Micellar effect on the kinetics of oxidation of malic acid by N-bromophthalimide

The effect of cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium lauryl sulphate (SDS) on the oxidation of malic acid (MA) by N-bromophthalimide (NBP) has been studied at 40 degrees C. The reaction exhibits first order dependence on [NBP], fractional and inverse fractional order dependence on [malic acid] and [HClO4], respectively. The effect of sodium perchlorate (NaClO4), phthalimide and mercuric acetate has also been done. The rate of reaction increased with an increase in dielectric constant of the medium. CTAB strongly catalyzes the reaction and typical k(obs), and [CTAB] profile was observed, i.e., with a progressive increase in [CTAB], the reaction rate increased, at higher concentration constancy in k(obs), was observed, where as SDS slightly retards the reaction. The results are treated quantitatively in terms of Menger and Portnoy and Piszkiewicz models. The various activation parameters in presence of CTAB and SDS have been also evaluated. A suitable mechanism consistent with the experimental finding has been proposed. The rate constants k(obs), cooperativity index (n), binding constants (K-s) with surfactants has been evaluated. (c) 2007 Elsevier B.V. All rights reserved.