A New Route to 4-Aminodiphenylamine via Nucleophilic Aromatic Substitution for Hydrogen: Reaction of Aniline and Azobenzene

A new example of nucleophilic aromatic substitution for hydrogen is described which encompasses reacting aniline and azobenzene (1) in the presence of base under aerobic conditions to generate 4-(phenylazo)diphenylamine (2) in high yield. Monitoring the time course of the reaction under anaerobic conditions revealed that hydrazobenzene (9) was formed as an intermediate in the reaction in equal molar amounts as 2. However, under aerobic conditions 9 was shown not to persist in the reaction mixture. The kinetic effect of isotopic substitution on this reaction was probed by competition experiments utilizing equal molar mixtures azobenzene-d 10 and undeuterated material which gave a k H /k D of 4.6±0.1. It was concluded from these studies that azobenzene was functioning as both the electrophile and oxidant in this reaction. Catalytic hydrogenation of 2 generates 4-amidinodiphenylamine (4-ADPA) (10) and aniline. These reactions form the basis of a novel synthetic route to 4-ADPA which does not utilize halogenated intermediates or reagents and ultimately relies on O 2 as the terminal oxidant in the system