o-Phenylenediamine

o-Phenylenediamine

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Names
IUPAC name Benzene-1,2-diamine
Other names o-Phenylene diamine 1,2-Diaminobenzene 1,2-phenylenediamine
Identifiers
CAS Number	95-54-5 Y
ChEBI	CHEBI:34043 N
ChEMBL	ChEMBL70582 Y
ChemSpider	13837582 Y
Jmol 3D model	Interactive image
UNII	8B713N8Q0F N
InChI InChI=1S/C6H8N2/c7-5-3-1-2-4-6(5)8/h1-4H,7-8H2 Y Key: GEYOCULIXLDCMW-UHFFFAOYSA-N Y 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	108.1 g/mol
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 pka2 = 4.57
Vapor pressure	{{{value}}}
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

o-Phenylenediamine 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, and is commonly referred to as OPD.

Preparation

Commonly 2-nitrochlorobenzene is treated with ammonia, and the resulting 2-aminonitrobenzene is then hydrogenated:

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. 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 prepared 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 give benzotriazole, a corrosion inhibitor. Condensation of substituted o-phenylenediamine with various diketones is used in the preparation of a variety of pharmaceuticals.

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.

o-Phenylenediamine can be used to make Tiabendazole, pyrazinamide, Morinamide, clemizole, chlormidazole,..

N-Methyl-1,2-phenylenediamine is used to make telmisartan.

Safety

With an LD₅₀ of 44 mg/L (aquatic), 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.