Micellar Effects on the Chromium(VI) Oxidation of d (+)-Xylose

Abstract

Chromic acid oxidation of d (+)-xylose in water and in presence of surfactants has an induction period followed by autoacceleration. The kinetics and mechanism of the induction period have been studied spectrophotometrically in both media. Due to precipitate formation, the effect of cetyltrimethylammonium bromide (CTAB, cationic) cannot be studied whereas the oxidation rate increased with increase in sodium dodecyl sulphate (SDS, an-ionic) and octylphenoxypolyethoxy ethanol (TX-100, nonionic) concentration. Reaction is routed through the same mechanism as shown by the kinetic study in the absence and presence of surfactants. Micellar catalysis has been traced to partitioning of the chromic acid species and xylose between the aqueous and micellar pseudo-phases. Rate enhancement in SDS micelles is decreased by ammonium, lithium and sodium ions. Micellar binding/association constants and activation parameters were evaluated and discussed. A mechanism consistent with the results is proposed.