The kinetics of oxidation of L-Cysteine in aqueous HClO 4 medium were studied using a one-equivalent oxidant, hexachloroiridate(IV). The reaction exhibits second-order dependence with respect to hexachloroiridate(IV) and first-order in cysteine. The rate decreases with increase in hydrogen ion concentration indicating that the zwitterionic form of cysteine is more reactive. Cysteic acid is identified as the product of oxidation. A suitable mechanism involving the formation of [IrCl 6 ] 2) -sulphur bonded intermediate is proposed. The activation parameters of the reaction are computed using the linear least squares method and the values of E a and DS # are found to be 27.97±1.82 kJ mol )1 and )51.30±6.0 J K )1 mol )1 , respectively.
The kinetics of oxidation of L-Cysteine by pyridinium chlorochromate (PCC) was studied at 0.1-0.3 mol dm )3 HClO 4 in the range 25-40°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 DS # are found to be 46.0 ± 2.0 KJ mol )1 and )38.0 ± 3.2 JK )1 mol )1 respectively.
Kinetics of oxidation ofL-cystine by hexacyanoferrate(III) was studied in alkaline medium at 30 °C. The reaction was followed spectrophotometrically at λmax = 420 nm. The reaction was found to be first order dependence each on [HCF(III)] and [cystine]. It was found that the rate of the reaction increases with increase in [OH-]. The oxidation product of the reaction was found to be cysteic acid. A plausible mechanism has been proposed to account for the experimental results.
ABSTRACT. The kinetics of the title reaction was studied spectrophotometrically in HClO4 medium at 380 nm. The data suggested that the order with respect to cystine is fractional, whereas chromium(VI) follows first order kinetics. The reaction was second order in [H + ]. Cysteic acid was found to be the main product of oxidation. A suitable mechanism was proposed leading to the rate law. The activation parameters were computed using linear least squares method.
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