An Empirical Kinetic Approach To Study The Occurrence Of Ion-Exchange At The Aqueous Cationic Micellar Surface: Alkaline Hydrolysis Of N-Benzylphthalimide

Abstract

Pseudo‐first‐order rate constants, kobs, for alkaline hydrolysis of N‐benzylphthalimide (1), obtained at constant [CH3CN], [CTABr]T (total concentration of cetyltrimethylammonium bromide), and varying concentrations of inert salt MX (MX = sodium bromide) follow the relationship: kobs = (k0+FX/S kobsMX KX/S [MX])/(1+KX/S [MX]), where FX/S and KX/S are empirical constants, kobsMX = kobs at a typical value of [MX] in the absence of micelle and S− = HO−. The values of KX/S decrease with the increase in [CTABr]T. The values of FX/S and KX/S are explained in terms of a pseudophase micellar (PM) model coupled with an empirical relationship: KS = KS0/(1+KX/S [MX]), where KS is the CTABr micellar binding constant of HO−, in the presence of MX and KS0 = KS at [MX] = 0. The magnitude of empirical constant (KX/S) is the measure of the ability of an ion, X−, to expel another reactive co‐ion or counterion (HO−) from the cationic micellar pseudophase to the aqueous phase.