|Jmol-3D images||Image 1|
|Molar mass||184.24 g/mol|
|Appearance||Grayish-yellow, reddish-gray, or white crystalline powder|
|Melting point||122-125 °C|
|Boiling point||400 °C|
|Solubility in water||0.94 g/100 mL at 100 °C|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Benzidine (trivial name), also called 4,4'-diaminobiphenyl (systematic name), 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 has been linked to bladder and pancreatic cancer. Since August 2010 benzidine dyes are included in the EPA's List of Chemicals of Concern.
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.
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 Ka values of 9.3 × 10−10 and 5.6 × 10−11. Its solutions react with oxidizing agents to give deeply coloured quinone-related derivatives.
The test for cyanide relies on similar reactivity.
A variety of derivatives of 4,4’-benzidine are commercially produced on the scale of one to a few thousand kilograms per year, mainly as precursors to dyes and pigments. These derivatives include, in order of scale, the following:
- 3,3'-dichlorobenzidine (CAS# 91-94-1, m.p. 132–133 °C)
- o-tolidine (2,2'-dimethyl-4,4’-benzidine, CAS# 119-93-7, m.p. 130 °C)
- o-dianisidine (2,2'-dimethoxy-4,4’-benzidine, CAS# 119-90-4, m.p. 133 °C)
- 3,3',4,4'-Tetraaminodiphenyl (CAS# 91-95-2, m.p. 178 °C) is a precursor to polybenzimidazole fiber, a high-strength, flame-resistant material.
- NIOSH Pocket Guide to Chemical Hazards Centers for Disease Control and Prevention. 2011-04-04
- "Known and Probable Carcinogens". American Cancer Society. 2011-06-29.
- "Benzidine Dyes Action Plan Summary". U. S. Environmental Protection Agency. 2010-08-18.
- Schwenecke, H.; Mayer, D. (2005). "Benzidine and Benzidine Derivatives". Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.
- March, J. (1992). Advanced Organic Chemistry (5th ed.). New York: J. Wiley and Sons. ISBN 0-471-60180-2.
- Shine, H. J.; Zmuda, H.; Park, K. H.; Kwart, H.; Horgan, A. G.; Collins, C.; Maxwell, B. E. (1981). "Mechanism of the benzidine rearrangement. Kinetic isotope effects and transition states. Evidence for concerted rearrangement". Journal of the American Chemical Society 103 (4): 955–956. doi:10.1021/ja00394a047..
- Shine, H. J.; Zmuda, H.; Park, K. H.; Kwart, H.; Horgan, A. G.; Brechbiel, M. (1982). "Benzidine rearrangements. 16. The use of heavy-atom kinetic isotope effects in solving the mechanism of the acid-catalyzed rearrangement of hydrazobenzene. The concerted pathway to benzidine and the nonconcerted pathway to diphenyline". Journal of the American Chemical Society 104 (9): 2501–2509. doi:10.1021/ja00373a028.