CHEMICAL-MEDIATED AND SEDIMENT-MEDIATED REDUCTION OF THE AZO-DYE DISPERSE-BLUE-79

Disperse Blue 79, a large volume disperse azo dye, and 2-bromo-4,6-dinitroaniline (BDNA), an important intermediate in the preparation of Disperse Blue 79, were readily reduced chemically and in three anoxic sediment-water systems studied; half-lives were on the order of minutes to hours. No reduction of Disperse Blue 79 or BDNA was observed however in a sediment-water system containing sediment with low organic carbon. The reaction kinetics of Disperse Blue 79 in the reducing Sediments are biphasic, that is, the initial rapid loss of dye is followed by a much slower rate of transformation. The reaction pathways for the chemical and sediment-mediated reduction of Disperse Blue 79 were quite similar, suggesting that the chemical reduction of such complex chemicals can provide valuable insight into their reaction pathways in environmental systems. For Disperse Blue 79, a number of reaction products resulting from the reduction of both the azo linkage and aromatic nitro groups were formed. The sediment-mediated reduction of BDNA was regioselective resulting in the formation of a 3-bromo-5-nitro-1,2-diaminobenzene, which was further reduced at a much slower rate to B-bromo-1,2,4-triaminobenzene. These results suggest that Disperse Blue 79 and BDNA may undergo reduction in some natural anoxic sediments, resulting in the subsequent release of potentially hazardous aromatic amines to the water column.