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BENZIDINE (DIPARA-DIAMINO-DIPHENYL), NH2

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Originally appearing in Volume V03, Page 756 of the 1911 Encyclopedia Britannica.
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BENZIDINE (DIPARA-DIAMINO-See also:DIPHENYL), See also:NH2 • See also:C6H4 • C6H4 • NH2, a chemical See also:base which may be prepared by the reduction of the corresponding dinitro-diphenyl, or by the reduction of azobenzene with See also:tin and hydrochloric See also:acid. In this latter See also:case hydrazo-See also:benzene C6H5NH•NH•C6H5 is first formed and then undergoes a See also:peculiar re-arrangement into benzidine (see H. See also:Schmidt and G. See also:Schultz, Annalen, 1881, 207, p. 320; O. N. Witt and Hans v. See also:Helmont, Berichte, 1894, 27, p. 2352; P. Jacobson, Berichte, 1892, 25, p. 994). Benzidine crystallizes in plates (from See also:water) which melt at 122° C., and See also:boil above 36o° C., and is characterized by the See also:great insolubility of its sulphate.

It is a di-acid base and forms salts with the See also:

mineral acids. It is readily brominated and nitrated; when the nitration is carried out in the presence of sulphuric acid, the nitro-See also:groups take up the See also:meta position with regard to the amino-groups. Benzidine finds commercial application since its tetrazo See also:compound couples readily with amino-sulphonic acids, phenol carboxylic acids, and phenol and naphthol-sulphonic acids to produce substantive See also:cotton dyes (see See also:DYEING). Among such dyestuffs are chrysamine or flavophenine, obtained from salicylic acid and diazotized benzidine, and See also:congo red obtained from See also:sodium naphthionate and diazotized benzidine. On the constitution of benzidine see G. Schultz (Annalen, 1874, 174, p. 227). The Ben€idine and Semidine See also:Change.—Aromatic hydrazo compounds which contain See also:free See also:para positions are readily converted by the See also:action of acids, acid chlorides and anhydrides into diphenyl derivatives; thus, as mentioned above, hydrazobenzene is converted into benzidine, a small quantity of diphenylin being formed at the same See also:time. The two products are separated by the different solubilities of their sulphates. This reaction is known as the benzidine transformation. If, however, one of the para positions in the hydrazo compound is substituted, then either diphenyl derivatives or See also:azo compounds are formed, or what is known as the semidine change takes See also:place (P. Jacobson, Berichte, 1892, 25, p.

992; 1893, 26, p. 681; 1896, 29, p. 268o; Annalen, 1895, 287, p. 97; 1898, 303, p. 290). A para mono substituted hydrazo compound in the presence of a hydrochloric acid See also:

solution of stannous chloride gives either a para diphenyl derivative (the substituent See also:group being eliminated), an ortho-semidine, a para-semidine, or a diphenyl base, whilst a decomposition with the formation of See also:amines may also take place. The nature of the substituent exerts a specific See also:influence on the reaction; thus with See also:chlorine or See also:bromine, ortho-semidines and the diphenyl bases are the See also:chief products; the dimethylamino, -N(See also:CH3)2, and acetamino, -NHCOCH3, groups give the diphenyl base and the para-semidine respectively. With a methyl group, the chief product is an ortho-semidine, whilst with a carboxyl group, the diphenyl derivative is the chief product. The ortho- and para- semidines can be readily distinguished by their behaviour with different reagents; thus with nitrous acid the ortho-semidines give azimido compounds, whilst the para-semidines give complex diazo derivatives; with formic or acetic acids the ortho-semidines give anhydro compounds of a basic See also:character, the para-semidines give acyl products possessing no basic character. The See also:carbon disulphide and salicylic aldehyde products have also been used as means of distinction, as has also the formation of the stilbazonium bases obtained by condensing ortho-semidines with benzil (0. N. Witt, Berichte, 1892, 25, p.

1017). Structurally we have: NH2 -NH•NH—( > —j NH2<)—< >NH2 and NH2 < >—<—% Hydrazohenzene. Benzidine. Diphenylin. NH2 R< >—NH•NH—< > —> < )—NH—<----> or RK > —NH— NH_, R Ortho-semidine. Para-semidine. NH2 or( >—< )NIH2.

End of Article: BENZIDINE (DIPARA-DIAMINO-DIPHENYL), NH2

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