July 5 ) 19G4
2643
SOLVOLYSIS O F 4-CHLORO-4-METHYL-2-PENTYNE
[COSTRIBCTIOS S
O
1205 F R O M
THE
DEPARTMEST O F CHEMISTRY
OF
INDIANA UNIVERSITY, BLOOMISGTON, IND.]
The Effects of Deuterium Substitution on the Rates of Organic Reactions.
X. The Solvolyses of 4-Chloro-4-methyl-2-pentyneand Its Deuterated Analogs BY V. J . SHINER, JR.,
AND
GEORGES. KRIZ,J R .
RECEIVEDFEBRUARY 24, 1964 ~-Chloro-4-methy1-2-pentyne ( I a ) and its I , l , l - & ( I b ) and 4-methyl-dS-5,5,5-&( I C analogs ) have been synthesized and their solvolysis rates measured at 25’ in several aqueous solvent mixtures. The rate retardation due to deuterium in compound I b is a new example of transmission of an isotope effect across an unsaturated linkage. The k H / k D for I b is about 1.09 and is not appreciably solvent dependent. Compound IC shows an isotope effect, k H / k D , of 1.66. These results conform to predictions based on hyperconjugation as t h e governing mode of interaction between isotopic and reaction centers. The contribution to the rate effect oi &deuterium substitution from relief of steric strain is estimated to be a t most only a small fraction of t h e total observed.
Introduction The transmission of isotope effects through unsaturated linkages was first reported by Lewis and Coppinger,l who found t h a t k H l ’ k D for p-methyl-ds-a-phenylethyl chloride solvolysis in acetic acid was 1.10. Subsequently, Lewis, Johnson, and Coppinger2 reported i t to be only 1.01 for solvolysis in aqueous acetone. Meanwhile, Shiner and Verbanic3 had reported k H , ’ ’ k D for p-methyl-ds-benzhydryl chloride solvolysis to vary from 1.06 in “807,” to 1.02 in “66.70/’ aqueous acetone. These authors interpreted their results in terms of hyperconjugation, which had been invoked b y Lewis and Boozer4 and by Shiner6 as an explanation of solvolysis rate retardations due to /3-deuterium substitution. The aromatic system was thought to be able to transmit the electron delocalization from the C-H bonds of the p-methyl group to the carbonium ion center, thus accounting for the observed rate retardations due to deuterium substitution rather distant from the reaction center. In the classic work of Bartlett and Rosen6 the triple bond was first used to distinguish between steric and electronic effects on reactivity. There have been no reports dealing with the transmission of isotope effects through a triple bond, but Burawoy and Spinner7 showed that the solvolysis of 3-chloro-3-methyl-lbutyne was accelerated about 2000-fold by a 1-methyl substituent. This large substituent effect should be associated with the ability of the methyl group to release electrons by hyperconjugation and demostrates t h a t the triple bond is a very efficient conductor of electronic effects. By comparison, a p-methyl group accelerates the solvolysis of a-phenylethyl chloride by only about 60-fold and an a-methyl group accelerates the solvolysis of isopropyl chloride b y an estimated factor of 4000. Burawoy and Spinner further found that a 1-t-butyl group accelerated the solvolysis of 3-chloro-3-methyl-1-butyneless than a 1methyl group. Such “Baker--r\;athan” reactivity orders have also been attributed to large hyperconjugation interaction. I t thus appeared that despite the remoteness of isotopic substitution from the reaction center, a reason(1) E S Lewis a n d G 31 Coppinger, J . A m . Chem Soc , 76, 4495 (1954). ( 2 ) E S L e a i s , R. R . J o h n s o n , a n d G M . Coppinger, ibid., 81, 3140 (1439). ( 3 ) V. J. Shiner, J r . , a n d C J T’erhanic, ibid., 79, 373 (1957). < 4 ) II. S Lewis a n d C . I< Boozer, ibit/., 74, 6306 (1952). ( 5 ) V. J. Shiner, J r , i b i < i ,76, 29’25 (1953). (6) P. D. B a r t l e t t and I>. J Rosen, ibid , 64, 643 (1942). (7) A . R u r a w o y a n d E. Spinner, J C h e m . Scc.. 3752 (1954).
ably large isotope effect should be observed in the solvolysis of 4-chloro-4-methyl-1-pentyne-1, 1,1-ds(Ib), if hyperconjugation were an important mode of interaction in causing the large effects of p-deuterium substitution on solvolysis reactions. In addition, the solvolysis rate of compound IC would be useful to give a direct comparison between “remote” and CH3
CHa
1 CHj--C-C=C-CHs i C1
1
CH3-C-C-C-CDz
I
CI
Ia
Ib
CD3
1 1
CD~-C-CEC-CH~
c1
IC
/3-deuterium substitution in the same reaction. The syntheses and solvolysis rate measurements of these compounds were accordingly undertaken. Experimental 2-Methyl-3-butyn-2-01 11’:~skindly supplied by the Xir’Reduction Co.
3-Methoxy-J-rnethyl-l-butyne.-The three necks of a 2-I., round-bottom flask were fitted with a Trubore stirrer, a condenser cooled with a Dry Ice-acetone b a t h , and a gas inlet tube. About 1200 ml. of ammonia was condensed into the flask and about 500 mg. of ferric nitrate nonahydrate was added. Clean sodium cubes (23.5 g . , 1.02 g.-atonis) were added during 2 hr. T h e mixture was then stirred for about 45 niin. T h e gas inlet tube was replaced by a dropping funnel, and 2-1nethyl-3-butyn-2-ol (83.7 g., 0.995 mole) was added dropwise over a period of 1 h r . Methyl iodide (143.8 g., 1.01 moles) was added dropwise during i a min. The mixture was allowed to stir for an hour afterward. T h e dropping funnel m-as replaced by a bent-necked flask containing 62.3 g. (1.16 moles) of ammonium chloride. The solid was added during 1 h r . , and the mixture was stirred for U . j hr. after the addition was complete. T h e stirrer and condenser were replaced by a 13 X 470 mm. vacuum-jacketed I’igreux colunin fitted with a distilling head cooled with a Dry Ice-acetone b a t h . T h e liquid ammonia was evaporated by allo\ving it t o distil through t h e column. .2fter removal of the arnttionia, t h e reaction mixture was extracted with twelve 50-lii~.portions of ether. X few grams of sodium carbonate was added to the ether solution, which was subsequently distilled through a column packed with stainless steel helices. T h e product was collected over a range of 77-79”; yield 46.9 g. (0.478 mole), 48.0‘~;. 2-Methoxy-2-methyl-3-pentynewas prepared by a modification of the method of Hennion and Boissclle.* .kfter the final addition of ammonium chloride, the mixture wiis stirred for 0.5 h r . T h e ammonia was then alloived to distil through ii vacuum-jacketed Vigreux colunin in the same manner as described above for 31i1ethoxy-3-~iietIiyl-l-butyiie. Distilkition as before yielded the product, boiling over the range 117-119”; yield 31 .O g. (0.276 mole), 70.3‘1;;.
--
(8) G. F. H e n n i o n a n d A . P. Boisselle, J
OYE C h e m . , 2 6 , 72.5 (1961)
Z(i44
V. J. SHINER, JR.,
AND
4-Chloro-4-methyl-Z-pentyne (Ia).-2-Metho~y-2-nietliyl-3pentyne (11.2 g . , 0.097 mole) and a b o u t 1 g . of hydroquinone were placed into a three-necked, round-bottom 100-nil. flask. 'The flask was inaintainrd xt O " , :rnd stirring was provided with a magnetic stirrer. Llry hydrogen chloride was bubbled through tlic reaction mixture for 15 inin. T h e hydrogen chloritle addition nxs tlieii stopped, a sinall sainple of t h e reaction mixture t o be used for an i i . i i i . r . spectrurn iv:is rerriovetl, a n d t h e flask was iiniiiersctl in a I)ry Ice-acetone b a t h . The n.ni.r. spectrum was itniiietli:itely t a k e n , and the ratio of t h e peaks a t 8.68 T due t o the protoils on tlie t\vo equivalent methyl groups of 2--rnethosy2-iiietliyl-:i-pentyne, a n d a t 8.22 T , d u c t o t h e corresponding protons of t h e product, was observed, as a measure of t h e extent of t h e reaction. This procedure, involving addition of hydrogen chloritle for 15 inin., followed by the n.in.r. spectrum, w a s continued until tlic total reaction time was 1 h r . A t this time, t h e peak a t 8.W T \vas prxctically gone, antl t h e peak a t 8.31 7 , due t o an :>.llcniciinpurity, had not yet formed. T h e reaction mixture was purifictl b y vitcuuiii line fractionation t o give t h e product; yield 8.1 g. (0.068 niolej, 09.8' ;. .\lthough this material sloivly deconiposed a t room teniperature, i t was found t h a t storage in a Dry Ice- acetone b a t h over extcncletl periods of a year or more left the ii.m.r. spectrum unchanged. Trimethylsulfoxonium Iodide-ds.-Triinetliylsulfoxoiiiutn iodidr v a s prepared according t o t h e rriethod of Kuhn a n d Trischr n a t i ~ i . ~I t W:LS then subjected t o sodiurn carbonate-catalyzed eschuigc in deuterium oxide according t o t h e method of C o t t o n , et
nl.l('
Trideuteriomethyl Iodide .-Trimethylsulfosoniurri
GEORGE S. KRIZ,JR.
Vol. 86
were processed by means of a least-squares kinetic program used \\ith IRM 709 digital computer.
Results The table gives the results of the kinetic runs, along with an indication of their reliability TABLE I SOLVOL\SIS RATESA ~ ISOTOPE D EFFECTS AT 25' Compound Ia
Ib
IC
Solvent "SO6&" EtOH-HrO "Y5c/c" E t O H - H 1 0 " 8 0 ~ c "acetone-HrO "8007' EtOH--H20 "9,5%" EtOH-H.0 "80V0" acetone-H?O " S O Y c ' EtOH-HsO
R a t e c o n s t a n t . sec - i .i420 z 0 00; X 10-4 H 1649 i 0002 x 3 87 zk 01.5 X 10-5 1 9633 i ,0007 X IO-' 2 8907 i ,0008 X 10-6 .i 203 I 00.; X 10-3 3 27.j z t 005 X I O - ,
k H fill
10-5
+
1 .OH2 0 1 0!MU i 1 087 I I 6.i.i =
001 000-1 004 004
The inconsistency in the observed errors appears to be due to a deviation from precise first-order kinetics. This appears to be due to an isomerization of the type described by Shiner and W'ilson" causing the formation of an allenic chloride which also solvolyzes, b u t a t a much slower rate.
Discussion
iodide-dg The table above shows t h a t @-deuteration retards was pyrolyzed according to t h e method of Cotton, tf nZ.'o T h e the solvolysis rate by an amount similar to that obproduct was distilled through a 10 )< 390 i n i i i . column packed with 0.33 in. glass helices. T h e product was collected over t h e served for other t-alkyl halides.18 The effect is, howrange of 40 t o 44'; yield 57.8 g . (0.399 mole), S7.5c;. -1deuever, significantly smaller than 1.84, the k H ' k D value terium analysis h y means of n.ni.r. showed t h a t t h e percentage previously observed in the solvolysis of 3-bromo-3deuterium was 99.Tri, Corresponding t o 2.99 a t o m s of D per m e t h y l - d a - l - b u t y n e - ~ , 4 , ~ - d aThe . ' ~ p-deuterium isomolecule. tope effect in the solvolysis of a-phenylethyl bromide 4-Chloro-4-methyl-2-pentyne-l,l,l-d~ (1b)wasprepared from hydrogen chloride ancl 2-inethosy-2-tnetliyl-3-pentyne-3,j,j-~~.The has been found to be very similar to t h a t for the reaction \vas monitored b y n.1n.r. b y following t h e same peaks chloride.': Thus it may be inferred t h a t the methyl a s in t h e preparation of ~ - c h l o r o - ~ - ~ n e t h y l - ~ - p e n t y nBecause e. group in compound IC causes. relative to hydrogen, of tlic tendency of this material to give explosions in t h e combusa decrease in the 0-effect from 1.81to 1.G55. Similar tion train, a deuterium analysis by t h e combustion method described by Shiner" could not be accomplished. As a result, i t reductions in the @-effectare associated with electronwill be.necessary t o assume t h a t n o undesirable exchange occurred releasing ring substituents in the solvolysis of o(in t h e synthesis from trideuterionietliyl iodide. phenylethyl chloridelj and are apparently due to the Acetone-& was prepared by t h e method of Shiner a n d Cross.'* ability of these groups to disperse the positive charge Deuterium a d y s i s by ii .ni.r. indicated t h a t there was 99.97, developed in the transition state and reduce the dedeuterium excliaiige, corresponding t o 6.OO atoms of deuterium per molecule. mand for hyperconjugation. The methyl group re2-Methyl-d3-3-pentyn-2-ol-l,1,l-da was prepared by t h e action duces the isotope free energy effect in the same proof propynylinagiiesiuiii bromide on acetone-&, according t o t h e portion to its reduction of the free energy of activation nietliod of Ilurd arid C o I i e ~ i . ' ~ in both cases. 4-Chloro-4-methyl-dr-2-pentyne-5,5,5-da (IC)was prepared b y &Deuteration also causes a significant effect, about bubbling d r y hydrogen chloride into 2-niethyl-da-~-pent~~n-2-ol1 , l , l - &in a manner siiiiil:ir t o t h a t used in t h e preparatirrn of 4one-third as large per D atom as p-deuteration. cliloro--l-iiietIi~l-8-pcntyiie. T h e reaction was monitored, a s Further, in a set of solvents in which p-methyl-d3before, by ti.iii.r. except in this case t h e disappearance of t h e peak benzhydryl chloride showed a strong solvent dependdue to tlie tcriiiinal riirtliyl protons of tlie alcohol a t 8.22 T a n d ency of the isotope rate e f f e ~ tthe , ~ effect of 6-deuterat h e appearance of t h c correspondiiig peak of t h e chloride a t 8.18 tion is relatively constant and somewhat larger. I t T h e total time required for t h e addition of T \vere folloivctl. liydrogcn ch1i)ride x i s 33 inin. Purification b y vacuum line is also larger than the solvolysis isotope effect shown transfer gave 1.2 g. (0.0:34 niolcj, yield 79.7' i . by p-methyl-d3-a-pheny1ethyl chloride in similar solKinetic Procedure.-The solvolysis reactions were followed vents.* Thus the present results confirm and contlucti~~netric~illy, T h e A x a n d .C, for HC1 in "80'";'' ethanol strengthen the conclusion originally drawn from the were determined b y l I u r r , 1 4 ancl A m and .Ye for HCI in "95cc" experiments designed after the classic method of organic ethanol a n t l "XO' " acetitnc \\-?re determined by Shiner a n d Rudtlelibauni
.I>
T h e reactions were follon-ed by tlie conductance method descrihrd by M u r r a r i d Shitier.'G T h e results of t h e kinetic runs 8,R)
P K u h n a n d 11. 'l'rischmann,
1 1 2 1 \. J Shiner, J r , a n d S . Crois, rbui , I ? ' i' 1) I l i i r d a n d I' I. C o h e n , i h i i i . . 141 T? I. l l i i r r , I T , 1'11 I ) T h e q i s , I n d i a n a l-niver,ity, 1861, p . 7 7 . \. I . Yhincr, l r , a n d \V.t;. U u d d c n b a u m . unpublished results. I3 I. 5 1 u r r . J r and \. J . S h i n e r J r , J . A711 C h c m . .?oc , 8 4 , 4672 (1c)6?1.
chemistry to show t h a t the ,&deuterium isotope effect was caused by an elcctronir interaction with the reaction center. Although these earlier results have subsequently been ignored or discounted for being small and solvent dependent,*"," by the proponents (17) V. J Shiner, Jr., a n d J . TV Wilson, % b i d ,8 4 , 2102 (1962) (18) V . J Shiner, J r , B L. L f u r r , a n d G H e i n e m a n n , ibtti , 85, 2413 (1963). ( 1 0 ) V.J Shiner, J r . , J U'. LYilson. G H c i n e m a n n . a n d S Solliday r b i d , 84, 2408 (1062) ( 2 0 ) I,, S. Bartell, ihrd , 83, 3,767 ( 1 9 R 1 ) , ioru~i SLiiii. .I .\cr , 36, 137 (1961) T h e simple steric mudel ignoring charge delocalization predicts a null effect for isotopic substitution a t these remote sites I n the secund
July 5, 1964
REACTIONS O F 3-PHENYL-2-CYCLOBUTENONE
of the steric origin of all secondary isotope rate effects, i t appears unlikely t h a t the present results can be explained by change in either steric or solvent interactions on activation without the incursion of electronic interactions with the reaction center. If the &effect is entirely electronic in origin, it remains to predict from this what fraction of the approximately 3-fold larger effect in the P-position is similarly electrical in origin and to estimate by difference what residual amount could be attributed to changes in nonbonded interactions. I t has been found that the triple bond generally attenuates the inductive effect by a factor around three or four.22 However, the present effect is certainly mainly conjugative in nature. Kochi paper t h i s problem is m e t b y a model involving charge delocalization. This is t a n t a m o u n t t o invoking hyperconjugation b u t includes t h e novel idea t h a t relief of n o n b o n d e d interactions assists hyperconjugative electron release. (21) M. J S. Dewar, “Hyperconjugation,” T h e Ronald Press, New York, X. Y., 1962, p. 141. , 1167 (1961), a n d (22) R. E Dessy a n d J . - Y . K i m , J . A m . Chem S O L . 83, references there cited.
[CONTRIBUTIOX S o . 3051
2645
and H a m m ~ n dhave ~ ~ estimated that the carboncarbon triple bond is a four- or fivefold poorer conjugative electron releaser than the double bond. Thus we can infer that the part of the P-effect caused by electronic interactions would be much larger than 1.10 and might be large enough to account for the total observed. Nevertheless, i t is not possible a t the present time to conclude that there is no small “steric” component in the /?-effect. The strong solvent dependencies of isotope effects transmitted by conjugation through the benzene ring remain to be elucidated by further experiments. Acknowledgment.-This research was supported in part by a grant from the Petroleum Research Fund administered by the American Chemical Society. Grateful acknowledgment is hereby made to the donors of this fund. The facilities of the Indiana University Computing Center were used for the machine computations. (23) J K . Kochi a n d G S H a m m o n d , ibid , 75, 3452 (1953)
GATESA N D CRELLINLABORATORIES OF CHEMISTRY, CALIFORNIA ISSTITUTE OF TECHSOLOGY, DEPARTMEXT O F CHEMISTRY, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, hfASS.1
FROM THE
PASADENA, C A L I F . , A S D THE
Small-Ring Compounds. XLII. Synthesis and Reactions of 3-Phenyl-2-cyclobutenone and Some Related Compounds’,2 BY
STANLEY
L.
y I A N A T T , 3 M A R T I N VOGEL,
DAVID KNUTSON, AWD
JOHN
n. ROBERTS
RECEIVED JANUARY 20, 1964 Hydrogenation of either l,l-difluoro-2,2-dichloro-3-phenylcyclobutane ( V I I ) or l,l-difluoro-2,2-dichloro-2phenylcyclobutene ( V I ) over a palladium-on-charcoal catalyst gave l,l-difluoro-3-phenylcyclobutane(1.) Bromination of 1- by S-bromosuccinimide produced 1,l-difluoro-3-brorno-3-phenylcyclobutane ( I X ) which on dehydrobroinination by potassium hydroxide in ethanol afforded 1,l-difluoro-3-phenyl-2-cyclobutene (11.). Hydrolysis of 11?by concentrated sulfuric acid gave 3-phenyl-2-cyclobutenone ( I ) . Treatment of I with hot dilute aqueous base produced mixtures of benzoic acid, acetophenone, and benzoylacetone. The ring opening of I in boiling acetic acid gave P-methyl-trans-cinnamic acid. Catalytic hydrogenation of I produced 3-phenylcyclobutanone ( X I ) . Sodium borohydride reduction of I afforded 3-phenyl-2-cyclobutenol ( S I I ) which on catalytic hydrogenation gave cis-3-phenylcyclobutanol( X I I I ) ; XI11 was also obtained by catalytic hydrogenation of 2-chloro-3-phenyl-2-cyclobutenol(XVI) from the sodium borohydride reduction of 2-chloro-3phenyl-2-cyclobutenone ( X V ) ,
Introduction The present research was concerned with the synthesis and ring-opening reactions of 3-phenyl-2-cycloThe cycloaddition reactions of styrene and phenylacetylene with either 1,l-difluoro-2,2-dichloroethylene,butenone itself (I) as well as the chemistry of some of its derivatives. A synthesis of I was desired as a pre1,1,2-trifluoro-2-chloroethylene, or tetrafluoroethylene cursor to derivatives from which a 3-phenyl-2-cyclogive adducts whose conversion to substituted (either butenyl cation (11) might be generated by suitable halogen- or alkoxyl-substituted) 3-phenyl-2-cyclobutensolvolyses or deamination reactions. Simpie LCXOones has been described in earlier paper^.^ The ringmolecular orbital calculations suggest that delocalizaopening reactions of a number of substituted 3-phenyl2-cyclobutenones have also been discussed previously.4a,4c.5
7
(1) Presented in p a r t a t the Fourteenth X-ational Organic Chemistry S y m p o s i u m of t h e American Chemical Society, L a f a y e t t e , I n d . , J u n e , 195.5, a n d a t t h e 138th S a t i o n a l RIeeting of t h e rlmerican Chemical Society, New Y o r k , N Y , S e p t . 15, 1900, Abstracts of Papers, p 7 2 P ( 2 ) Supported in p a r t by t h e S a t i o n a l Science Foundation. (3) hlonsanto Chemical Co Predoctoral Fellow, 1957-1958 (4) ( a ) J 13. Roberts. G B Kline, a n d H E Simmons. Jr , J A m Chem. Soc , 76. l i 6 . 5 (1953); (b) E F Silversmith a n d J D Roberts, ibid , 80, 4083 (1958) i c ) E. F Silversmith, Y . K i t a h a r a , 51. C Caserio, a n d J D. Roberts, ibid., 80, 58-10 (1958); (d) E J S m u t n y , If C . Caserio, and J . D . Roberts, ibid., 82, 1793 (1960); (e) 51 C. Caserio, H E. Simmons, J r . , A E. Johnson, a n d J. D . Roberts. ibid , 82, 3102 (1960); (f; Y . K i t a h a r a , h f C Caserio, F. Scardiglia. a n d J D . R o b e r t s , i b i d , 82, 3106 (1960). ( , 5 ) ( a ) E F Jenny a n d J . 1) Rvberts, i b t d , 78, 2005 (1956); ( b ) E F. Silversmith a n d J D. R o b e r t s , i b i d . , 78, 4023 (1956); ( c ) I.. Skatteb@l a n d J . D. Roberts, ibrd., 80, 4085 (1958); ( d ) E. F Silversmith, Y . K i t a h a r a , a n d J . D Roberts, ibid.,80, 4088 (1958).
I
B
I1
I11
tion of electrons as the result of a-overlap between the p-orbitals on the 1- and 3-positions in the cations I1 and I11 could well result in significant enhancement of the sN1 solvolysis rates of substances which could yield I1 and I11 over those for suitable model compounds. The cations in question are of the homocyclopropenyl type and are expected to possess a t least some of the stabilization predicted by the simple LCXO-110
