The N–O single bond is a common function group in organic contaminants. This work examined the reduction of various N-oxides by dissolved FeII or FeII-tiron complex. The trend in the reactivity follows aliphatic N-oxides &gt;&gt; aromatic N-oxide &gt;&gt; iminic N-oxide, suggesting the importance of N partial charge to the reactivity. Reduction products of the N-oxides were identified by HPLC/QToF-MS to be the deoxygenated analogs. The potential energy surface scan of different reduction pathways of pyridine N-oxide indicated that all protonation reactions are barrierless, which is consistent with the experimental solvent (H2O:D2O) kinetic isotope effect of 1.07. The calculations also showed that the N–O bond cleavage is spontaneous. Thus, the most likely rate-limiting step for the reduction of simple N-oxides is electron transfer. Electrochemical cell experiments proved that the reduction of carbadox can be facilitated by complexation with aqueous Fe(II), either through the side chain or through the N-oxide O atom. All the above results suggest that the reduction of various N-oxides undergoes different pathways including protonation, complexation, electron transfer and N–O bond cleavage. Our ongoing work examines the activation energy of the potential rate-limiting steps for the reduction of all N-oxides and calculates molecular descriptors that can be correlated to reactivity.

Experimental and computational evidence for reduction mechanisms of N-oxides by soluble FeII species

249th National Meeting (2015)

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