1911 Encyclopædia Britannica/Phthalazines

PHTHALAZINES (benzo-orthodiazines or benzopyridazines), in organic chemistry a group of heterocyclic compounds containing the ring complex shown in formula I. They are isomeric with the cinnolines (q.v.). The parent substance of the group, phthalazine, C₈H₆N₂, is best obtained from the condensation of ω-tetrabromorthoxylene with hydrazine (D. Gabriel, Ber., 1893, 26, p. 2210), or by the reduction of chlorphthalazine with phosphorus and hydriodic acid (Ber., 1897, p. 3024). 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, (formula II.), is obtained by condensing hydrazine with orthophthalaldehydo-acid. On treatment with phosphorus oxychlonde 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.

	N		CO	|NH N
	N		CH
I. Phthalazine.		II. Phthalazone.