Electrochemical Study of Some New Sulfa-nitrone Compounds and ...

Journal of Chemistry and Chemical Sciences, Vol. 5(4), 169-179, April 2015 (An International Research Journal), www.chemistry-journal.org

ISSN 2229-760X (Print) ISSN 2319-7625 (Online)

Electrochemical Study of Some New Sulfa-nitrone Compounds and Their Electrosynthesis with Selected Ketones Huda S. Abood1, Anis A. Al-najar2 and Nisreen N. Majeed2 1

Department of Pharmaceutical Chemistry, College of Pharmacy, University of Basrah, IRAQ. 2 Department of Chemistry, College of Science, University of Basrah, IRAQ. e-mail: [email protected]. (Received on: April 24, 2015) ABSTRACT The electrochemical behavior of nitrone compounds and electrosynthesis of nitrone with some ketones were established by cyclic voltammetry (CV), for oxidation and reduction at a platinum electrode in DMF at scan rates 0.5 to 2 vs-1 at a potential range of 2 to -2 v. The study of cyclic voltammetry with different scan rates offers much information about electron transfer, kinetics, and transport properties of electrolysis reactions. The current was measured as a function of the linear potential applied. The resulting products were identified by physical properties like melting point (m.p.) and color. Also compounds showed the expected data in identification techniques like FTIR, 1HNMR, mass spectroscopy and Elemental analysis (CHN). The results verified the chemical structures of electrosynthesized compounds. Keywords: nitrones, cyclic voltammetry, electrosynthesis, electroreduction, sulfa nitrone.

INTRODUCTION Various organic compounds are synthesised and studied by cyclic voltammetry1-9. McIntire and co-workers7 studied nitrone electrochemistry in aqueous and non-aqueous media in order to conclude a range of inactivity suitable for electrochemical generation of free radicals. In this study the nitrones were synthesized10 and their mixtures with the selected ketones were study by cyclic voltammetry in order to determine specifically the April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org

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Huda S. Abood, et al., J. Chem. & Cheml. Sci. Vol.5 (4), 169-179 (2015)

required potentials to reduction –coupling with numbers of ketones through electrosynthesis processtoleading series of some new hydroxylamines. R1

R2

R3

2e 2H DMF

N

O O

R2

R3

R1 OH

NR4OH

R4

EXPERIMENTAL SECTION 2.1. Chemical Materials Sulfaguanidine, sulfafisoxazole, sulfathiazole, DMF, Butyraldehyde were obtained from Sigma-Aldrich Salicylaldehyde, 3-methoxy acetophenon, cyclohexanone, calciumchloride were obtained from B.D.H. Camphor was obtained from H.W, 4bromoacetophenone, 3-pentanone,n-hexane ,ethyl acetate were obtained from Alpha. Solvents were used after being purified according to the standard method. 2.2. Cyclic Voltammetry Cyclic voltammetry was performed with a DY 2300 Series Potentiostat/ Bipotentiostat, potentiostate-galvanostate fully computerized in the processed data analysis. All potentials are reported versus the silver –silver chloride electrode at 25 ± 2 oC. Cyclic voltammetry was carried out in a thermostated one compartment three –electrode cell. The working electrode was a platinum wire of nominal area 0.0785 cm2. This was controlled by silver-silver chloride as a reference electrode through which no current flows. The auxiliary (secondary) electrode was a platinum wire. In cyclic voltammetry the negative initial potential value was set mostly equal to final positive one. The scan rate (ν) was varied from 0. 5 to 5 vs-1, while the voltage was scanned between -2 to 2V. Molar concentration of supporting electrolyte Bu4NBF4 was 0.15 M. The solutions of electro synthetic compounds (E1, E2, E3, E4 and E5) have been prepared in molar concentration (5x10-4 M) which is appropriate for getting cyclic voltammogram, followed by comparison with the measured precursor cyclic voltamograms of nitrones. Hence the related cyclic voltammograms of these nitrones mixed with the specified ketones have been done in order to demonstrate the intervening of electroreduction coupling between the nitrones and ketones. 2.3. Electrosynthesis compounds The cell consists of glass vessel (75 ml) volume the vessel contained Tin (Sn) electrode as cathode (3.5x7.8 cm2) and carbon anode (0.6x15 cm2) immersed in DMF (50 ml) containing Bu4NBF4 as supporting electrolyte (2 g). A constant current of 20 mA as maximum value was used with the aid of a coulometer. April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org

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Controlled–current electrolysis was carried out in one compartment undivided, two electrode cell of 75ml volume .The cathode was a tin pure metal electrode (4x8 cm2), while a carbon rod was used as an anode ( 0.6 x15 cm2). To a mixture of (0.002 mol) of nitrone, (2g) of Bu4NBF4 and (40-50 ml) of DMF, (0.005 mol) of the definite ketone was added followed by mixing the soluble solution with a magnetic stirrer until attaining a complete homogeneous solution. Then a constant current of 20µA at (25 ᵒC) was passed until most of ketone is consumed, which is indicated by assaying TLC. Before that, a change in the color of solution was observed giving a good indication to switch off the coulometer as shown in Table (1). The reaction mixture was poured into (200 ml) water and the required compound was extracted with CH2Cl2 (3x20). To the combined organic layers, anhydrous CaCl2 was added followed by filtration. The specified compound was dried in a vacuum oven at 60 ᵒC. Table-1: shows symbols, structures of the nitrones and products. symbol

Mixture reaction

of

E1

N1 + 3-methoxy acetophenone

Structure of nitrone

Structure of electrosynthesis compounds OH

α

Time of changing color hrs. 3

N NH2

O S N

OH

NH2

O O

E2

N1 + cyclohexanone

2 H2N

α

OH

O

N

S

HO

E3

O HO

N2 + 3-pentanone

N

NH2 N

O S

α

3.5

NH O

O

OH

N

NO2

E4

N3 +camphor

3

HO N

α

O S

HO HO

NH

O N S

E5

N3+4-bromo acetophenone

Br

3.5 OH N

α

O N

OH

HO

S

S NH

O

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N-diaminomethylene-4-(hydroxyl-(1-(1-hydroxy-1-methoxyphenyl)ethyl)butyl)amino benzenesulfonamide(E1) Melting point (m.p) 179-182oC ,Yellow-orange crystalsyield 75%,FTIR ῡ /cm:1602(C=C),3425(OH),2800-2925(C-Haliph) 3250-3315(NH),3000 (C-Harom).1HNMR (500MHz, dimethyl sulfoxide (DMSO)); δ: 2.27(s, H-α), 6.01(s, N-OH), 3.55(s, C-OH), 8.17-8.32 (AA`BB` Harom),7.03-8.49 (m, Harom), 0.94-1.18(m, Haliph),4.21(NH). For C20H28N4O5S (found) 54.85% C, 6.50 % H, and 13.04 % N. 1

N-diaminomethylene-4-(hydroxy-(1-(1-hydroxy-cyclohexyl)-butyl)amino)benzenesulfonamide (E2) m.p160-162oC , dark yellow- crystals yield 70%, FTIR ῡ /cm-1:1570(C=C), 3450(OH),2873-2960 (C-Haliph), 3196-3367(NH),3080 (C-Harom).Mass (m/z): 384 [M]+, 268, 253, 98. For C20H28N4O5S (found) 54.85% C, 6.50 % H, and 13.04 % N. N-(3,4-Dimethyl-isoxazol-5-yl)-4-((2-ethyl-2-hydroxy-1-(4-nitro-phenyl)-butyl)hydroxy-amino)-benzenesulfonamide (E3) m.p 178-180oC, browncrystalyield 67%, FTIR ῡ /cm-1:1596(C=C), 3350(OH), 2927 (C-Haliph), 3180 (NH),3050 (C-Harom).1HNMR(500MHz, dimethyl sulfoxide (DMSO)); δ: 2.14(s, H-α), 6.60(s, N-OH), 5.13(s, C-OH), 7.37-8.28(AA`BB` Harom),7.66,8.40 (d, Harom), 0.94,1.32(t,q, Haliph). For C26H25N3O5S (found) 63.51% C, 4.91 % H, and 8.72% N. 4-(Hydroxy-((2-hydroxy-phenyl)-(2-hydroxy-1,7,7-trimethyl-bicyclo(2.2.1)hept-2-yl)methyl)-amino)-N-thiazol-2-yl-benzenesulfonamide (E4) m.p134oCdec, yellow-browncrystalyield 65%, FTIR ῡ /cm-1:1583(C=C), 3446(OH), 2962(C-Haliph), 3250 (NH),3100 (C-Harom).1HNMR(500MHz, dimethyl sulfoxide (DMSO)); δ: 3.17 (s, H-α), 5.84 (s, N-OH), 4.22(s, C-OH),12.65(Ar-OH), 6.85-7.52 (AA`BB` Harom),6.55-7.56 (m, Harom), 0.94,1.32(t,q, Haliph). For E4 with DMF C29H38N4O6S2 (found) 57.80% C, 6.34 % H, and 9.28% N. 4-((2-(4-Bromo-phenyl)-2-hydroxy-1-(2-hydroxy-phenyl)-propyl)-hydroxy-amino)-Nthiazol-5-yl-benzenesulfonamide (E5) Oily dark purple, 70%, FTIR ῡ /cm-1: 1627(C=C), 3350(OH), 2962(C-Haliph), 3250 (NH),3090 (C-Harom).1HNMR (500MHz, dimethyl sulfoxide (DMSO)); δ: 1.34 (s, H-α), 5.85 (s, N-OH), 3.19(s, C-OH), 7.74-7.89 (AA`BB` Harom),6.75(t), 7.07 (t) 7.19(d)(Harom), 0.98 (s, Haliph). ForC29H39BrN4O6S2 (found) 49.47% C, 5.08 % H, and 8.68% N. April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org


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RESULTS AND DISCUSSION 3.1. The electron transfer of N1 (Z)-N-butyl(diaminomethylene)sulfamoyl)aniline oxide The electrochemical behavior of this compound was established by cyclic voltammetry (CV) for oxidation and reduction at a platinum electrode in DMF at scan rate 2vs-1 at a potential range of 2 to -2 v, the reduction peak was Epred= - 0.95v, as shown in Figure (1).

Figure-1: Cyclic voltammogram of compound N3 in THF at platinum electrode, scan rate 2 vs-1.

a. Electron transfer of mixture N3 with 3-methoxy acetophenone compared with that of electrosynthesis of (E1) Comparing the CV measurements of the mixture of nitrone with ketone and its electrosynthesis of them, it was found that their cyclic voltammograms are analogues, as shown in Figure(1) The overall suggested mechanism of electrosynthesis between nitrone and ketone can be detailed in Scheme (1) below: .

R3

HC

N

N

O

R1

R3

HC

R4

H

O

R3 HC

+e

N

R4

HO

R2

R4

R3

+e

R1

+H

O

+ O

R1

HC

R2

R2

N HO

R4

R3 NR4OH

OH

Scheme-1: The mechanism of electroreduction coupling betweennitrone and ketone. April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org

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b

a

Figure-2: Cyclic voltammogram of mixture N1 with 3-methoxy acetophenone in DMF, at 0.5vs-1(a) cyclic voltammogramm of E1 in DMF, at 0.5 vs-1(b).

b. Electron transfer of mixture of N1 and cyclohexanone compared that of electrosynthesis (E2). Figure (3a) represents the cyclic voltammogram of the mixture of N1 and cyclohexanone which shows the appearance of oxidation peak that belongs to the oxidation of C= NH group in guanidine to NO, at Epred= -0.8v. The electron transfer of mixture of N1 withcyclohexanone compared that of electrosynthesis (E2)gives the same results, as shown in Figure (3b). a

b

Figure-3: Cyclic voltammogram of the mixture of N1 and cyclohexanonein THF, at scan rate0.5 v-1(a) cyclic voltammogram of the E2 in THF, at scan rate 0.5 vs-1(b)

3.2. The electron transfer of N2 (Z)-4-(N-(4,5-dimethylisoxazol-3-yl) sulfamoyl)-N-(4-nitrobenzylidene)aniline oxide Cyclic voltammogram of N2 at scan rate 0.5 vs-1, two reduction peaks were observed Epred1= -1.26 v and Epred2=-0.44 v, and the cathodic peaks current were Ipred1=1.30x10-5 A and Ipred2=2.40x10-5A respectively, as shown in Figure (4). The first peak results from the reduction of the nitrone group to hydroxylamine. April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org


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By referring to the cyclic voltammogram of N2 at different scan rates, as shown in Figure (5), data in Table (2) was computed for reduction peaks current and plotted as a function of ν1/2 indicating the electrochemical reduction of this nitrone accompanied by one electron transfer step to each reduction process.

Figure-4: Cyclic voltammogram of N2 in DMF at scan rate 0.5 vs-1. 2 vs-1 a 1 vs-1 b 0.5vs-1 c 0.2 vs-1 d 0.1 vs-1 e

a b c

Figure-5: Cyclic voltammogram of N2 in DMF at different scan rates.

Figure (6) shows the linear relationships with both reduction peaks indicating again one electron transfer for each process, while Figure (7) showed clearly the possibility of chemical reactions at slow scan rates followed by electron transfer only at fast scan rates, particularly after 0.5vs-1. Table-2: The values of Ipred of reduction current and Fpred of N2. -1

ν V.s 0.1 0.2 0.5 1 2

ν 1/2 0.316 0.447 0.707 1 1.414

Ipred1 Ax 10-5 1.99 2.68 3.74 5 6.60

Fpred1 A/(v.s-1) x10-5 6.32 6 5.28 5 4.66

Ipred2 A x10-5 1.01 1.4 2.4 2.96 4.15

Fpred2 /(v.s-1) 3.2 3.15 3.04 2.96 2.94


176


Figure (6) Relation between Ipred1 (a) and Ipred2 of reduction current and ν1/2 for CV(b) of N2 (b).

Figure-7: Current function Fp for first(a) and secondreduction current versus scan rates of N2 (b).

a. The electron transfer of the mixture N2 and 3- pentanone compared to electrosynthesis of E3 After the addition of 3-pentanone to nitrone N2, the obtained CV showed a merge of two reduction peaksto form one peak at Epred = -1.18v at scan rate 1vs-1, as shown in Figure (8a).The electro reduction between N2 and 3-pentanone was driven to obtain E3.The cyclic voltammogram of this compound is shown in Figure (8b) illustrating a new irreversible reduction peak at Epred= - 1.38 v.

a

b

Figure-8: Cyclic voltammogram of mixture of N2 with 3-pentanone in DMF at scan rate 1v.s-1(a) cyclic voltammogram of E3 in DMF at scan rate 1v.s-1(b). April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org


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3.3. The electron transfer of N3 (Z)-N-(2-hydroxybenzylidene)-(N-thiazol-5-ylsulfamoyl) aniline oxide The cyclic voltammogram of this compound (N5) in DMF at scan rate 0.5 vs-1 and potential range from 2 to -2 ,shows a reduction peak at -1.1 v with peak reduction current Ipred1 = 4.8 x10-5A and Epred2 = -0.37 v with Ipred2 = 3 x10-5 A. At the same scan rate and potential range, the cyclic voltammogram shows also an oxidation peak Epox= 0.68v with peak oxidation current Ipox= 0.4x10-4 A, as shown as in Figure (9).

Figure-9: Cyclic voltammogram of N3 at scan rate 0.5 v.s-1.

a. The electron transfer of the mixture between N3 and camphor compared to electrosynthesis of compound E4. On addition of camphor to compound N3, the reduction peaks clearly appear. The first reduction peak in Epred1= -1.15 v and second reduction peak in Epred2 =-0.48v as shown in (Figure 10 a). So, in the electrochemical reduction of this compound with camphor a product E4 was obtained at which the oxidation peak current in 0.75V fully disappears. At the same time, a shift in reduction peaks occurs, the first reduction peak Epred1 = - 0.6 v established together with a peak reduction current Ipred1 = 0.4x10- 4 A, as well as, a second reduction peak Epred2 = -1.02 v with Ipred2 = 0.6 X10-4 A, as shown in (Figure 10 b).

Figure-10:Cyclic voltammogram of mixture of N3 with camphor in DMF, at scan rate 0.5 vs-1 (a) cyclic voltammogram of E4 in DMF, at scan rate 0.5 vs-1(b). April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org

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The irreversibility appears clearly when the potential range is changed from (2 to -2 v) to the range (-1.4 to -0.2 v). The cyclic voltammogramm at different scan rates is shown in Figure (11). The behavior here is exactly similar to other systems mentioned earlier11. a

2 v.s-1 a 1 v.s-1 b 0.5 v.s-1 c 0.1 v.s-1 d

b

c

d

Figure-11: Cyclic voltammogram of E4 in DMF at different scan rates.

b. The electron transfer of the mixture of N3 and 4-bromo acetophenone compared to electrosynthesis of compound E5. When 4-bromo acetophenone is added to nitrone N3, the peak of reduction fades, and another reduction peak appears at Epred1= -1v with Ipred1 0.5x10-4 A, in addition to a second reduction peak Epred2 = -0.53 v with Ipred2= 0.8x10-4 A. These are attributed to the reduction of ketone, as shown in Figure (12a). Similarly, in electroreductive intermolecular coupling of this (N3) with 4-bromo acetophenone leading to the product E5, the reduction peak -1v fully disappears, while a new reduction peak appears Epred= -0.4 v, as shown in Figure (12b). Br OH N

a

b

α

O N

OH

HO

S

S NH

O

Figure-12: Cyclic voltammogram of mixture of N3 with 4-bromo acetophenoneat scan rate 0.5 vs-1(a) cyclic voltammetry of E5at scan rate 0.5 vs-1(b). April, 2015 | Journal of Chemistry and Chemical Sciences | www.chemistry-journal.org


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CONCLUSION Some of the mentioned synthesized nitrones have been used through the electroreductive intermolecular couplings with various selected ketones. So, in order to get the desired information concerned with such electrosynthesis, during the active regions of oxidation and reduction processes. Cyclic voltammetry was carried out for the following nitrones (N1, N2 and N3) with ketones to prove the possibility of electrosynthesis of nitrone with a number of ketones to obtained new compounds from electroreduction-coupling reactions.Cyclic voltammetry was used to prove the possibility of electrosynthesis of nitrone with a number of ketones to obtained new compounds from electroreduction-coupling reactions. ACKNOWLEDGMENT We thank Assist. Prof. Dr. Usama H. Ramadhan, college of Pharmacy, University of Basrah for his assistance to finish this work, gratefully acknowledged. REFERENCES 1. R. Tucceri, The Open Physical Chemistry Journal, 4, 45-61 (2010). 2. P. Ojha , A. Sharma , P. S. Verma; L. K. Sharma, Int. J. ChemTech Res.,3(2), 917-927 (2011). 3. N. V. Vasilieva , I. G. Irtegova, N. P. Gritsan, A.V. Lonchakov, A.Y. Makarov, L . A. Shundrin; A.V. Zibarev, J. Phys. Org. Chem., 23, 536-543 (2010). 4. M. C. Moncada, M. F. deMesquita; M. M. C. dosSantos, Journal of Electroanalytical Chemistry, 636, 60-67 (2009). 5. AAAl-Najar; TI Al-Salih; MANaser,Basrah J. of Science, 12(2), 43-56 (1994). 6. MA Oturan; M Mēdebielle; SAPatil; RS Klein, Turk. J. Chem., 26, 317-322 (2002). 7. GLMcIntire; HN Blount; HJ Stronks; RV Shetty; EG Janzen, J. Phys. Chem., 84,916 (1980). 8. DK Root; WH Smith, J. Electrochem. Soc.,129, 1231 (1982). 9. M Murahashi, T Shiota; Y Imada, Organic Syntheses, 9, 632 (1998). 10. HS Abood; NN Majeed; AA Al. najar, Res. J. Chem. Sci.,5(4),53-56 (2015). 11. H Lund, Organic electrochemistry 2nd Edition, Edited by MMBaizer; Marcel Dekker, New York, (1983).
