Kinetics and mechanisms of the reaction of chromium(III) and 2,4-hexanedione in aqueous solution

Abstract

The kinetics and mechanism of the reaction between Cr(III) and 2,4-hexanedione in aqueous solution have been studied. Complexation occurs by coordination of both oxygen atoms of the ligand to the chromium(III) center, with concomitant loss of a proton yielding 1:1 complex of the type [Cr(CH3COCHCOC2H5)(H2O)4]2+. When the metal ion is in pseudo first-order excess the concentration dependence of the observed rate constants agrees with a mechanism involving reversible reaction between the enol tautomer of 2,4-hexanedione and the metallic species Cr(H2O)63+ and Cr(H2O)5OH2+, with rate constants of 8.0 × 10−4 and 3.5 × 10−2 dm3 mol−1 s−1, respectively. Keywords: chromium(III), β-diketones, β-diketonates, kinetics, complexation.