Kinetics of the reaction between thioglycolic acid and parabenzoquinone-Micellar effect of cetyltrimethyl ammonium bromide

Parabenzoquinone (PBQ) undergoes 1-4 addition reaction with thioglycolic ac id (TGA) forming parabenzoquinone monothioglycolic acid when the quinone is present in excess. To understand the mechanism of the reaction a detailed kinetic study of the reaction has been undertaken. The reaction obeys first order kinetics with respect to PBQ and TGA, but is inhibited by H+ ion. A plot of the reciprocal of the pseudo-first order rate constant vs [H+] is l inear with a positive slope and intercept. The reaction is markedly acceler ated by the positively charged cetyl trimethyl ammoniumbromide micelles. Th e rate-[surfactant] profile shows a limiting behaviour indicative of unimol ecular rate-determining reaction in the micellar pseudo-phase.