Oxidative-coupling reaction of TNT reduction products by manganese oxide

Abiotic transformation of TNT reduction products via oxidative-coupling reaction was investigated using Mn oxide. In batch experiments, all the reduction products tested were completely transformed by birnessite, one of natural Mn oxides present in soil. Oxidative-coupling was the major transformation pathway, as confirmed by mass spectrometric analysis. Using observed pseudo-first-order rate constants with respect to birnessite loadings, surface area-normalized specific rate constants, k_surf, were determined. As expected, k_surf of diaminonitrotoluenes (DATs) (1.49-1.91 L/m² d) are greater about 2 orders than that of dinitroaminotoluenes (DNTs) (1.15×10^-2-2.09×10 ^-2 L/m² d) due to the increased number of amine group. In addition, by comparing the value of k_surf between DNTs or DATs, amine group on ortho position is likely to be more preferred for the oxidation by birnessite. Although cross-coupling of TNT in the presence of various mediator compounds was found not to be feasible, transformation of TNT by reduction using Fe⁰ followed by oxidative-coupling using Mn oxide was efficient, as evaluated by UV-visible spectrometry.