Kinetics of reactions of pentane-2,4-dionato complexes of manganese(III) with glyoxylate anion in aqueous perchlorate media

Abstract

Glyoxylate (gox) catalyses the reduction of [Mn(pd)3] to MnII in aqueous perchlorate media (pH 5.5–7.5) containing excess of pentane-2,4-dione (Hpd). In this process, 1 mol of Hpd, but no gox, is consumed per mol of MnIII reduced. E.p.r. studies indicate the generation of a pd˙ radical in a cyclic redox process. The kinetically active manganese(III) species are [Mn(pd)2(gox)] and [Mn(pd)2(H2O)(OH)]; [Mn(pd)3] makes no appreciable contribution to the rate. The rate constants for the [Mn(pd)2(gox)] and [Mn(pd)2(H2O)(OH)] paths are (1.27 ± 0.03)× 10–4s–1 and (9.58 ± 0.26)× 10–2 dm3 mol–1 s–1 respectively while the formation constant for [Mn(pd)2(gox)] from [Mn(pd)2(H2O)2]+ and gox is 902 ± 42 dm3 mol–1 at 30°C, I= 1.0 mol dm–3. Inner-sphere paths seem reasonable.