Kinetics and Mechanism of the Oxidation of a Ferrous Complex with an &#945,&#945'-Diimine Chelate Ligand by Ceric Sulfate in Aqueous Acidic Medium by UV-Vis Absorption Spectroscopy

Kinetics of the oxidation of tris(2,2′-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(2,2′-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] 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 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 ions, suggests that Ce(SO4)3 is the active species of cerium(IV). A rate law consistent with the observed kinetic data and the proposed mechanism is suggested to be: