Spectra and structure of derivatives of p-dihydroxypyridazine and phthalazine was written by Cheinker, Yu. N.;Gortinskaya, T. V.;Sycheva, T. P.. And the article was included in Journal de Chimie Physique et de Physico-Chimie Biologique in 1958.Reference of 18393-54-9 This article mentions the following:
IR and UV spectra of the dihydroxy derivatives of pyridazine and phthalazine, as well as their Me and Cl derivatives, were studied with a view to establishing the structure of the dihydroxy derivatives It was concluded that the compounds have mixed hydroxyoxo structures, both in the crystalline state and in solution Mols. of 3-hydroxy-6-pyridazine (I), as well as the 1-Me derivative, form chains in the crystalline state, in which each mol. is linked to 2 others by very stable H bonds. The H-bonds in 1-hydroxy-4-phthalazinone (II) do not lead to such chain formation in the crystalline state. The heats of fusion, solubility, and acidity of I, II, and derivatives are consistent with the proposed structures. IR spectra of the following compounds are given between 20 and 14 μ: 1,2-dimethyl-3,6-pyridazinedione, I, 3,6-dimethoxypyridazine, 1-methyl-3-methoxy-6-pyridazinone, 3-methoxy-6-pyridazinone, 1-methyl-3-hydroxy-6-pyridazinone, 2,3-dimethyl-1,4-phthalazinedione II, 1-methoxy-4-phthalazinone, 1-methoxy-4-chlorophthalazine, 3-chloro-6-pyridazinone, 3,6-dichloropyridazine, 3,6-bis(methylthio)pyridazine, 3-mercapto-6-thiopyridazinone, all in the crystalline state; also UV spectra in alc. In the experiment, the researchers used many compounds, for example, 2-Methyl-2,3-dihydrophthalazine-1,4-dione (cas: 18393-54-9Reference of 18393-54-9).
2-Methyl-2,3-dihydrophthalazine-1,4-dione (cas: 18393-54-9) belongs to phthalazine derivatives. Phthalazine is isomeric with other naphthyridines including quinoxaline, cinnoline and quinazoline. New methods for the functionalization of pyridazine, phthalazine, and cinnoline rings emerged in 2016. Buchwald and his group devised an asymmetric hydroarylation of vinylarenes.Reference of 18393-54-9
Referemce:
Phthalazine – Wikipedia,
Phthalazine | C8H6N2 – PubChem