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

Abstract

Pseudo-first-order rate constants ( k obs) 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 ( k n obs) 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 ( K N) of Tris appear to be so small that it could not be determined kinetically. The characteristic effect of CTABr micelles on k n obs 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.