Anodically generated manganese(III) sulphate for the oxidation of dipeptides in aqueous sulphuric acid medium: A kinetic study

The kinetic of oxidation of dipeptides (DP) namely valyl–glycine (Val–Gly), alanyl–glycine (Ala–Gly) and glycyl–glycine (Gly–Gly), by Mn(III) have been studied in the presence of sulphate ions in acid medium at 26C. The reaction was followed spectrophotometrically at lmax = 500 nm. A firstorder dependence of the rate on both [Mn(III)]o and [DP]o was observed. The rate is independent of the concentration of reduction product, Mn(II) and hydrogen ions. The effects of varying the dielectric constant of the medium and addition of anions such as sulphate, chloride and perchlorate were studied. The activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of DP with Mn(III) in the ratelimiting step is suggested. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of these dimers, where increased hyphobicity results in increased rate of oxidation.