General procedure for the synthesis of 4,5-dichloropyridazine-3,6-diol from 2,3-dichloromaleic anhydride: water (170 mL) and hydrazine dihydrochloride salt (41.9 g, 398.8 mmol) were added to a round bottom flask. The solution was heated to reflux followed by the addition of 2,3-dichloromaleic anhydride (66.6 g, 398.9 mmol) in batches. The reflux condition was maintained and the reaction mixture was stirred continuously for 30 minutes. Upon completion of the reaction, the solution was cooled to room temperature and the precipitated solid was collected by filtration to afford the target product 4,5-dichloropyridazine-3,6-diol (i.e., 4,5-dichloro-1,2-dihydropyridazine-3,6-dione, 65 g, 90% yield) as a white solid. Mass spectral analysis showed (M + H)+ = 181.0.
