Medicinal nitro-compounds. Part I. Photo-rearrangement of N-Aryl-2-nitrobenzamides

2-Nitrobenzanilide (4a) rearranges to 2-(2-hydroxyphenylazo)benzoic acid (5a) on exposure to light. Azoxybenzene-2-carboxylic acid (6a) is an intermediate in this transformation and also rearranges to the acid (5a) in high yield. Other N-aryl-2-nitrobenzamides (4b-f) afford the analogous azo-compounds (5b-f), but when the N-aryl system carries electron-attracting substituants (4g-j) the compounds are photostable. Irradiation of 2-nitro-benzo-m-toluidide (12) yields a mixture of two isomeric azocarboxylic acids. The scope of the rearrangement has been explored: N-(1-naphthyl)-2-nitrobenzenesulphonamide (18) affords the analogous azobenzenesulphonic acid (19) but N-alkyl- or N-aralkyl-2-nitrobenzamides. N-substituted 4-nitrobenzamides, and N,N'-diphenyl-2-nitrobenzamidine (16) do not yield azo- or azoxy-compounds.