Kinetics of permanganate oxidation of synthetic macromolecule poly(vinyl alcohol)

Abstract

Oxidation of poly(vinyl alcohol) (PVA) by permanganate has been studied spectrophotometrically at 525 and 420nm. Under pseudo-first order conditions ([PVA] >> [MnO₄⁻]), the reaction rate increases with [PVA] and the kinetics reveals complex order dependence on [PVA]. The second-order kinetics with respect to [H₂SO₄] at low concentration shifts to first-order at higher concentration. Water soluble colloidal MnO₂ has been identified as an intermediate in the reduction of MnO4- by PVA. The hydrogen ions decrease the stability of colloidal MnO₂. Poly(vinyl ketone) is found to be the final oxidation product of PVA. Inorganic electrolytes like NaF, Na₄P₂O₇ and MnCl₂ (a product of the reaction), have inhibitory and composite effects (inhibition and catalysis) on the reaction rate. Arrhenius and Eyring equations have been used to evaluate the activation parameters. The observed results are discussed in terms of Michaelis-Menten kinetic model. A mechanism has been proposed on the basis of experimental findings.