Effects of [C 6H 5COONa] on rates of intramolecular general base-catalyzed piperidinolysis and n-butylaminolysis of ionized phenyl salicylate in the presence of cationic micelles

Abstract

Pseudo-first-order rate constants ( k obs), obtained for the cleavage of ionized phenyl salicylate (PS −) at constant [NaOH]; [C 6H 5COONa]; [MeCN]; [CTABr] T (total concentration of cetyltrimethylammonium bromide) and varying concentrations of n-butylamine and piperidine ([Am] T), follow the relationship: k obs= k 0+ k n obs[Am] T. The values of k 0 and k n obs at different [CTABr] T and [C 6H 5COONa] are explained in terms of pseudophase model of micelle coupled with an empirical relationship: K S= K S 0/(1+ ψ[C 6H 5COONa]) where K S is the CTABr micellar binding constant of PS −. The calculated respective values of k ns M K N (where K N is the micellar binding constant of amine and k ns M= k n M/ V M with k n M and V M representing nucleophilic second-order rate constant for the reaction of amine with PS − in the micellar pseudophase and micellar molar volume, respectively) and ψ are (12.2±0.6)×10 −3 M −1 s −1 and 127±10 M −1 for n-butylamine and (14.8±1.7)×10 −3 M −1 s −1 and 124±5 M −1 for piperidine. The values of K N for both amines turn out to be so small that they could not be determined kinetically. The values of k 0 for n-butylamine are relatively more reliable and these k 0 values yield k h M (pseudo-first-order rate constant for hydrolysis of PS − in the micellar pseudophase) and ψ as (7.0±1.9)×10 −5 s −1 and 104±21 M −1, respectively.