4692
STANLEYJ. CRISTOLAND FRANK R. STERMITZ
benzophenone azine: 290, 4.22; 323, 4.20. P,P,Pf,Pf-Tetramethoxybenzophenone azine: 278, 4.46; 335, 4.2. Benzophenone hydrazone: 275, 4.09. Benzophenone semicarbazone: 282, 4.32. Benzophenone phenylhydrazone: 293, 338, 4.26. Benzophenone oxime: 250. Fluorenone hydrazone: 330, 5.00.
[CONlRIBUTION FROM THE
DEPARTMENT OF
Vol. s 2
Acknowledgment.-We are pleased to acknowledge generous support of this research by the Science Foundation, Grant No* G4244, and Guggenheim and Fullbright fellowships (to S.G.C,).
CHEMISTRY, UNIVERSITY OF COLORADO]
Mechanisms of Elimination Reactions. XXII. Some cis- and fvans-2Phenylcyclohexyl Derivatives. The Hofmann Elimination1 BY STANLEY J. CRISTOLA N D FRANK R. STERMITZ RECEIVED JANUARY 13, 1960 T h e products and rates of reaction of the cis and tvans isomers of 2-phenylcyclohexyltrimethylammonium ion, %phenylcyclohexyldimethylsulfoiiium ion and 2-phenylcyclohexyl p-toluenesulfonate with potassium hydroxide in ordinary ethanol have been investigated. T h e cis and trans isomers of t h e onium compounds differ in elimination reactivity (to give l-phenylcyclohexene) by factors of 133 (ammonium) and 383 (sulfonium), trans elimination being favored over cis A comparison of the rates of reaction with the acyclic (2-phenylethyl) analogs suggests t h a t the cis ammonium phenylcyclohexyl isomer is abnormally unreactive, presumably because of conformational difficulties, while the trans sulfonium isomer is abnormally reactive. T h e results are interpreted in terms of a concerted elimination process for the cis isomers (trans coplanar transition state), and some multistage elimination process (dipolar-ion intermediate) for the tram onium compounds (cis elimination).
Although a number of bimolecular elimination base-promoted isomerization of V to IV was slow reactions have been studied in detail regarding the enough so that IV was not obtained through V as an effect of stereochemistry upon rate, generally only intermediate, but probably directly from cis- and qualitative information is available concerning the trans-I. The isomers of I thus appeared to repreHofmann elimination. Several workers2have found sent an excellent system for a study of cis and trans that this reaction, similar to other bimolecular, Hofmann eliminations. base-promoted elimination reactions, shows a prefAt the same time, it appeared worthwhile to study erence for trans elimination. The present study the corresponding sulfonium ions (cis- and transwas undertaken to provide more quantitative in- 11) as another example of an “onium” system and formation regarding this preference. The cis and the corresponding p-toluenesulfonates (cis- and trans isomers in the 2-phenylcyclohexyl system trans-111) as an example of a presumably “normal” were chosen since the presence of the phenyl group system. For further comparison, elimination rates on the &carbon would activate the /3-hydrogen, were studied on 2-phenylethyltrimethylammonium causing an increase in rate and obviating the bromide (Ia).5 Data for the corresponding sulnecessity for using very high-boiling solvents as is fonium compound IIa and p-toluenesulfonate IIIa common in work on the Hofmann elimination. were available from the literature. Arnold and Richardson3 had observed that eliPreparation of Materials.-The 2-phenylcyclomination from cis- and trans-I gave l-phenylcylo- hexyltrimethylammonium iodides (cis- and trans-I) hexene (IV) rather than 3-phenylcyclohexene (V) were previously prepared and characterized by and Weinstock and Bordwel14 showed that the Arnold and Richardson3and by Cope and Bumgardner.6 A different synthetic route was employed here, in which a mixture of the corresponding amines was l’ll(.H*~’I1*Y prepared and the isomers separated by chromatography on alumina of the N-benzoyl derivatives. PI, The amine mixture was obtained either from the Ia, Y = KMes I, Y = Nhle:, Leuckart reaction on 2-phenylcyclohexanone or from + IIa, Y = SMez 11, Y = SMez the reduction of the corresponding oxime with lithI I a , Y = OTs 111, Y = OTs ium aluminum hydride. Based upon the amount of K-benzoyl derivatives formed, the Leuckart reaction gave about seven parts of trans-amine to four parts of cis-amine while reduction of the oxime gave five parts PI1 Pll of trans to four parts of the cis compound. The latter 11‘ T‘ ratio is in contrast to that reported by Smith, llaienthal and Tipton7 who obtained only trans(1) Previous paper in series. S. J . Cristol and R. S . Bly, Jr., THIS amine in the lithium aluminum hydride reduction of JOURNAL, 82, 142 (1960). (2) See for example: W. Hiickel, W. T a p p e a n d G. Legutke, Ann., some methylcycloliexanone oximes. The N-ben643, 191 (1940); N. L. McNiven and J. Read, J . Chem. Soc., 153 (1952); R . D. Haworth, J . McKenna and R. G. Powell, i b i d . , 1110 (1953); F. E . King and H . Booth, ibid., 3798 (1954); K. Jewers and J. hlcKenna, ibid.. 2209 (1958). (3) R. T. Arnold a n d P. N. Richardson, ‘THIS T O U R N A L 76, 3649 (1954). (4) J . Weinstock and 1 7 , C; B r r d n e l l . ibcd., 77,( i i O t i ( l ! l . j . j l .
( 5 ) This compound was kindly supplied by Prof. A . h-. Bourns, hlchtaster University. Hamilton, Ontario. (e) A. C. Cope a n d C . L. Bumgardner, THIS J O U R N A L , 79, Q(i0 (1957). (7) D. R. Smith, M . Maienthal and J . Tipton, J . Olg. Chem., 17, 294 (19x2).
Sept. 5, 1960
2-PHENYLCYCLOHEXYL DERIVATIVES
4693
TABLE I zoyl derivatives were hydrolyzed with 20% hydrochloric acid and the resulting hydrochlorides treated RATE CONSTANTS FOR ELTMINAwith sodium carbonate and methyl iodide in nitro- DATAAND SECOND-ORDER TION TO ~-PHENYLCYCLOHEXENE WITH POTASSIUM HYmethane to produce the quaternary ammonium DROXIDE I N ETHANOL' compounds, cis and trans-I. A solution of 1-phenylcyclohexene in methyl Te,mp., Compound C. mercaptan was irradiated with ultraviolet light for cis-I11 43.95 23.8 f0 . 1 12 hours and from this reaction two isomeric 263.70 190 f 96 phenylcyclohexyl methyl sulfides were isolated. One sulfide was obtained in 95ojO yield and this was cis-I 63.71 9.71 f 0.16 assigned the cis structure in accordance with a 75.03 40.0 f 0 . 1 similar reaction studied by Goering, Relyea and 169 f1 86.30 Lawrence.8 In addition, 2% of the trans-sulfide trans-I 95.80 1 0 . 2 rt 0 . 1 was isolated. Both sulfides were converted to sul107.00 36.8 f 1 . 4 fones for further characterization. In order to ob116,82 116 rt 2 tain a larger amount of the trans-sulfide, the cisI a' 33.90 7 . 1 2 f 0.05 sulfone was epimerized to the trans-sulfone by 43.95 29.2 f 0 . 6 heating a t reflux with ethanolic base. The trans53.00 9 3 . 6 It 0 . 7 sulfone was then reduced to the corresponding sulcis-11 16.98 65.3 f 0 . 1 fide in 79ye yield with lithium aluminum hydride, 25.20 209 f8 using the procedure of Bordwell and M ~ K e l l i n . ~ 667 f 12 33.90 The success of the sulfone isomerization indicated luans-I1 33.90 2 . 7 5 f 0.04 that the correct assignment of configuration had been made. The sulfides were converted to the 43.95 15.2 f 0 . 9 53.00 70.7 f 1.3 dimethylsulfonium iodides (11) with methyl iodide in nitromethane. All experiments were conducted at compound concenThe cis- and trans-2-phenylcyclohexyl p-toluene- trations of 0.006 to 0.01 A4 and potassium hydroxide concensulfonates (111) were prepared by treating a com- trations of ca. 0.2 M . Each rate constant given in t h e table mercial mixture of the alcohols with 9-toluenesul- is the average of two or three runs. When the base confonyl chloride in pyridine. The tosylate mixture centration was dropped t o 0.11 M, the rate constant was 200 X Product is styrene rather than l-phenylcyclowas then separated by fractional crystallization. hexene. Since the cis isomer was quite sensitive to base, a pure sample of the trans-tosylate could be obtained by recrystallizing the mixture from basic ethanol. to styrene in the case of the 2-phenylethyl comThis isomer was identical to that prepared from a pound. The formation of olefin was followed by pure sample of trans-2-phenylcyclohexanol. The observing the increase in absorption a t 247 mu and cis isomer was unstable and decomposition could corrections were applied where the yield of olefin be noted in two days a t room temperature. Melt- was not quantitative or nearly so. A large excess ing point behavior of both isomers was extremely of base was used and the pseudo-first-order rate erratic and dependent upon the method of isolation constant was determined graphically. In order to or crystallization. In subsequent experiments on show that the reactions were also first-order in base, the cis-tosylate, 8-10y0 of the trans isomer was iso- the base concentration was decreased by one-third lated as a residue. I t is not known if this was due to one-half in a number of runs. In the case of the to isomerization or to the presence of that much cis-tosylate, the agreement in k was good. In applytrans in the cis compound originally. Since the ing this test with the onium compounds, it was trans isomer reacted much slower in the reactions necessary to add an inert salt in the amount needed studied, i t would have only a negligible effect on to keep the ionic strength of the solution constant, the results obtained in the cis-tosylate rate studies. as decreased ionic strength causes an increase in Treatment of the trans-tosylate with sodium methyl rate. However, when neutral salt was added, an mercaptide in ethanol gave the same sulfide as was over-compensation was observed and the rates assigned the cis configuration. This is additional were 10-50% slower for the five onium compounds structure proof for the cis- sulfide since one would investigated. The type of salt added (sodium ioexpect a direct displacement reaction to produce in- dide, sodium perchlorate or potassium iodide) did version a t the carbon being substituted. Corre- not result in appreciably different behavior and it is sponding treatment of the cis-tosylate yielded only thought possible that the high concentration (about 0.2 molar) of the solutions may be the cause of the olefin. It seems, however, that the reacdiscrepancy. Results.-The results of the kinetic measurements are listed in Table I . N o data are given for tions must be second order and not of a solvolytic trans-2-phenylcyclohexylp-toluenesulfonate since a type since no solvolysis products are obtained (2second-order elimination was not observed. The phenylcyclohexyl ethers or alcohols), except with solvent used was ordinary ethanol (92.6 wt.%) and the trans-tosylate which was indeed found not to the base was potassium hydroxide. The rate con- give a strictly second-order rate. Also, solvolysis stants are for elimination to 1-phenylcyclohexene in experiments on the sulfonium iodides gave only a the case of the 2-phenylcyclohexyl derivatives and minor amount of elimination from the cis isomer and none from the trans. The first-order carbon(8) H . L Goering, D I. Relyea and D '& Lawrence, THIS JOURNAL, ium-ion type mechanism for onium compounds has 7 8 , 348 (1956) (9) F C, Rordrrell arid 1%' H LIcKellin, rbrd , 78, 2251 (1951). only been observed in extreme cases such as those
STANLEY J. CRISTOLAND FRANK R. STERMITZ
4694
1'01. 82
TABLE I11 reported by Norcross and Openshawlo and by &ICKenna and Singer." PnoDUcTs OF SOLVOLYSIS OF SOME SULFUXIUM A S U SLTLIn addition to the study of the kinetics of eliminaFOSOXY COMPOUNDS I N 92.6 W T . y o ETHANOL tion, a study of the products of the reaction of each Yield of product, 5% 1-Phenyl3-PhenylSubstn. substrate under conditions similar to the rate study Compound cyciohexene cyclohexene product was made. In most cases, elimination to l-phenyltrans-11 .. .. 85 1-111 cyclohexene (IV) represented the principal reaction, cis-I1 13 1 74 1'11 but this was not uniformly true (see Table 11). I t trans-111
T.4BLE
11
PRODUCTS O F REACTIONWITH POTASSIUM HYDROXIDE IS 92.6 WT. 70ETHANOL OF SOME ONIUMSALTS AND P-TOLU-
Cumpound
tyans-I
Temp., 'C.
ESESULFOSATES -Yield of products, %3Ph e n y 11-Phenylcyclocyciohexene hexenea
107 86 44 75
2
Substn. producta
8 1.1
c c >93* Ia 100 styreneh .. ..... truns-I1 20," 2.30 2 61 VI11 cis-IT /a 69," 750 1 7.5VII trans-I11 75 20 53 7 I X , lox rcis-I11 I3 87," 80* 7 Yields b y ultraviolet spectra a Yields are by isolatioiis. determinations. Xot investigated.
cis-I
--
may be noted that all of the cis isomers gave largely 1-phenylcyclohexene (IV) as the principal elimination product with small amounts of the 3-phenyl olefin V or substitution products as by-products. The trans onium compounds gave substantially greater amounts of substitution products (demethylation to amine VI or thioethers VI1 and VIII), but the principal elimination product (>go%) was again the 1-phenyl olefin IV. On the other hand, the trans-sulfonate I11 gave large amounts of the 3-phenyl olefin under these conditions. In agreement with the report of U'einstock and B ~ r d w e l l it , ~ was found that the &olefin did not isomerize to IV under the conditions used in the alkaline reactions fast enough to account for the formation of the 1-olefin.
SlIe2 VI
,
Slle VI I
1
Shle \'Ill
I
OH IX
OEt X
Interpretation of the results on elimination from the trans-sulfonate is clouded because i t is clear that a t least a portion of the reaction with this material is zero order in alkali. Solvolyses in ordinary ethanol (92.6 wt. yo)were performed on the cis- and frans-sulfonium compounds and cis- and trans-tosylates. The products isolated from each are given in Table 111. In each case, vapor-phase chromatography indicated that the products listed were the only ones formed in each reaction. Hence, low total yields are believed to be the result of losses in reaction work-up and not failure to isolate some additional product. The approximate solvolysis rate was checked. In the case of the cis- and trans-sulfoilium compounds and the cis-tosylate, the rate was (10) G. Xorcross and H. T . Openshaw, J . Chcm. Soc., 1174 (1049). (11) J . hIcKenna and J . B. Singer, i b i d . , 2759 (1958).
29
30
12 1); 16 S
c is-I I I 50" 2" cro rrs-I1I 20 53 7 IS 1F S ($0.4 MKOH) a Losses in isolation procedure; sole products foriiied; ratio probably correct.
too slow to interfere with the rate of base-promoted elimination. This was not true of the trans-tosylate. The products of solvolysis of the trans-tosylate i n the presence of 0.4 N ethanolic potassium hydroxide are also recorded in Table 111. As a larger amount of the 3-olefin was found here as compared to the solvolysis experiment, it was thought that isomerization in the latter case might be occurring because of the acid which is formed. However, heating 3-phenylcyclohexene a t 63.70" with 9-toluenesulfonic acid for 44 hours in ethanol showed no increase in ultraviolet absorption a t 247 r n p . Rough first-order rate constants for solvolysis ill ordinary ethanol for the cis- and trans-tosylates a t ti3.7" were 3.6 x 10-5 and 0.06 x ] O F 5 sec.-l, respectively. Thus the compound with the cisphenyl group is about 60 times more reactive than the trans compound.12 Discussion of Results.-Table 11' summarizes data on all of the conipounds studied, giving extrapolated or interpolated rate constants for elimination from the phenylcyclohexyl compounds to 1-phenylcyclohexene and from the @-phenyl(12) I t is of some interest t h a t solvolysis of rrans-111 gave unrearranged olefins and substitution products. while it has been reported t h a t deamination of f~uizs-2-phenylcyclohexylaminegives only t h e ring-contracted cyclopentylphenylcarbinol~~and dehydration with phosphoric acid gives largely benzylcyclopentene and henzalcyclopentane."s'b Infrared spectra o n our products, vapor-phase chromatography and infrared spectra on t h e fractions indicated, b y comparison t o reported peaks," t h a t there were little or no ring-contracted products formed. This obviously represents another case in which presumably similar cationic intermediates lead t o different products or t o different mixtures of products.ls-'g Conformational differences d o not appear significant14,21in explaining t h e results. and i t is difficult t o involve phenyl neighboring-group participation" in a solvolysis where a cis-phenyl group induces greater reactivity than a lriincphenyl group (even thvugh stereochemical r e s u l t s i v m ~ l df d v c x this interpretatton). We hope t o in\-estigatc theae redictiuns more conipletely in t h e future (13) D. V. Sightingale and 11 XIaienth:il, THIS.IOURXAI., 72, 1823 (1930). (14) 11. J. Schaeffer and C. 1. Collins, ibid.. 78, 124 (1956). (1.5) E. I,. Eliel, J. K. XIcCoy and C. C Price, J . 01,s. Che?ri., 22, 1533 (1957). (16) J. G. Burr, Jr., and I.. S. Ciereszko, IS J O U R X A L . 74, 5426, 5431 (1952). (17) D. Y. Curtin and h l . C. Crew, i b i d , 7 6 , 3i15) (1954). (18) D. J . Cram and J . E. hIcCarty, ibid., 79, 2866 (1957). (19) A. Streitwieser, Jr., and W. D. Schaeffer,ibid., 79, 2888 (1957). (20) S. Winstein and N. J . Holness, i b i d . , 77, 5.562 (1E.j). (21) S . Winstein, E , Grunrvald and I,. I,. Ingraham, ibid., 7 0 , 821 (1948); S. Winstein and E. G r u n a a l d , i b X , 70, 81'8 (1948); S Winstein, B K. Morse, E . G r u n \ \ a l d I;. C. Schreilier aiid J . C i n e , ibid., 74, 1113 (1952).
Sept. 5 , 1960
2-PHENYLCYCLOHEXYL DERIVATIVES
4695
ethylammonium compound to styrene, as well as entropies and hrrhenius energies of activation for these processes. In addition, data from the literat ~ r e are ~ given ~ , ~for ~ elimination from P-phenylethyldimethylsulfonium ion and p-phenylethyl p toluenesulfonate. The values in this table have been compared in Table V in such a fashion as to give in the first column the ratio of the rate of elimination from the cis isomer to that from the trans, in the second column the ratio of elimination from the open-chain analog to that of the cis isomer and in the third, that of the acyclic analog to that of the trans isomer.
particularly instructive and argue against a simple common interpretation. They show that while the differences between the rates of trans and cis elimination are not very large and are about the same whether the leaving group is trimethylamine or dimethyl sulfide, the reasons for this similarity are quite different. The data suggest that when the departing group is the trimethylamine group, elimination from the cis compound (trans elimination) is inordinately slow compared with the acyclic compound, while that from the trans isomer (cis elimination) is consistent with data which we have found previously in cis and trans eliminations. On the other hand, when the departing group is the TABLEI V dimethyl sulfide molecule or the p-toluenesulfonate R A T E COXSTANTS ASD QCASTITIESOF ACTIVATIOXFOR ion, the cis isomer (trans elimination) eliminates a t ELIMINATIOS TO 1-PHESYLCYCLOHEXENE OR T O STYRENE the same rate as the acyclic analog. The discrepWITH POTASSIUM HYDROXID INE 92.6y6 E T H A N O L ancy with the sulfonium compounds is that the Em, AS trans isomer (cis elimination) appears more reactive C o m p o un d I./mole/sec. kcal./mole cal./deg. than anticipated. 30.3 11 2 &-I 2 . 6 9 x 10-7" Two explanations offer themselves to rationalize 33.4 11.9 trans-I 2 . 0 2 x 10-9" these results. First, the cis compounds may have 25.5 3.7 Ia 2 . 1 5 x io-5a two conformations X I and XI1 depending upon k u O ,
x
1.98 10-3 24.3 8 7 5.17 X 1 0 F 33.8 28.8 I Ia 2 . 5 4 x 10-3b 23.9b 7.7b cis-I11 4.60 X 22.4 -6.4 IIJa 3 . 9 X10-3"td .. ... a Extrapolated. * Determined b y Saunders and iVi1liamsZ2using sodium ethoxide in absolute ethanol; the rate constant would be expected to be somewhat lower in ordinary ethanol. 30.10'. Determined by DePuy and FroemsdorfZ3using sodium ethoxide in ahsolute ethanol. Ci2-I1 trans-I1
Y
I
Ph XI
I
Y XI1
whether the substitute Y and the phenyl take up equatorial and axial positions, respectively, as in I t may be seen that while trans elimination (cis X I or vice versa as in XII. For facile elimination to isomer) is favored over cis elimination (trans isomer) take place, the substituent Y should have the in both onium series, the difference in reactivity is axial conformation in the transition state since only 133 for the ammonium compounds and 383 for then the P-hydrogen is also axial, trans and coplanar. the sulfonium salts. These small differences may Although some steric interactions with the axial be compared with much larger differences observed hydrogens occur if the phenyl, tosylate or dimethylwith alkyl halides, as for example, the benzene hex- sulfonium groups are in the axial position, these, as a c h l o r i d e ~where , ~ ~ ratios in reactivity between iso- evidenced by models, can be made negligible by mers undergoing trans and cis eliminations are rotating the group slightly. However, with the above 10,000. trimethylammonium group the interactions are One might suggest that these lowered ratios re- much more severe and cannot be minimized by rotaflect a difference simply between elimination in neu- tion. In this regard, it is quite similar to the ttral compounds and those in onium compounds, and butyl group, whose effects on conformation have thus might reflect differences in intimate mecha- been discussed by Winstein and Holnesszuand by nisms between Hofmann eliminations of onium Eliel and his co-workers.25 Conceivably then, the compounds and other e l i i n i n a t i ~ n s . However, ~~~~~ slower rate of elimination with the cis-quaternary comparisons of the cyclic compounds with each compound could be the result of the increase in other and with their acyclic analogs (Table V) are energy of activation necessary to force the ammonium group into the axial position or to cause TABLE 1' the elimination to proceed before the most favorRELATIVE K h r s s OF ELIMISATIOS FROM THE cis ASD t u n s able stereochemistry had been achieved. ISOMERS OF 2-PHESYLCYCLOHEXYLTRIMETHYLAMMONIUM If the cis-ammonium compound had eliminated I O K , 2-PHEXYLCYCLOHEXYLDIMETHYLSULFOSIUM I O S , 2P H E N Y L C Y C L O H~ETXOYLLU E S E S U L F O SAANTDETHE CORRE- a t about the same rate as the 2-phenylethyl analog, then trans elimination would have been favored SPOSDING 2-PHESYLETHYL COMPOUSDS over cis elimination by a factor of about lo4. Leaving group L/ktran8 kna/kcl. kn/klwna Thus, the apparent difference between the HofSMea 133 SO 10,700 mann elimination from ammonium compounds and SMe2 383 1.28 -191 other eliminations as regards the dependence of OTs.. 0.85 .... rate upon stereochemistry may be entirely due t o a k, = r a t e of elimination of the 2-phenylethyl compound. the conformational problem just discussed. (22) W. H. Saunders and R . A. Williams, THISJOURNAL, 79, 3712 On the other hand, the rate and product data (1957). could be rationalized upon the basis of a competi(23) C . H. DePuy and D. H . Froemsdorf, ibid., 79, 3710 (1957). (24) S. J . Cristol, ibid., 69, 838 (1947); and J . S. Meek. ibid., 73, 674 (1951).
S.J. Cristol, N. L.
Hause
( 2 5 ) E. I,. Eliel and R G Haber, rbtd., 81, 1249 (1959), and preceding papers
4696
STANLEY
J.
CRISTOL AND FR,4NK
tion between /3-elimination and a-exchange accompanied by isomerization of trans to cis isomer. For example, the trans-sulfonium (or ammonium) ion could react with base to give the zwitterion (ylide) XI11 as I
R.STERMITZ
VOl. 52 Y6
+
>c-c< H
Ba-
s\
SMe,
mediate or rearrangement process.Y2 These interpretations find support in the work of Professor A. N. Bourns33of McMaster University on nitrogen kinetic isotope effects on the quaternary amnionium ions we have studied kinetically and product-wise. Any rearrangement of trans isomer to cis would of Acknowledgments.-The authors are indebted course lead to elimination to 1-phenylcyclohexene, to the Office of Saval Research, the National as the cis compounds are much more reactive than Science Foundation and the Eastman Kodak Co. their trans isomers. Thus the apparent rates of for support of this work. elimination of trans-I or trans-I1 might be the rate Experimental of isomerization of trans to cis isomer and the cis elimination observed may be an artifact. Ex-111 melting points are corrected. The puritj- of the isochange in the a-position in onium compounds is mers prepared below was tested by observing diagnostic in the infrared which were present in one isomer b u t known,26-28and is likely to be much more rapid bands not the other. Such bands were found in each isomer, with with sulfonium (11) than with ammonium com- the possible exception of the cis-2-phenylcyclohexyl p-tolupounds (I).?'j The possibility of such epimerization enesulfonate. In this compound, shoulders were always is fortunately amenable to test by deuterium ex- present a t the same points where the tmns isomer showed strong absorption. discussed, this may have been due change, and we have begun work on this test. t o some of the trans isomer present in the cis compound. .A11 Xn alternative mechanism for cis elimination also infrared spectra of solid compounds were taken in potassium involving an ylide intermediate XIV, may be writ- bromide Dressings and the spectra of liquids were taken of the pure compounds in sodium chloride cells. ten as
x1vThis mechanism finds analogy in the work by Wittigz9 on elimination from cyclooctyltrimethylammonium bromide with phenyllithium and the high temperature decomposition of ethyltrimethylammonium hydroxide, 30 which mechanism has been termedz9 an a',p-elimination. Such a mechanism could, of course, explain why 1-phenylcyclohexene, rather than 3-phenylcyclohexene, is the principal product. This mechanism is also amenable to test with isotopic labels in our systems. One of the latter two mechanisms seems appealing for elimination from the trans isomer of the sulfonium compound to explain its relatively rapid rate of reaction, and of course might also be involved with the trans-ammonium compound.31 The rate data thus appear consistent with the idea that trans elimination, even with onium compounds, prefer a concerted mechanism via a transition state such as XV, where the atoms involved must be trans and coplanar, while those eliminations which are sterically unable to produce a transition state such as XV, or where another path is energetically favorable, react via a carbanion interi 2 ( i ) U'. v . I!. Doering aiid A . K. Hoffman, l'iiis J O U H K A I - , 77, :PI ( I Y55). ( 2 7 ) V. .i.Shiner, J r . , and 11. 1,. Smith, ibid., 80, 405'3 (1923). (28) T. l l a s a m u n e , Bull. Chern. SOC.J a p a n , 30, 491 (1'337); C. A , 62, 6 3 l l i (1S58). ( 2 9 ) G. Wittig and R . Polster, A n i i , 612, 102 (1958). (30) F. Weygand, H. Daniel and H. Simon, Chern. B e l , 91, 1691 i1958). ( ~ 3 1 )Dr. U . I . Davie, of this Laboratory (unpuhlislied work) lids demonstrated t h a t an ylide related t o SI11 cdniiot be ai1 intermediate nith Ivuiis-I.
Preparation of cis- and trans-2-Phenylcyclohexyltrimethylammonium Iodides.-One procedure used t o prepare a mixture of the amines was via a Leuckart reaction, adapted from t h a t of Kost and Grandberg.a4 X-Phenylcyclohexanone3j je50.0g., 0.29 mole) was added in portions t o a hot mixture of 80 ml. of 905~; formic acid, 60 g. of formamide a n t 0.3 g. of Kaney nickel. The mixture was kept at 110-117 during the addition, which was over a period of 50 minutes. The mixture was then stirred for an additional 2 hours, maintaining the temperature at the same level. After i t had cooled slightly, it was poured into 500 nil. of concentrated hydrochloric acid. This was then allowed t o evaporate t o dryness under an air jet while being kept warm. The residue was dissolved in 600 ml. of water, made strongly basic and extracted with ether. The ethereal solution was dried over anhydrous magnesium sulfate and the ether was removed by distillation. The oily residue was treated with base and benzoyl chloride t o yield 53.9 g. of a mixture of c-is- and tiens-S-benzoj-1-2-phenylcyclol~exylamine, m.p. 123-165'. S o attempt was made t o analyze the isomer mixture accurately, but subsequent purifications indicated a t r a n s l r i s ratio of about seven t o four. I n a second method, 2-plienylcj-clohexan1~neoxime (10.0 g , 53.5 mmoles) was dissolved in 500 m1. of dry ether containing 20 nil. of dry benzcne and this solution was added to a slurry of 5 g . of lithium aluminum hydride in 100 ml. of dry ether a t a rate causing slow reflux. The mixture was then heated for 19 hours. After the complex was decomposed mith wet ether and aqueous acid, the aqueous layer was separated, made basic and extracted with ether. The solu(32) A comparison of the products of solvolysis of the lI'ai&s-tosylate 111 in ethanol with and without added 0 4 M potassium hydroxide iTahle 111) suggests t h a t bimolecular elimination in this case (as Opjirlsed t o l i n i z s - I and 11- c i , Table 11) gives largely 3-phenylCyCkhexene (1') and not 1-phen~lcyclohexene ( I ) . A similar result (~1)tains with methyl mercaptide ion. This seem5 t o indicate t h a t base is pr
