Micellar Enhanced Base Catalyzed Hydrolysis of Ethyl Acetate Using TTAB

Abstract

Surfactants can increase the low rate of heterogeneous liquid-liquid reactions involving partially miscible substrates through formation of micelles. This is a direct consequence of higher solubilization of substrates by micelles in reaction zones. In this case, rate enhancement of NaOH (base) catalyzed hydrolysis of ethyl acetate was studied. Micelles by cationic surfactant tetradecyl trimethyl ammonium bromide (TTAB) made the rate enhancement. In the presence of NaOH, CMC (critical micellar concentration) of TTAB decreases from its original value and attains the value of 2.97 × 10-4 M. In the absence of TTAB, the second order rate constant increases linearly with temperature. The hydrolysis reaction follows second order kinetics at different temperatures in the presence of different concentrations of TTAB. For a particular temperature, on addition of TTAB beyond CMC, rate constant first increases sharply and then becomes almost constant. At TTAB concentration of 1.485 × 10-3 M, rate constant attains maximum value (2.65 times of rate constant without TTAB) and then it becomes almost constant. The applied model successfully explains change in rate constant due to incorporation of micelles by the addition of TTAB. This model involves certain assumptions like one substrate molecule is solubilized in one micelle; substrate molecule doesn't form a complex with monomer of surfactant; and no competitive inhibition occurs during reaction. Correlations between bulk phase rate constant (k0), micellar phase rate constant (km) and temperature (T) are incorporated into the model for this particular system.