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Oxidation of L ‐amino acids by metal ion (Mn 3+ ) in sulfuric acid medium: Effect of nucleophilicity and hydrophobicity on reaction rate
Author(s) -
Kumara M. N.,
Mantelingu K.,
Bhadregowda D. G.,
Rangappa K. S.
Publication year - 2011
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20572
Subject(s) - chemistry , decarboxylation , sulfuric acid , reaction rate constant , nucleophile , inorganic chemistry , kinetics , reaction rate , rate determining step , metal , alanine , phenylalanine , amino acid , leucine , valine , medicinal chemistry , organic chemistry , catalysis , biochemistry , physics , quantum mechanics
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 (Mn 3+ ) was studied in the presence of sulfuric acid medium at 26°C by a spectrophotometrical (λ max = 500 nm) method. In all cases, the kinetics of reactions was of first‐order with respect to each [AA] and [Mn 3+ ]. Increased [H + ], [Mn 2+ ] (the reduction product of Mn 3+ ), 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–g and 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