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Mechanistic Investigations of Oxidation of Some Dipeptides by Sodium N ‐chloro‐ p ‐toluenesulfonamide in Alkaline Medium:A Kinetic Study
Author(s) -
VAZ Nirmala,
RAJENAHALLY VGOWDA Jagadeesh
Publication year - 2008
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.200890101
Subject(s) - chemistry , kinetics , glycylglycine , medicinal chemistry , reaction rate constant , ionic strength , arrhenius equation , reaction rate , stereochemistry , inorganic chemistry , amino acid , activation energy , organic chemistry , catalysis , glycine , aqueous solution , biochemistry , physics , quantum mechanics
The kinetics of oxidation of five dipeptides (DPP) viz. , glycylglycine (Gly‐Gly), L ‐alanyl‐ L ‐alanine (Ala‐Ala), L ‐valyl‐ L ‐valine (Val‐Val), L ‐leucyl‐ L ‐leucine (Leu‐Leu) and phenylglycyl‐phenylglycine (Phg‐Phg) by sodium N ‐chloro‐ p ‐toluenesulfonamide or chloramine‐T (CAT) in NaOH medium was studied at 308 K. The reactions follow identical kinetics for all the dipeptides, being first‐order dependence each on [CAT] o , [DPP] o and fractional‐order on [OH − ]. Addition of p ‐toluenesulfonamide or halide ions (Cl − or Br − ) has no significant effect on the rate of reaction. The reaction rate was found to increase with increase in ionic strength of the medium. The solvent isotope effect was studied using D 2 O. The activation parameters for the reaction were computed from Arrhenius plots. Equilibrium and decomposition constants were evaluated. The oxidation products of the dipeptides were identified as their corresponding aldehydes. An isokinetic relationship was observed with β =352 K, indicating that enthalpy factors control the reaction rate. CH 3 C 6 H 4 SO 2 NCl − of the oxidant has been postulated as the reactive oxidizing species. Under comparable experimental conditions, the rate of oxidation of the dipeptides increases in the order:Phg‐Phg>Ala‐Ala>Val‐Val>Leu‐Leu>Gly‐Gly. The kinetics of oxidation of the dipeptides have also been compared with those of their corresponding monomer amino acids. The observed results have been explained by a plausible mechanism and the related rate law has been deduced.