Reaction of phenols with ammonia, amines, and hydrazines

Acid catalysts must be used if substitution of an amino group for a hydroxyl group on an aromatic ring is to be fast enough for preparative purposes and even then it usually requires energetic conditions. 

Certain nitroso phenols and polyhydroxy compounds are exceptions where the exchange takes place under relatively mild conditions and sometimes without the need for a catalyst. For example,/7-nitrosophenol and ammonium salts, when heated on a steam-bath for 0.5 hour, give 50% of /7-nitrosoaniline, 1049.cf.1050 and l-nitroso-2-naphthol and aqueous methylamine solution at 35° give 90% of iV,iV-dimethyl-1 -nitroso-2-naphthylamine.1051 The easier reaction s due to the tautomerism of these phenols with the ketonic isomers, e.g.9 for nitrosophenol  

Nitro groups also increase the reactivity of phenols, but replacement of the hydroxyl by an amino group still needs temperatures of 150-200° and thus usually the use of pressure vessels.1054 Primary amines can be obtained at normal pressures from di- and tri-nitrated phenols and naphthols by melting them with urea 1055 1056 picramide, m.p. 188°, for instance, was formed in 88% yield by heating picric acid with 3 equivalents of urea at 173° for 36 h.1056 

In spite of its limited applicability the Bucherer reaction1057 is the most important method of preparing aromatic amines from phenols. This consists of the conversion of phenols into amines, and the reverse conversion of amines into pnenols, as well as transamination of aromatic amines (cf. page 538), each in the presence of hydrogen sulfite ions. 

The mechanism of this interesting reaction, long disputed, was recently clarified by Rieche and Seeboth.1057 1058 It involves a series of reversible reactions, that can be formulated as follows for the case of 1-napthol-l-naphthylamine  

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