Aromatic Azo Reduction

The reduction of aromatic azo compounds is a four-electron process that proceeds through the hydrazobenzene (Florence, 1965). 

Because the hydrazobenzene is more labile than the parent azo compound, its formation is generally not detected and complete reductive cleavage of the azo linkage occurs, resulting in the formation of aromatic amines. 

As predicted, the initial rate of formation of aniline was twice the disappearance rate of azobenzene (2 molecules of aniline are formed for every molecule of azobenzene that is reduced). However, the apparent rate of formation of aniline falls off with time, due to reactions of aniline with the sediment-associated organic matter. In what appears to be a general phenomenon for reductive transformations, no reduction of azobenzene was observed in the filtrate of the sediment-water system, sug- 

More recently, the study of the reduction of aromatic azo compounds in anaerobic sediment-water systems has been extended to the azo dyes, particularly those for which there is concern that reductive cleavage of the azo linkage will result in the formation of mutagenic and carcinogenic aromatic amines. For example, reductive cleavage of the bisazo linkages of Direct Red 28 in anoxic sediments would result in the release of benzidine into these systems. 

The carcinogenicity and mutagenicity of benzidine is well documented (Ames et al., 

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