Hg (II ) Catalysed Oxidation of D - Arabinose and D - Mannose by Acidic Solution of Potassium Permanganate: Kinetics and Mechanism

Abstract

The kinetics of Hg (II) catalyzed oxidation of D-Arabinose (Ara) and D-Mannose (Man) by potassium permanganate in acidic medium have been studied spectrophotometrically in the temperature range 30-50C. The reactions exhibit first order kinetics with respect to [Man] and [MnO4 ] while second order with [Ara]. The reaction rates were found to be unaffected by the change in [H]. It has been observed that Hg (II) catalyzed the reaction but as the [Hg(II)] increases, reaction rate becomes independent. Negligible effect of ionic strength (μ) on the rate of oxidation has also been noted which supports the presence of at least one neutral specie in the rate determining step. The rate of oxidation was influenced by the change in temperature. Various activation parameters have been calculated. Formic acid and erythronic acid were identified as main oxidation product in case of arabinose while for mannose formic acid and arabinonic acid were identified. A mechanism consistent with the above findings has also been proposed.