Orientation on Electron-Transfer Nature for Oxidation of Some Water-Soluble Carbohydrates: Kinetics and Mechanism of Hexacholroiridate (IV) Oxidation of Methyl Cellulose in Aqueous Perchlorate Solutions

Abstract

The kinetics and mechanism of oxidation of methyl cellulose (MC) polysaccharide by hexacholroiridate (IV) in aqueous perchlorate solutions at a constant ionic strength of 0.1 mole dm-3 has been investigated, spectrophotometrically. The experimental results showed first-order dependence in [IrCl6]2- and fractional first-order kinetics with respect to the MC concentration. The reaction rate was found to increase with decreasing the [H+]. A kinetic evidence for formation of 1:1 intermediate complex was revealed. The reaction kinetics seems to be of considerable complexity where one chloride ion from hexacholoiridate (IV) oxidant may act as a bridging ligand between the oxidant and the substrate within the formed intermediate complex. However the added chloride ions and oxidation products were found to have negligible effects on the reaction rate, the added acrylonitrile indicated the intervention of free-radical mechanism during the oxidation process. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is discussed