3730
Chromyl Chloride Oxidations. IV.’12 Kinetics and Mechanism of the Addition to Styrene Fillmore Freeman and Nira J. Yamachika3
Contribution from the Department of Chemistry, California State College, Long Beach, California 90801. Received April 14, 1969 Abstract: The kinetics of the chromyl chloride addition to (oxidation of) the carbon-carbon double bond of styrene, to give the chromyl chloride-styrene adduct, have been investigated via spectrophotometric stopped-flow techniques. The reaction is overall second order, first order in each reactant. A correlation of U+ substiutent values and rate constants has been obtained for the substituents p-CH,, p-C8H5,H, p-C1, p-Br, m-C1, and rn-NOz with p = - 1.99. AH* is 8.4 kcal/mol, and AS is -23.8 eu. The data are consistent with a mechanism which involves an electrophilic attack of chromyl chloride at the carbon-carbon double bond to give either a partially bridged resonance-stabilized five-membered-ring activated complex or an epoxide-like cyclic three-membered-ring activated complex in the rate-determining step.
*
A
lthough numerous studies have been devoted to the oxidation of alkenes and styrenes by chromyl acetate and chromic acid,4 no kinetic studies of the chromyl chloride oxidation of styrenes have apCycloalkenes ‘0 and styrenes” have been peared. postulated as intermediates in the chromyl chloride oxidation of cycloalkanes and arylalkanes (Etard reaction), 4*6b~12~13respectively. The intermediacy of styrenes in the Etard reaction has been recently demon~ t r a t e d . ’ ~Intermediates ~ ~ ~ ~ ~ ’ ~ 1-111 have been suggested to account for the variety of products from arylalkanes and unsaturates (Scheme I). 134,6-g I11 was invoked to explain the formation of chlorohydrins in the oxidation of alkenes and cy~loalkenes.5~~*14-~~ Also, it is possible for I or I1 to rearrange to the epoxide (IV) which can isomerize to the observed carbonyl products during the acidic hydrolysis step. Owing to the absence of previous kinetic studies, this investigation was undertaken in order to gain a clearer understanding of the mechanism of the chromyl chloride addition t o (oxidation of) styrene, and of the properties of resulting activated complex. We now
Scheme I CGH&HJCHLR R = H or CH,
+
CrOLCli
-
-+
135-g
(1) Part 111: F. Freeman and N. J. Yamachika, Tetrahedron Lett., 3615 (1969). ( 2 ) Presented in part at the 158th National Meeting of the American Chemical Society, New York, N. Y., Sept 11, 1969. (3) Petroleum Research Fund Scholar, 1968-1970. (4) The subject has been reviewed by K. B. Wiberg, “Oxidation in Organic Chemistry,” Part A, Academic Press, New York, N. Y., 1965,p 69 ff. (5) W.H.Hartford and M. Darren, Chem. Reu., 58, 1 (1958). (6) (a) F. Freeman, P. J. Cameron, and R. H. DuBois, J . Org. Chem., 33, 3970 (1968); (b) F.Freeman, R. H. DuBois, and N. J. Yamachika, Tetrahedron, 25, 3441 (1969). (7) C. N. Rentea, M. Rentea, I. Necsoiu, and C. D. Nenitzescu, ibid., 24, 4667 (1968). (8) R. A. Stairs. D. G. M. DiaDer. and A. L.Gatzke. Can. J . Chem., 41;-i059(1963). ’ (9) C. N. Rentea, M. Rentea, I. Necsoiu, and C. D. Nenitzescu, Reo. Roum. Chem., 12, 1495 (1967). (10) C. D. Nenitzescu, Bull. SOC.Chem. Fr., 4, 1349 (1968). (11) I
