Kinetics and mechanism of the reduction of pentacyanonitroferrate(III) by L-ascorbic acid in acidic aqueous solution

Abstract

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.