Compartmentalization of reactants in supercritical fluid micelles

Abstract

The hydrolysis of acetylsalicylic acid, a model reaction, in sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/supercritical ethane reverse micelles has been studied in the presence of imidazole catalyst using in situ UV-vis spectroscopy. An increase of rate constant by 55 times was observed in AOT/supercritical ethane micellar medium compared to the reaction carried out in aqueous buffer. The reaction had a strong dependence on the water content of micelles, which decelerated to a large extent when the water content of the micelles was increased. The acceleration of the reaction in micelles compared to aqueous buffer and the water content dependence of the reaction rate have been confirmed to be due to compartmentalization of the water-soluble reactant and catalyst in the aqueous core of the micelles. The local concentration of substrate and catalyst increases when they are enclosed in the aqueous core of the micelles, resulting in an increase in the rate constant and shortening of the reaction time, rather than the existence of a diluted solution in the aqueous buffer. No pressure dependence of the reaction has been found in the pressure range of 27 to 44 MPa at 310 K.