An Empirical Kinetic Approach for the Determination of the Ion Exchange Constants for Counterions of Cationic Micelles: The Rate of pH-Independent Hydrolysis of Phthalimide as the Kinetic Probe: Effects of (CH3)4N+ on (X=Br− and Y=Cl−)

Abstract

Pseudo-first-order rate constants (k obs ) for pH-independent hydrolysis of phthalimide (1), obtained at constant total concentration of cetyltrimethylammonium bromide (CTABr]T), 2.0 × 10−4 M 1, 0.02 M KOH and varying concentration of inert salt MX (=(CH3)4NCl and (CH3)4NBr), follow a kinetic equation derived in terms of pseudophase micellar (PM) model coupled with an empirical equation. This derived equation gives empirical constants. F X/S and K X/S where S represents anionic 1. The magnitude of F X/S is the measure of the fraction of micellized anionic 1 transferred to the aqueous phase by the limiting concentration of X − and the magnitude of K X/S is the measure of the ability of the ion X −, to expel another counterion ion S − from the cationic micellar surface to the aqueous phase through ion exchange process X −/S −. The values of the empirical constants, F X/S and K X/S , are used to determine the usual ion exchange constant . The values of F X/S are ∼1 for MBr and in the range 0.97–0.78 for MCl within [CTABr]T range 0.006 −≤0.016 M. The mean value of is 2.4 ± 0.1 and it is comparable with those obtained by other kinetic probes (with M+ = Na+) as well as physicochemical techniques.