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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, C 8 H 6 N 2 , is best obtained from the condensation of co-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, CsHjONj, (formula II.), is obtained by condensing hydrazine with orthophthalaldehydoacid. On treatment .with phosphorus oxychloride it yields a chlorphthalazine which with zinc and hydrochloric acid gives isoindole, C 8 H 7 N, and with tin and hydrochloric acid phthalimidine, the second nitrogen atom being eliminated as ammonia.

I. Phthalazine. II. Phthalazone.

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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