Alicja Wanat, Rudi van Eldik and Grazyna Stochel
The electron transfer reaction between [Fe(CN)5(NO2)]3– and ascorbic acid was subjected to a detailed kinetic and thermodynamic study as a function of pH, ascorbic acid concentration, temperature and pressure. The pH profile indicates a pH independent region in the pH 5.0–5.5 range, which is ascribed to the oxidation of the ascorbate anion HA– present in solution under such conditions. The experimental rate and activation parameters suggest that this redox process follows an outer-sphere electron transfer mechanism. The Marcus, Fuoss and Stranks–Marcus–Hush relationships were applied to estimate the self-exchange rate constant for the [Fe(CN)5(NO2)]3–/4– couple, the ion-pair formation constant, the rate constant for electron transfer and the value of ΔV
et
‡
. The results are discussed in reference to related systems reported in the literature.