Benzidine: Difference between revisions

{{Chembox

| Verifiedimages = changed

| Verifiedfields = changed

| verifiedrevid = 413886113

| ImageFile_Ref = {{chemboximage|correct|??}}

| ImageFile = Benzidine 200.svg

| ImageAlt = Skeletal formula of benzidine

| ImageFile1 = Benzidine-3D-balls.png

| ImageSize1 = 210

| ImageAlt1 = Ball-and-stick model of the benzidine molecule

| PIN = [1,1′-Biphenyl]-4,4′-diamine

| OtherNames = Benzidine, di-phenylamine, diphenylamine, 4,4'-bianiline, 4,4'-biphenyldiamine, 1,1'-biphenyl-4,4'-diamine, 4,4'-diaminobiphenyl, p-diaminodiphenyl, p-benzidine

|Section1={{Chembox Identifiers

| KEGG_Ref = {{keggcite|correct|kegg}}

| KEGG = C16444

| CASNo = 92-87-5

| CASNo_Ref = {{cascite|correct|CAS}}

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = 2X02101HVF

| PubChem = 7111

| ChEBI_Ref = {{ebicite|changed|EBI}}

| ChEBI = 80495

| EC_number = 202-199-1

| RTECS = DC9625000

| UNNumber = 1885

| ChemSpiderID =6844

| SMILES = c2c(c1ccc(N)cc1)ccc(N)c2

| Formula =C₁₂H₁₂N₂

| MolarMass =184.24 g/mol

| Appearance = Grayish-yellow, reddish-gray, or white crystalline powder<ref name=PGCH>{{PGCH|0051}}</ref>

| Density =1.25 g/cm³

| MeltingPtC = 122 to 125

| MeltingPt_notes =

| BoilingPtC = 400

| BoilingPt_notes =

| Solubility = 0.94 g/100 mL at 100 °C

| MagSus = -110.9·10⁻⁶ cm³/mol

|Section3={{Chembox Related

| OtherCompounds = [[biphenyl]]

| MainHazards =carcinogenic

| FlashPt =

| AutoignitionPt =

| PEL = occupational carcinogen<ref name=PGCH/>

| GHSPictograms = {{GHS07}}{{GHS08}}{{GHS09}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|302|350|410}}

| PPhrases = {{P-phrases|201|202|264|270|273|281|301+312|308+313|330|391|405|501}}

}}

'''Benzidine''' ([[trivial name]]), also called '''1,1'-[[biphenyl]]-4,4'-diamine''' ([[systematic name]]), is an [[organic compound]] with the [[chemical formula|formula]] (C₆H₄NH₂)₂. It is an [[aromatic]] [[amine]]. It is a component of a test for [[cyanide]]. Related derivatives are used in the [[organic synthesis|production]] of [[dyes]]. Benzidine has been linked to [[bladder cancer|bladder]] and [[pancreatic cancer]].<ref>{{cite web | url = http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp?sitearea=PED | title = Known and Probable Carcinogens | publisher = American Cancer Society | date = 2011-06-29 | access-date = 2007-01-12 | archive-date = 2008-03-17 | archive-url = https://web.archive.org/web/20080317051133/http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp?sitearea=PED | url-status = dead }}</ref>

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.<ref name=Ullmann>{{Ullmann |author1=Schwenecke, H. |author2=Mayer, D. | title = Benzidine and Benzidine Derivatives | year = 2005 | doi = 10.1002/14356007.a03_539 }}</ref> The '''benzidine rearrangement''', which proceeds intramolecularly, is a classic [[reaction mechanism|mechanistic]] puzzle in [[organic chemistry]].<ref>{{ cite book | author = March, J. | title = Advanced Organic Chemistry | edition = 5th | publisher = J. Wiley and Sons | year = 1992 | location = New York | isbn = 0-471-60180-2 }}</ref>

The conversion is described as a [5,5][[sigmatropic reaction]].<ref>{{ cite journal |author1=Shine, H. J. |author2=Zmuda, H. |author3=Park, K. H. |author4=Kwart, H. |author5=Horgan, A. G. |author6=Collins, C. |author7=Maxwell, B. E. | title = Mechanism of the benzidine rearrangement. Kinetic isotope effects and transition states. Evidence for concerted rearrangement | journal = Journal of the American Chemical Society | year = 1981 | volume = 103 | issue = 4 | pages = 955–956 | doi = 10.1021/ja00394a047 }}.</ref><ref>{{ cite journal |author1=Shine, H. J. |author2=Zmuda, H. |author3=Park, K. H. |author4=Kwart, H. |author5=Horgan, A. G. |author6=Brechbiel, M. | title = 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 = Journal of the American Chemical Society | year = 1982 | volume = 104 | issue = 9 | pages = 2501–2509 | doi = 10.1021/ja00373a028 }}</ref>

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|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]].

[[File:Congo-red-2D-skeletal.png|thumb|left|240px|The popular dye [[congo red]] is derived from benzidine.]]

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.<ref name=Ullmann/> These derivatives include, in order of scale, the following:

* [[3,3'-Dichlorobenzidine]]

* [[tolidine|''o''-tolidine]], 3,3'-dimethyl-4,4’-benzidine

* [[O-Dianisidine|''o''-dianisidine]] (3,3'-dimethoxy-4,4’-benzidine, CAS# 119-90-4, m.p.&nbsp;133&nbsp;°C)

* [[3,3'-Diaminobenzidine|3,3',4,4'-Tetraamino-diphenyl]], precursor to [[polybenzimidazole fiber]].

==Safety==

As with some other [[aromatic amine]]s such as [[2-naphthylamine]], benzidine has been significantly withdrawn from use in most industries because it is so carcinogenic. In August 2010 benzidine dyes were included in the U.S. EPA's List of Chemicals of Concern.<ref>{{ cite web |url=http://www.epa.gov/oppt/existingchemicals/pubs/actionplans/benzidine.html |title=Benzidine Dyes Action Plan Summary |publisher=U. S. Environmental Protection Agency |date=2010-08-18 |url-status=dead |archiveurl=https://web.archive.org/web/20100821232316/http://www.epa.gov/oppt/existingchemicals/pubs/actionplans/benzidine.html |archivedate=2010-08-21 }}</ref>

The manufacture of Benzidine has been illegal in the UK since at least 2002 under the Control of Substances Hazardous to Health Regulations 2002 (COSHH).

{{Organic reactions}}

{{Authority control}}

[[Category:Anilines]]

[[Category:Biphenyls]]

[[Category:Diamines]]