Oxidation of gum arabic by soluble colloidal MnO 2

Abstract

In the present work, the oxidative degradation of gum arabic by colloidal manganese dioxide (MnO 2) was carried out. Monitoring the disappearance of the MnO 2 spectrophotometrically at 375 nm was used to follow the kinetics. The oxidation obeyed fractional-order kinetics with respect to the [gum arabic]. Effect of various experimental parameters such as the initial colloidal [MnO 2], [HClO 4], temperature, and complexing agents (P 2O 7 4−, F −, and Mn 2+) for the oxidation of gum arabic was studied. The reaction was acid catalyzed. Addition of P 2O 7 4−, F −, and Mn 2+ ions enhances the rate of oxidation significantly. Gum arabic adsorbs onto the surface of the colloidal MnO 2 through the equatorial –OH groups of the rhamnose moiety, and the complex breaks down into products. The Arrhenius equation was valid for the oxidation kinetics between 40 and 60 °C. To explain the observed kinetic results, a suitable mechanism and rate law for the reaction taking place at the surface of the colloidal particle has been proposed. The reducing nature of gum arabic is found be due to the presence of –OH group in the skeleton.