Tuesday, March 20, 2012

Benzidine



  • Benzidine is a synthetic chemical that does not occur naturally. It is a crystalline (sandy or sugar-like) solid that may be grayish-yellow, white, or reddish-gray in color. 
  • Benzidine, the trivial name for 4,4'-diaminobiphenyl, is the solid organic compound with the formula (C6H4NH2)2. This aromatic amine is a component of a test for cyanide and also in the production of dyes.
  • 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.
  • Benzidine - based dyes are largely classified as direct dyes, since they may be applied directly to fabrics or other substrates without pre-treatment or without subsequent processes that firmly attach the dye to the substrate.



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