[OH2:1].Cl[C:3]1[N:4]=[N:5][C:6]([O:9][C:10]2[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=2)=[CH:7][CH:8]=1.[OH-].[Na+]>C(O)=O>[O:9]([C:6]1[CH:7]=[CH:8][C:3](=[O:1])[NH:4][N:5]=1)[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=13.1 21 ml of water are added to a solution of 3.10 g (15.0 mmol) of 3-chloro-6-phenoxypyridazine in 21 ml of formic acid, and the mixture is heated at 95° C. for 85 hours. The reaction mixture is cooled and brought to a pH of 6 using 23% aqueous sodium hydroxide solution. The precipitate formed is filtered off with suction, washed with water and dried in vacuo, giving 6-phenoxy-2H-pyridazin-3-one as colourless crystals; ESI 189.
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