616-02-4

5754-18-7

The general procedure for the synthesis of 4-methylpyridazine-3,6-dione from citraconic anhydride was as follows: citraconic anhydride (24.0 mL, 270 mmol) was slowly added dropwise to a mixture of ice-bath-cooled hydrazine (4 M aqueous solution buffered to pH 6.5 by AcOH; 200 mL) and ethanol (250 mL), and the reaction mixture appeared to be in a light-yellow heterogeneous state. Subsequently, the mixture was heated under mild reflux conditions for 24 hours. Upon completion of the reaction, the mixture was allowed to cool to room temperature and the ethanol was evaporated under reduced pressure to give a white heterophase mixture. This mixture was diluted with water (250 mL) and the resulting white precipitate was collected by filtration. The precipitate was washed with water, placed on phosphorus pentoxide and dried under vacuum at room temperature for 24 h. A white powder of 4-methylpyridazine-3,6-dione was finally obtained (21.8 g; 65% yield). The product was characterized by 1H NMR (200 MHz, DMSO-d6): δ 2.00 (3H, s), 6.85 (1H, s), 11.22 (2H, brs).