The general procedure for the synthesis of 3-methoxy-1-methyl-1H-pyrazole-5-carboxylic acid from methyl 3-methoxy-1-methyl-1H-pyrazole-5-carboxylate was as follows: to a solution of methanol (5 mL) containing methyl 3-methoxy-1-methyl-1H-pyrazole-5-carboxylate (220.7 mg, 1.30 mmol) was added 1 M aqueous sodium hydroxide (1.30 mL, 1.30 mmol). The reaction mixture was stirred at room temperature for 5 hours. Upon completion of the reaction, the methanol was removed by concentration under reduced pressure, and the pH was adjusted to acidic with 1 M hydrochloric acid solution, followed by extraction with ethyl acetate (3 × 10 mL). The organic layers were combined, washed with saturated aqueous sodium chloride solution (10 mL) and dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure to give the title compound 3-methoxy-1-methyl-1H-pyrazole-5-carboxylic acid (163 mg, 80% yield) as a white solid. Mass spectrum (ESI-): m/z 155 [M-H]-. 1H NMR (300 MHz, DMSO-d6) δ 3.77 (3H, s), 3.92 (3H, s), 6.20 (1H, s), 13.38 (1H, br s).
