Kinetic study on the effects of mixed nonionic–cationic micelles on the rate of alkaline hydrolysis of N-hydroxyphthalimide

Abstract

Pseudo first-order rate constants ( k obs) for the alkaline hydrolysis of N-hydroxyphthalimide ( 1) remain independent of the total concentration of C nE 20, with n = 16,18 ([C nE 20] T) at ≤ 0.17 M C 16E 20 and 0.10 M C 18E 20. The values of k obs, obtained at different [C nE 20] T (with n = 16,18) in the presence of a constant post CMC value of [CTABr] T, follow the empirical relationship: k obs = ( k 0 + θ K [C nE 20] T)/(1 + K [C nE 20] T), where θ and K are empirical constants. The values of θ are not affected whereas the values of K decrease nonlinearly with increase in [CTABr] T at ≥ 0.003 M CTABr in a mixed C nE 20–CTABr micellar system where n = 16,18. The effects of [CTABr] T on K and θ are explained in terms of the pseudophase model of micelles coupled with the empirical relationship: K S = K S 0/(1 + K CnE20/S [C nE 20] T) with n = 16,18, where K S and K S 0 represent respective mixed C nE 20–CTABr and pure CTABr micellar binding constant of anionic 1 (S −) and K CnE20/S is an empirical constant whose magnitude is the measure of the ability of the C nE 20 surfactant to change the micellar affinity of S − from pure CTABr micelles to pure C nE 20 micelles.