Aug., 1951
DIPHENYLKETENE DIMETHYLACETAL
3807
tion was chilled and filtered to remove a dark amorphous The oxime was prepared from the above dimethyl ester impurity. After removal of the solvent the acid was dis- by heating it under r d u x with an equal weight of hydroxylsolved in ethanol, treated with Norite and crystallized by amine hydrochloride in an alcohol solution containing excess the gradual addition of water. The product (0.23 g., pyridine. After recrystallization from dilute methanol the 48%), melted at 165-168'. Further recrystallization product melted at 192-194'. A d . Calcd. for CnsHslOsN: yielded 0.16 g. of material with a melting point of 169-170°. C, 68.8; H, 7.8; N, 3.5. Found: C, 69.0; H, 7.9; N, This product did not depress the melting point of an au- 3.6. thentic sample of dehydroabietic acid (I). Oxidation of 6-Carboxydehydroabietic Acid (III).-To a The methyl ester, prepared with dimethyl sulfate, melted solution of 1g. of this acid (111) in 40 ml. of water containing at 62-63'. A mixed melting point with an authentic 0.38 g. of potassium hydroxide there was added with stirsample of methyl dehydroabietate showed no depression. ring a solution of 0.94 g. of potassium permanganate in 20 Oxidation of Chloromethyldehydroabietic Acid (VIII).-ml. of water over a period of three hours. The reaction A sample (4.2 g.) of crude chloromethyldehydroabietic acid, mixture was saturated with sulfur dioxide and the precipicontaining 8.2% of chlorine, was partially dissolved in a tate was filtered off and washed with water. It was then solution of 0.4 g. of potassium hydroxide in 100 ml. of water. dissolved in sodium bicarbonate solution and treated with A solution of 4.7 g. of potassium permanganate and 1 g. of Norite. Upon a c i d i f i c a p there was obtained 0.75 g. of potassium hydroxide in 100 ml. of water was slowly added crude acid ([&]*D +31 , 1% in absolute ethanol). The with stirring over a period of five hours. Saturation of the product was recrystallized from ethanol and water. reaction mixture with sulfur dioxide produced a precipitate Treatment of this acid with diazomethane and recrystalwhich was filtered off, washed with water and dissolved in lization from dilute methanol gave the dimethyl ester (XV) ether. The ether solution was extracted with dilute sodium which melted a t 94-95'. A mixture of this ester with the bicarbonate and the aqueous extract was acidified. Upon dimethyl ester obtained from oxidized chloromethyldehydrothe addition of ether to this extract the product crystallized abietic acid (above) melted at the same temperatures. and was filtered off. The f i s t crop weighed 1.82 g.; an Ultraviolet Absorption Spectra.-The absorption spectra additional 0.10 g. was obtained upon concentrating the ether were obtained from measurements made with a Beckman layer to a small volume. The neutral equivalent of the model DU quartz spectrophotometer. The solvent for crude product was 182. It did not melt below 280'. It dehydroabietic acid was ethanol and the concentration was was purified by recrystallization from ethanol and water. 500 mg. per 1.; that for the other compounds was methanol A n d . Calcd. for C21H2605:C , 70.4; H, 7.3; neut. equiv., and the concentrations were approximately 20 mg. per 1. 179. Found: C , 70.6; H , 7.5; neut. equiv., 179; [ C U ] ~ D Acknowledgment.-The author wishes to thank $38' (1%in absolute ethanol). The dimethyl ester (XV) prepared by treating the acid Dr. Harold M. Spurlin for his helpful interest in with diazomethane and recrvstallizina from methanol and this work. water, melted at 94-95', -Anal. ealcd. for C23H&: RECEIVED NOVEMBER 24, 1950 C, 71.5; H, 7.8. Found: C, 71.7; H , 8.0. COLLEGE PARK, MD.
[CONTRIBUTION FROM
THE
LABORATORY OF ORGANIC CHEMISTRY OF THE UNIVERSITY OF WISCONSIN]
Ketene Acetals. XXV. Diphenylketene Dimethylacetal BY s. M. MCELVAIN, STANLEY B. MIRVISS' AND CALVIN L. STEVENS' The preparation of diphenylketene dimethylacetal (IV) by the dehydrochlorination of diphenylchloroacetaldehyde dimethylacetal (111)is described. This is the principal reaction between I11 and potassium t-butoxide in dioxane, but in tbutyl alcohol this base causes nearly an equal amount of replacement of the halogen to form the t-butoxyacetal (V). Similar reactions occur between I11 and sodium pinacolate in pinacol solution. IV shows the expected reactions with water, methanol, benzyl bromide and bromine; it is, however, singularly unreactive toward acyl chlorides. IV undergoes a novel reaction with potassium t-butoxide to yield the potassium enolate of methyl diphenylacetate and methyl t-butyl ether. Diphenylhaloacetaldehyde acetals (11, I X and X ) are found to undergo a novel thermal rearrangement into the corresponding diphenylacetic ester and alkyl halide. An attempt to prepare diphenylketene diethylacetal from I X was unsuccessful because of the interference of the halogen replacement reaction and the decomposition of the ketene acetal to the potassium enolate of ethyl diphenylacetate.
Diphenylketene dimethylacetal (IV) has been prepared by the dehydrochlorination of diphenylchloroacetaldehyde dimethylacetal (111), obtained from methyl dimethoxyacetate (I) v i a the sequence of reactions shown below. The dehydrochIorination of I11 with potassium t-butoxide in t-butyl alcohol, which has been used effectively for the dehydrohalogenation of a variety of haloacetals to the corresponding ketene acetals, was accompanied by a concurrent replacement reaction that yielded the t-butoxyacetal (V). This compound and the ketene acetal (IV) were formed in 39 and 47% yields, respectively, as determined from the refractive index of a distilled mixture of these products. This (1) Wisconsin Alumni Research Foundation Research Assistant 1949-1960. (2) Wisconsin Alumni Research Foundation Research Assistant 1944-1947. (3) S. M. McElvain, et a l . , THISJOURNAL, 18, 529 (1936); 69, 2266 (1937); 60, 2210 (1938); 70, 3781 (1948).
mixture was partially separated by fractional distillation after a portion (cu. 65%) of IV, m.p. 666 8 O , crystallized from the mixture on cooling. Similarly the reaction of I11 with sodium pinacolate in pinacol gave the ketene acetal (IV) and a compound corresponding to the pinacoloxyacetal (VI); because of the greater difference in boiling points of I V and VI, they were readily separated by fractionation in yields of 38 and 42%, respectively. The most satisfactory procedure for the dehydrochlorination oi I11 utilized dry potassium t-butoxide in refluxing dioxane. In this reaction none of the t-butoxyacetal (V) was formed and the pure ketene acetal (IV) was obtained readily in 50% yield. The use of the higher boiling dibutyl ether instead of dioxane pave only a 30% yield of IV, the potassium enolate of methyl diphenylacetate (see below for the formation of this product), and a considerable amount of tar.
S.M. MCELVAIN, STANLEY B. MIRVISSAND CALVINL. STEVENS
3806
Vol. 73
CeH5MgBr soc12 (CH30)2CHCOOCHa - j (CeHj)zC(OH)CH(OCH3)z + pyridine I I1 KOCaHg(t) -------e CeH5)C=C( OCH,), I 11.
after an extended period of heating to yield VI11 and methyl t-butyl ether. This novel reaction doubtless occurs with the ketene acetal IV KOChHy(t) because the conjugated (CsHs)2CClCH(OCHa)z-! -+ IV (CsH5)aC(OCaH9)CH(OCHa)z phenyl groups enhance I11 t-CaHOqH v the electroDhilic characI S a pinacolate of the ðyl group L+Il' + C ~ H 4 C ( O C ( C H ~ ) ~ C ( C H 3 ) ~ o H ) ~ H ( O cter toH ~the ) 2 point of reaction piiiacol with the t-butoxy anion.
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VI
The hydroxyacetal I1 was obtained in 79% yield from the ester I ; the corresponding diethylacetal was similarly prepared from ethyl diethoxyacetate. In each of these preparations a small amount of benzophenone was obtained, doubtless as a result of partial hydrolysis of these acetals to VI1 and the pyrolysis of this hydroxyaldehyde during distillation. The conversion of I1 to I11 proceeded in 88% yield. The chloroacetal I11 may be distilled under diminished pressure, but if heated to 180' it rapidly evolved methyl chloride and was transformed to methyl VI1 diphenylacet ate. The haloacetals IX and X were prepared from CeHaCHOHCOCeHs H' the corresponding hydroxyacetals and thionyl halTreatment of V with 48% hydrobromic acid yielded ides. An impure sample that showed the approxit-butyl bromide together with benzil (39%) and mate chlorine and ethoxyl content of IX was obtained, (C6H5)2CXCH(0R)2 benzophenone (48%). but this compound could not Diphenylketene dimethylacetal (IV) shows most & ~ ~ $ i ~ ~ ! is Br, is CzH, of the expected reactions of a ketene acetal. It be completely purified by distillation because of decomreacts with water in dioxane in the presence of a trace of acid to give a quantitative yield of methyl position, which occurs a t about 140', into ethyl chlodiphenylacetate ; with methanol it yields methyl or- ride and ethyl diphenylacetate. The preparation thodiphenylacetate, m.p. 39-43'; and with bro- and distillation of IX has been reported.6 An atmine it gives a quantitative yield of methyl diphenyl- tempt was made to dehydrochlorinate IX to diphenbromoacetate with the evolution of methyl bro- ylketene diethylacetal. Potassium t-butoxide in tmide. A temperature of 200' is required to pro- butyl alcohol pave an inseparable mixture, that apduce a reaction of IV with benzyl bromide. The peared to consist mainly of the t-butoxyacetal corproducts of this reaction were methyl diphenylace- responding to V and a smaller amount of the ketene tate (27%)) methyl a,a,@-triphenylpropionate acetal. Potassium t-butoxide in dioxane a t 100' (31%) and a viscous, high boiling, red oil. The converted IX into the potassium enolate of ethyl ketene acetal IV showed an unexpected inertness diphenylacetate and a tar. The bromoacetal X was obtained quite pure as to acyl halides, which have been found to react readAt 120' i t decomposed rapily with other ketene acetals6 After extended pe- a solid, m.p. 57-60'. riods of heating with acetyl chloride, benzoyl chlo- idly into methyl bromide and methyl diphenylaceride or methyl chloroformate, IV and each of these tate. After standing for a month, X had decomacyl halides were recovered substantially un- posed to an oil containing free bromine. From this oil methyl diphenylacetate, benzophenone and changed. It was noted above that the dehydrochlorination diphenylhydroxyacetaldehyde (VII) were sepaof I11 in dibutyl ether produces some of the potas- rated. The acetal XI appeared to be too unstable sium enolate of methyl diphenylacetate (VIII). to permit preparation by the procedure used for This salt apparently is produced by the interaction 111,IX and X. of the ketene acetal (IV) and potassium t-butoxide, 1% as these compounds were found to react in dioxane The structure of V was indicated by its analyses and chemical properties. Oxidation of V gave a quantitative yield of benzophenone and refluxing 10% hydrochloric acid converted it to benzoin in 66% yield. The latter transformation indicates the intermediate formationof diphenylhydroxyacetaldehyde (VII), which Danilow4 has shown is converted to benzoin by heating with acid and to benzophenone and formaldehyde by distillation
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