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o-Phenylenediamine

(Redirected from 1,2-Diaminobenzene)

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.

o-Phenylenediamine[1]
Names
Preferred IUPAC name
Benzene-1,2-diamine
Other names
o-Phenylene diamine
1,2-Diaminobenzene
1,2-Phenylenediamine
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.002.210 Edit this at Wikidata
EC Number
  • 202-430-6
RTECS number
  • SS7875000
UNII
UN number 1673
  • InChI=1S/C6H8N2/c7-5-3-1-2-4-6(5)8/h1-4H,7-8H2 checkY
    Key: GEYOCULIXLDCMW-UHFFFAOYSA-N checkY
  • InChI=1/C6H8N2/c7-5-3-1-2-4-6(5)8/h1-4H,7-8H2
    Key: GEYOCULIXLDCMW-UHFFFAOYAR
  • Nc1ccccc1N
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)
  • 0.80 (doubly protonated form; 20 °C, H2O)
  • 4.57 (conjugate acid; 20 °C, H2O)[2]
-71.98·10−6 cm3/mol
Hazards
GHS labelling:
GHS06: ToxicGHS07: Exclamation markGHS08: Health hazardGHS09: Environmental hazard
Danger
H301, H312, H317, H319, H332, H341, H351, H410
P201, P202, P261, P264, P270, P271, P272, P273, P280, P281, P301+P310, P302+P352, P304+P312, P304+P340, P305+P351+P338, P308+P313, P312, P321, P322, P330, P333+P313, P337+P313, P363, P391, P405, P501
NFPA 704 (fire diamond)
[3]
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
1
0
Flash point 156 °C (313 °F; 429 K)
Safety data sheet (SDS) Oxford MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Preparation

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Commonly, 2-nitrochlorobenzene is treated with ammonia to generate 2-nitroaniline, whose nitro group is then reduced:[4]

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.[5]

Reactions and uses

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o-Phenylenediamine condenses with ketones and aldehydes to give rise to various valuable products. Its reactions with formic acids to produce benzimidazole.[6] 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.[4] Condensation with potassium ethylxanthate gives 2-mercaptobenzimidazole.[7] With nitrous acid, o-phenylenediamine condenses to give benzotriazole, a corrosion inhibitor.[8]

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.[9]

OPD is a ligand in coordination chemistry. Oxidation of metal-phenylenediamine complexes affords the diimine derivatives.[10] OPD condenses with salicylaldehyde to give chelating Schiff base ligands.

Safety

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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.[11]

References

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  1. ^ "DuPont Specialty Intermediates: o-Phenylenediamine (OPD)". Archived from the original on June 22, 2008. Retrieved April 25, 2006.
  2. ^ Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 5–89. ISBN 978-1498754286.
  3. ^ "Hazardous Substances Data Bank (HSDB) : 2893 - PubChem". PubChem.
  4. ^ a b Smiley, Robert A. (2000). "Phenylene- and Toluenediamines". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_405. ISBN 3527306730.
  5. ^ E. L. Martin (1939). "o-Phenylenediamine". Organic Syntheses. 19: 70. doi:10.15227/orgsyn.019.0070.
  6. ^ Wagner, E. C.; Millett, W. H. (1939). "Benzimidazole". Organic Syntheses. 19: 12. doi:10.15227/orgsyn.019.0012.
  7. ^ VanAllan, J. A.; Deacon, B. D. (1950). "2-Mercaptobenzimidazole". Organic Syntheses. 30: 56. doi:10.15227/orgsyn.030.0056.
  8. ^ Damschroder, R. E.; Peterson, W. D. (1940). "1,2,3-Benzotriazole". Organic Syntheses. 20: 16. doi:10.15227/orgsyn.020.0016.
  9. ^ See for example, Renault, J.; et al. (1981). "Heterocyclic quinones. Quinoxaline-5,6 and 5,8 diones, potential antitumoral agents". Eur. J. Med. Chem. 16: 545–550.
  10. ^ 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.
  11. ^ 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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