Effects of pure non-ionic and mixed non-ionic-cationic surfactants on the rates of hydrolysis of phenyl salicylate and phenyl benzoate in alkaline medium

The pseudo-first-order rate constants (k(obs)) for the alkaline hydrolysis of phenyl benzoate (PB) decrease monotonically from 72.0 x 10(-4) to 7.4 x 10(-4) s(-1) with increase in the concentration of polyoxyethylene 23 lauryl ether ([C12E23](T)) from 0.0 to 0.01 M at 0.01 M NaOH and 35 degreesC. The results fit satisfactorily to a pseudophase model of micelles. The values of k(obs) for the hydrolysis of ionized phenyl salicylate (PS-) are almost independent of [IC12E23](T) within the range 0.0-0.02 M at 0.01 and 0.03 M NaOH and 35 degreesC. The rate of alkaline hydrolysis of PB appears to be negligible in the micellar pseudophase than in the aqueous pseudophase, which is ascribed to the extremely low concentration of HO- in the micellar region of micellized PB molecules. The values of k(obs) for hydrolysis of PB and PS- at 0.01 M NaOH become almost zero at greater than or equal to0.02 and greater than or equal to0.03 m C12E23, respectively. The effects of mixed C12E23-CTABr on k(obs) for the alkaline hydrolysis of PB reveal that mixed micelles behave like pure CTABr micelles within the [C12E23](T) range 0.0-5 x 10(-4) M whereas an increase in [C12E23](T) from greater than or equal to7 x 10(-4) to 0.02 M decreases k(obs) at 0.006, 0.01, 0.02 and 0.03 M CTABr. However, the values of k(obs) are significantly higher at [CTABr](T) = 0.006, 0.01, 0.02 and 0.03 M than at [CTABr](T) = 0 in the presence of [C12E23](T) in the range >5 x 10(-4) 0.02 M. An increase in [C12E23](T) from 0.0 to 0.015 M causes nearly a twofold increase in k(obs) at 0.01, 0.02 and 0.03 M CTABr and 0.01 M NaOH. Copyright (C) 2001 John Wiley & Sons, Ltd.