Electrochemical reduction of 2,2'-dinitrophenyl ether and 2,2'-dinitrodiphenylamine at mercury cathodes

Abstract

2,2'-Dinitrophenyl ether (I) is reduced at less negative potentials than 2,2'-dinitrodiphenylamine (II); the respective mechanism of their reduction differ essentially. (I) is electrolytically reduced in a single wave with an uptake of eight electrons per molecule, giving rise to a bishydroxylamine intermediate which undergoes an intramolecular disproportionation. The resulting 2-nitroso-2'-amino-diphenyl ether undergoes a chemical follow-up reaction leading on the one hand to dibenzo-(b,e)-(1,4,5)-oxadiazepine, on the other hand to a diphenylamine product (resulting by a chemical rearrangement) which reacts with reductants present in the solution and yields dihydrophenazine. It is merely by chance that in the electrolytical reduction of II dihydrophenazine also results in addition to other products. 2,2'-dinitrodiphenylamine (II) enables here, however, a partial electrolytical reduction in which 2-amino-2'-nitrophenylamine is formed in a single 6-electron wave. In the following, more negative wave, is clearly separated only in alkaline media, the other nitro group reduces with an uptake of 4 electrons to an intermediate which eliminates the hydroxylamine group with the corresponding electron pair. The subsequent chemical reaction leads to dihydrophenazine. This substance is the reduced form of an chemicaly and electrochemically reversible system, this system participates in the chemical reactions of reaction intermediates. Its regeneration readily proceeds at potentials more positive than the reduction potential of II. Phenazine is oxidized in the catholyte by the hydroxylamine set free to phenazine N-oxide. Nitrogen is thus eliminated in its elemental form via hydroxylamine from the substrate molecule.