EFFECTS OF CATIONIC MICELLES ON RATES AND ACTIVATION PARAMETERS OF INTRAMOLECULAR GENERAL BASE-CATALYZED HYDROLYSIS OF IONIZED SALICYLATE ESTERS

摘要

The effects of micelles of cetyltrimethylammonium bromide (CTABr) on the hydrolysis of ionized phenyl salicylate (PS-) and methyl salicylate (MS(-)) have been studied at 37 degrees C. An increase in the total concentration of CTABr from 0.0 to 0.12 M results in a decrease in the first-order rate constants (k(obs)) by a factor of nearly 8 for PS- and 6 for MS(-). These micellar inhibitions of hydrolysis of PS- and MS(-) were explained in terms of the pseudophase model of the micelles. Kinetically calculated micellar binding constants (K-s) are 6340 and 1700 M(-1) for PS and MS, respectively, The temperature effects on k(obs) indicate that the ratios k(obs) (in H2O)/k(obs) (in 0.03 M CTABr) remain essentially unchanged with the change in temperature from 37-60 degrees C. The presence of 0.03 M CTABr, where both PS- and MS(-) molecules are fully micellar bound, reveals the increase in both Delta H* and Delta S*. (C) 1996 Academic Press, Inc. [References: 44]