C[O:2][C:3]([C:5]1[CH:6]=[N:7][N:8]([C:11]([CH3:14])([CH3:13])[CH3:12])[C:9]=1[CH3:10])=[O:4].[OH-].[Na+]>CO>[C:11]([N:8]1[C:9]([CH3:10])=[C:5]([C:3]([OH:4])=[O:2])[CH:6]=[N:7]1)([CH3:14])([CH3:12])[CH3:13]A solution of 1-tert-butyl-5-methyl-1H-pyrazole-4-carboxylic acid methyl ester (2.0 g, 10.19 mmol) in methanol (6.8 mL) cooled to 0° C. was treated dropwise with a 4N aqueous sodium hydroxide solution (5.1 mL, 20.4 mmol). The reaction was allowed to slowly warm to 25° C. The reaction was stirred at 25° C. overnight. At this time, the reaction was concentrated in vacuo to remove methanol. The residue was diluted with water (25 mL) and was then extracted with ethyl acetate (1×25 mL). The aqueous layer was then acidified to pH=1 with a 3N aqueous hydrochloric acid solution. The resulting precipitate was collected by filtration, washed with water and hexanes, and then dried in vacuo to afford 1-tert-butyl-5-methyl-1H-pyrazole-4-carboxylic acid (1.43 g, 78%) as a white solid.
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