Oxidation of Histidine by Pyridinium Bromochromate in A quo-Acetic Acid Medium:A Kinetic Investigation

摘要

Amino acids do not react with C1O3 and KsCraO7 but react with pyridinium bromochromate.Oxidation of histidine with pyridinium bromochromate (PBC) has been studied in 30% acetic acid-70% water (v/v) mixture containing perchloric acid and leads to 2-imi-dazole aldehyde,carbon dioxide and ammonia as products.The reaction rate is first order with respect to each in [histidine]and [PBC]while inverse second order with respect to [H~+].Michaelis-Menten type kinetics is observed with respect to histidine.The rate of reaction increases with decrease in polarity of solvent indicating ion-dipole interaction.Absence of primary kinetic isotope effect (kH/kD)=1.12 at 303 K) rules out the alpha-C-H bond fission in the rate determining step.Activation parameters have been evaluated.A rate limiting C-C bond fission of the chromic-ester formed by zwitter ion of histidine and unprotonated PBC is consistent with the observed results.The rate law proposed and derived is in agreement with experimental results.