Microheterogeneous Solvation for Aminolysis Reactions in AOT-Based Water-in-Oil Microemulsions

摘要

A kinetic study was carried out on the aminolysis of p-nitrophenyl acetate(NPA)by n-decylamine(DEC),piperazine(PIP)and sarcosine(SAR)in AOT/isooctane/water(w/o)microemulsions.By using the pseudo-phase model both the rate constants at the interface,k_2~1,and the water micro-droplet,k_2~w,can be obtained.The obtained results show that k_2~1 increases together with the water content of the microemulsion,whereas k_2~w increases as the water content of the system decreases.In the aqueous microdroplet the predominant interaction Na~+...OH_2 causes a decrease in the strength of the hydrogen bonds and therefore facilitates the desolvation of the reagents as W decreases.This desolvation of the reagents causes the increase of k_2~w as W decreases.In the interface of the microemulsion the predominant interaction SO_3~-...HOH causes an increase in the electronic density on the water molecules and the consequent decrease in their efficiency in the solvation of the partial negative charge,which develops on the carbonyl oxygen atom in the transition state of the reaction.This decrease in the solvation causes k to decrease together with the water content of the system.