Kinetics of the Exchange of Chlorine Atoms between Hydrogen Chloride and Benzyl Chlorides. Solvent Effects1,2

Abstract

The rate of exchange of chlorine atoms between hydrogen chloride and p- nitrobenzyl chloride (PNBC) in 82% dioxane-- 18% water by weight solution is represented by the rate law: Re = 2.59 x 10/sup 6/ STAPNBC!e/sup -20,900/RT/ + 1.60 x 10/sup 9 alpha STAHC1! STAPNBC!e/sup -19,900 /RT/ where alpha is the degree of dissociation of the hydrogen chloride and R, is the rate of exchange in mole liter/sup -1/ sec/sup -1/. The reaction mechanlsm is believed to be an example of concurrent S/sub N/1 and S/sub N/2 processes in which the chloride ion rather than the hydrogen chloride ion-pair is the effective nucleophilic reagent. Ordinary fluorescent light has no detectable effect on the rate of exchange, and the overall rate of exchange is decreased by added lithium perchlorate. Analytical expressions were developed which allow for the hydrolysis of the organic halide during the exchange. No exchange was detected between hydrogen chloride and p-nitrobenzyl chloride in anhydrous benzene after 363 hours at 60.00 deg . Similarly, no exchange was observed with benzyl chloride in benzene and acetone. The exchange with benzyl chloride proceeds at a faster rate in ethanol than in dioxane. In dioxane, p-nitrobenzyl chloride exchanges at a faster ratemore » than benzyl chloride. (auth)« less