ISOMERIZATION OF cis-BENZALACETOPHENONE
Oct. 20, 1959
5423
identical conditions: experiment 1, dinitrogen tetroxide (0.115 g., 0.00125 mole) in ethyl ether (10 ml.) was added Attempted Isomerization of I and I1 (Action of Dinitrogen dropwise in 15 minutes a t 0' t o a solution of trans-stilbene Tetroxide).--meso-1,2-Dinitrc-1,2-diphenylethane (I, 0.1 (0.45 g., 0.0025 mole) in ethyl ether (50 ml.); experiment 2, dinitrogen tetroxide (0.115 g., 0.00125 mole) in ethyl ether g., m.p. 225" uncor.) was stirred for 8 hours in ethyl ether (200 ml.) a t 0' containing excess dinitrogen tetroxide. After (10 ml.) was added dropwise in 15 minutes a t 0' t o a solution of cis-stilbene (0.45 g., 0 0025 mole) in ethyl ether (50 the mixture had been poured on ice, allowed to stand, washed ml.); experiment 3, dinitrogen tetroxide (0.69 g., 0.0075 with water, dried over magnesium sulfate and evaporated. mole) in ethyl ether (10 ml.) was added dropwise in 15 minCompound I was recovered essentially quantitatively, m.p. 220-225'; the product was colored by trace amounts of a- utes a t 0' to a solution of trans-stilbene (0.45 g., 0.0025 mole) in ethyl ether (50 ml.); and experiment 4,dinitrogen nitrostilbene. In a similar experiment, d,Z-1,2-dinitro-l,2-diphenylethane tetroxide (0.69 g., 0.0075 mole) in ethyl ether (10 ml.) was (11, 0.5 g., n1.p. 138-145') was stirred for 2 hours in ethyl added dropwise in 15 minutes a t 0" to a solution of cis-stilbene (0.45 g., 0.0025 mole) in ethyl ether (50 ml.). ether (100 ml.) a t 0' containing dinitrogen tetroxide (2 g.). After the additions were completed, each reaction mixture After the mixture had been handled as in a preparative exwas stirred for 75 minutes. Ten drops from each reaction periment, I1 was recovered almost completely (0.49 g.), mixture was mixed with potassium bromide (450 mg.); the m.p. 110-135°. ethyl ether and the excess dinitrogen tetroxide were imme(Action of Acetic Acid).-A solution of I(0.4 g.. m.p. 237" diately evaporated under vacuum. On using the potassium cor.) in glacidl acetic acid (60 ml.) was refluxed for 1 hour. bromide pellets, the complete infrared spectrum of each Upon cooling the mixture, compound I (0.31 g., 77.5% reaction mixture was determined. The spectra of the prodrecovery) was recovered as long white needles, m.p. 237". ucts from experiments 1 and 2 (excess stilbene) are identical Upon addition of water to the acetic acid solution, or-nitrostilbene, a yellow solid, m.p. 61-62", wasrecoveredcontam- and practically superimposable; the infrared spectra of the products from experiments 3 and 4 (excess dinitrogen teinated with traces of I . troxide) also are identical and superimposable. Compound I1 (1.0 g., m.p. 150-152') was also refluxed in The region between 10.8 and 11.2 p was used for further glacial acetic acid (30 ml.) for 40 minutes. After cooling the mixture, unisomerized I1 (0.855 g.) was isolated, m.p. 150". comparison. trans-Stilbene absorbs a t 11.07 p whereas cisUpon diluting the acid solution with water, additional I1 stilbene has an absorption band a t 10.83 p . The products (0.05 g.) was obtained. The total amount of I1 (0.905 g ) from experiments 3 and 4 (excess dinitrogen tetroxide) do not absorb a t 10.83 or 11.07 p. The products from experiments isolated corresponded to a recovery of 90.5%. The remaining product obtained was a-nitrostilbene, m.p. 65O, 1 and 2 (excess stilbenes) exhibit absorption a t 11.07 p , not a t 10.83 p . I t is thus apparent that excess cis-stilbene in containing traces of 11. Infrared Analysis of Reaction Products from cis- and experiment 2 is isomerized essentially completely to frans-stiltrans-Stilbenes and Dinitrogen Tetroxide.-The following bene under the conditions of nitration. four separate reactions were effected simultaneously under COLUMBUS 10, OHIO Anal.
N, 9.94.
N, 10.29. Found:
Calcd. for CUH12N20( (11'"):
[CONTRIBUTION FROM
THE
DEPARTMENT O F CHEMISTRY, UNIVERSITY OF CALIFORNIA, BERKELEY]
Carbonyl Reactions. X. The Acid-catalyzed Isomerization of cis-B enzalacetophenone
s.
BY DONALD NOYCE,WILLIAMA.
PRYOR3 AND PAUL
A.
KING4
RECEIVEDFEBRUARY 24, 1959 The isomerization of cis-benzalacetophenone ( I ) t o trans-benzalacetophenone(11)is subject t o smooth acid catalysis and proceeds t o completion. The rate of the isomerization does not parallel the acidity function HOin aqueous sulfuric acid or perchloric acid. However, the rate may be correlated with the measured acidity function values in anhydrous acetic acid. T h e acid-catalyzed reaction of P-phenyl-0-hydroxypropiophenone (111) does not give complete dehydration a t the higher acidities. Furthermore the rate of dehydration is slower than the rate of isomerization of cis-benzalacetophenone. These results exclude I11 as an intermediate in the cis- t o trans-isomerization. I t is concluded that the rate-determining process in aqueous solution is the addition of water t o the conjugate acid of I t o produce the enol of 111, which suffers rapid loss of water before ketonization. A very similar mechanism obtains in acetic acid.
Introduction The cis to trans isomerization of unsaturated
and cis-2-buteneg; comparison with reaction rate theory has been made.'" Isomerization in solution compounds has been the subject of extensive study has also been studied. l1 Catalyzed isomerization from several points of view. Investigations of has been observed with a wide range of catalysts,I2 thermal gas phase reactions have been carried out but fewer quantitative kinetic studies have been for dimethyl maleate,6 methyl cis-cinnamate,6 carried out under these conditions. The isomerizastilbene' and more recently for dideuterioethylene* tion of maleic acid to fumaric acid has received the most attention.13-16 The reaction is complex; (1) Supported in part by the office of Ordnance Research, Contract formation of either malic acid or chlorosuccinic No. DA-04-200-ORD-171. (2) Presented in part a t the 129th Meeting of the American Chemi-
cal Society, Dallas, Tex., April, 1956.
(3) Union Carbide and Carbon Fellow, 1952-1953; U. S. Rubber Co. Fellow, 1953-1954. (4) Union Carbide and Carbon Fellow, 1956-1957. (5) M. Nelles and G. B. Kistiakowsky, THISJOURNAL, 64, 2208 (1932). (6) G. B. Kistiakowsky and W. R. Smith, ibid., 67, 269 (1935). (7) G. B. Kistiakowsky and W. R . Smith, i b i d . , 66, 638 (1934). (8) J. E. Douglas, B. S. Rabinovitch and F. S. Looney, J . Chem. Phys., 23, 315 (195.5).
(9) W. F. Anderson, J. A. Bell, J. M. Diamond and K. R . Wilson. THISJ O U R N A L , 60, 2384 (1958). (10) J L. Magee, W. Shand and H. Eyring, ibid., 63, 677 (1941). (11) M. Calvin and H. W . Alter, J . Chem. Phys., 19, 768 (1951). (12) L. Crombie, Quart. Revs., 6, 108, 139 (1952). ( 1 3 ) K . Hojendahl, J .Phrs. Chem., 28, 758 (1924): B. Tamamushi and H. Akiyama, Bull. Chem. SOC. J a p a n , 12,382 (1937). (14) E. M. Terry and L. Eichelberger, THISJOURNAL, 47, 1402 (1925). (15) K . Nozaki and R. Osg, ibid.. 63, 2583 (1941). (16) M. Davies and F. P. Evans, Trans. Faraday Soc., 62, 74 (1956)
5424
DONALD S. NOYCE, WILLIAMA,, PRYOR AND PAUL A. KING
Vol. 81
acid competes with simple isomerization. The not include any correction for this effect. It was possible in reaction is strongly a~id-catalyzedl~ and shows aqueous solution to follow the disappearance of the absorption of I at 250 mp as well as the appearance of 11 a t 300 or definite sensitivity to the nature of the acid used. 310 nip. D a t a were consistent at both wave lengths, and There is strong acceleration by certain anions.I5 the spectrum of the reaction mixture after several half-lives The order of the reaction in maleic acid has been was consistent with t h a t of 11. The apparent percentage reported to be both first ~ r d e r ' ~ and ~ l second ~ or- reaction was again 1007, a t the higher acidities where it be conveniently reached. der.I4J6 The observation of Horrex" that carbon- could Rate of Dehydration of p-Phenyl-p-hydroxypropiophenone bound deuterium is not incorporated during the (HI).-Solutions were prepared by dissolving an accurately isomerization with HCl severely limits acceptable weighed quantity of 111, about 1 mg., in 2 mi. of ethanol, and then diluting to a total volume of 100 ml. x i t h sulfuric mechanistic interpretations. acid of the appropriate concentration. The appearance of I n conjunction with studies of the acid-catalyzed trans was followed spectrophotometrically a t 310 nip. condensation of benzaldehyde and a c e t o p h e n ~ n e ~ From *~~~ the optical density after completion of the reaction thc we have undertaken a study of the isomerization fraction of dehydration was determined, and b>-difference of cis-benzalacetophenone to tmns-benzalaceto- the percentage of the reversal of the condensation which ocphenone. The reaction has been followed spectro- curred simultaneously. Results and Discussion photometrically, and proceeds to completion. The isomerization has been studied under four condiIsomerization in Aqueous Acids.--An individual tions: in aqueous sulfuric acid, in aqueous per- kinetic run showed smooth first-order behavior, chloric acid, in acetic acid containing sulfuric acid both in the disappearance of cis-benzalacetopheand in acetic acid containing small amounts of none and in the appearance of tvans-benzalacetophewater and added sulfuric acid. We feel that our none. There was no indication of the forniation of results provide valuable additional information any quantity of an intermediate. The reaction concerning catalyzed isomerizations, and offer pos- proceeded to completion within the precision of the sible explanations for the previous observations. spectrophotometric method of analysis. The results of the rate measurements carried out Experimental in sulfuric acid and perchloric acid solution are presented in Table I. Materials.-cis-Benzalacetophenone (I) was prepared by the procedure of Lutz and Jordan.20 T h e method was someTABLE I what capricious in our hands, succeeding only during the month of June in Berkeley. Reduction of phenylbenzoj-I- RATEOF ISOMERIZATIUS OF ~ ~ ~ - B E N Z A L A C E T U P H IN E~-~SE acetylene with Lindlar catalyst was much morc successful. AQUEOUSACID trans-Benzalacetophenone (11)was crystallized from ethanol H?SO4, 111 No = ki, set.-' log k + IIo to constant spectrum and melting point. Acetic acid and sulfuric acid were prepared as previouslj- reported.18 H2S04, 35.93' Light Sensitivity.-The spectrum of I1 in anhydrous G.00
