Many substitution derivatives are known: the monosubstitution derivatives being capable of existing in three isomeric forms. Of the disubstitution derivatives the most important are those derived from diparadiaminodiphenyl or benzidine (q.v.).
Orthoaminodiphenyl,
is prepared by the action of bromine and caustic soda on orthophenylbenzamide (R. Hirsch, Berichte, 1892, 25, 1974); when its vapour is passed over heated lime, carbazol (q.v.) is formed.
Diorthodiaminodiphenyl,
is obtained by the reduction of the corresponding nitro compound (obtained by the action of ethyl nitrite at 0° C. on metadinitrobenzidine hydrochloride). Its tetrazo compound on reduction gives a hydrazine which, on warming with hydrochloric acid at 150° C., decomposes into ammonium chloride and phenazone,
One of the most important derivatives of diphenyl, from the theoretical point of view, is diphenic acid or diorthodiphenyl carboxylic acid, which can be obtained from diparadiaminodiphenyldiorthocarboxylic acid,
