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

摘要

Pseudo first-order rate constants (k(obs)) for the alkaline hydrolysis of N-hydroxyphthalimide (1) remain independent of the total concentration of CnE20, with n=16,18 ([CnE20](T)) at <= 0.17 M C16E20 and 0.10 M C18E20. The values of k.bl, obtained at different [CnE20](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)+theta K [CnE20](T))/(1 + K [CnE20](T)), where theta and K are empirical constants. The values of theta are not affected whereas the values of K decrease nonlinearly with increase in [CTABr](T) at >= 0.003 M CTABr in a mixed CnE20-CTABr micellar system where n = 16,18. The effects of [CTABr](T) on K and theta are explained in terms of the pseudophase model of micelles coupled with the empirical relationship: K-S = K-S(0)/(1 + K-CnE20/S [CnE20](T)) with n = 16,18, where K-S and K-S(0) represent respective mixed CnE20-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 CnE20 surfactant to change the micellar affinity of S- from pure CTABr micelles to pure CnE20 micelles.