The general procedure for the synthesis of 3,6-dichloro-5-nitropyridazin-4-amine from 3,6-dichloropyridazin-4-amine is as follows: Commercially available 3,6-dichloropyridazin-4-amine (15 g, 92 mmol, 1 eq.) was slowly added dropwise to concentrated fuming nitric acid (12 ml, 290 mmol, 3.15 eq.). Concentrated sulfuric acid (60 ml) was slowly added to the reaction mixture at 0 °C. The reaction system was warmed up to 60 °C and the reaction was stirred at this temperature for 3 hours. After completion of the reaction, the reaction mixture was carefully poured into crushed ice and neutralized with aqueous sodium hydroxide to pH=7. The aqueous phase was extracted with dichloromethane, the organic phase was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure and the residue was washed with tert-butyl methyl ether to give pure 3,6-dichloro-5-nitropyridazin-4-amine (8.5 g, 45% yield).
