Phthalazines

Phthalazines, also called benzo-orthodiazines or benzopyridazines, are a group of heterocyclic compounds containing a ring complex. They are isomeric with the cinnolines. The parent substance of the group, phthalazine, C8H6N2, is best obtained from the condensation of w-tetrabromorthoxylene with hydrazine, or by the reduction of chlorphthalazine with phosphorus and hydroiodic acid. It possesses basic properties and forms addition products with alkyl iodides. On oxidation with alkaline potassium permanganate it yields pyridazine dicarboxylic acid. Zinc and hydrochloric acid decompose it with formation of orthoxylylene diamine. The keto-hydro derivative phthalazone (C8H6ON2), is obtained by condensing hydrazine with orthophthalaldehydoacid. On treatment with phosphorus oxychloride it yields a chlorphthalazine, which with zinc and hydrochloric acid gives isoindole (C8H7N), and with tin and hydrochloric acid, phthalimidine (C8H7ON), the second nitrogen atom being eliminated as ammonia.