Kinetics and mechanisms of the reactions of chromium(III) and heptane-3,5-dione in aqueous solution
Abstract
The equilibra and kinetics of mono-complex formation of chromium(III) with heptane-3,5-dione have been investigated spectrophotometrically in aqueous solution at 50 °C and 0.5 mol dm–3 NaClO4. The mechanism proposed to account for the kinetic data involves pathways in which both Cr3+ and Cr(OH)2+ react with the enol tautomer of the ligand with rate constants of 6.60 × 10–2 dm3 mol–1 s–1 and 1.42 dm3 mol–1 s–1, respectively. By comparing rate laws derived on the basis of the theory of coupled sets of first-order reactions with rate laws derived using the steady-state approximation, a useful confirmation of the validity of this mechanism has been provided. The assumptions made in the steady-state approach that the keto–enol equilibrium is maintained and that the protolytic reactions are rapid compared with complex formation are valid.