Reduction of carbadox, olaquindox and other aromatic N-oxides were investigated in aqueous solutions containing FeII and tiron. Rapid degradation of carbadox (CDX) and olaquindox was observed. Consistent with previous findings, the 1:2 FeII-tiron complex, FeL26-, is the dominant reactive species; and the observed pseudo-first order rate constants of the N-oxides were highly dependent on the concentration of FeL26-. The N-oxides without any side chains were much less reactive, suggesting direct reduction of the N-oxides is slow. The FeII in FeL26- likely forms a 5-membered ring with CDX and olaquindox through the N and O atoms on the side chains. The formed inner-sphere complexes significantly facilitated electron transfer from FeL26- to the N-oxides. QSAR analysis showed that the first electron transfer is the rate-determining step for mono-N-oxides but not for di-N-oxides. Kinetic modeling of reduction of di-N-oxides suggested that reduction at N4 is kinetically favored compared with at N1. Reduction products of the N-oxides were identified to be mainly deoxygenated analogs. All the experimental results suggest that FeII-tiron reduces N-oxides through free radical intermediates where electrons transfer from FeL26- to the resonance structures of N-oxides, followed by electron delocalization on the aromatic ring, and deoxygenation from the N-oxide groups.

Complexation facilitated reduction of aromatic N-oxides by aqueous Fe<sup>II</sup>-tiron complex: Reaction kinetics and mechanisms

246th National Meeting (2013)

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Complexation facilitated reduction of aromatic N-oxides by aqueous FeII-tiron complex: Reaction kinetics and mechanisms

Complexation facilitated reduction of aromatic N-oxides by aqueous Fe^II-tiron complex: Reaction kinetics and mechanisms