Kinetics and the mechanism of iron(II) reduction of cis-α-halogeno(cetylamine)(triethylenetetramine)cobalt(III) complex ion in aqueous acid medium

The kinetics and mechanism of iron(II) reduction of cis- alpha-chloro/bromo(cetylamine)(triethylenetetramine) cobalt(III) surfactant complex ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co-III using an excess of the reductant under pseudo-first-order conditions: [Fe-II] = 0.25 mol dm(-3), [H+] = 0.1 mol dm(-3), [mu] = 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 Co-III concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe-II], [H+] and [mu] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of Fe2+(aq) with Co-III complex proceeds by an inner-sphere mechanism.