Oxidation of L-amino acids by metal ion (Mn3+) in sulfuric acid medium: Effect of nucleophilicity and hydrophobicity on reaction rate

• Published in: International journal of chemical kinetics 2011-11, Vol.43 (11), p.599-607
• Main Authors: Kumara, M. N., Mantelingu, K., Bhadregowda, D. G., Rangappa, K. S.
• Format: Article
• Language: English
• ISSN: 0538-8066; 1097-4601
• DOI: 10.1002/kin.20572

The kinetics of oxidation of L‐amino acids (AAs) glycine(1a), alanine(1b), valine(1c), isoleucine(1d), leucine(1e), proline(1f), and phenylalanine(1g) by a transition metal ion (Mn3+) was studied in the presence of sulfuric acid medium at 26°C by a spectrophotometrical (λmax = 500 nm) method. In all cases, the kinetics of reactions was of first‐order with respect to each [AA] and [Mn3+]. Increased [H+], [Mn2+] (the reduction product of Mn3+), sulfate, and chloride had no effect on the reaction rate. However, the reaction rate increased with increased dielectric constant of the medium. Oxidation rate increased for 1a–gand an apparent correlation was observed between the rate of oxidation and nucleophilicty of AAs except for 1a and 1g. The reaction rate also linearly depended on the hydrophobicity of AAs except for 1f and 1g. The thermodynamic parameters for AA‐metal ion complex formation and activation parameters for the rate‐limiting steps have been evaluated. Analysis of the oxidation products indicated that the AAs underwent oxidative deamination and decarboxylation to form corresponding aldehydes. Based on these data, plausible mechanisms involved in the oxidation of AAs are proposed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 599–607, 2011