Azobenzenes from aromatic nitro compounds

Aromatic sym-disubstituted hydrazines are obtained by reduction of azo compounds, which in turn are intermediates in properly controlled reductions of nitro compounds. The over-all reduction can be accomplished with zinc dust and alkali or electrolytically. For example, hydrazobenzene, the simplest member, is made by both procedures. Chemical reduction is carried out on o-nitrobromobenzene to form 2,2 -dibromohydrazobenzene (57%), the halo groups remaining intact. Many examples of the electrolytic procedure have been cited the yields vary from 50% to 95%. To a limited extent, a magnesium-magnesium iodide system has been employed as a reducting agent for the azobenzenes. ... 

---