Kinetics and Mechanism of Hexachloroiridate(IV) Oxidation of Arsenic(III) in Acidic Perchlorate Solutions

01/1992; DOI: 10.1135/cccc19921451
Source: OAI

ABSTRACT The kinetics of oxidation of arsenic(III) by hexachloroiridate(IV) at lower acid concentrations and at constant ionic strength of 1.0 mol dm-3 have been investigated spectrophotometrically. A first-order reaction in [IrCl62-] and fractional order with respect to arsenic(III) have been observed. A kinetic evidence for the formation of an intermediate complex between the hydrolyzed arsenic(III) species and the oxidant was presented. The results showed that decreasing the [H+] is accompanied by an appreciable acceleration of the rate of oxidation. The activation parameters have been evaluated and a mechanism consistent with the kinetic results was suggested.

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    ABSTRACT: The kinetics of oxidation of L-Cysteine in aqueous HClO4 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 [IrCl6]2− – sulphur bonded intermediate is proposed. The activation parameters of the reaction are computed using the linear least squares method and the values of Ea and ΔS# are found to be 27.97±1.82kJ mol−1 and −51.30±6.0JK−1mol−1, respectively.
    Transition Metal Chemistry 09/2005; 30(7):773-777. · 1.40 Impact Factor