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NMR spectra of 3-hydroxypyridazine 1-oxides and their monomethylated derivatives were examined and structural propriety of their nitrated and halogenated products was confirmed by the analyses of the NMR spectra. Furthermore, in 3-hydroxypyridazine 1-oxides, predominance of enol form tautomer was proved by NMR data. The conclusion was also drawn by other spectral data (UV and IR).

3-Hydroxypyridazine 1-oxide (I) and its methyl homologs (II), (III), and (IV) were submitted to electrophilic substitutions such as nitration and halogenation. Due to the additional polar effect of both N-oxide and hydroxyl groups, introduction of nitro group and halogen in 4-and/or 6-positions was successfully concluded. By heating with potassium hydrosulfide, nucleophilic substitution of the brominated compounds (XXXI and XXXVI) was also carried out, affording mercapto compounds (XXXII and XXXVII).

3-Halogenopyridazines (I) were alloued to react with hydrazine hydrate in the presence of Pd-CaCO3 and alkali to afford the symmetrical 3, 3'-bipyridazines (IIa-IIg). When an equimolar mixture of two kinds of 3-chloropyridazines of different substituents was subjected to this condensation reaction, the unsymmetrical 3, 3'-bipyridazines (VIIa-VIId) were formed. Various 3-chloropyridazine N-oxides (X) were subjected to the condensation reaction and the expected 3, 3'-bipyridazine di-N-oxides (XI) were obtained in low yields.