Linear free energy relation in MnII catalyzed oxidation of some α-amino acids by CeIV -: Kinetics and mechanism

Oxidation of alpha-amino acids (phenylalanine, glycine, alanine, valine, nor-leucine and iso-leucine) by Ce-IV is catalyzed by Mn-II in sulfuric acid-water medium and gave aldehyde. All these reactions are first order with respect to amino acid, oxidant, catalyst and inverse. second order with respect to H+. Rate increases with increase in [HSO4-] at constant [H+] but decreases with [H+] at constant [HSO4-]. Active species in this oxidation suggested is [Ce(SO4)](2+). Mn-II is first oxidized to Mn-III, which act as oxidant for the substrate. Thermodynamic parameters for rate determining step have been evaluated. Formation of cyclic intermediate and free radical mechanism involving C-C fission have been suggested. Linear Free Energy Relationship is satisfied. Reaction constant p = +1.313, suggesting involvement of formation of electron-deficient species in the reaction. The reactivity decreased as carbon chain length increased and the observed order is phenylalanine > glycine > alanine > valine > nor-leucine > iso-leucine.