o-Phenylenediamine

o-Phenylenediamine[1]
Names
	Preferred IUPAC name Benzene-1,2-diamine
	Other names o-Phenylene diamine; 1,2-Diaminobenzene; 1,2-Phenylenediamine
Identifiers
CAS Number	95-54-5 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:34043 ;
ChEMBL	ChEMBL70582 ;
ChemSpider	13837582 ;
ECHA InfoCard	100.002.210
EC Number	202-430-6;
PubChem CID	7243;
RTECS number	SS7875000;
UNII	8B713N8Q0F ;
UN number	1673
CompTox Dashboard (EPA)	DTXSID3025881 ;
	InChI InChI=1S/C6H8N2/c7-5-3-1-2-4-6(5)8/h1-4H,7-8H2 Key: GEYOCULIXLDCMW-UHFFFAOYSA-N ; InChI=1/C6H8N2/c7-5-3-1-2-4-6(5)8/h1-4H,7-8H2 Key: GEYOCULIXLDCMW-UHFFFAOYAR;
	SMILES Nc1ccccc1N;
Properties
Chemical formula	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)
Solubility in water	soluble in hot water
Acidity (pKa)	0.80 (doubly protonated form; 20 °C, H2O); 4.57 (conjugate acid; 20 °C, H2O)[2];
Magnetic susceptibility (χ)	-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
GHS precautionary statements	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)	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).
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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. It is isomeric with m-phenylenediamine and p-phenylenediamine.

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 herbicides benomyl and fuberidazole are made in this manner. Thiophanate-methyl is another herbicide produced from o-phenylenediamine.[3]

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]

References

"DuPont Specialty Intermediates: o-Phenylenediamine (OPD)". Archived from the original on 2008-06-22. Retrieved 2006-04-25.
Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 5–89. ISBN 978-1498754286.
Smiley, Robert A. (2000). "Phenylene- and Toluenediamines". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_405.
E. L. Martin (1939). "o-Phenylenediamine". 19: 70. doi:10.15227/orgsyn.019.0070. Cite journal requires |journal= (help)
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.
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.
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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[dupont-1] "DuPont Specialty Intermediates: o-Phenylenediamine (OPD)". Archived from the original on 2008-06-22. Retrieved 2006-04-25.

[CRC97-2] Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 5–89. ISBN 978-1498754286.

[Ullmann-3] Smiley, Robert A. (2000). "Phenylene- and Toluenediamines". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_405.

[4] E. L. Martin (1939). "o-Phenylenediamine". 19: 70. doi:10.15227/orgsyn.019.0070. Cite journal requires |journal= (help)

[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.