Effects of non-ionic and mixed cationic-non-ionic micelles on the rate of alkaline hydrolysis of phthalimide

Pseudo-first-order rate constants (k(obs)) for the alkaline hydrolysis of phthalimide (PTH) show a monotonic decrease with the increase in [C16E20](T) (total concentration of Brij 58) at constant [CH3CN] and [NaOH]. This micellar effect is explained in terms of the pseudophase model of micelles. The rate of hydrolysis of PTH in C16E20 micellar pseudophase appears to be negligible compared with that in the aqueous pseudophase. The values of k(obs) for C12E23 (Brij 35) show a sharp decrease at very low values of [C12E23](T) followed by a very slow decrease with increase in [C12E23](T) at relatively higher values of the latter. The rate of hydrolysis becomes too slow to monitor at [C12E23]T greater than or equal to0.04 m in the absence of cetyltrimethylammonium bromide (CTABr) and at [C12E23](T) greater than or equal to0.05 M in the presence of 0.006-0.02 M CTABr at 0.02 m NaOH whereas such characteristic behavior is kinetically absent with C16E20. The values of k(obs), obtained at different [NIS](T) (where NIS represents C16E20 and C12E23) in the presence of a constant amount of CTABr, follow the empirical relationship k(obs) = (k(0) + kK[NIS](T))/(1 + K[NIS](T)) where k and K are empirical parameters. The values of k are only slightly affected whereas the values of K decrease with increase in [CTABr]T for the mixed C16E20-CTABr micellar system. The rate of hydrolysis of PTH at greater than or equal to0.01 M C12E23 and greater than or equal to0.01 M CTABr reveals the formation of phthalic anhydride whereas this was not observed in the mixed C16E20-CTABr micellar system under similar experimental conditions. Copyright (C) 2002 John Wiley Sons, Ltd.