Self-Catalytic Aminolysis of Aerosol-OT in Reverse Micelles by Diamines

Abstract

Self-catalytic aminolysis of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) induced by ethylenediamine (EDA) and by propylenediamine (PDA) solubilized in reverse AOT micelles in isooctane has been investigated. When decomposition of ester groups in AOT due to aminolysis reaches about 5-7%, the micellar solution suddenly becomes turbid. Reaction rates of the AOT aminolysis were studied in micellar and in nonmicellar solutions. This aminolysis process is analyzed in terms of a mechanism in which each ester group in AOT reacts with one of two amino groups in an EDA or PDA molecule by synergistic action with the other amino group. The rate constant for the aminolysis of AOT in micelles is about 360 times larger than in nonmicellar solution. This large difference in the rate constants appears to be based on the micelle effect for aminolysis. From the temperature dependency of the rate constants, the activation energy for aminolysis was determined to be 33.5 kJ mol -1 for the micellar system and 35.2 kJ mol -1 for the nonmicellar system. This slight difference indicates that essentially the same aminolysis mechanism applies in both systems. The magnitude of this micellar effect is explained by the idea that favorable proximity of a diamine molecule to ester groups of AOT in micelles accelerates the reaction rate of aminolysis. Such an effect is called "self-catalytic" because the aminolysis of AOT is promoted by AOT micellization.