Langmuir, Vol.13, No.15, 3959-3964, 1997
Effects of Cationic Micelles on Rate of Intramolecular General Base-Catalyzed Aminolysis of Ionized Phenyl Salicylate
Effects of cetyltrimethylammonium bromide (CTABr) micelles on second-order rate constants (K-n(obs)) for the nucleophilic reactions of amines (n-butylamine, piperidine, and pyrrolidine) with ionized phenyl salicylate (PS-) reveal a decrease of nearly 4-fold for n-butylamine, 13-fold for piperidine,and 17-fold for pyrrolidine with an increase in [CTABr](T) from 0.0 to 0.01 M at 35 degrees C. These results show that the binding constants (K-N) of amines with CTABr micelles vary in the order K-N for n-butylamine > K-N for piperidine > K-N for pyrrolidine. The observed data are explained in terms of the pseudophase model of the micelle. The values of K-N for n-butylamine, piperidine, and pyrrolidine turn out to be so small that they could not be determined kinetically. The significantly lower rate of aminolysis in the micellar pseudophase compared to that in the aqueous pseudophase is attributed to both micellar medium effect and different locations of amine and PS- in the micellar pseudophase.