Synthesis and kinetics of oxidation of some dipeptides with anodically generated manganese(III) sulphate: Mechanistic study

Dipeptides (DP) namely phenylalanyl–proline (Phe–Pro), isoleucyl–proline (Ile–Pro), and leucyl–proline (Leu–Pro) were synthesized by classical solution method and characterized. The kinetics of oxidation of these DP by Mn(III) have been studied in the presence of sulphate ions in acidic medium at 26°C. The reaction was followed spectrophotometrically at λ_max = 500 nm. A first‐order dependence of rate on both Mn(III)]₀ and DP]₀ was observed. The rate is independent of the concentration of reduction product, Mn(II), and hydrogen ions. The effects of varying 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 rate‐limiting step is suggested. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 438–444, 2002