O-Phenylenediamine

o-Phenylenediamine is a chemical compound with the formula C6H4(NH2)2. This aromatic diamine is an important precursor to many heterocycles. It is isomeric with m-phenylenediamine and p-phenylenediamine.

o-Phenylenediamine condenses with ketones and aldehydes to give rise to Schiff bases. This reaction allows the synthesis of substituted benzimidazoles. Also, quinoxaline dione may be prepared by condensation of o-phenylenediamine with dimethyl oxalate.

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 coloured and often exist in multiple stable oxidation states.