Autoxidation Reactions of Different Aromatic o-Aminohydroxynaphthalenes That Are Formed during the Anaerobic Reduction of Sulfonated Azo Dyes

Abstract

Mono- and disulfonated naphthalene derivatives with a hydroxy group in ortho-position to an amino group are commonly occurring products of the anaerobic reduction of azo dyes by microorganisms. These substituted o-aminohydroxybenzenes and o-aminohydoxynaphthalenes are oxygen-sensitive and decompose under aerobic conditions. To evaluate their behavior under aerobic conditions, 1-amino-2-hydroxynaphthalene-6-sulfonate [AHNS; a reduction product of Sunset Yellow FCF (FDC a reduction product of Amaranth (Acid Red 27, C.I. No. 16185)], and 1,2,7-triamino-8-hydroxynaphthalene-3,6-disulfonate [TAHNDS; a reduction product of Naphthol Blue Black B (Acid Black 1, C.I. No. 20470)] were chemically prepared and exposed to air at neutral pH. The reactions were analyzed, and the autoxidation products were characterized mainly by LC−MS and UV/VIS spectroscopy. Autoxidation of AHNS led to the formation of a dimer. With AHNDS, 1,2-naphthoq...