In this study, the capability of an abiotic system consisting of MnO2 in oxalic acid that generates MnIII intermediate was revealed to extensively reduce two quinoxaline-di-N-oxides, carbadox and oalquindox � compounds previously recognized to be reduced under biotic conditions. The importance of MnIII was demonstrated by correlating MnIII concentration and the reaction rate. MnIII, functioning as a catalyst in the reaction, was stabilized by oxalate to yield MnC2O4+ complex which couples with carbadox or oalquindox forming a three-membered complex. Besides manonic acid, no other organics tested in this study behave the same as oxalic acid to induce the transformation. The formation of C2O4- and CO2-� radical within the complex was proposed mainly responsible for carbadox and oalquindox reduction. The reaction sites were suggested at their N1-oxide groups and the partially reduced products were identified as their N4-oxide monodesoxy derivatives. Formation of N4-oxide monodesoxy derivatives is of special concern because they exhibit mutagenic activity and absorb stronger to soil than their parent compounds. These results suggest that the co-existence of MnO2 and oxalic acid will likely affect the fate of quinoxaline-di-N-oxides and make them more persistent in the aquatic environment via reduction transformation.

Reduction of carbadox and olaquindox mediated by Mn(III) in the presence of oxalic acid

248th National Meeting (2014)

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