Preparation of 3,5-Dichloropyridazine:
2,4,4,4-Tetrachlorocrotonaldehyde is dissolved in a solvent, and a mixture of semicarbazide hydrochloride, water, and solvent is added dropwise under controlled temperature conditions. The reaction is stirred for 5 hours. Afterward, the reaction mixture is concentrated under reduced pressure to remove the solvent. Water is added, and the temperature is lowered to 5°C, allowing a solid to precipitate. The solid is filtered and recrystallized using a dichloromethane/petroleum ether mixture, yielding 3,5-dichloropyridazine as a white crystalline solid.
