Oxidation of glyoxylic acid by a mononuclear manganese(IV) complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane: A kinetics and mechanistic study

The oxidation of glyoxylic acid (HGl) by MnIVL {L4− = 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 MnIIIL− as the reactive intermediate. MnIV was reduced to MnII. The products of oxidation of HGl were identified as formic acid and CO2 in acidic medium, and oxalate in basic medium, consistent with the stoichiometry: −Δ[MnIV]/−Δ[HGl] = 1. In acidic medium, both MnIVL and MnIIIL− formed outer-sphere adducts with the neutral HGl {HC(OH)2COOH} molecule, with an association constant Qav of 28 and 70 M−1, respectively. A similar adduct formation was not observed for the glyoxylate mono anion {Gl−, CH(OH)2(CO2−)} and glyoxylate dianion {Gl2−, CH(OH)(O−)CO2−}. The rate and activation parameters for the various paths are reported and an outer-sphere electron transfer mechanism is suggested.

A detailed investigation of the oxidation of glyoxylic acid by MnIVL, {L4− = tetra deprotonated 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane} has been carried out. The reduction of MnIVL follows biphasic kinetics via the formation of a MnIIIL− reactive intermediate, yielding formic acid and CO2 in acidic medium and oxalate in basic medium as the oxidation products of glyoxylic acid.Figure optionsDownload as PowerPoint slideHighlights
► Glyoxylic acid is oxidized by MnIVL {L4− = tetra deprotonated 1,8 bis(2-hydroxybenzamido)-3,6-diazaoctane} to formic acid, CO2 and oxalate.
► MnIV is reduced to MnII via a MnIII intermediate.
► CH(OH)2COOH and CH(OH)(O−)COO− are the major reducing species in acidic and basic media respectively.
► The reaction features equilibrium preassociation of MnIVL(MnIIIL−) with HC(OH)2COOH followed by a rate limiting outer sphere electron transfer.