The general procedure for the synthesis of 6-hydroxypyridazine-3-carboxylic acid from 6-oxo-1,4,5,6-tetrahydropyridazine-3-carboxylic acid was as follows: to a solution of 6-oxo-1,4,5,6-tetrahydropyridazine-3-carboxylic acid (2.50 g, 17.59 mmol) in toluene (44 mL) was added sequentially copper acetate (450 mg, 2.48 mmol), sodium carbonate ( 7.01 g, 66.14 mmol) and pyridine (4.4 mL). The reaction mixture was stirred and mixed at room temperature, then warmed to 100 °C and stirred continuously for 16 hours. After completion of the reaction, the insoluble solid was removed by filtration and the filtrate was concentrated under reduced pressure to afford 6-oxo-1,6-dihydropyridazine-3-carboxylic acid as an off-white solid (1.80 g, 73% yield). Mass spectrometry result: m/z = 177.0 [M + H]+.
