19039

Kinetics and Mechanism of the Oxidation of a Ferrous Complex with an ƒ؟,ƒ؟پŒ-Diimine Chelate Ligand by Ceric Sulfate in Aqueous Acidic Medium by UV-Vis Absorption Spectroscopy

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Kinetics of the oxidation of tris(2,2پŒ-bipyridine)iron(II) sulfate by ceric sulfate was spectrophotometrically studied in an aqueous sulfuric acid medium. Different methods, including isolation, integration and half-life, were employed to determine the reaction order. The redox reaction was found to be first-order with respect to the reductant, tris(2,2پŒ-bipyridine)iron(II) sulfate, and the oxidant, ceric sulfate. Complex kinetics was observed with an increase in the initial concentration of the oxidant. The influence of the dielectric constant, [H+] and [SO4 2-] on the rate was also investigated. The increase in the dielectric constant and H+ ion concentration of the medium retard the rate, while an increase in the SO4 2- ion concentration first accelerates the rate, and then retards the reaction. The effect of each factor, i.e., the dielectric constant, H+ ions and SO4 2- ions, suggests that Ce(SO4)3 2- is the active species of cerium(IV). A rate law consistent with the observed kinetic data and the proposed mechanism is suggested to be: [ ( ) ] [ ( ) ][ ] [ ] [ ]d i a t a IV d K K SO k K K Fe bipy Ce SO dt d Fe bipy . + + . + . = 2 4 2 2 4 2 1 3 2 3

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