Hydrochloric Acid → 4-carboxy-6-(3-fluoro-4-methylphenyl)-2H-pyridazin-3-one

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To a solution of ethyl 2-ethoxycarbonyl-4-(3-fluoro-4-methylphenyl)-2-hydroxy-4-oxobutanoate (8.41 9, 25.8 mmol) in isopropanol (100 mL) was added hydrazine monohydrate (2.84 g, 56.8 mmol), and the mixture was heated under stirring at 100 for 6 hours. Then, 2 mol/L sodium hydroxide was added, and the mixture was stirred further at the same temperature for 4 hours. The reaction mixture was ice-cooled, and concentrated hydrochloric acid was added to acidify the system. The precipitate was collected by filtration, thoroughly washed with water and dried to yield the title compound as a slightly yellow crystalline powder (5.67 g, 87.7%).

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