Kinetics and Mechanism of the Reduction of DI-u-oxo-tetrakis(1,10-Phenanthroline)Dimanganese(III,IV) Perchlorate by Ascorbic Acid in Acid Medium

Abstract

The kinetics of the reduction of di-µ-oxo-tetrakis(1,10-phenanthroline) dimanganese (III,IV) perchlorate, (MnIIIO2MnIV) by ascorbic acid (H2A) in acid medium has been investigated. The reaction was found to exhibit second order kinetics, with first order each in [MnIIIO2MnIV] and [H2A]. The reaction had an inverse dependence in hydrogen ion concentration, and so the general rate law is suggested as follows: 3 d[MmmO2Mmw] = a{a+b[H]1} [MmmO2Mmw][H2A] 2 dt

where a = 1.50 x 10-4s-1 and b = 7.94 x 10-4 dm3mol-1s-1 respectively. The rate was found to increase with increase in ionic strength of the reaction medium. The presence of CH3COO-, NO3- and K+ is independent of the rate constant while the reaction has no effect on the polymerization of acrylamide. A mechanism which is consistent with the proton coupled electron transfer, has been proposed herein.