o-Phenylenediamine

o-Phenylenediamine (OPD) is an organic compound with the formula C6H4(NH2)2. This aromatic diamine is an important precursor to many heterocyclic compounds. 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
EC Number
  • 202-430-6
RTECS number
  • SS7875000
UNII
UN number 1673
Properties
C6H8N2
Molar mass 108.144 g·mol−1
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
Safety data sheet Oxford MSDS
GHS pictograms
GHS Signal word Danger
GHS hazard statements
 H301, H312, H317, H319, H332, H341, H351, H400, 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)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
2
0
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).
N verify (what is YN ?)
Infobox references

Preparation

Commonly, 2-nitrochlorobenzene is treated with ammonia and the resulting 2-aminonitrobenzene is then hydrogenated:[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.[4] This compound darkens in air; impurities may be removed by treating a hot aqueous solution with sodium dithionite (reducing agent) and activated carbon, and allowing the product to cool crystallize.

Reactions and uses

o-Phenylenediamine condenses with ketones and aldehydes to give rise to a variety of useful products. Reactions with carboxylic acids and their derivatives afford benzimidazoles. The herbicide benomyl is made in this manner. Also, quinoxalinedione may be prepared by condensation of o-phenylenediamine with dimethyl oxalate. Condensation with xanthate esters affords mercaptoimidazoles, which are used as antioxidants in rubber products. Treatment with nitrous acid gives benzotriazole, a corrosion inhibitor. Condensation of substituted o-phenylenediamine with various diketones is used in the preparation of a variety of pharmaceuticals.[5]

In coordination chemistry, phenylenediamine is an important ligand precursor. Schiff base derivatives, such as those derived from salicylaldehyde, are excellent chelating ligands. Oxidation of its metal-phenylenediamine complexes affords the diimine derivatives, which are intensely colored and often exist in multiple stable oxidation states.[6]

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.[7]

gollark: A fellow chaotic neutral, interesting.
gollark: They're defined that way in DND.
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gollark: It is very boring of you to put CON/DEX/STR/INT/WIS/CHA *all* at identical slightly-above-average levels.
gollark: Anyway, lawful good, *really*?

References
  1. "DuPont Specialty Intermediates: o-Phenylenediamine (OPD)". Archived from the original on 2008-06-22. Retrieved 2006-04-25.
  2. Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 5–89. ISBN 978-1498754286.
  3. Robert A. Smiley "Phenylene- and Toluenediamines" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_405
  4. E. L. Martin (1943). "o-Phenylenediamine". Organic Syntheses.; Collective Volume, 2, p. 501
  5. 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.
  6. Warren, L. F. (1977). "Synthesis of [M'-N4] and [M'-N6] Complexes Based on o-Benzoquinone Diimine with Cobalt, Iron, and Ruthenium". Inorg. Chem. 16 (11): 2814–2819. doi:10.1021/ic50177a028.
  7. 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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