MECHANISM OF HYDROCHLORINATION OF T-BUTYLETHYLENE AND STYRENE IN ACETIC ACID

The hydrochlorination of t-butylethylene in acetic acid yields 3-chloro-2,2-dimethylbutane (SC), 2-chloro-2,3-dimethylbutane (TC), and 3-acetoxy-2,2-dimethylbutane (SA) in the approximate ratio 2:2:1. Since SC and SA are stable to the reaction conditions, rearrangement is a kinetically controlled process; however, 2-acetoxy-2,3-dimethylbutane (TA) is rapidly converted to TC so that either TA or TC (or both) may be primary product(s). Although the rate of reaction varies significantly with chloride salt concentration (0-1.5 M (CH3-)4 NCl), water concentration (0-2.5 M), and temperature (25-125°), there is little accompanying change in the product composition. The hydrochlorination of styrene in acetic acid yields α-methylbenzyl chloride (C) and α-methylbenzyl acetate (A) in the approximate ratio 13:1 under conditions of kinetic control. The reaction is first order in [HCl] at low acid concentration <0.1 M) and linear in effective acidity at high acid concentration. The ratio C/A varies little with [HCl] (0.006-0.5 M), with [(CH3)4NCl] (0-0.3 M), or with temperature (16.5-50°). From studies of the reactions in DCl-DOAc, kinetic isotope effects kH/kD = 1.2 and 1.4 were determined for addition to T-butyl ethylene and styrene, respectively. The results are discussed in terms of rate-limiting protonation of olefin by HCl to form a carbonium-chloride ion pair; collapse or rearrangement of the ion pair occurs at rates faster than or comparable to that of a diffusion-controlled process. © 1969, American Chemical Society. All rights reserved.