Effects of non-ionic and mixed non-ionic-cationic micelles on the rate of aqueous cleavages of phenyl benzoate and phenyl salicylate in alkaline medium

Pseudo-first-order rate constants (k(obs)) for the hydrolysis of phenyl salicylate (PSH) and phenyl benzoate (PB) in the alkaline medium 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. These results show a characteristic difference between the effects Of [C16E20](T) and previously published effects of [C12E23](T) (total concentration of Brij 35) on the rates of aqueous cleavage of PSH and PB at [CnEm](T)/[NaOH] greater than or equal to similar to3. The values of k(obs), obtained at different [C16E20](T) in the presence of a constant amount of CTABr, follow the empirical relationship k(obs) = (k(0) + thetaK[C16E20](T))/(1 + K[C16E20](T)), where theta and K are empirical parameters. The values of 0 are not affected whereas the values of K decrease with increase in [CTABr](T) in a mixed C16E20-CTABr micellar system. The values of theta at different [CTABr](T) show that theta > k(0) for hydrolysis of PSH and theta < k(0) for hydrolysis of PB in the presence of 0.01 M NaOH. The effects of [CTABr]T on K and 0 are explained in terms of the pseudophase model of micelles coupled with the empirical relationship K-S = K(S)0/(1 +K-Cl6E20[C16E20](T)). Copyright (C) 2004 John Wiley Sons, Ltd.