Diphenyl

Diphenyl (phenyl benzene), C6H5·C6H5, a hydrocarbon found in that fraction of the coal-tar distillate boiling between 240-300° C., from which it may be obtained by warming with sulphuric acid, separating the acid layer and strongly cooling the undissolved oil. It may be artificially prepared by passing benzene vapour through a red-hot tube; by the action of sodium on brombenzene dissolved in ether; by the action of stannous chloride on phenyldiazonium chloride; or by the addition of solid phenyldiazonium sulphate to warm benzene (R. Möhlau, Berichte, 1893, 26, 1997) C6H5N2·HSO4 \+ C6H6 = H2SO4 \+ N2 \+ C6H5·C6H5. L. Gattermann (Berichte, 1890, 23, 1226) has also prepared it by the decomposition of a solution of phenyldiazonium sulphate with alcohol and copper powder. It crystallizes in plates (from alcohol) melting at 70-71° C. and boiling at 254° C. It is oxidized by chromic acid in glacial acetic acid solution to benzoic acid, dilute nitric acid and chromic acid mixture being without effect. It is not reduced by hydriodic acid and phosphorus, but sodium in the presence of amyl alcohol reduces it to tetrahydrodiphenyl C12H14.

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,  or from phenanthrene (q.v.), the constitution of which it determines. See Benzidine for diparadiaminodiphenyl.

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