Benzidine

Benzidine
Names


IUPAC name 1,1'-biphenyl-4,4'-diamine
Other names Benzidine, di-phenylamine, diphenylamine, 4,4'-bianiline, 4,4'-biphenyldiamine, 1,1'-biphenyl-4,4'-diamine, 4,4'-diaminobiphenyl, p-diaminodiphenyl
Identifiers
CAS Number	92-87-5^Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:80495^N
ChEMBL	ChEMBL15901^Y
ChemSpider	6844^Y
ECHA InfoCard	100.002.000
KEGG	C16444^Y
PubChem	7111
InChI InChI=1S/C12H12N2/c13-11-5-1-9(2-6-11)10-3-7-12(14)8-4-10/h1-8H,13-14H2^Y Key: HFACYLZERDEVSX-UHFFFAOYSA-N^Y InChI=1/C12H12N2/c13-11-5-1-9(2-6-11)10-3-7-12(14)8-4-10/h1-8H,13-14H2 Key: HFACYLZERDEVSX-UHFFFAOYAX
SMILES c2c(c1ccc(N)cc1)ccc(N)c2
Properties
Chemical formula	C₁₂H₁₂N₂
Molar mass	184.24 g/mol
Appearance	Grayish-yellow, reddish-gray, or white crystalline powder
Density	1.25 g/cm³
Melting point	122 to 125 °C (252 to 257 °F; 395 to 398 K)
Boiling point	400 °C (752 °F; 673 K)
Solubility in water	0.94 g/100 mL at 100 °C
Magnetic susceptibility (χ)	-110.9·10⁻⁶ cm³/mol
Related compounds
Related compounds	biphenyl
Hazards
Main hazards	carcinogenic
US health exposure limits (NIOSH):
PEL (Permissible)	occupational carcinogen
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N (what is ^YN ?)
Infobox references

Benzidine (trivial name), also called 1,1'-biphenyl-4,4'-diamine (systematic name), is an 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.

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.

Conversion of benzidine to the bis(diazonium) salt was once an integral step in the preparation of direct dyes (requiring no mordant). Treatment of this bis(diazonium) salt with 1-aminonaphthalene-4-sulfonic acid gives the once popular congo red dye. In the past, benzidine was used to test for blood. An enzyme in blood causes the oxidation of benzidine to a distinctively blue-coloured derivative. The test for cyanide relies on similar reactivity. Such applications have largely been replaced by methods using phenolphthalein/hydrogen peroxide and luminol.

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