Effects of cationic micelles on the rate of intramolecular general base-catalyzed reaction of ionized phenyl salicylate (PS−) with Tris(hydroxymethyl)aminomethane (Tris)

Pseudo-first-order rate constants (kobs) obtained for the aminolysis of ionized phenyl salicylate (PS−) at a constant [NaOH] and [Surf] (where Surf=CTABr or CTACl with CTABr and CTACl representing cetyltrimethylammonium bromide and cetyltrimethylammonium chloride, respectively) and 35°C show a linear increase with increase in the total amine concentration. Nucleophilic second-order rate constants (knobs) for the reactions of Tris with PS− reveal a decrease of nearly ten- to 11-fold with the increase in [Surf] from 0.0 to 0.01 M. These observed data are explained in terms of the pseudophase model of the micelle. The CTABr and CTACl micellar binding constants (KN) of Tris appear to be so small that it could not be determined kinetically. The characteristic effect of CTABr micelles on knobs is similar to that of CTACl micelles. Significantly lower rate of aminolysis of PS− in the micellar pseudophase than that in aqueous pseudophase is partly or fully attributed to the different locations of PS− and Tris molecules in the micellar pseudophase.