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 (k(obs)) obtained for the aminolysis of i onized phenyl salicylate (PS-) at a constant [NaOH] and [Surf] (where Surf = CTABr or CTACl with CTABr and CTACl representing cetyltrimethylammonium b romide and cetyltrimethylammonium chloride, respectively) and 35 degrees C show a linear increase with increase in the total amine concentration. Nucl eophilic 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 con stants (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 si milar 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. (C) 2000 Elsevier Science B.V. All rights reserv ed.