Chemistry:O-Phenylenediamine
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| Names | |||
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| Preferred IUPAC name
Benzene-1,2-diamine | |||
| Other names
o-Phenylene diamine
1,2-Diaminobenzene 1,2-Phenylenediamine | |||
| Identifiers | |||
3D model (JSmol)
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| ChEBI | |||
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PubChem CID
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| UNII | |||
| UN number | 1673 | ||
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| Properties | |||
| C6H8N2 | |||
| Molar mass | 108.144 g·mol−1 | ||
| Appearance | white solid | ||
| Density | 1.031 g/cm3 | ||
| Melting point | 102 to 104 °C (216 to 219 °F; 375 to 377 K) | ||
| Boiling point | 252 °C (486 °F; 525 K) Other sources: 256 to 258 °C (493 to 496 °F; 529 to 531 K) | ||
| soluble in hot water | |||
| Acidity (pKa) |
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| -71.98·10−6 cm3/mol | |||
| Hazards | |||
| Safety data sheet | Oxford MSDS | ||
| GHS pictograms |    
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| GHS Signal word | Danger | ||
| H301, H312, H317, H319, H332, H341, H351, H410 | |||
| P201, P202, P261, P264, P270, P271, P272, P273, P280, P281, P301+310, P302+352, P304+312, P304+340, P305+351+338, P308+313, P312, P321, P322, P330, P333+313, P337+313, P363, P391, P405 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | 156 °C (313 °F; 429 K) | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |||
 verify (what is   ?)
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| Infobox references | |||
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 and the resulting 2-nitroaniline, whose nitro group is then reduced:[3]
- 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.[4]
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.[5] 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.[3] Condensation with potassium ethylxanthate gives 2-mercaptobenzimidazole.[6] With nitrous acid, o-phenylenediamine condenses to give benzotriazole, a corrosion inhibitor.[7]
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.[8]
OPD is a ligand in coordination chemistry. Oxidation of metal-phenylenediamine complexes affords the diimine derivatives.[9] OPD condenses with salicylaldehyde to give chelating Schiff base ligands.
Safety
With an LD50 of 44 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.[10]
References
- ↑ "DuPont Specialty Intermediates: o-Phenylenediamine (OPD)". http://www.dupont.com/specintermediates/opd.html.
- ↑ "Hazardous Substances Data Bank (HSDB) : 2893 - PubChem". PubChem. https://pubchem.ncbi.nlm.nih.gov/source/hsdb/2893.
- ↑ 3.0 3.1 Smiley, Robert A. (2000). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_405.
- ↑ E. L. Martin (1939). "o-Phenylenediamine". Organic Syntheses 19: 70. doi:10.15227/orgsyn.019.0070.
- ↑ Wagner, E. C.; Millett, W. H. (1939). "Benzimidazole". Organic Syntheses 19: 12. doi:10.15227/orgsyn.019.0012.
- ↑ VanAllan, J. A.; Deacon, B. D. (1950). "2-Mercaptobenzimidazole". Organic Syntheses 30: 56. doi:10.15227/orgsyn.030.0056.
- ↑ Damschroder, R. E.; Peterson, W. D. (1940). "1,2,3-Benzotriazole". Organic Syntheses 20: 16. doi:10.15227/orgsyn.020.0016.
- ↑ See for example, Renault, J. (1981). "Heterocyclic quinones. Quinoxaline-5,6 and 5,8 diones, potential antitumoral agents". Eur. J. Med. Chem. 16: 545–550.
- ↑ Broere, Daniël L. J.; Plessius, Raoul; Van Der Vlugt, Jarl Ivar (2015). "New Avenues for Ligand-Mediated Processes – Expanding Metal Reactivity by the Use of Redox-Active Catechol, o-Aminophenol and o-Phenylenediamine Ligands". Chemical Society Reviews 44 (19): 6886–6915. doi:10.1039/C5CS00161G. PMID 26148803.
- ↑ Deshpande SS (1996). Enzyme Immunoassays: From Concept to Product Development. New York: Chapman & Hall. p. 169. ISBN 978-0-412-05601-7.
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