63001-30-9

65202-50-8

B. Methyl 6-hydroxypyridazine-3-carboxylate prepared as described above was mixed with phosphorochloridic acid, slowly heated to reflux temperature and the reaction was maintained for 2.5 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the excess phosphoryl chloride was subsequently evaporated under reduced pressure. The residue was carefully decanted into ice water and the precipitated solid was collected by filtration. The precipitate was washed sequentially with saturated sodium bicarbonate solution and deionized water and finally dried in a vacuum drying oven to afford the target product, methyl 6-chloropyridazine-3-carboxylate, as a yellow solid (4.359 g, 79% yield).