BENZIDINE (DIPARA-DIAMINO-DIPHENYL),NH 2 C 6 H 4 C 6 H 4 NH2, a chemical base which may be prepared by the reduction of the corresponding dinitro-diphenyl, or by the reduction of azobenzene with tin and hydrochloric acid.
Its tetramethyl-diamino derivative, which is formed by condensing formaldehyde with dimethyl-meta-aminophenol and subsequent elimination of water from the resulting diphenyl methane derivative, is the leuco base of pyronine, into which it passes by oxidation.
This grouping is not always colour-producing, since diphenyl is colourless.
Silicobenzoic acid, C 6 H 5 S10.0H, results from the action of dilute aqueous ammonia on phenyl silicon chloride (obtained from mercury diphenyl and silicon tetrachloride).
Passed through a red-hot tube, benzene vapour yields hydrogen, diphenyl, diphenylbenzenes and acetylene; the formation of the last compound is an instance of a reversible reaction, since Berthelot found that acetylene passed through a red-hot tube gave some benzene.