. On the other hand, the modern boronising technology is took the thermochemical process with pastes4–7. This is a very simple technology and additional procedures staff and equipment are not required. In previous papers8,9 is shown that simultaneous saturation of the surface of carbon and alloy steels with boron and aluminium can be achieved with a Borozar paste, as a result of which boronaluminised layers are with an enhanced microhardness (Hμ100=21500 MPa) in comparison with only boronised layers are produced. The purpose of the present paper is to investigate the structure, chemical composition and oxidation stability of layers obtained by boronaluminising of steels with the Borozar paste. EXPERIMENTAL The samples of carbon steel (C3) and tool steels 55NiCrMoV6 with dimensions L=15×15 mm and H=10 mm were subjected to diffusion saturation with the paste. The samples were cleaned with acetone before coating with the paste. The paste was coated on the samples surface with a thickness of 2–3 mm after that the samples were thermochemically treated in air at 950oC. The oxidation kinetics of the samples of carbon steel (C3) and the tool steels were investigated by measuring the change in the weight of the samples with time at 850oC. This temperature was chosen because 1-component layers resulting from boronising increase the oxidation stability of the steels up to 800oC (Ref. 10). The structure of the boronaluminised layer obtained with the Borozar paste was investigated by a scanning electron microscope JEOL 733. RESULTS AND DISCUSSION The typical structure of a boronaluminised layer on the tool steel obtained with the Borozar paste is shown in Fig. 1. The phase of iron aluminide – Fe3Al is located at the surface zone. The typical needle crystals of iron boride (Fe2B)2 phase are observed below the surface zone.
498
Fig. 1. Typical structure of boronaluminised layer on tool steel obtained with a Borozar paste (SEM)
EDS analyses of boroaluminised layer of tool steel 55NiCrMoV6 at the surface zone and in inner zone (in needles) has been performed and the data are shown in Tables 1 and 2, respectively. Table 1. Elemental analysis of boronaluminised layer of tool steel at the surface zone
Element OK Al K Cr K Fe K Ni K Total
Weight (%) 17.06 4.77 1.39 74.60 2.18 100.00
Atomic (%) 40.34 6.70 1.01 50.55 1.40
Table 2. Elemental analysis of boroaluminised layer of tool steel in the needles (inner zone)
Element BK CK Cr K Fe K Ni K Total
Weight (%) 16.41 6.27 1.51 74.22 1.58 100.00
Atomic (%) 44.31 15.25 0.85 38.80 0.79
Boronaluminising of carbon steel C3 has been performed with a paste containing various amounts of aluminium powder and aluminium oxide (3–50 wt.%). Figure 2 presents comparative tests on the oxidation stability of boronised and boronaluminised C3 with various compositions of the Borozar paste. Addition of 30 and 50 wt.% aluminium powder ensures the highest oxidation stability of the steels investigated (Fig. 2). As can been seen from the photographs on Fig 3a,b the surface of carbon steel sample with boronaluminised layer before and after oxidation is very smooth,
499
while the surface of the sample with boronising layer after oxidation is rather furrow (Fig. 3c). 1 4 3 5 2
weight loss × 10–3 (g/cm2)
100
80
60
6
40
20
7 0
0
1
2
3
4
5
6
7
8
9
10
11
time (h)
Fig. 2. Oxidation stability of layers on carbon steel (C3) obtained by boronising and boronaluminising 1 – after boronising; 2 – after boronaluminising with 5% Al2O3; 3 – after boronaluminising with 30% Al2O3; 4 – after boronaluminising with 50% Al2O3; 5 – after boronaluminising with 5% aluminium powder; 6 – after boronaluminising with 30% aluminium powder; 7 – after boronaluminising with 50% aluminium powder
Fig. 3. Photographs of boronaluminised carbon steel sample before oxidation (a), after oxidation (b) and after oxidation of ‘pure’ – boronised sample (c)
The layers obtained on 55NICrMoV6 steel by the Borozar paste containing 10% aluminium oxide or 10% aluminium powder possess much higher oxidation stability than that of 1-component layers obtained by boronising (Fig. 4). The layer obtained by boronaluminising ensures reliable protection of the steel used for producing of stamps by hot deformation process. These stamps are subjected to wear due to abrasion and oxidation. Local heating at the contact point between stamps and deformation metal sometimes exceeds 750oC.
500
9
weight loss × 10–3 (g/cm2)
70
2
60
1 8
50 40 30 20
4 3 6 5 7
10 0
0
2
4
6
8
10
12
14
16
18
20
22
24
26
time (h)
Fig. 4. Oxidation stability of boronised steel 55NiCrMoV6 (1), boronmetallised with: 10% ZrO2 (2), 10% CrB (3), 10%Cr2O3 (4), 10% Al2O3 (5), 10% AlB12 (6), 10% Al powder (7), ZrB2 powder (8) and uncoated steel 55NiCrMoV6 (9)
At this temperature (up to 850oC) the layer resulting only from boronising can not protect the steel against oxidation. When the temperature is above 850oC it is recommended to use boronaluminising of the steels. It is of interest to compare the oxidation stability of a layer obtained by boronaluminising of 55NiCrMoV6 steel with the stability of the other 2-component boronmetal diffusion layers obtained with a modified paste composition (55% boron carbide (B4C) and 45% sodium hexafluoroaluminate (Na3AlF6 ) and 10% metal oxide (or metal boride)) (Fig. 4). It is obvious that the boronaluminised steel 55NiCrMoV6 exceeds in oxidation stability the other investigated steels with a boron-metal layer. During thermochemical treatment of the steel samples with the paste composed by the above described metal and metal oxides, both phases of iron borides and iron aluminides appear in the diffusion layer, part of the penetrating aluminium being dissolved in the iron boride. This explains the very high oxidation stability combined with an enhanced microhardness of the steels investigated. CONCLUSIONS The oxidation stability of the layers obtained by boronaluminising of 55NiCrMoV6 steel is higher than those of the layers, obtained by 2-component boron-chromium or boron-zirconium paste. It is established that the samples containing 30–50 wt.% aluminium powder possess the highest oxidation stability. The experimental results show that boronaluminising with the Borozar paste is especially suitable for thermochemical treatment of tools parts subjected to wear and high temperature simultaneously. REFERENCES 1. L. S. LYUKHOVICH, L.G. VOROSHNIN, G.G. PANICH, E.D. SCHERBAKOV: Multicomponent Diffusion Coatings. Nauka i technika, Minsk, 1974 (in Russian).
501
2. K.-S. NAM, K.-H. LEE, D. Y. LEE, Yo-S. SONG: Metal Surface Modification by Plasma Boronizing in a Two-temperature-stage Process. Surf. Coat. Technol., 197, 51 (2005). 3. X. LUO, D. LI , K.CHEN: The Formation of a Boronised Layer on Aluminised Steel and Surface Corrosion Behaviours. Intern. J. Microstr. Mater. Prop., 1, 88 (2005). 4. U. BANDIS, S. WIGGER: US Patent No 6503344 (2003). 5. J. H.YOON, Y. K. JEE, S. Y. LEE: Plasma Paste Boronizing Treatment of the Stainless Steel AISI 304. Surf. Coat. Technol., 112, 71 (1999). 6. BorTec GmbH, Catalog Munih, Germany, 2000. 7. S. WIGGER, U. BANDIS: US Patent No 2298046 (2006). 8. R. PETROVA, Z. ZAKHARIEV: Structure of Boraluminized Layers on Steels. Bulg. Chem. Commun., 26, 82 (1993). 9. Z. ZAKHARIEV, R. PETROVA, L. LACKOV, V. G. TUMBALEV: Gas Phase Deposition of Aluminium and Boron on Iron Surface. Bulg. Chem. Comun., 28, 711 (1995). Received 23 April 2009 Revised 10 June 2009
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Oxidation Communications 35, No 2, 503–511 (2012) Technological aspects of oxidation processes
Thermodynamic Properties of Rare Earth Tellurites – Experimental Determination, Calculation and Prognosis G. Baikusheva-Dimitrovaa*, G. Vissokovb Department of Inorganic and Analytical Chemistry, Assen Zlatarov University, 8010 Burgas, Bulgaria b Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria E-mail:
[email protected] a
ABSTRACT The perspectives of the rare earth tellurites are in their application in the contemporary technologies such as nanotechnologies, silicate industry, as a dielectric and ferroelectric material; in the medicine as additions to different kinds of drugs for curing of hard healing diseases; and also as agricultural microfertilisers. The aim of the present work is to determine experimentally, calculate and predict the specific molar heat capacity (Cp) of the rare earth tellurites products of the type Ln2(TeO3)3 synthesised by us. The compositions studied were of the type Ln2(TeO3)3 where Ln = Y, Er, Yb. They were synthesised in vacuumed ampoules and characterised by chemical and X-ray analyses. The specific molar capacities (Cp) of the compounds studied were determined in the temperature range 399–587 K using a differential scanning calorimeter DSC (Setaram, France). The values measured were computer-processed by the linear regression method to obtain empirical formulae for the corresponding compound and the coefficients a, b and c in the equation Cp = a + bT + cT 2 were determined. The dependencies of the experimentally measured and the calculated values of Cp for the compounds studied Y2(TeO3)3, Er2(TeO3)3 and Yb2(TeO3)3 had regression coefficients R2 close to unity which means that the calculation procedure used was precise and correct. This provided a possibility to employ regression analysis to predict Cp in temperature ranges for which there are no experimental data. On the other hand, the specific molar heat capacities calculated allowed determination of the temperature dependences of entropy (ΔST0), change of enthalpy (ΔHT0 – ΔH2980) and the Gibbs function (ΔGT0), as well as predict the thermodynamic values in non-studied temperature intervals. The data on the thermodynamic proper*
For correspondence.
503
ties were necessary for development of industrial technologies for synthesis of compounds containing rare earth elements and products on their basis with preselected properties. Keywords: rare-earth metals, tellurites, thermodynamic, specific molar capacities, thermodynamic methods. AIMS AND BACKGROUND Tellurites of rare earth elements are comparatively new class of inorganic substances attracting still more attention during the last few years1,2. The aim of the present work is to determine experimentally, calculate and predict the specific molar heat capacity (Cp) of the rare earth tellurites products of the type Ln2(TeO3)3 synthesised by us. On the other hand, the calculated specific molar capacities allow finding the temperature dependences of entropy (ΔST0), change of enthalpy (ΔHT0 – ΔH2980) and the Gibbs function (ΔGT0). The studies on the specific molar capacity allow calculating the thermodynamic values in wide temperature interval3,4. The temperature dependence of Cp at low temperatures is known to be related to the characteristics of the solid matter crystalline structure. The calculation of the Debye temperature from the data on Cp provides possibilities to use data on the movement of crystal lattice vibrations and, hence, the strength of the chemical bonds. Besides, the data on Cp allow studies on the versatile processes of arrangement which determine, for instance, the magnetic, ferroelectric properties or superconductivity, as well as the formation of point defects. The rare earth tellurites synthesised were of the type Ln2(TeO3)3 and their thermodynamic characteristics are necessary for the development of industrial technologies for synthesis of rare earth compounds and products based on them and will be a contribution to an important chapter of inorganic chemistry, such as chemistry of tellurium. EXPERIMENTAL The metal tellurites of rare earth elements of the type Ln2(TeO3)3 necessary for the experiments were synthesised from tellurium dioxide TeO2 and high purity (99.99%) oxides of rare earth elements: Y2O3, Er2O3, Yb2O3, through vacuum synthesis in ampoules. For the experimental determination of the thermodynamic values like specific molar capacity, differential scanning calorimeter DSC (Setaram, France) was used by the method described in Refs 3 and 5. The parameters of the empty crucible, reference sample and substance studied were taken into account. The measurements were carried out at scanning rate of 2oC/min, recorder speed of 5 mm/min and amplifier range 250 V. The working temperature interval was 300–600 K. The main part of DSC is a block of heat-conducting material with 2 seats for flat aluminium ampoules. The block 504
temperature is raised at controlled rate while room temperature is maintained in the outer chamber. The thermal batteries placed near the working seat are connected by bridged circuit. The disturbances in the heat development in the seat are compensated and the consumption of differential power for the heating is registered on a recorder. For the determination of the specific molar capacities of the tellurites studied, the samples were finely ground and sieved through 0.25 mm2 sieve. Then the substance was homogenised and 0.2 to 0.7 g of it were placed in a capsule. The specific molar capacities were determined as follows: 1. Record the base line under hating the 2 empty capsules of the same weight. 2. Record the curve for the capsule with the reference substance – Al2O3. 3. Record the curve for the capsule with the substance studied. Cp =
I m´ I´ m
Cp´,
where І´ is the distance from the curve of empty capsule to the reference (Al2O3) (cm); І – the distance from the curve for empty capsule to the curve for the substance studied (cm); m´ – reference weight (g); m – substance studied weight, (g); Ср´ – specific molar capacity of the reference Al2O3 (J mol–1 K–1); Ср – specific molar capacity of the substance studied (J mol–1 K–1). RESULTS AND DISCUSSION The experimental results for Cp of the substances of the type Ln2(TeO3)3, where Ln=Yb, Er or Y studied in the temperature interval 388–587 К are presented in Table 1. The values obtained were computer-processed by the linear regression method to derive empiric formulae for the individual substances and the coefficients a, b and c in the general equation:
Cp = a + bT + сT2.
(1)
The standard molar entropies of Yb2(TeO3)3, Er2(TeO3)3, Y2(TeO3)3, were calculated by the method of Kelly6,7; the coefficients a, b and c, as well as the regression coefficients R2 for the individual substances are shown in Table 2. The plots of the temperature dependencies of the experimentally determined specific molar capacities in the interval 388–587 K and the empiric equations derived for the individual substances are presented in Figs 1–3.
505
Table 1. Experimental results for Cp of Yb2(TeO3)3, Er2(TeO3)3 and Y2(TeO3)3
T (K)
Ср (J mol–1 K–1) Er2(TeO3)3 354.42 348.63 352.09 350.71 352.10 354.74 359.00 364.27 362.18 363.27 361.55 361.63 362.14 361.50 365.57 385.99 389.10 386.92 387.80 387.50 388.08
Yb2(TeO3)3 306.68 315.84 316.07 319.81 319.67 326.98 322.58 315.66 320.54 324.03 320.06 327.85 333.57 337.54 336.81 338.21 340.26 345.11 333.38 335.67 337.50
388 398 408 418 428 438 448 458 467 477 487 497 507 517 527 537 547 557 567 577 587
Y2(TeO3)3 305.56 306.09 305.24 309.11 308.67 305.95 302.25 309.69 302.56 322.92 319.51 317.15 318.49 318.21 320.56 319.90 320.56 322.33 326.00 329.22 329.73
Table 2. Standard molar entropy ∆S0298, coefficients a, b and c and regression coefficients R2
Compound
Yb2(TeO3)3 Er2(TeO3)3 Y2(TeO3)3
∆S0298 (J mol–1 K–1) 363.55 377.79 321.25
b
c
R2
–0.0006 0.0008 0.0005
0.7011 –0.6103 –0.3452
123.95 459.92 365.81
0.8769 0.8876 0.8704
y = –0.0006x 2 + 0.7011x + 123.95 R2 = 0.8769
360 specific molar heat capacity Cp (J mol–1 K–1)
a
340
320
300 300
350
400
450 500 temperature T (K)
550
600
650
Fig. 1. Dependence of the experimental results for Cp on temperature for Yb2(TeO3)3
506
specific molar heat capacity Cp (J mol–1 K–1)
400 y = 0.0008x 2 – 0.6103x + 459.92 R 2 = 0.8876
390 380 370 360 350 340 300
350
400
450
500
550
600
650
temperature T (K)
Fig. 2. Dependence of the experimental results for Cp on temperature for Er2(TeO3)3
specific molar heat capacity Cp (J mol–1 K–1)
335 y = 0.0005x 2 – 0.3452x + 365.81 R 2 = 0.8704
330 325 320 315 310 305 300
300
350
400
450 500 temperature T (K)
550
600
650
Fig. 3. Dependence of the experimental results for Cp on temperature for Y2(TeO3)3
The dependencies between the experimentally determined and calculated by regression specific molar capacities for Yb2(TeO3)3, Er2(TeO3)3, Y2(TeO3)3 are shown in Figs 4–6. It can be seen from Figs 4–6 that the dependencies of the experimentally measured and calculated by regression specific molar capacities have R2 close to unity which means that the calculation procedure used was precise and correct. It made possible the use of regression analysis to predict the values of Cp at temperatures for which there are no experimental data. 340
Yb2(TeO3)3
ɋɪ (calculated value) (J mol–1 K–1)
335 330 325 320
y = 0.6628x + 104.09
315
2
R = 0.7314
310 305 305
310
315
320
325
330
335
340
345
350
ɋɪ (experimentally determined) (J mol–1 K–1)
Fig. 4. Dependence between the measured and calculated by regression specific molar capacity for Yb2(TeO3)3
507
ɋɪ (calculated value) (J mol–1 K–1)
380 375 370 365 360 355 350 345 340 340
Er2(TeO3)3
y = 0.696x + 100.23 2
R = 0.8814 345
350 355 360 365 370 375 380 385 ɋɪ (experimentally determined) (J mol–1 K–1)
390
395
ɋɪ (calculated value) (J mol–1 K–1)
Fig. 5. Dependence between the measured and calculated by regression specific molar capacity for Er2(TeO3)3 340 335 330 325 320 315 310 305 300 300
Y2(TeO3)3
y = 0.9061x + 32.526 R2 = 0.8007 305
310 315 320 325 330 ɋɪ (experimentally determined) (J mol–1 K–1)
335
340
Fig. 6. Dependence between the measured and calculated by regression specific molar capacity for Y2(TeO3)3
The specific molar heat capacities calculated by equation (1) allow finding the temperature dependencies of entropy (∆S0T), change of enthalpy (∆H0T – ∆H0298) and the Gibbs function (∆G0T) using the formulae below. The results are presented in Tables 3–5. T
∆S0T = ∆S0298 +
298
T
(2)
dT ,
T
∆H 0T – ∆H 0298 =
∫ C p dT ,
(3)
298
Cp
∫
∆G0T = ∆S0T –
∆H
0
T
− ∆H T
0
298
(4)
.
The good agreement between the experimentally determined and calculated values of Cp provided possibility to predict the thermodynamic vales in an non-studied temperature interval. The values of Cp calculated by linear regression for temperatures outside the temperature interval of the experiments, as well as the values of ∆S0T, (∆H0T – ∆H0298) and ∆G0T calculated by equations (2)–(4) are presented in Tables 3–5. 508
Table 3. Standard molar thermodynamic values for Yb2(TeO3)3
T (K)
298.15 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Cp (J mol–1 K–1) 279.65 280.28 295.84 308.39 317.95 324.50 328.06 328.61 326.17 320.72 312.28 300.83 296.39 288.94 283.50 279.05
∆S0T (J mol–1 K–1) 363.55 365.28 407.38 442.07 470.84 494.55 513.77 528.87 540.11 547.67 551.69 552.27 555.98 556.77 558.08 559.40
∆H0T – ∆H0298 (J mol–1) 0 518.5 15339.0 31409.5 48279.9 65500.3 82620.6 99190.9 114761.2 128881.3 141101.5 150971.5 163562.8 173898.5 184799.5 195851.2
∆G0T (J mol–1 K–1) 363.55 364.09 402.44 440.45 465.56 487.65 500.39 519.82 535.18 540.50 547.77 550.07 553.21 554.60 556.87 558.71
∆H0T – ∆H0298 (J mol–1) 0 645.3 17852.7 35016.0 52735.2 71610.3 92241.3 115228.2 141171.0 170669.7 204324.3 242734.8 286501.2 336223.5 392501.7 455935.8
∆G0T (J mol–1 K–1) 395.31 396.29 435.32 480.80 500.63 532.30 559.84 585.30 600.69 635.02 665.30 692.55 729.77 761.97 801.15 850.30
Table 4. Standard molar thermodynamic values for Er2(TeO3)3
T (K)
298.15 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Cp (J mol–1 K–1) 349.07 348.83 344.32 343.80 347.29 354.77 366.26 381.74 401.23 424.71 452.20 483.68 519.17 558.65 602.14 649.62
∆S0T (J mol–1 K–1) 395.31 397.46 446.32 482.85 512.50 538.53 563.02 587.36 612.50 639.12 667.74 698.73 732.37 768.89 808.47 851.24
509
Table 5. Standard molar thermodynamic values for Y2(TeO3)3
T (K)
298.15 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Cp (J mol–1 K–1) 306.34 307.15 307.24 307.73 311.72 318.21 327.20 338.69 352.68 369.17 388.16 409.65 433.64 460.13 489.12 520.61
∆S0T (J mol–1 K–1) 321.25 323.15 366.62 399.61 426.44 449.71 471.08 491.64 512.16 533.18 555.11 578.23 602.79 628.95 656.87 686.64
∆H0T – ∆H0298 (J mol–1) 0 568.4 15878.5 31342.3 47334.7 64230.7 82405.3 102233.6 124090.5 148351.0 175390.1 205582.9 239304.2 276929.2 318832.9 365390.1
∆G0T (J mol–1 K–1) 321.25 322.08 325.30 332.37 340.14 367.75 386.25 406.66 417.02 439.32 459.58 470.81 485.01 501.19 528.35 548.50
The data on the thermodynamic values allow developing industrial technologies for synthesis of compounds of rare earth elements and products based on them. CONCLUSIONS Tellurites of rare earth elements of the type Ln2(TeO3)3, were synthesised. Their purities and individualities were determined by chemical and X-ray analyses. The results obtained from the chemical analysis were compared to the theoretically calculated values and the agreement was found to be good. The specific molar heat capacities of the tellurites synthesised were determined and for the first time a prediction was made for non-studied compounds using the interpolation method and regression analysis. Using the relationship between the standard entropy heat capacities, the temperature dependencies of the thermodynamic functions were determined. The thermodynamic characteristics of the compounds studied can be used to develop industrial technologies for synthesis of compounds of rare earth elements and products on their basis with predetermined properties. REFERENCES 1. J. DOBROWOLSKY: Les tellurites des elements des terrea rares. Rocz. chem., 40, 1169 (1966). 2. I. BARIN: Thermochemical Data of Pure Substances. VCH Verlag gesellschaft mbH. D-6940 Weinheim, part I and part II, 1993, 777–972.
510
3. I. McNAUGHTON, C. MORTIMER: Differential Scanning Colorimetry. Perkin Elmer Corporation Norvalk Connection, 1975, р. 11. 4. R. DEHOFF: Thermodynamics in Materials Science. Taylor&Francis Group, New York, 2006. 5. G. HOHNE, W. HEMMINGER, H. FLAMMERHEIM: Differential Scanning Calorimetry – An Introduction for Practitioners. Berlin, Springer Verlag, 1996. 6. S. GORDIENKO, B. FENOTACHKA, G. VIKSMAN: Thermodynamics of Lantanoid Compounds. Naukova Dumka, Kiev, 1979. 7. E. H. P. GORDFUNKE, R. CLUISTRA, J. C. van MILTENBURG: The Thermodynamic Properties of Six Compounds in (Tellurium + Oxygen + Hydrogen) from 10 to 1000 K. J. Chem. Thermodynamics, 17, 1079 (1985). Received 21 March 2011 Revised 21 April 2011
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Oxidation Communications 35, No 2, 512–515 (2012) Green chemistry
A Proper Evaluation of Interaction between Solvent and Thiophene from the Middle Distillation Fraction of Oil Through Extraction Y. K. Kolevaa*, Y. Ts. Tashevab Department of Organic Chemistry, ‘Prof. Assen Zlatarov’ University, 1 Prof. Yakimov Street, 8010 Bourgas, Bulgaria E-mail:
[email protected] b Department of Industrial Technology and Management, ‘Prof. Assen Zlatarov’ University, 1 Prof. Yakimov Street, 8010 Bourgas, Bulgaria E-mail:
[email protected] a
ABSTRACT The trend for limiting the sulphur content in transportation fuels, due to environmental pollution, is gradually declining. The price of crude oil, the major backbone of a developed economy, is largely decided by the amount of sulphur in it. Moreover, sulphur being the most abundant hetero-element in crude oil, is of more concern than other heteroatoms. Sulphur exists both in aliphatic and aromatic forms in crude oil. All are collectively termed organic sulphur compounds. Crude oil needs to be refined before its use as a source of energy. Therefore, the refining process is of utmost importance for the quality of petroleum products. This process involves quite complex steps. A great deal of attention has been paid to selective solvents for extracting aromatic compounds from hydrocarbon mixtures and petroleum fluids. One of these solvents, which have been used for this purpose, is N-methylpyrrolidone (NMP). The aim of this work was to research the quantum chemical calculations for the possible mechanism of interaction between the solvent (NMP) and thiophene, which is a product of extraction of petroleum products. Keywords: sulphur compounds, thiophene, evaluation, oil. AIMS AND BACKGROUND The aim of this work was to research the quantum-chemical calculations for the possible mechanism of interaction between the solvent (NMP) and S-containing compound (thiophene), which is a product of extraction of petroleum products. Energy is one of the fundamental requirements in a civilised society to maintain the pace of modernisation with respect to time. Petroleum is one of the most complex *
For correspondence.
512
mixtures known with respect to the number of individual species, which probably ranges from 10 000 to 100 000 (Ref. 1). The composition of crude oil can vary greatly from source to source. However, all crude oils are mainly composed of carbon and hydrogen in the form of alkanes, cycloalcanes and arenes, i.e. hydrocarbons. In addition, minor amount of sulphur-, oxygen- and nitrogen-containing heterocycles, and trace amount of metals like vanadium and nickel are also found. The abundance of heteroatoms rises with increase in average molecular weight of the sample, which in turn is related to boiling point of distillation2. Although heterocycles containing S, O and N represent a minor portion in most crude oils, they are of crucial importance for exploration, production and refining of petroleum. Sulphur, being the 3rd most abundant element next to carbon and hydrogen, poses a serious threat in view both of economy and environment. Generally, sulphur content in crude oils varies from 0.05 to 13.95 wt. % (Ref. 3). For many years, a great deal of attention has been paid to selective solvents for extracting aromatic compounds from hydrocarbon mixtures and petroleum fluids. One of these solvents, which have been used extensively for this purpose, is furfural4. Due to problems reported regarding the lube-oil extraction processes in which furfural is used as the solvent, attempts have been made to replace it with other solvents such as NMP (Ref. 5). The most important advantages of NMP over furfural are as follows: (a) lower energy consumption in the utilities section of the lube-oil extraction units; (b) lower solvent to oil ratio in the lube-oil extraction units; (c) lower toxicity, and (d) lower fouling of rotating disk contactors used as extracting equipment. Quantitative structure activity relationship (QSAR) methods enable predictions of the properties of a wide range of chemical compounds based on the correlation between these properties and molecular descriptors. Many descriptors feature molecular electronic properties derived from quantum mechanics6. Others are mathematical indices derived from the graph theory that characterises the shape and branching of the molecular skeleton7. RESULTS AND DISCUSSION Chemistry is the science of bond making and bond breaking. A thorough knowledge of these processes in the course of the chemical reaction is a keystone of any reaction mechanism. In the heterolytic cleavage of a bond, the electron pair lies with one of the fragments, which becomes electron-rich, while the other fragment becomes electron-deficient. An electron-rich reagent gets attracted to the center of the positive charge and forms a bond with an electron-deficient species by donating electrons. The electron-rich species is known as a nucleophile, and the electron-deficient one – as an electrophile8–11. The aim of the current work is to be suggested the possible mechanism of interaction between thiophene and a solvent (NMP) based on the local quantumchemical descriptors. Computing tools of the optimised approach based on a structural indices set software package12,13 were used in this investigation, including an automatic 3-dimen513
sional model builder from molecular connectivity14, integrated molecular force-field optimiser, and interface to standard programs for computing the electronic structure15. Some global (EHOMO and ELUMO) and local (donor and acceptor superdelocalisability) molecular descriptors related to the structures and their reactivity were calculated by semi-empirical method (AM1). The calculated global and local molecular descriptors of N-methyl pyrrolidone (Fig. 1) are presented in Table 1. 7
CH3 N
6
O
5
CH3
N
4
1
2
O
3
Fig. 1. Structure of N-methyl pyrrolidone and number of the atoms Table 1. Global and local molecular descriptors of N-methyl pyrrolidone
ComGlobal deLocal descriptors pound scriptors N-methyl EHOMO ELUMO C1 O2 C3 C4 & C5 N6 C7 pyrro(eV) (eV) A D A D A D A D A D A D lidone (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) –9.52 1.46 0.28 0.12 0.10 0.29 0.25 0.16 0.24 0.17 0.16 0.24 0.24 0.16
*A – acceptor delocalisability; **D – donor delocalisability.
The global and local molecular descriptors of thiophene (Fig. 2) are presented in Table 2. 2
1
5
4
3
S
S
Fig. 2. Structure of thiophene and number of the atoms Table 2. Global and local molecular descriptors of thiophene.
Compound
Global descriptors EHOMO ELUMO (eV) (eV)
Local descriptors C1
C2
C3
S4
C5
A D A D A D A D A D (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) (a.u.) Thiophene –9.22 0.24 0.24 0.21 0.24 0.21 0.26 0.22 0.23 0.33 0.26 0.22 *A – acceptor delocalisability; **D – donor delocalisability.
All atoms of both molecules (N-methyl pyrrolidone and thiophene) are calculated for their donor and acceptor reactivity. The electrophilic site of N-methyl pyrrolidone is the carbon atom of carbonyl group and the nucleophilic site of thiophene are the carbon atoms of heterocyclic. A probable mechanism of electrophilic substitution between both compounds (N-methyl pyrrolidone and thiophene) is suggested in the Scheme. 514
Scheme Mechanism of electrophilic substitution (SE) between N-methyl pyrrolidone and thiophene CH3 N
O
S
S
C
O N
CH3 CH3
CONCLUSIONS A mechanistic study of both compounds (N-methyl pyrrolidone and thiophene) by their quantum-chemical descriptors (donor and acceptor superdelocalisability) has been done. The carbon atom of the carbonyl group of N-methyl pyrrolidone is suggested as an electrophilic center, while the carbon atom to sulphur atom of heterocyclic is a probable center of nucleophilicity. A mechanism of electrophilic substitution between N-methyl pyrrolidone and thiophene was suggested. REFERENCES 1. A. G. MARSHALL, R. P. RODGERS: Petroleomics: The Next Grand Challenge for Chemical Analysis. Accounts of Chemical Research, 37, 53 (2004). 2. S. K. PANDA: Liquid Chromatography and High Resolution Mass Spectrometry for the Speciation of High Molecular Weight Sulfur Aromatics in Fossil Fuels. NRW Graduate School of Chemistry University of Münster, Germany, 2006. 3. C. D. CZOGALLA, F. BOBERG: Sulfur Compounds in Fossil Fuels. Sulfur Reports, 3, 121 (1983). 4. M. BERTAGNALIO: Modernizing a Lube Plant. Hydrocarbon Processing, 103 (1983). 5. A. BONDI: Physical Properties of Molecular Crystals, Liquids and Glasses. Wiley, New York, 1968. 6. M. KARELSON, V. S. LOBANOV, A. R. KATRITZKY: Quantum-chemical Descriptors in QSAR/ QSPR Studies. Chem. Rev., 96, 1027 (1996). 7. J. DEVILLERS, A. T. BALABAN: Topological Indices and Related Descriptors in QSAR/QSPR. Gordon & Breach, New York, 1999, p. 59. 8. F. A. CAREY, R. J. SUNDBERG: Advanced Organic Chemistry. Part B: Reactions and Synthesis. 4th ed. Kluwer Academic/Plenum Publishers, New York, 2001. 9. T. H. LOWRY, K. S. RICHARDSON: Mechanism and Theory in Organic Chemistry. 3rd ed. Harper & Row, New York, 1987. 10. M. B. SMITH, J. MARCH: Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. 5th ed. John Wiley & Sons, New York, 2001. 11. P. SYKES: A Guidebook to Mechanism in Organic Chemistry. 6th ed. Orient Longman Ltd., New Delhi, 1970. 12. O. G. MEKENYAN, S. H. KARABUNARLIEV, D. G. BONCHEV: The Microcomputer OASIS System for Predicting the Biological Activity of Chemical Compounds. Comput. Chem., 14, 193 (1990). 13. O. G. MEKENYAN, S. H. KARABUNARLIEV, J. M. IVANOV, D. N. DIMITROV: A New Development of the OASIS Computer System for Modeling Molecular Properties. Comput. Chem., 18, 173 (1994). 14. J. M. IVANOV, S. H. KARABUNARLIEV, O. G. MEKENYAN: 3DGEN: A System for an Exhaustive 3D Molecular Design. J. Chem. Inf. Comput. Sci., 34, 234 (1994). 15. J. J. P. STEWARD: MOPAC 93. Steward Computational Chemistry, Colorado Springs, CO, USA, 1993. Received 9 May 2011 Revised 13 June 2011
515
Oxidation Communications 35, No 2, 516–522 (2012) Green chemistry
Investigation of the Energy Processes in the Greenhouse Z. Nikolaevaa*, G. Baikusheva-Dimitrovaa, G. Vissokovb Department of Mathematics and Physics, ‘Prof. Assen Zlatarov’ University, 1 Prof. Yakimov Street, 8010 Bourgas, Bulgaria E-mail:
[email protected] b Institute of Catalysis, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Bl. 11, 1113 Sofia, Bulgaria E-mail:
[email protected] a
ABSTRACT The greenhouse effect and the global warming are of a great importance and live questions concerning the life on Earth. A model of a flat greenhouse made of adequate light plastic material, which is thermally insulated and tanned inside, is prepared. The beams of the light stimulator hit perpendicularly a transparent covering (made of glass and plastic folio). The temperature inside the greenhouse is measured with a preliminary calibrated differential thermal coupling of chromel-copel with a precision of 0.1°С. During the process of investigation theoretically a formula for the temperature fluctuations inside the greenhouse as a function of time is worked out. It is suggested that the input energy (from Sun light or light source and environment) is constant. The proposed calculation method allows the temperature value calculation inside the greenhouse in the course of time. The graphically measured during the experiment temperatures (Texp) and the theoretically calculated temperatures (Tcalc) are compared. Good concurrence of the experiment and theoretical data is observed. Keywords: greenhouse effect, global warming, differential thermal coupling, enthal pies, carbon dioxide. AIMS AND BACKGROUND The greenhouse effect and the resulting global warming are one of the most important and pressing issues concerning life on Earth1–4. It causes an increased temperature of the lower atmospheric layers in comparison with the heat radiation of the planet. *
For correspondence.
516
Without this effect, the average temperature would be about –18°C (255 K) instead of the current 15°C (288 K). This would make the presence of water in a liquid form nearly impossible (apart from around volcanoes), which would deprive the Earth of liquid oceans, which are the main prerequisite for the origin and diversity of life. The temperature inside the greenhouse is measured with a pre-calibrated differential chromel-copel thermocouple with a precision of 0.1°С. The obtained degree line of the employed thermocouple is presented in Fig. 1. 4.5
thermoelectric voltage (mV )
4 3.5 3 2.5 2 1.5 1 0.5 0
0
5
10
15
20 25 30 35 temperature (°C)
40
45
50
Fig. 1. The obtained degree line of the employed thermocouple
The constant of the thermoelement and the absolute error of the measurements are as follows: k = 0.09739 mV/K; ∆k = 0.00054 mV/K
The temperature inside the mini-greenhouse (t2) is calculated using a formula known from laboratory practice:
t2 = t1 + ET/k,
(1)
where t1 is the temperature at one end of the differential thermocouple immersed in distilled water and ice in the inner chamber of a calorimeter, and ET – the thermoelectric voltage measured with a suitable millivoltmeter. The other end of the thermocouple is placed inside the greenhouse, which is located 20 cm away from the light stimulator (a 200 W lamp). EXPERIMENTAL A model of a flat greenhouse (Fig. 2) was made from suitable light plastic material, which was thermally insulated with Styrofoam or Fibran (2) and tanned on the inside. The beams of the light stimulator hit a transparent covering (made of glass and plastic folio) perpendicularly (1). The temperature inside the greenhouse T was measured with a pre-calibrated differential thermocouple (3).
517
W in
W rad
1
2 Ɍ0
W Ɍ
ɨ
ɋ0 3
Fig. 2. Model of a flat greenhouse
The experiment was carried out with distilled water in a plastic vessel with a volume of 400 cm3 and the light source was a 200 W electric lamp located 20 cm from the transparent covering and directed at it at a right angle. The present work offers a new theoretical model for investigation of the processes inside a greenhouse when temperature changes. It is assumed that the input energy Win (from the sun or a light source and the immediate surroundings) is constant. The symbols used in the model are as follows: Wrad is the energy radiated from the greenhouse wall covered with glass or a plastic foil and open to the solar rays; W – the energy inside the greenhouse; t0 = 0, T0 is the inside temperature (at the beginning of the experiment); W0 – the energy inside the greenhouse at the beginning of the experiment (t0 = 0, T0). It is minimum (W0 = min). When a stationary equilibrium state is reached, the input and radiated energies are equal: Win = Wrad
The inside energy is at its maximum Wmax (Fig. 3). During the heating, if at a time t the inside energy is W, then at a time t + dt we will have W + dW. W rad
W in
Ɍ0
W = W ɨ = min initial state
W rad
W in
for time t
T max
W = W max equilibrium state
Fig. 3. New theoretical model for investigation of the processes inside a greenhouse
The energy change is greater than zero (dW > 0), because there is heating. The increase of energy at any given time is proportional to the difference between the 518
maximum energy Wmax and the energy inside the mini-greenhouse W as well as to the time interval (the main hypothesis of the theoretical model in first approximation): dW = μ(Wmax – W)dt
(2)
where µ is a proportionality coefficient that depends on the greenhouse, its walls, volume, material, outside temperature, etc. From equation (2) we obtain that dW Wmax – W
= μdt.
(3)
After multiplying the 2 sides of the above differential equation by (–1) and integrating it, we come to ln(Wmax – W) = –µt + C.
(4)
The integration constant C is determined by the initial conditions: at t0 = 0, the energy inside the greenhouse is W = W0: C = ln(Wmax – W0).
(5)
After substituting the integration constant (5) in formula (4) and making simple mathematical transformations, we obtain that
WMAX – W = (Wmax – W0) e–μt.
(6)
As a result of equation (6), the inside energy W is equal to
W = Wmax – (Wmax – W0) e–μt.
(7)
From the classical kinetic molecular theory of the ideal gas, we use the relation between mean kinetic energy and temperature5,6 and divide equation (7) by the Boltzmann constant (k = 1.38×10–23 J/K): W k
=
Wmax k
W0 Wmax – – e–μt. k k
(8)
where W/k = T (the temperature inside the greenhouse); Wmax/k = Tmax (the temperature at reaching equilibrium state), and W0/k = Т0 (the inside temperature at the initial moment when t0 = 0). Thus we get the following formula:
T = Tmax – (Tmax – T0) e–μt.
(9)
It can be seen from equation (9) that for our theoretical model the temperature inside the greenhouse T increases with time t exponentially. The difference between the temperature at equilibrium state Tmax and the initial temperature T0 is designated as ∆Tmax: ∆Tmax = (Tmax – T0).
519
Then formula (9) will have the following form:
T = Tmax – ∆Tmax e–μt
(10)
Formula (9) was obtained theoretically by considering the energy processes in the greenhouse, assuming that the input energy Win (from the sun or a light source and the immediate surroundings) is constant. RESULTS AND DISCUSSION For the conducted experiment: (a) the equilibrium temperature is Tmax = 300 K; (b) the maximum temperature fluctuation is ∆Tmax = 13 K. Then equation (10) has the following form:
T = 300 – 13 e–μt.
(11)
Let us calculate the temperature inside the greenhouse using formula (11) for the time intervals of the conducted experiment Тcalc and compare them with the measured temperature values Тexp. Coefficient µ from equation (10) is: ln μ=
∆Tmax Tmax – T
.
t
(12)
When substituting with Tmax = 300 K and ∆Tmax = 13 K from equation (12), we obtain that ln μ=
13 300 – T t
.
(13)
Coefficients µ for the measured temperature values, except for its initial value (t0 = 0) and stationary state (Tmax), for which equation (13) is not true, are worked out from equation (13). Afterwards, the arithmetic mean μ of the conducted experiment is calculated: μ = 0.000197 s–1.
The obtained value of coefficient μ (the arithmetic mean) is substituted in equation (11) and thus the calculated temperature values Тcalc for any time interval of the experiment are obtained. Table 1 shows the temperatures measured during the experiment (Тexp) and the temperatures calculated using the theoretically worked out formula (Тcalc).
520
Table 1. Temperatures measured during the experiment (Тexp) and temperatures calculated using the theoretically worked out formula (Тcalc)
t (min) 0 2 4 6 8 10 20 25
Тexp (K) 287.0 287.2 287.5 288.0 288.2 288.6 289.2 290.0
Tcalc (K) 287.0 287.3 287.6 287.9 288.2 288.4 289.7 290.3
t (min) 30 40 50 60 70 80 90 100
Тexp (K) 290.2 291.0 292.4 293.2 294.1 294.5 295.2 296.1
Тcalc (K) 290.9 291.9 292.8 293.6 294.3 294.9 295.5 296.0
t (min) 120 140 160 180 200 220 240 260
Тexp (K) 297.5 298.0 298.5 299.0 299.4 299.8 300.0 300.0
Тcalc (K) 296.9 297.5 298.1 298.5 298.8 299.2 299.4 299.5
Figure 4 offers a comparison of the curves of Тexp = f(T) and Тcalc = f(T). Good concurrence of the experimental and theoretical data is observed. 302 300 temperature T (K)
298
series 1 experimental temperature
296 294
series 2 calculated temperature
292 290 288 286
0
100 200 time t (min)
300
Fig. 4. Comparison of the curves of Тexp = f(T) and Тcalc = f(T)
The proposed calculation method using the worked out formula (10) makes it possible to determine the temperature T for any time value. Data processing and graphic representation were carried out by means of Microsoft Excel. CONCLUSIONS 1. The present modelling of the conversion of the solar radiation into heat provides a physical explanation of the temperature fluctuation with time in the greenhouse. 2. Besides, the proportionality coefficient µ is calculated and its meaning is clarified. It depends on the greenhouse, its walls, volume, material, outside temperature, etc. 3. The temperature inside the mini-greenhouse is measured with a pre-calibrated differential thermocouple (chrome-copel) with a precision of 0.1°С. 4. Good concurrence of the theoretically calculated temperatures (Тcalc) and experimentally measured temperatures (Тexp) is observed.
521
REFERENCES 1. 2. 3. 4. 5.
http://www.epa.gov/climechange/index.html http://bg.wikipedia.org/wiki/Парников_ефект http://scienceinschool.org/2008/issue8/climate/bulgarian http://www.dadalos-iizdvv.org/nachhaltigkeit_bg/grundkurs_4.htm R. SERWAY, J. BEICHER, J. JEWETT: Physics for Scientists and Engineers. North Carolina State University and California State Polytechnic University – Pomona, 2000, p. 579. 6. I. SAVELEV: Physics. Vol. 1, Mechanic, Molecule Physics. Science, Moscow, 1977. Received 15 June 2010 Revised 28 July 2010
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5. D. GAL: Modelling of Processes Proceeding in the Presence of Oxygen: from the Model to Reality. Oxid. Commun., 20, 1 (1997). In preparing the list of References attention must be drawn to the following points: (a) Names of all authors of cited publications should be given. Use of ‘et al.’ in the list of references is not acceptable; (b) Only the initials of first and middle names should be given. Tables – each bearing a brief title and typed on a separate sheet, should be numbered in Arabic numerals. The tables should be placed after the list of References. Figures and captions – should be grouped together at the end of the manuscript with figures numbered consecutively and captions typed on a separate sheet. Figures (graphs) should be marked by pensil on the margin or at the back with the name of the first author and the beginning of the title. Particular attention is drawn to the use of SI Units, IUPAC nomenclature for compounds and standard methods of literature citation. Manuscripts (without figures) should not exceed 20 typewritten pages. Electronic Submission of Manuscripts
Manuscripts should be submitted in electronic form. Submission not in electronic form may face a delay in publication. All text (including the title page, abstract, keywords, all sections of the manuscript, figure captions, and references) and tabular material should be in one file, with the complete text first, followed by the tabular material. The manuscript must be prepared using MS Word 6.0 and above. Manuscripts in PDF are not accepted. Chemical equations must be supplied using equation editor. Tables must be created using table format feature. Graphics, i.e. figures, schemes, etc. should be in a separate file. The file name should be descriptive for the graphic. Structures and schemes may be supplied in ChemWindow format and other graphics in Microsoft Excel or Microsoft PowerPoint format. Submission of manuscripts
Manuscripts should be sent to the following address: Prof. Dr. Slavi K. Ivanov SciBulCom Ltd., P. O. Box 249, 7 Nezabravka Str., 1113 Sofia, Bulgaria Phone/Fax: +359 2 872 42 65, +359 2 978 72 12 E-mail:
[email protected] All manuscripts are subject to critical review and the names of referees will not be disclosed to the authors. The manuscript sent back to the author for revision should be returned within 2 months in duplicate. Otherwise it will be considered withdrawn. Revised manuscripts are generally sent back to the original referees for comments, unless (in case of minor revisions) the editors accept them without seeking further opinions. Proofs should be corrected and re turned as soon as possible. The authors receive CD-ROM containing copy of the book.
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