Rate and product analytical study of the solvolysis of 3-chlorobenzyl arenesulfonates in aqueous 2,2,2-trifluoroethanol

Abstract

The rates of solvolysis of 3-chlorobenzyl 4-methyl-, 4-methoxy-, and 4-bromo-benzenesulfonates at different temperatures in 1 : 1 (v/v) 2,2,2-trifluoroethanol–water have been measured and the activation parameters determined. Qualitatively, the rate constants show the expected dependence upon the substituent in the benzenesulfonate leaving group, and the toluenesulfonate is 42 times less reactive (at 25 °C) than benzyl toluenesulfonate itself. In the product analytical study, the ratio of the 3-chlorobenzyl alcohol to the 3-chlorobenzyl trifluoroethyl ether was determined in each of the three cases, and shown to be independent of the nature of the nucleofuge. Introduction of the 3-chloro substituent into the electrophile, however, causes the selectivity for water as opposed to trifluoroethanol to be increased by ca. 50%. The results are discussed in terms of a substitution reaction which is concerted but not synchronous, a solvent-induced, largely uncoupled SN2 mechanism.