[OH-:1].[Na+].[F:3][CH:4]([F:15])[C:5]1[C:9]([C:10](F)=[O:11])=[C:8]([F:13])[N:7]([CH3:14])[N:6]=1.Cl>S1(=O)(=O)CCCC1>[F:13][C:8]1[N:7]([CH3:14])[N:6]=[C:5]([CH:4]([F:15])[F:3])[C:9]=1[C:10]([OH:1])=[O:11]To 400 ml of a 1N sodium hydroxide aqueous solution, was added dropwise 67.5 g of a solution (10% molar) of 3-(difluoromethyl)-5-fluoro-1-methyl-1H-pyrazole-4-carbonyl fluoride in tetrahydrothiophene 1,1-dioxide. The temperature was kept below 20° C. during the addition. After 2 hours of stirring at room temperature, the reaction mixture was carefully acidified to pH 2 with concentrated aqueous hydrochloric acid. The resulting white precipitate was filtered, washed with water, and dried to yield 6 g of 5-fluoro-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid as a white solid.
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