Kinetics and the Mechanism of Iron(II) Reduction of cis-α-halogeno(cetylamine) (triethylenetetramine)cobalt(III) Complex Ion in Aqueous Acid Medium

Abstract

The kinetics and mechanism of iron(II) reduction of cis- α-chloro/bromo(cetylamine)(triethylenetetramine) cobalt(III) surfactant complex ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of CoIII using an excess of the reductant under pseudo-first-order conditions: [FeII = 0.25 mol dm−3, [H+ = 0.1 mol dm−3, [µ = 1.0 mol dm−3 ionic strength in a nitrogen atmosphere at 303, 308 and 313 K. The reaction was found to be second order and showed acid independence in the range [H+ = 0.05−0.25 mol dm−3. The second order rate constant increased with CoIII concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [FeII], [H+] and [ µ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of Fe2+(aq) with CoIII complex proceeds by an inner-sphere mechanism.