Sterically hindered aromatic compounds. IX

Sterically hindered aromatic compounds. IX. Electron spin resonance and product studies of the dediazoniation reaction L. Ross C. BARCLAY, A L E X A N D E RBRIGGS, G. WILLIAM E. BRIGGS, JULIAN M. DUST,andJEAN A . GRAY

Can. J. Chem. Downloaded from www.nrcresearchpress.com by 95.77.97.146 on 05/28/13 For personal use only.

Deptrrttnc,trr ofCirc~tnisrry.Molttrt Alli~otrUtricrrsity, Srrc~k~ille, N.B., Corrorlrr EOA 3C0 r y 1979 Received F e b r ~ ~ a 23.

L. ROSSC. BARCLAY, ALEXANDER G. BRIGGS,WILLIAM E. BRIGGS,JULIANM. DUST,and JEANA. GRAY.Can. J. Chem. 57,2 172 (1979). An esr study of the dediazoniation of 2,4,6-tri-tert-butylaniline with butyl nitrite in methylene chloride indicated the formation of the 2,4,6-tri-tert-butylphenyl radical which was spin trapped by the butyl nitrite. The persistent 2,4,6-tri-tert-butylphenoxy radical was also formed. Product studies from reactions catalyzed by pivalic acid indicate a novel rearrangement of an orthotert-butyl group under dediazoniation conditions forming such products as: 3-(3,5-di-tertbutylpheny1)-2-methylpropene (4), 1-(3,5-di-tert-butylpheny1)-2-methylpropen(5), 3-(33-ditert-butylpheny1)-2-methyl-2-propanol (6), 3-(3,5-di-tert-butylphenyl)-2-butoxy-2-methylpropane (7), 3-(3,5-di-rerr-butylphenyl)-2-methyl-2-trimethyacetoxypropane(8), 2,4,6-tri-terrbutylphenyl trimethylacetate (9), and 2,4,6-tri-tert-butyl-1,4-quinol (10). The major products (47) are accounted for by a free radical pathway by rearrangement of the 2,4,6-tri-rerr-butylphenyl radical. The minor products (esters 8 and 9) probably form by competing ionic reacdecomposes (at least in part) by a radical pathtions. N-Nitroso-2,4,6-tri-tert-butylacetanilide way leading to the rearranged radical (cH~),&ZH,-A~ which was spin trapped by the nitroso group of the substrate. Spin trapping experiments during the dediazoniation of 2,5-di-rerrbutylaniline similarly gave evidence for the formation of aryl radicals. L. Ross C. BARCLAY, ALEXANDER G. BRIGGS,WILLIAM E. BRIGGS,JULIANM. DUST et JEANA. GRAY.Can. J. Chem. 57.2 172 ( 1979). Une Ctude rpe de la dediazotation de la tri-rert-butyl-2,4,6 aniline avec le nitrite de butyle en solution dans le chlorure de mkthyle indique qu'il y a formation du radical tri-terr-butyl2,4,6 phenyle dont le spin est piige par le nitrile de butyle. Il y a aussi formation du radical tri-rert-butyl-2,4,6 phenoxyle. Une Ctude des produits formes lors de reactions catalysees par I'acide pivalique indique qu'il se produit, dans les conditions de didiazotation, une nouvelle transposition d'un groupe ortho rert-butyle conduisant a la formation des produits suivants: (di-tert-butyl-3,5 phCny1)-3 methyl-2 propkne (4), (di-tert-butyl-3,5 phCny1)-l methyl-2 propene (5), (di-tert-butyl-3.5 phCny1)-3 methyl-2 propanol-2 (6), (di-tert-butyl-3,5 phenyl)-3 butoxy-2 methyl-2 propane (9, (di-terr-butyl-3,5 phenyl)-3 methyl-2 trimethylacCtoxy-2 propane (8), trimethylacitate de tri-rert-butylphCny1e-2,4,6 (9) et tri-tert-butyl-2,4,6 quinol-1,4 (10). On peut expliquer la formation des produits principaux (47) a I'aide du chemin rtactionnel radicalaire impliquant une transposition du radical tri-rert-butyl-2,4,6 phenyle. Les produits mineurs (esters 8 et 9) se forment probablement par des reactions ioniques en competition. Le N-nitroso tri-terr-butyl-2,4,6 acetanilide se decompose (au. moins en partie) par un mecanisme ridicalaire conduisant au radical transpose (CH3),CCHZ-Ar dont le spin est pikg6 par un groupe nitroso du substrat. Des experiences de piegeage de spin au cours de la didiazotation de la di-tert-butyl-2,5 aniline fournissent des donnees relatives a la formation de radicaux aryles. [Traduit par le journal]

Introduction The aromatic dediazoniation reaction is receiving considerable attention by a number of investigators (1-7). In particular the role of reactive aryl intermediates, aryl cations, aryl radicals, and arynes, is frequently discussed. Ortho-tert-butyl-aryldiazonium salts, including the 2,4,6-tri-tert-butyldiazonium ion (1) (8), are known to be very unstable and this has been attributed to rapid formation of an aryl cation due to steric acceleration (7). There is substantial kinetic evidence for the formation of the aryl cation from benzenediazonium salts (1, 3) and this cation has been the subject of theoretical (9) and some recent

experimental (esr) (10) study. On the other hand, aryl dediazoniations are capable of proceeding by either homolytic or heterolytic pathways (6, 7) and small changes in conditions, such as the addition of pyridine (1 1) or the presence of oxygen (12) appear to cause a changeover in mechanism. We have independently observed the 2,4,6-tri-tert-butylphenyl radical (3) directly in solution and followed its rearrangement (13). The known properties of this radical should aid in the discrimination between radical and ionic pathways for the reaction of 1. In addition, formation of an aryne (via 2) is blocked unless there is extrusion of a tert-butyl cation which would be de-

0008-4042/79/162172-08$01 .OO/O @ 1979 National Research Council of CanadaIConseil national de recherches du Canada


BAKCLAY ET AL.

tected by product analysis. Such dealkylations may account for anomalies previously reported in the aqueous acid diazotizations of 2,4,6-tri-tert-butylaniline (14). We are investigating the unusual reactivity in dediazoniation of 1 and, with the above features in mind, have undertaken an exploratory study on the esr and product studies from 1. Some comparative studies are also reported for the 2,5-ditert-butylaryl system.

2173

FIG.1. Electron spin resonance spectrum from diazotization of 2,4,6-tri-terf-butylaniline with butyl nitrite and pivalic acid in methylene chloride at 0°C.

ported (16) from the reaction of aniline with pentyl nitrite. This radical showed a nitrogen splitting (15.75 G ) similar to other simple alkoxyphenylnitroxides (17). The interesting variation in the nitrogen splitting of our substituted alkoxyarylnitroxides (a, = 23.86-23.98 G) contrasted with the a, = 15.75 G for the phenyl case is attributed to the steric hindrance provided by two ortho-tert-butyl groups in our hindered nitroxides which force a non-coplanar conformation of the radical so that the a, approaches the values found for alkylalkoxy nitroxides (17). This effect has been observed before in related aryl nitroxide radicals (18, 19). It was of interest to study the formation of these free radical species in the absence of pivalic acid when the overall reaction proceeded more slowly according to product studies (see (b) below). Under this condition, it was possible to readily observe the consecutive formation of the radicals, as illustrated in Fig. 2a-d The first species observed was the tritert-butylphenoxy radical (Fig. 2a), followed by butoxy-2,4,6-tri-tert-butylphenylnitroxide(Fig. 26, when the tri-tert-butylphenoxy radical was now hardly observable), then the tri-tert-butylphenoxy radical became more prominent as usual (Fig. 2c). Finally, on extended reaction time, it was still possible to observe the above two radicals plus a third very persistent species (Fig. 2d). This third radical (Ar-N-0-(CH2),CH3) from its close relationship has not been definitely characterized. Assuming that to the analogous ethoxy-2,4,6-tri-tert-butylphenylni- the central portion lies under the prominent tri-tertbutylphenoxy, it is estimated that there is a 1 : 1 : 1 0. triplet of 1 :2: 1 triplets where a, = 15.6 G, I troxide radical (Ar-N-0-CH2CH3, a, = 23.98, a,(,, ,,,, = 1.4 G, and g = 2.0058. This suggests = 2.52, aH(2Hmefa) = 0.78 G, a n d g = 2.00528) an aromatic nitroxide radical, possibly of the type generated by spin trapping of ethoxy by photolysis of diethylperoxide in the presence of 2,4,6-tri-tertbutylnitrosobenzene. While this work was in pro~r-N-c(cH,),cH~-~r' gress, the pentoxyphenylnitroxide radical was re(Ar = 2,4.6-tri-tert-butylphenyl,Ar' = 3.5-di-tert-butylphenyl)

Results Dediazoniation of 2,4,6-Tri-tert-butylphenyldiazo Conlpounds (a) Electron Spin Resonance Studies Treatment of 2,4,6-tri-tert-butylaniline with butyl nitrite and pivalic acid in methylene chloride (aprotic diazotization (1 5)) in the probe of the esr spectrometer at -40°C generated two sets of esr signals in 30-40 min (see Fig. 1). These became more intense as the temperature was raised through 0°C and the solution quickly became blue in color. The central part of the spectrum consisted of a very persistent 1 :2: 1 triplet of multiplets (aH(2H) 1.6 G). This proved to be the well-known 2,4,6-tri-tert-butylphenoxy radical. The center triplet could be enhanced by injecting a sample of the latter prepared independently by lead dioxide oxidation of the phenol and observing the increase in the superimposed signals. The second radical appeared to be a 1 : 1 : 1 triplet (the centre portion only partially observed at higher gain due to the more intense signal of the above phenoxy radical) of 1 : 2: 1 triplets (a, = 23.86, a,(,,, = 2.80, and a,(,, ,,, = 0.75 G , and g = 2.00521). This second radical is assigned to n-butoxy-2,4,6-tri-tert-butylphenylnitroxide .o

-


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C A N . J. CHEM. VOL. 57, 1979

FIG.2. Electron spin resonance spectra from diazotization of 2,4,6-tri-tert-butylaniline with butyl nitrite in methylene chloride at - 10°C: (a) after 2-5 h, appearance of 2,4,6-tri-tert-butylphenoxy(12); (b) after 39 h, illustrating the butoxy2,4,6-tri-tert-butylphenylnitroxideradical (11); (c) after 49 h, showing the mixture of radicals 11 and 12; ( d ) extended reaction time, showing the appearance of a third radical (triplets) between 11 and 12.

Decomposition of N-nitroso-2,4,6-tri-tert-butylace-aniline, under similar conditions as the esr studies, tanilidel in methylene chloride in the esr spectrom- yielded a complex mixture containing the hydrocareter at room temperature or above (20-40°C) gave bons 3-(3,5-di-tert-butylpheny1)-2-methylpropen (4), an esr spectrum consisting of a simple 1 : 1 : 1 triplet 1-(3,5-di-tert-butylpheny1)-2-methylpropen (5), the of 1 : 1 : 1 triplets without further additional fine alcohol 3-(3,5-di-te1.t-butylpheny1)-2-methyl-2-prostructure (aNa= 13.84 and a,, = 3.26 G and g = pan01 (6), the ether 3-(3,5-di-tert-butylpheny1)-22.00616). The couplings and g value observed are butoxy-2-methylpropane (7), the esters 3-(3,5-di-tertindicative of a hydrazoxy radical (21) and the lack of butylphenyl) -2 - methyl - 2 - trimethylacetoxypropane additional coupling to hydrogen is suggestive of a (8) and 2,4,6-tri-tert-butylphenyl trimethylacetate radical of the type (9), and the 2,4,6-tri-tert-butyl- 1,4-quinol (10) (see Table 1). COCH, 0 I I The hydrocarbons 4 and 5 were identified by their Ar-N-N-C(CH3)?CH2-Ar' nmr spectra (see Experimental), by the ready acid(Ar.= 2,4,6-tri-r~rt-butylphenyl.Ar.' = 3,5-di-tert-butylphenyl) catalyzed isomerization of 4 to 5, and by the oxidaformed by spin trapping by the starting nitroso com- tion of 5 to the known 3,5-di-tert-butylbenzoicacid. pound of a radical generated in the system (see Dis- The alcohol 6 gave the expected spectroscopic data cussion). There was no evidence for the tri-tert- and it readily underwent dehydration to yield 5. The butylphenoxy radical in this reaction. ether 7gave a complex 'Hmr spectrum due to the overlap of the n-butyl resonances with those of the other (b) Product Studies Butyl nitrite diazotization of 2,4,6-tri-tert-butyl- alkyl hydrogens. The structure was determined from its 13Cn.m.r. spectrum and the fact that it underwent 'Such compounds were reported (20) to be too unstable to partial decomposition under glc conditions to yield isolate in pure form. However, we were able to purify this some 4,5, and n-butyl alcohol. The ester 8 was identiconlpound by tlc suitable for analytical and spectroscopic data. Product analyses from this decomposition will be re- fied from its spectroscopic properties and it also underwent some decomposition on the glc to yield ported separately.

2175

BARCLAY ET AL.

TABLE1. Products from diazotization of 2,4,6-tri-terr-butylaniline

% yields Run 2 (Air)b

Run 3 (NzY

Hydrocarbon 4 Hydrocarbon 5 Alcohol 6 Ether 7 Ester 8 Ester 9 Quinol 10

19.0 7.4 36.1 24.6 8.5 2.6 -

22.4 6.1 32.7 19.2 7.8

Totals

98.2

90.8


Compound

Run I (Air)"

Run 4 (02)'

-

2.6

nProducts were separated by column chromatography o n alumina a n d fnrther purified by tic. bRelative percentages, determined by glc. 'Products were separated by tlc and the percentages of 4 a n d 5 estimated by nmr. *This value is for 4 a n d 5

the hydrocarbons 4 and 5. The ester 9 gave the expected spectroscopic data and unlike 8 was stable under various glc conditions. A minor product, the quinol 10, was identified as 2,4,6-tri-tert-butyl-4hydroxy-2,5-cyclohexadien-I-oneby its nmr spectrum and by comparison with properties given in the literature. The various compounds 4-10 were formed when the reaction was carried out in air, or in a nitrogen or oxygen atmosphere. Furthermore, the percent yields of the various coinpounds identified remained approximately the same under these conditions (see Table I). The reaction was also observed directly in the ninr probe whereby the formation of the inajor components (4-7) could be observed qualitatively. A comparative small scale (nmr) run was also carried out with triethylsilane added. The latter has been used in inethylene chloride as a trap for carbonium ions (22, 23). The same inajor components were observed (nmr) to form with and without added triethylsilane and the product analyses

(glc) were also similar. In the absence of pivalic acid, the conversion t o these products at temperatures below 0°C was extremely slow and estimated (ninr) to be less than 5 0 x after 6 days. After an additional 2 days at room temperature, this reaction was 82% complete (based on recovered amine). This reaction mixture also contained the hydrocarbons 4 and 5, the alcohol 6, the ether 7, and traces of the quinol10. Aprotic Diazotization of 2,5-Di-tert-butylanilit7e The aprotic diazotization of 2,5-di-tert-butylaililiile leads to arynoid adducts in the presence of furan (1 5) and it has been proposed (7, 15) that this is a case of rapid formation of an ortlzo-tert-butylaryl carbonium ion through steric acceleration of dediazoniation. We reinvestigated this reaction to determine if aryl radicals could be trapped. Using 2,5-di-tertbutylnitrosobenzene as a trap at room temperature, this reaction did indeed produce a very persistent esr signal consisting of a triplet (1 : 1 : 1) of multiplets radical (24) (Ar = 2,5-diassigned to the Ar,N-0 tert-butylphenyl) (a, = 11.0 and a, 0.5-1 G and g = 2.00579). With tetraphenylcyclopentadienone (tetracyclone) as a trap in this reaction, we observed a very persistent radical (stable for days at room temperature) consisting of a complex 16-line pattern (g = 2.00302) almost superimposable on the radical formed in a similar way by addition of a phenyl radical to position 2 of tetracyclone (g = 2.0032) (2).

-

Discussion The following conclusions are derived from these dediazoniations studied to date. I. The aprotic diazotizations of the aromatic amines, aniline, 2,5-di-tert-butylaniline, and 2,4,6tri-tert-butylaniline, with butyl nitrite gave evidence for aryl radicals in solution. With the first two amines, the aryl radicals were trapped with tetracyclone. The 2,5-di-tert-butylaryl radical was also spin trapped with 2,5-di-tert-butylnitrosobenzene. In the case of 2,4,6-tri-tert-butylaniline, the derived aryl radical (3) was trapped by the butyl nitrite used to form the n-butoxy-2,4,6-tri-tert-butylphenylnitroxide radical (11). The forination of the 2,4,6-tritert-butylphenoxy radical (12) in carefully degassed solutions, at the same time or preceding the forination of 11, can be accounted for by some spin trapping of 3 at the oxygen of butyl nitrite (Scheme 1). Steric effects are known to cause spin trapping a t oxygen of a nitroso group, for example, in the case of 2,4,6-tri-tert-butylnitrosobenzene(25). Alternatively 12 could form by hydrogen atom transfer from the corresponding phenol. The latter could form from the combination of the aryl radical (3) with hydroxy radical (Scheme 2, ( u ) ) .

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C A N . J . CHEM. VOL. 57. 1979

0 1

points to its important role in the generation of aryl radicals and related radical reactions. The rearAr-N-0-R rangements in step (iv) (3 + 14 + 15) are consistent O=N-0-R 11 with the observed behavior of the aryl radical 3 generated independently (1 3). AT-0+ JNz + . O R [A~-O-N-ORI 4. There are several possibilities for the formation 12 of the oxygenated products. For example, the major SCHEME I oxygen-containing products, the alcohol 6 and the 2. Decomposition of N-nitroso-2,4-6-tri-tert-butyl- ether 7, could be formed by free radical combinations acetanilide gave a radical apparently formed by spin of 15 with hydroxy radical and butoxy radical as shown in steps (v) and (vi). Other speculations intrapping of the rearranged radical ~r'-CH,-c(CH,), (15, Scheme 2) by the nitroso group of the clude the oxygenation of 15 by 13 (step vii) (and analogously of 3 by 13 leading to the stable radical substrate. 3. The unusual hydrocarbon products 4 and 5 12). Furthermore, the trapped radical 11 could be a from the butyl nitrite diazotization of 2,4,6-tri-tert- source of alkoxy radicals via the reported (16) decom0 butylaniline can be accounted for by a free radical pathway as outlined in Scheme 2. Steps (i)-(iii) folI + Ar-NO f .OR. low the generally accepted (7, 26) Riichardt mech- position route Ar-N-0-R anism (27) for the formation of aryl radicals by The quinol 10, a minor product, probably results homolytic decomposition of an unstable diazoanhy- from hydroxylation of 12 at the para position (31) dride intermediate. Although the rather elusive aryl (step (viii)), although we cannot rule out oxygenation diazotate radical (i.e., 13 in Scheme 2) reported by of 12 by 13 followed by hydrogen abstraction or even Cadogan (28) was questioned on the basis of nuclear air oxidation of 12 during work-up (32). 5. The esters 8 and 9 most probably form in compolarization studies (29), more recent evidence (30)


___[

(iii) Ar-N=N-0-N=N-Ar

(oiii) 12 + . O H

-+

+ --+

Ar. 3

+ N Z + . O-N=N-Ar

13

FH3

10

A r = 2,4,6-tri-rerr-butylphenyl, Ar'

=

3.5-di-ferf-butylphenyl

BARCLAY ET AL

(i) Ar-N2+

-N2

,A;

(CH,),CCOOH

I

electron transfer

I

Ar-N=N-0

+

+ Ar-N=N-0

AI.CH,-C(CH,)~

-

16

15


, A;

Free radical reactions (Scheme 2)

9

(ii) A ~ c H ? - ~ ( c H , ) ~

-

[ArNH2] or [Ar-N=N-0]

,

7 S C H E M3E

C4HsOH

I

(CH,)CCO~

,8

. calcd. for C Z O H ~ Z N Z O C Z72.24, : peting polar side reactions. The ester 8 is not a result and 7.40 (s, 2H, a r ~ l )Anal. of secondary reactions. We found that neither the 8.43; found: 8.56. hydrocarbons (4 and 5) nor the alcohol 6 react with Electron Spitz Resonance Strrdies Electron spin resonance spectra were measured on a Varian pivalic acid or pivalic anhydride under these conditions to give this ester. -l-hus the formation of 8 and 9 E-3 spectrometer or where notedZ on a Varian E-104A spectrometer. The diazotizations of the amines were carried out in is a strong indication Of a carbonium ion an esr reactor tube equipped with a glass capillary inlet and type reaction. We further speculate that such a r ~ l outlet for purging with dry oxygen-free nitrogen and a third cationic and free radical reactions may be directly side arm for injecting reactants through a septum. In a typical related by electron transfer processes (i.e., step (i), run, a solution of the amine (0.11 mmol) and ~ i v a l i cacid mmol) in 0.5 mL of methylene chloride was thoroughly scheme 3). -l-he other oxygen-containing products, (0.14 purged with nitrogen. The tube was cooled to -40°C in the such as the and ether could esr probe, then butyl nitrite (0.11 mmol) in an equal volume from ionic reactions on the cation 16 in contrast to of methylene chloride was injected through the septum while the free radical steps (0) and (0i) suggested in Scheme the reaction solution was mixed with the inlet nitrogen. The 3. -l-he cation 16 could result from electron transfer temperature was slowly raised to 0°C while spectra were determined. The same procedure was used in runs without pivalic to the a r ~ diazotate l (ii), Scheme 3)' A acid and typical spectra are illustrated in Figs, 1 and 2, Such somewhat similar electron transfer from a carbon spectra were also obtainedZ during the diazotization of 2,4,6radical t o phenyl diazotate has recently been postu- tri-tert-butylaniline when the solutions were carefully degassed under high vacuum by alternately freezing and thawing. lated (30). Experiments with radical traps (2,5-di-rert-butylnitrosoben6. l-here was no evidence for the formation of zene or tetracyclone) were carried out by mixing equimolar products from a substituted benzyne by the elimina- amounts of the amine and the trap before the addition of tion of an orrllo-rert-butyl from the 2,4,6-tri-ferf- butyl nitrite as above. The ethoxy-2,4,6-tri-rert-butylphenylnitroxide radical was generated by ultraviolet irradiation of a butylphenyl cation (2). 9.707

71.631

9.759

77

Experimental The procedures for spectroscopic and chromatographic analyses given earlier (33) were followed unless otherwise stated herein

solution of diethylperoxide and 2,4,6-tri-tert-butylnitrosobenzene in pentane at -40°C in the esr ~ p e c t r o m e t e r .The ~ g values were measured relative to that of tetracene in sulfuric acid,g = 2,002604 (35),

Prodr~ctAtznlysis The preparative scale reaction on 2,4,6-tri-tert-butylaniline was carried out by adding a solution of the amine (10.6 g, 0.0406 mol) and pivalic acid (5.30 g, 0.0473 mol) in 100 mL of methylene chloride over a 1 h period to a stirred solution of butylnitrite (5.90 g, 0.0573 mol) in 100 mL of methylene chloride kept at 0°C. The solution was kept cold overnight, then allowed to warm to room temperature. The reaction mixture was extracted with aqueous sodium hydroxide, water, dried over sodium sulfate, and the solvent distilled under reduced pressure. The residual oil (11.9 g) was chromatographed on a neutral alumina column by elution with petroleum ether followed by petroleum ether -ethyl ether. The first fraction contained the hydrocarbons 4 and 5. Fraction 2 contained a mixture of the hydrocarbons with the ether 7 (mainly), fraction 3 contained the ether 7, fraction 4 the ether mixed with the ester

Materinls 2,4,6-Tri-rert-butylaniline was prepared by reduction of the nitro compound with sodium amalgam (34). 2,5-Di-tertbutylaniline was best prepared by the catalytic hydrogenation procedure (34). These amines were purified by colun~nchromatography on acidic alumina by elution with petroleum ether-benzene mixtures. The butyl nitrite, pivalic acid, and solvents used were all freshly distilled. The tetracyclone used was comn~ercialmaterial (Eastman). 2,5-Di-tert-butylnitrosoand 2,4,6-tri-tert-butylnitrosobenzenewere described earlier (33). N-Nitroso-2,4,6-tri-tert-butylacetanilide, prepared by nitrosation of the anilide (mp 273°C) with nitrosyl chloride, was purified by preparative tlc using chloroforn~solvent, the solvent removed under reduced pressure and the product analyzed without further purification or drying. It melted at 121°C. showed ir (CCI,) ZThese studies were made in the laboratory of Dr. K. U. . .. bands at 1750 (C=O) and 1375 (-N=O) c m - ' , and nmr bands at 6: 1:12 (s,' 18H, 2 x Ingold, Division of Chemistry, National ~ e s e a r c hCouncil of (CHAC-), 1.30 (s, 9H, (CH3)3C-), 2.80 (s, 3H, CH3CO), Canada, Ottawa, Ont.


2178

CAN. J . CHEM. VOL. 57, 1979

8, fraction 5 was a mixture of the esters 8 and 9, and fraction 6 contained the alcohol 6 mixed with the quinol 10. The various compounds in the above chromatograph fractions 2-6 were further separated and purified by preparative tlc on silica gel that had been acid treated with 0.1 ~n HCI, with benzene eluent. The compounds eluted on tlc in the order hydrocarbons (4 and 5), ether (7), esters (9 then 8), quinol (lo), and alcohol (6). The percentages of the various compounds are given in Table I (run 1). Gas-liquid chromatographic analysis (8 ft x 114 in. column, 20% Carbowax on Chronlosorb W at 175°C and helium at 30 cm3/min) of the products from another run gave the results summarized in Table 1 (run 2). Gas-liquid chromatographic analysis of the purified (tlc) ether 7 showed that it undergoes partial decomposition into hydrocarbons 4 and 5 and 12-butyl alcohol under these conditions. Similarly the ester 8 yielded some 4 and 5 under these conditions. Product analyses from smaller scale runs (4 mmol) were carried out by preparative tlc directly after removal of solvent (Table 1, runs 3 and 4). On this scale we failed to detect the ester 9. Details on the individual products are given below.

-

The less stable n o n c d n j ~ ~ a t ehydrocarbon d 4 in the hydrocarbon fraction. Hydrocarbon 4 showed nmr bands at 6 : 1.35 (s, 18H, 2 x (CH3),C), 1.72 (t, J 1 Hz, 3H, H3C-C=C), 3.40 (s, broad, 2H, benzylic-CH2-), 4.89 I

I

(multiplet, 2H, C=CH,), 7.23 (d, J -. 2 Hz, 2H, aryl H's 2 and 6), and 7.45 (t, J -. 2 Hz, l H , aryl H 4). A sample of this hydrocarbon mixture (270 mg) (mainly 4) was converted into 5 by refluxing for 30 min in benzene containing 22 mg of p-toluenesulfonic acid. Nuclear magnetic resonance analysis of the product showed that it was almost entirely the conalkene 5. The nmr spectrum of 5 showed bands at 6 : -iugated 1.35 (s, 18H, 2 x (CH3)3C)ri.91 (d, J r 1 HZ,6H, (CH3)2C=), H

I

/

), 7.29 (d, J -. 2 Hz, 2H, aryl H's 2 \ and 6), and 7.46 (t, J E ?HZ, l H , aryl H 4). A sample of 5 (1.9 mmol) in 80% pyridine-water was oxidized overnight at room temperature by a mixture of potassium permanganate (37 mg) and periodic acid (4.7 g). One millilitre of this solution was distilled into a solution of 2,4-dinitrophenylhydrazine reagent. The precipitate was collected and chromatographed on neutral alumina by elution with benzene t o yield yellow crystals, m p 126°C alone or mixed with authentic acetone 2,4-dinitrophenylhydrazone.The solution from the oxidation was evaporated t o dryness, the residue extracted with ethyl ether, which in turn was extracted with aqueous sodium hydroxide. Acidification gave a colorless solid which after sublimation melted at 164°C. This proved to be 3,5-ditert-butylbenzoic acid by mixture melting point and identical infrared spectra with an authentic sample of acid (mp 163164°C) (36). 1-(3,5-Di-tert-butylp/renyl)-2-propnnol(6) The alcohol 6, purified by sublimation in vncuo, gave a mp of 83.5-84°C. It showed a strong band in the infrared at 3400

6.49 (m, l H , ~r-C=C'

I

(-OH) cm-' and nmr bands at 6: 1.15 (s, 6H, (CH3),C-0), 1.30 (s, 18H, 2 x (CH3),C-), 1.43 (s, exchanges with D 2 0 , l H , OH), 2.67 (s, 2H, Ar-CH2-), 6.94 (d, J E 2 Hz, 2H, aryl H's 2 and 6), and 7.18 (t, J -. 2 Hz, l H , aryl H 4). Annl. calcd. for C 1 8 H 3 0 0 :C 82.38, H 11.52, Mol. Wt. 262; found: C 82.98, H 11.52, Mol. Wt. (mass spectrum t~l/e262 M f ) .

TABLE2. The 13Cmr spectrum of ether 7"

Carbon

Chemical shift (decoupled)

Multiplicity (~ndecoupled)~

OArral. calcd. for C 2 , H , , 0 : C 83.02, H 11.95, Mol. Wt. 318; found: C 82.86, H 11.70, Mol. Wt. (mass spectrum nrle 318 M + ) . bAbbreviations: s, singlet: d, doublet: t, triplet: 4 , quartet.