2-Naphthol orange (acid orange 7), C16H11N2NaO4S, is a mono-azo water-soluble dye that extensively used for dyeing paper, leather and textiles. The structure of acid orange 7 involves a hydroxyl group in the ortho-position to the azo group. This resulted an azo-hydrazone tautomerism, and the formation of two tautomers, which each show an acid−base equilibrium. Despite the number of articles dealing with acid−base properties of the acid orange 7, this topic is not yet well known, and only one pKa, (pKa = 11.4) is reported. On the other hand, azo dyes have been widely used for developing and testing theories of color and constitution, tautomerism, indicator action, and acid-base equilibria. Therefore, detailed mechanistic information is important in understanding of the stability and in identifying of the intermediates structure resulting from the oxidative or reductive decomposition of dye. Consequently, detailed mechanistic information is particularly attractive from the point of view of environmental pollution because of residual dye and the commercial applications. additionally, green/sustainable synthesis is much more important than conventional synthetic methods. The concept and significance of green sustainable chemistry (GSC), has been recognized throughout the world, and nowadays new processes cannot be developed without consideration of GSC. In recent years, much attention has been paid to electroorganic synthesis as a typical environmentally friendly process. This method contains the simultaneous incidence of both oxidation (at the anode) and reduction (at the cathode). In conventional electroorganic synthesis, the synthesis of the desired products is done either by the anodic or by the cathodic reaction and so; the reaction product at the counter electrode is undesirable. The simultaneous use of both oxidation and reduction reactions to synthesis of a product is the dream of an organic electrochemist and is a wonderful strategy. At ideal conditions, a 200 % current efficiency is achievable for paired electrosynthesis when both anodic and cathodic reactions to provide the similar product (convergent strategy).
The results discussed above prompted us to investigate the electrochemical oxidation and reduction of acid orange 7 in aqueous solutions with different pH values to achieve the following goals: (i) new insights into the electrochemical oxidation and reduction of acid orange 7, (ii) definitive detection of intermediates formed during the oxidative and reductive degradation of acid orange 7, and (iii) convergent paired electrochemical synthesis of new 1-amino-2-naphthol derivatives by constant current electrolysis of acid orange 7 in the presence of arylsulﬁnic acids as nucleophiles.