Effect of Premicellar Complexes and Micellar Headgroup Size upon the Basic Hydrolysis of 2-(4-Chlorophenoxy)quinoxaline

摘要

Rates of the basic hydrolysis of 2-(4-chlorophenoxy)quinoxaline 1 were measured in aqueous cetyltrislkylsmmonium vhlotifrd, C_16H_33NR_3Cl, R=Me(CTACl), Et(CTEACl), n-Pr (CTPACl), n-Bu (CTBACl). The shape of the rate versus surfactant concentration profiles depends on substrate concentration. At low substrate concentration, first-order rate constants go through maxima with increasing surfactant concentration, but at higher concentration, double-rate maxima are observed. The presence of single- or double-rate maxima is ascribed to reaction in micelles or in premicellar complexes. At low substrate concentration, micellar effects were analyzed by means of a mass-action model. Second-order rate constants, k_M, for reactions in the micellar pseudophase increase with headgroup size.