Abstract
The oxidation of glyoxylic acid (HGl) by Mn IVL {L 4− = tetra deprotonated 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane} was investigated in the pH range 1.67–10.18, at 25–45 °C and 0.5 M ionic strength. The reaction exhibited biphasic kinetics with Mn IIIL − as the reactive intermediate. Mn IV was reduced to Mn II. The products of oxidation of HGl were identified as formic acid and CO 2 in acidic medium, and oxalate in basic medium, consistent with the stoichiometry: −Δ[Mn IV]/−Δ[HGl] = 1. In acidic medium, both Mn IVL and Mn IIIL − formed outer-sphere adducts with the neutral HGl {HC(OH) 2COOH} molecule, with an association constant Q av of 28 and 70 M −1, respectively. A similar adduct formation was not observed for the glyoxylate mono anion {Gl −, CH(OH) 2(CO 2 −)} and glyoxylate dianion {Gl 2−, CH(OH)(O −)CO 2 −}. The rate and activation parameters for the various paths are reported and an outer-sphere electron transfer mechanism is suggested.
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