[F:1][CH:2]([F:13])[C:3]1[C:7]([C:8](F)=[O:9])=[C:6]([F:11])[N:5]([CH3:12])[N:4]=1.[OH-:14].[Na+].Cl>S1(=O)(=O)CCCC1>[F:11][C:6]1[N:5]([CH3:12])[N:4]=[C:3]([CH:2]([F:13])[F:1])[C:7]=1[C:8]([OH:14])=[O:9]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 were added dropwise to 400 mL of an aqueous 1N NaOH solution. During the addition, the temperature was kept below 20. After 2 h of stirring at room temperature, the mixture was carefully acidified to pH 2 using concentrated hydrochloric acid. The white precipitate formed was filtered off, washed with water and dried. This gave 6 g of 5-fluoro-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid as a white solid.
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