Kinetics and mechanism of oxidation of amino acids by trichloromelamine in aqueous acetic acid

摘要

The kinetics of oxidation of seven amino acids (AA)-glycine, alanine, valine, leucine, phenylalanine, aspartic acid and serine, by trichloromelamine has bene studied in aqueous acetic acid in the presence of perchloric acid. The reactions show first order kinetics in [TCM], fractional order in [AA] and nearly zero order in [H~+]. The observed results have been explained by Michaelis-Menten type mechnaism. The rates are measured at different temperatures at varying [AA]. The coefficients of the rate-limiting steps at each temperature and the corresponding activation parameters have been computed. Further, the energies of activation of all the amino acids are optimised corresponding to the lg A of alanine using the equation E_a = 2.303 RT. The optimised E_a and lg A values remain almost the same. They do not show regular trends. This may probably be due to the sensitivity of the oxidation to the change in electron environment in the amino acids. The free energies of activation remain almost the same in both the optimisations indicating the operation of similar mechanisms in all the cases. The plot of #DELTA#H versus #DELTA#S for both the sets of values computed from k_(obs) and k_2 is linear with isokinetic temperatures of 333 K and 337 K, respectively.