Benzidine

Benzidine (trivial name), also called 1,1'-biphenyl-4,4'-diamine (systematic name), is the organic compound with the formula (C₆H₄NH₂)₂. it is an aromatic amine. It is a component of a test for cyanide. Related derivatives are used in the production of dyes. Benzidine has been linked to bladder and pancreatic cancer.

Synthesis and properties

Benzidine is prepared in a two step process from nitrobenzene. First, the nitrobenzene is converted to 1,2-diphenylhydrazine, usually using iron powder as the reducing agent. Treatment of this hydrazine with mineral acids induces a rearrangement reaction to 4,4'-benzidine. Smaller amounts of other isomers are also formed. The benzidine rearrangement, which proceeds intramolecularly, is a classic mechanistic puzzle in organic chemistry.

The conversion is described as a [5,5]sigmatropic reaction.

In terms of its physical properties, 4,4'-benzidine is poorly soluble in cold water but can be recrystallized from hot water, where it crystallises as the monohydrate. It is dibasic, the deprotonated species has K_a values of 9.3 × 10⁻¹⁰ and 5.6 × 10⁻¹¹. Its solutions react with oxidizing agents to give deeply coloured quinone-related derivatives.