Kinetics and mechanism of oxidation of L-Cysteine by Corey's reagent

The kinetics of oxidation of L-Cysteine by pyridinium chlorochromate (PCC) was studied at 0.1-0.3 mol dm(-3) HClO4 in the range 25-40 degrees C. The reaction exhibits first order dependence with respect to PCC and fractional order in cysteine. The increase in the oxidation rate with acidity suggests the involvement of a protonated chromium(VI) species in the rate-determining step. Cysteic acid is identified as the product of oxidation. A suitable mechanism involving the formation of a complex is proposed. The activation parameters of the rate-determining step are computed using the linear least squares method and the values of E-a and Delta S-# are found to be 46.0 +/- 2.0 KJ mol(-1) and -38.0 +/- 3.2 JK(-1) mol(-1) respectively.