[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:3][CH:4]([F:15])[C:5]1[C:9]([C:10]([OH:1])=[O:11])=[C:8]([F:13])[N:7]([CH3:14])[N:6]=1To 400 ml of a 1N sodium hydroxide aqueous solution, is added dropwise 67.5 g of a solution (0.1 M) of 3-(difluoromethyl)-5-fluoro-1-methyl-1H-pyrazole-4-carbonyl fluoride in tetrahydro-thiophene-1,1-dioxide. The temperature is kept below 20° C. during the addition. After 2 hours of stirring at room temperature, the reaction mixture is carefully acidified to pH 2 with concentrated aqueous hydrochloric acid. The resulting white precipitate is filtered, washed with water, and dried to yield 6 g of 3-(difluoromethyl)-5-fluoro-1-methyl-1H-pyrazole-4-carboxylic acid as a white solid. 1H NMR (400 MHz, DMSO-d6) δ ppm: 3.90 (s, 3H); 7.22 (t, 1H, JHF=53.55 Hz); 13.33 (s, 1H).
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