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4,4’-diaminodiphenyl, an organic compound.
Clear, lustrous crystals that darken in air and under the influence of light because of oxidation. Melting point Tm= 128° C; boiling point Tb = 400°C. It is readily soluble in alcohol and ether; it is an aromatic diamine. It forms salts with solutions of organic and inorganic acids—for example, with HC1, a dichlorhydrate, and with H2 SO4, a monosulfate. Benzidine is obtained by the isomerization of hydrazobenzene under the action of mineral acids. Benzidine was first obtained by this method by N. N. Zinin in 1845. It is an important intermediate product in the production of azo dyes. It is also widely used in analytical chemistry for the qualitative and quantitative determination of various cations and anions that oxidize benzidine to colored compounds (to yellow in a strongly acidic medium and blue in a neutral medium). Benzidine is a carcinogenic substance; its maximum permissible concentration in air is 1 mg/m3.