O-Phenylenediamine

{{DISPLAYTITLE:''o''-Phenylenediamine}} {{Use mdy dates|date=January 2023}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 415872334 | Name = ''o''-Phenylenediamine | ImageFile = o-phenylenediamine.png | ImageSize = 120px | ImageFileL1 = O-Phenylenediamine-from-xtal-Mercury-3D-bs.png | ImageSizeL1 = 125px | ImageFileR1 = O-Phenylenediamine-from-xtal-Mercury-3D-sf.png | ImageSizeR1 = 125px | ImageFile2 = 1,2-diaminobenzene sample.jpg | PIN = Benzene-1,2-diamine | OtherNames = ''o''-Phenylene diamine<br />1,2-Diaminobenzene<br />1,2-Phenylenediamine | Reference = <ref name=dupont>{{Cite web |url=http://www.dupont.com/specintermediates/opd.html |title=DuPont Specialty Intermediates: o-Phenylenediamine (OPD)<!-- Bot generated title --> |access-date=2006-04-25 |archive-url=https://web.archive.org/web/20080622070101/http://www.dupont.com/specintermediates/opd.html |archive-date=2008-06-22 |url-status=dead }}</ref> |Section1={{Chembox Identifiers | Abbreviations = | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 13837582 | InChI = 1/C6H8N2/c7-5-3-1-2-4-6(5)8/h1-4H,7-8H2 | InChIKey = GEYOCULIXLDCMW-UHFFFAOYAR | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 70582 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C6H8N2/c7-5-3-1-2-4-6(5)8/h1-4H,7-8H2 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = GEYOCULIXLDCMW-UHFFFAOYSA-N | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 95-54-5 | EINECS = 202-430-6 | PubChem = 7243 | UNII_Ref = {{fdacite|changed|FDA}} | UNII = 8B713N8Q0F | SMILES = Nc1ccccc1N | RTECS = SS7875000 | UNNumber = 1673 | MeSHName = | ChEBI_Ref = {{ebicite|changed|EBI}} | ChEBI = 34043 | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = }} |Section2={{Chembox Properties | C=6|H=8|N=2 | MolarMass= 108.144 g·mol⁻¹ | Appearance = white solid | Density = 1.031 g/cm³ | MeltingPtC = 102 to 104 | MeltingPt_notes = | BoilingPtC = 252 | BoilingPt_notes = Other sources: {{convert|256|to|258|C|F K}} | Solubility = soluble in hot water | SolubleOther = | Solvent = | pKa = {{ubl | 0.80 (doubly protonated form; 20&nbsp;°C, H₂O) | 4.57 (conjugate acid; 20&nbsp;°C, H₂O)<ref name="CRC97">{{cite book | editor= Haynes, William M. | year = 2016 | title = CRC Handbook of Chemistry and Physics | edition = 97th | publisher = CRC Press | isbn = 978-1498754286 | pages=5–89 | title-link = CRC Handbook of Chemistry and Physics }}</ref> }} | pKb = | MagSus = −71.98·10⁻⁶ cm³/mol }} |Section3={{Chembox Structure | CrystalStruct = | Coordination = | MolShape = }} |Section4={{Chembox Thermochemistry | DeltaHf = | DeltaHc = | Entropy = | HeatCapacity = }} |Section5={{Chembox Pharmacology | AdminRoutes = | Bioavail = | Metabolism = | HalfLife = | ProteinBound = | Excretion = | Legal_status = | Legal_US = | Legal_UK = | Legal_AU = | Legal_CA = | Pregnancy_category = | Pregnancy_AU = | Pregnancy_US = }} |Section6={{Chembox Explosive | ShockSens = | FrictionSens = | DetonationV = | REFactor = }} |Section7={{Chembox Hazards | ExternalSDS = [http://msds.chem.ox.ac.uk/PH/o-phenylenediamine.html Oxford MSDS] | MainHazards = | NFPA_ref = <ref>{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/source/hsdb/2893 |title= Hazardous Substances Data Bank (HSDB) : 2893 - PubChem| publisher=PubChem}}</ref> | NFPA-H = 3 | NFPA-F = 1 | NFPA-R = 0 | NFPA-S = | GHSPictograms = {{GHS06}}{{GHS07}}{{GHS08}}{{GHS09}} | GHSSignalWord = Danger | HPhrases = {{H-phrases|301|312|317|319|332|341|351|410}} | PPhrases = {{P-phrases|201|202|261|264|270|271|272|273|280|281|301+310|302+352|304+312|304+340|305+351+338|308+313|312|321|322|330|333+313|337+313|363|391|405|501}} | FlashPtC = 156 | AutoignitionPt = | ExploLimits = | PEL = }} |Section8={{Chembox Related | OtherAnions = | OtherCations = | OtherFunction = | OtherFunction_label = | OtherCompounds = }} }} '''''o''-Phenylenediamine''' ('''OPD''') is an organic compound with the formula C₆H₄(NH₂)₂. This aromatic diamine is an important precursor to many heterocyclic compounds. OPD is a white compound although samples appear darker owing to oxidation by air. It is isomeric with ''m''-phenylenediamine and ''p''-phenylenediamine.

==Preparation== Commonly, 2-nitrochlorobenzene is treated with ammonia to generate 2-nitroaniline, whose nitro group is then reduced:<ref name=Ullmann>{{Ullmann|doi=10.1002/14356007.a19_405|title=Phenylene- and Toluenediamines|year=2000|last1=Smiley|first1=Robert A.|isbn=3527306730}}</ref> :ClC₆H₄NO₂ + 2 NH₃ → H₂NC₆H₄NO₂ + NH₄Cl

:H₂NC₆H₄NO₂ + 3 H₂ → H₂NC₆H₄NH₂ + 2 H₂O

In the laboratory, the reduction of the nitroaniline is effected with zinc powder in ethanol, followed by purification of the diamine as the hydrochloride salt. Darkened impure samples can be purified by treatment of its aqueous solution with sodium dithionite and activated carbon.<ref>{{cite journal|title=''o''-Phenylenediamine |year=1939|volume=19|page=70|author=E. L. Martin|journal=Organic Syntheses|doi= 10.15227/orgsyn.019.0070}}</ref>

==Reactions and uses== ''o''-Phenylenediamine condenses with ketones and aldehydes to give rise to various valuable products. Its reactions with formic acids to produce benzimidazole.<ref>{{cite journal |doi=10.15227/orgsyn.019.0012 |title=Benzimidazole |journal=Organic Syntheses |date=1939 |volume=19 |page=12|first1=E. C.|last1=Wagner |first2= W. H.|last2=Millett }}</ref> Other carboxylic acids give 2-substituted benzimidazoles. The herbicides benomyl and fuberidazole are made in this manner. Thiophanate-methyl is another herbicide produced from o-phenylenediamine.<ref name=Ullmann/> Condensation with potassium ethylxanthate gives 2-mercaptobenzimidazole.<ref>{{cite journal |doi=10.15227/orgsyn.030.0056 |title=2-Mercaptobenzimidazole|journal=Organic Syntheses |date=1950 |volume=30 |page=56|first1=J. A. |last1=VanAllan|first2=B. D.|last2= Deacon }}</ref> With nitrous acid, ''o''-phenylenediamine condenses to give benzotriazole, a corrosion inhibitor.<ref>{{cite journal |doi=10.15227/orgsyn.020.0016 |title=1,2,3-Benzotriazole |journal=Organic Syntheses |date=1940 |volume=20 |page=16|first1=R. E.|last1=Damschroder|first2=W. D.|last2=Peterson }}</ref>

Quinoxalinedione may be prepared by condensation of ''o''-phenylenediamine with dimethyl oxalate. Mercaptoimidazole are commonly used as antioxidants in rubber production, obtained by condensing xanthate esters. Condensation of substituted ''o''-phenylenediamine with diketones yields various pharmaceuticals.<ref>See for example, {{cite journal | author = Renault, J.| title = Heterocyclic quinones. Quinoxaline-5,6 and 5,8 diones, potential antitumoral agents | journal = Eur. J. Med. Chem. | year = 1981 | volume = 16 | pages = 545–550|display-authors=etal}}</ref>

OPD is a ligand in coordination chemistry. Oxidation of metal-phenylenediamine complexes affords the diimine derivatives.<ref>{{cite journal | doi = 10.1039/C5CS00161G| title = New Avenues for Ligand-Mediated Processes – Expanding Metal Reactivity by the Use of Redox-Active Catechol, o-Aminophenol and o-Phenylenediamine Ligands| date = 2015| last1 = Broere| first1 = Daniël L. J.| last2 = Plessius| first2 = Raoul| last3 = Van Der Vlugt| first3 = Jarl Ivar| journal = Chemical Society Reviews| volume = 44| issue = 19| pages = 6886–6915| pmid = 26148803}}</ref> OPD condenses with salicylaldehyde to give chelating Schiff base ligands.

It reacts with thionyl chloride to give 2,1,3-benzothiadiazole: {{chem2|C6H4(NH2)2 + 2 SOCl2 -> C6H4(N)2S + SO2 + 4HCl}}

==Safety== With an LD₅₀ of 44&nbsp;mg/L (in water), ''o''-phenylenediamine is about 1000 times less toxic than the ''para''-isomer. Anilines are typically handled as if they are carcinogenic. For many applications, OPD has been replaced by safer alternatives such as 3,3',5,5'-tetramethylbenzidine.<ref>{{cite book|title=Enzyme Immunoassays: From Concept to Product Development|author=Deshpande SS|page=169|year=1996|isbn=978-0-412-05601-7|publisher=Chapman & Hall|location=New York}}</ref>

==References== <references/>

{{DEFAULTSORT:Phenylenediamine, o-}} Category:Diamines Category:Anilines Category:Chelating agents