The Autoxidation of Aromatic Amines

A few aromatic amines, formed during the anaerobic reduction of the azo dyes, are unstable under aerobic conditions and undergo auto-oxidation reactions. Examples are 5-ASA, phenylenediamine, o-amino hydroxy and o-dihydroxy naphthalenes

Fig. 4.3 Proposed pathways for the degradation of substituted naphthalene-sulfonates. NSDO naphthalenesulfonate dioxygenease; DHNDO 1,2-dihydroxynaphthalene dioxygenase; HCCAI 2-hydroxychromene-2-carboxylate isomersae; HBPA 2'-hydroxybenzal-pyruvate aldolase; SADH salicylaldehyde dehydrogenase; SMO salicylate 1-monooxygenase; GDO gentisate 1,2-dioxygenase; 5ASDO 5-aminosalicylate 1,2-dioxygenase; C1 2DO catechol 1,2-dioxygenase; MPI maleylpyruvate isomerase; TCC tricarboxylic acid cycle. Source Hinter et al. (2001)

(Jensen et al. 1993; Kudlich et al. 1999). Oxygen reacts with aromatic products, via free radical reactions, leading to the formation of undesirable colored oligomers and polymers which may be toxic and mutagenic. Further, these polymers are more recalcitrant to biodegradation. Thus, an effective mineralization of azo dyes, using anaerobic decolorization followed by aerobic degradation of amines, can only be possible, if the aerobic biodegradation rate for amines is much higher than the autoxidation rate.

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