Dec. 5 . 1959
DECOMPOSITION OF ACETYLPEROXIDE IN CYCLOHEXENE
steam-bath for 8 hours; 38 mg. of a precipitate was formed. I t was recrystallized from aqueous ethanol and then sublimed under 0.01-0.02 mm. a t 130". T h e analytical sample showed m.p. 218-220' dec. Anal. Calcd. for CI1Hl70N3:C, 63.74; H , 8.27. Found: C, 63.78; H, 8.27. cis-T-Bromocamphor.-Seventy ml. of methylene chloride in a 200-1111. round-bottom flask was saturated with hydrogen bromide gas a t 0" and 104 mg. of 3,s-cyclocamphor was ad$ed in 10 ml. of methylene chloride. After 30 minutes a t 0 , the mixture was stored a t room temperature for 10 hours. The reaction mixture was washed with 5% sodium carbonate, sodium chloride saturated solution and distilled water and the aqueous fraction was extracted with ether. The ethereal and methylene chloride solutions were combined, dried over magnesium sulfate and evaporated completely under aspirator pressure yielding 96 mg. of crude product. Recrystallization and sublimation under 0.01-0.02 mm. a t 70" gave cis-s-bromocamphor, m.p. 121.5122.5', [ C Y ] - ~ ~-95', D vmax 1740 and 1420 cm.-l, and Xmax 296 mp ( e , ~ 4 ) . Anal. Calcd. for CloHijBrO: C, 51.95; H, 6.54; Br, 34.60. Found: C, 52.31; H, 6.72; Br, 34.97. trans-x-Hydroxycamphor.-A solution of trans-r-aceto ~ y c a m p h o r (49 ' ~ g., 0.23 mole) in 500 ml. of 10% ethanolic potassium hydroxide was heated a t reflux for one hour and then concentrated to 200 ml. and diluted with saturated salt solution. Extraction with several portions of ether, evaporation of the ether and recrystallization of the residual solid from hexane-benzene afforded 31.2 g. (%yo) of hydroxy ketone, m.p. 238-240". trans-Isoketouinic Acid (XII).-To a solution of 40 g. of chromic anhydFide, 67.5 g. of manganous sulfate hydrate and 12 ml. of concentrated sulfuric acid in 100 ml. of water was added slowly a solution of 16.8 g. of trans-s-hydroxycamphor in 300 ml. of water. After completion of the addition (ca. 1 hour addition time) the mixture was stirred and heated a t 40-45' for 16 hours. Dilution with saturated salt solution and extraction with ether (three 150-ml. portions) removed the acid which then was purified by extraction with aqueous base, acidification, re-extraction and recrystallization from aqueous methanol. The yield of transisoketopinic acid, m.p. 248-251°, was 14 g. (7770). d-cis-~-Apoborneol-7-carboxylic Acid Lactone (IX) .Isoketopinic acid (1.82 g., 0.01 mole) was dissolved in 50 (14) P.C . Guha and S. C. Bhattacharyya, J . I n d i a n Chem. Soc., 21, 271 (lY44).
[CONTRIBUTION FROM
THE
6309
ml. of reagent grade methanol and neutralized with 10% potassium hydroxide in methanol until just alkaline to phenolphthalein. Sodium borohydride (4 g., 0.104 mole) then was added portionwise, and the solution was stirred overnight a t room temperature. The solvent was evaporated under aspirator pressure and the residue was taken up in water, acidified with dilute hydrochloric acid, saturated with salt and extracted with ether. T h e ether solution was dried over sodium sulfate and evaporated. The hydroxy acid (obtained a s a colorless, crystalline solid) was dissolved in 20 ml. of trifluoroacetic acid and 5 ml. of concentrated sulfuric acid, and heated a t reflux for 2.5 hours. Most of the trifluoroacetic acid was recovered by distillation (continued as long as the distillate formed easily; no attempt was made t o remove all the trifluoroacetic acid). The product was dissolved in ether, washed with water, cold 5% sodium carbonate, and again with water, then dried over sodium sulfate and evaporated. The product was recrystallized from hexane and then sublimed a t 130170' (12 mm.). There was obtained 1.1 g. (6670) of the lactone, m.p. 190-196" (lit.4 190-19l0), infrared absorption at 1765 cm.-' (chloroform). Other preparations gave yields ranging from 40-7070. cis-Isoketopinic Acid (XIII).-The lactone I>; (1.0 g., 0.06 mole) was oxidized by chromium trioxide (1.35 g., 0.0135 mole) in acetic acid (5 ml.) containing sulfuric acid (1.0 ml.) and water (2.5 ml.) a t 40-45'. The reaction mixture was stirred at 40-45" for 30 hours, diluted with water and extracted with ether. The crude keto-acid (0.988 9 . ) obtained after evaporation of ether and acetic acid was recrystallized from aqueous methanol t o yield 5300mg. (49',,) of colorless crystals (as plates), m.p. 273-276 . Concentrating the mother liquor gave an additional 60 mg. of the keto acid, infrared absorption a t 3460, 1740, 1695 c m - ' (chloroform). In other experiments, ethyl acetate-hexane proved to be a superior solvent for recrystallization. Methyl cis-1soketopinate.-To the cis-keto-acid dissolved in ether was added an ethereal solution of diazomethane until a pale yellow color persisted. The solution was allowed t o stand for 30 minutes, then treated with dilute hydrochloric acid, washed with mater and dried over sodium sulfate. There was obtained 180 mg. (92yG)of the methyl ester which was recrystallized from aqueous methanol. The methyl ester (126 mg., 65YO) had m.p. 73-75'; infrared absorDtion at 1750. 1728 cm.-' (carbon tetrachloride). Anal. Calcd. for C11H1603: C, 67.30; H, 8.22. Found: C, 67.56; H, 8.34. URBANA, ILL.
DEPARTMENT OF CHEMISTRY ASD CHEMICAL ENGINEERING, TEXAS TECHNOLOGICAL COLLEGE]
The Oxidation of Hydrocarbons. 111. The Decomposition of Acetyl Peroxide in Cyclohexene Solutions BY H. J. SHINEAND J. R. SLAGLE RECEIVEDMAY7, 1959 The thermal decomposition of acetyl peroxide in cyclohexene solution a t 80' and a t reflux temperature has been studied. The decomposition does not give the approximately quantitative yield of carbon dioxide that is usually associated with decomposition of this peroxide in solution. Instead, only 65-75y0 of the expected carbon dioxide is obtained. At the same time there are obtained l,l'-bi-2-cyclohexenyl and a n approximately 20Y0 yield of a mixture of 3-cyclohexenyl acetate and cyclohexyl acetate. Thus, these two esters account, approximately, for the missing carbon dioxide. The predominant component of the ester mixture is the saturated ester. This unique result from a decomposition of acetyl peroxide is most simply explained by the reactions of acetoxy radicals. That is, contrary to the general belief regarding acetoxy radicals, it appears that they are not necessarily so unstable that they must decompose either prior t o or during reaction with another entity.
It was found by Shine and Snyder1 that, in the oxidation of cyclohexene in acetic anhydride s o h tion under free-radical initiation, one of the products formed was cyclohexyl acetate. Although it is stated that small amounts of cyclohexyl acetate are formed by boiling cyclohexene in acetic anhy(1) H. J. Shine and R . H. Snyder, THISJOURNAL, 80, 3064 (1958).
dride solutionI2i t was felt that the large amount of cyclohexyl acetate obtained under the relatively gentle conditions of the free-radical work, and that the marked influence of acetic anhydride on the rate of oxidation of cyclohexene, were best interpreted as being due to reactions involving free acetoxy (2) H. Friese and D. Djiang, Bey., I l B , 667 (1938).
H. J. SHINEAND J. R.SLAGLE
6310
radicals. Thus, it was proposed that the cyclohexyl acetate was formed by addition of acetoxy radical to cyclohexene to give a saturated radical, which then abstracted a hydrogen atom from an available source. The involvement of free acetoxy radicals in reactions in which they might be formed has long been a matter of debate. I n numerous instances in which acetyl peroxide has been used as a radical source, the initial decomposition of the peroxide has been formulated as the homolytic scission to acetoxy radicals, but, although i t has been convenient to formulate the decomposition into acetoxy radicals, the involvement of free acetoxy radicals in subsequent reactions has been, for the most part, questioned. Thus, Jaffee, Prosen and Szwarc,S in computing the heat of dissociation of the acetate radical, point out that the strongly exothermic process favors dissociation. They refer to work by Levy and Szwarc4 and note that in the decomposition of acetyl peroxide “no reaction was observed in which acetate radicals survive as entities ; the products of abstraction or addition reactions indicate that decarboxylation occurred either prior to reaction or during the reaction.” This is not altogether exact since Levy and Szwarc4 noted that not all of their acetate radicals could be accounted for by decarboxylation. They noted that the literature shows that acetic acid has been found in decompositions of acetyl peroxide, although they preferred to account for lost acetate radicals in their work by the process AcO.
+ R. +AcOR
The formation of acetic acid in sizable amounts has been reported in several studies5 Concerning the acetic acid, Kharaschsa observed that “in all induced decompositions of acetyl peroxide about equimolar amounts of acetic acid and methane are formed, while in non-induced decompositions small amounts, if any, of acetic acid are formed, except in cases of very active hydrogen atoms (such as in aldehydes) that can be removed by free acetate radical.” Thus, although the formation of acetic acid may result from hydrogen abstraction by acetoxy radical, there is no certainty that it does. There are other reactions involving acetyl peroxide in which the participation of acetoxy radicals has been suggested. The reaction of phenols with acetyl peroxide is depicted by Wessely and Schinze1,6 in part, :is a reaction between a resonance-stabilized phenoxy1 radical and the acetate radical. On the other hand, Walling and Hodgson’ ha ve shown that the reactions of both benzoyl peroxide (3) L. Jaffee, E. J. Prosen and M. Szwarc, J . Chcm. P h y r . , 27, 416 (1957). (4) M. Levy and M. Szwarc. THIS JOURNAL, 76, 5981 (1954). (5) (a) M. S. Kharasch and G. Bdchi, J. O r g . Chcm., 14, 84 (1949), decompositions in allyl bromide; (b) A E tlirougli G correspond with dimers in the CIP-hydro- present and was not ideiitified. c:irbori chsses. All fractions il through H contained somc Identification of Bicyc1ohexene.-The fractiiiii IC was used. u~is~cturatiori. Identification of Cyclohexyl Acetate.-The ester was Analysis showed C, 89.08; H, 11.17;bromine nurriber 181; liydrolyzed with inethanolic sodium hydroxide following, mol. wt., 167. T h e calculated values for bicyclohexelle are C, 88.9; H, 11.11; Br no., 195; mol. wt., 162. scribed b y Slagle and Shine is very similar t o the method described iiy Rharasch, McBay arid Urry, J . Org. Chem., 10, 394 (1945); (see H. C. RIcBay, P h . D . Thesis, University of Chicago, 1946, for complete procedure). This regrettable duplication is offset, perhaps, by t h e fiict t h a t t h m e wishing t
