[F:1][C:2]1[CH:3]=[C:4]([CH:9]=[CH:10][C:11]=1[OH:12])[C:5](OC)=[O:6].O.[NH2:14][NH2:15].Cl>O>[F:1][C:2]1[CH:3]=[C:4]([CH:9]=[CH:10][C:11]=1[OH:12])[C:5]([NH:14][NH2:15])=[O:6]10.00 g (58.8 mM) of methyl 3-fluoro-4-hydroxybenzoate and 17.5 ml of 80%-hydrazine hydrate were mixed and stirred for 1 hour and 20 minutes at 100° C., followed by cooling to room temperature. The resultant mixture was poured into 150 ml of iced water and 16.8 ml of concentrated hydrochloric acid was added thereto (pH=about 8), followed by addition of common salt and stirring at room temperature to precipitate a crystal. The crystal was recovered by filtration and stirred in methanol at room temperature. The resultant crystal was recovered from the above mixture by filtration to obtain 9.26 g of 3-fluoro-4-hydroxybenzohydrazide (Yield: 92.6%).
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