Vol. 78
HARLANL. GOERINGAND HERBERTH. ESPY
1454
S02CI > CsHsSOzCl > ~ - N O G H S O Z C I I. n each case electron supply assists the reaction. The slow rate for 1-chloroethanesulfonyl chloride cannot be attributed to a steric effect, because in the car~ bonyl chloride series the following S N solvolytic rate sequence is observedls: ClzCHCOCl > CICHzCOCl > CH3COCI. As noted above, the reactions of methanesulfonyl and benzenesulfonyl chlorides may proceed by a hydration mechanism. An intimation that this may be the case for the latter is obtained by plotting Hedlund’s rate data2 for substituted benzenesulfonyl chlorides against the Hammett uconstants of the substituents (Fig. 3). The data for substituted benzoyl chlorides’ are included for comparison. It can be seen that both plots fall into two parts. This behavior can be interpreted in terms of a duality of mechanisms.6 Lines I1 and IV are considered to clescribe a region of reaction by direct displacement, while lines I and I11 describe a region where the hydration mechanism is dominant. Negative Nucleophiles.-Here the reaction will be facilitated by strong coulombic attraction between N and S, as 2
N-
I .._____ S+
c1-
/b
0- 0
CH, 0 -
I
1 I1
CHa--N==S-CI +
0
Acknowledgments.-We are indebted to Dr. Paul W. Morgan for inspiration and encouragement and to Mr. Donald G. Preis for invaluable technical assistance. WILMNGTON,DELAWARE
(18) R. Leimu, Ber., TO, 1040 (1037).
[CONTRIBUTION FROM
Therefore, i t is predicted that toward negative nucleophiles (hydroxide, phenoxide), methanesulfonyl chloride should be more reactive than benzenesulfonyl chloride. Again no data are available to test this prediction. A similar point of view has been taken by Swain and Scott3 in explaining the high reactivity of hydroxyl ion toward aromatic acid chlorides. Ionization.-The high positive charge on sulfur may also be responsible for the s N 1 sequence, (CH3)zNSOzCl < CH3OS02CI. Since dimethylamino is much more effective than methoxyl a t stabilizing a carbonylium ion, the observed sequence must mean that much of the stabilization by the former is already provided in the initial state by the resonance form :
THE
DEPARTMENT O F CHEMISTRY O F
THE
UNIVERSITY
OF
WISCONSIN]
The Solvolysis and Base-catalyzed Dehydrohalogenation of 1,l- and 1,Z-Dihalocyclohexanesl BY HARLAN L. GOERING AND HERBERT H. Espy2 RECEIVEDSEPTEMBER 6, 1955 The relative rates of second-order dehydrohalogenation of 1,l- and cis- and trans-1,2-dihalocyclohexanes(dibrorno-. dichloro- and bromochloro-) and cyclohexyl bromide and chloride in “80%” ethanol containing 0.1 -44 sodium hydroxide have been determined. Under the conditions of the kinetic experiments the reactions are second-order and E2 elimination is llot accompanied by sN2 substitution. The solvolytic reactivities of a number of the compounds in ‘‘80%” ethanol were determined and show that under the conditions of the dehydrohalogenations. the E2 reactions are essentially completely isolated from competing solvolysis except for the 1,l-dihalocyclohexanes. The order of reactivity for the E2 dehydrohalogena1,l- > trans-l,2-. Under the conditions of the present experiments the 1,ltion of the isomeric dihalides is: cis-1,2give two moleatld cis-1,2-dihalocyclohexaneseliminate one molecule of hydrogen halide. The tmns-1,2-dihalocyclohexanes cules of hydrogen halide. The stoichiometry and relative reactivities indicate that a trans-elimination is involved. The relative reactivities, together with conformational considerations, provide information concerning the effects of a- and 0halogen atoms on the rate of dehydrohalogenation.
>>
Introduction I n connection with other work3in this Laboratory pure samples of 1,l- and cis- and trans-1,Z-dihalocyclohexanes (dibromo-,dichloro- and bromochloro-) were obtained. These compounds are suitable simple models for studying the stereochemistry of dehydrohalogenation and the effect of a- and phalogen atoms on the rate of dehydrohalogenation. (1) This work was supported in part by the United States Air Force through t h e Office of Scientific Research of the Air Research and D e velopment Command, and in part by the Research Committee of t h e Graduate School with funds given by the Wisconsin AIumni Research Foundation. (2) Du Pout Summer Research Assistant, 1953, 1954. (3) (a) H. L. Goering and L. L. Sims, TEIS JOURNAL., 7 7 , 3465 (1955); (b) P. Bender, D. L. Plowers and H. L. Goering, ibid., 77, 3463 (1955); ( c ) H. L. Goering and 13. H. Espy, ibid.,77, 5033 (1955).
This paper describes the stoichiometry and relative rates of base-catalyzed dehydrohalogenation of these compounds and of cyclohexyl chloride and bromide in “80%” ethanol containing 0.1 M sodium hydroxide. With the isomeric 1,2-dihalocyclohexanes the orientation, and thus the stereochemistry, of the dehydrohalogenation can be determined readily from the stoichiometry, i.e., the number of molecules of hydrogel1 halide eliminated. If the elimination product is l-halocyclohexene only one molecule of hydrogen halide is eliminated. The initial formation of 3-halocyclohexene leads to the formation of two molecules of hydrogen halide since the allylic halide is rapidly dehydrohalogenated (or solvolyzed) under the conditions of the reaction.
DEHYDROHALOGENATION OF 1,l- AND ~,~-DI~IALOCYCLOIIEXANES 1455
April 5, 1956
TABLE I RATESOF BASE-CATALYZED DEHYDROHALOGENATION O F HALO-AND DIHALOCYCLOIXEXANES I N “8070” ETHANOL Cyclohexane derivative
[NaOH]
[Organic halide]
Moles of”
t f 0.02,
1OC kr,
AH*
f 0.4,b AS* f l , b
102, M HX produced OC. M 1. mole-’ sec.-l kcal. e.u. 2.37 1.001 79.75 10.74 28.9 f0.4 22.3 7 1.1-Dibromo2.37 49.80 1.34 f .03 10.74 10.74 2.09 30.05 0.136 f .001 79.75 0.996 10.72 32.5 f .3 2.38 21.9 -8 1-Bromo-1-chloro49.80 2.38 1.62 f .02 10.72 2.66 30.05 0.166 f .002 10.67 2.38 1.002 99.80 10.66 5.32 f .09 24.7 -8 1,l-Dichloro2.38 79.75 10.66 0.755 f .008 2.64 30.05 1.. 001 26.1 f .2 10.65 19.1 -7 cis-l,2-Dibromo2.19 10.65 20.03 8 . 5 0 f .19 2.91 30.05 1.001 7.92 f .06 10.3 cis- 1-B romo-2-chloro- 10.77 -9 2.20 20.03 10.66 2.56 f .01 2.86 1.007 79.75 10.72 28.3 f .2 22.9 -6 cis-1,2-Dichloro2.78 10.72 49.80 1.24 f .01 2.78 30.05 10.72 0.116 f .002 2.29 2.004 79.75 10.74 13.6 f .1 23.1 -7 trans-1.2-Dibromo2.29 49.80 10.74 .587 f ,004 1.71 99.80 1.912’ 10.69 19.7 f .2 23.3 -9 trans-l-Bromo-279.75 10.69 3.15 f .08 chloro1.51 1,860’ 10.66 20.0 f .4 99.80 79.75 3.12 f .05 10.66 2.01 0.721 f .004d 99.80 10.66 26.3 -7 trans-1,2-Dichloro2.01 I O . 66 ,0910 .00002d 79.75 79.75 2.17 0.997 17.0 f .1 10.69 22.0 -9 Bromo2.17 49.80 10.69 ,842 f ,013 2.10 2.22 f .06 99.80 10.67 24.9“ - 9” Chloro2.10 79.75 ,311 f ,0094 10.67 a Determined from initial concentrations and “infinity” titers. These errors calculated from high and low values of k a t the extreme temperatures, assuming an average deviation in k f
