Any one of three isomeric aromatic compounds, C6H4(NH2)2, with strong basic properties. 1,2-Diaminobenzene is a yellow-brown crystalline solid, m.p. 104°C, used as a photographic developer and in making dyes. 1,3-Diaminobenzene is a colourless crystalline solid, m.p. 63°C, which turns brown on standing in air. It is made by reducing 1,3-dinitrobenzene with iron and hydrochloric acid, and is used for making dyes. 1,4-Diaminobenzene is a white crystalline solid, m.p. 147°C, which rapidly darkens on standing in air. It is made by the reduction of 1,4-nitrophenylamine and is used as a photographic develop and hair dye.