Kinetics of oxidation of pyridoxine by anodically generated manganese(III) in aqueous acetic acid medium

Abstract

Manganese(III) acetate was prepared by the electrolytic oxidation of Mn(OAc)2 in aqueous AcOH. The electro-generated manganese(III) species was characterised by spectroscopic and redox potential studies. The kinetics of oxidation of pyridoxine (PRX) by manganese(III) in aqueous AcOH were investigated and is first order with respect to [MnIII]. The effects of varying [MnIII], [PRX], added manganese(II), pH and added anions such as AcO−, F−, Cl− and ClOinf4sup−and SOinf4sup2−were studied. The rate decreased slowly with increasing [H+] up to 0.2 mol dm−3 and increased steeply thereafter. The orders in [PRX] and [MnII] were unity and inverse fractional, respectively, in both low and high [H+] ranges. The dependence of reaction rate on temperature was studied and activation parameters were computed from Arrhenius and Eyring plots. A mechanism consistent with the observed results is proposed and discussed.