The kinetics of the hexacyanoferrate (III)-sulphite reaction

Mechanism of the Osmium(Viii)-Catalysed Oxidation of Fursemide by Alkaline Hexacyanoferrate(Iii) and Analysis of Fursemide by a Kinetic and Catalytic Method

The kinetics of the title reaction showed first-order behaviour both in hexacyanoferrate(III) and osmium(VIII) and fractional order each in fursemide and alkali concentrations. The added product, [Fe(CN)6]4-, retarded the rate of reaction. The active species of osmium(VIII) in alkali appears to be [OsO5(OH)]3-. A mechanism involving a complex formed between osmium(VIII) and fursemide, followed by its oxidation with hexacyanoferrate(III) in a rate-determining step is proposed. A rate law for the mechanism was derived and verified. The formation constant, K2 for [OsO5(OH)]3-, K3 for the complex, and the rate constant of the slow step, k, were evaluated. The activation parameters Ea, Δ H#, Δ S#, Δ G# and log A were calculated as 55.2 ± 2kJ mol−1, 52.7 ± 2 kJ mol−1, - 52.0 ± 2 JK−1 mol−1, 69.8 ± 2.5 kJ mol−1 and 6.5 ± 0.1 respectively.

Fursemide is used in the pharmacotherapy for various diseases and it is also considered as a doping agent in sports. A simple and specific procedure for its analysis was developed being based on its oxidation by alkaline hexacyanoferrate(III) in the presence of trace amount of osmium(VIII) catalyst. Three different methods have been recommended, namely, the rate constant method, fixed time method and fixed change in optical density method. of these, the latter two were found to be fast, simple, and accurate. from these methods, fursemide could be analysed from a few micrograms to milligrams per cm3. The interference by binders of tablets, and other possible substances like proteins and amino acids, have also been studied.