Ethyl 4-methyl-5-trimethylsilylpyrazole-3-carboxylate (3.3 g, 14.6 mmol) was dissolved in ethanol (100 mL) and 1 M aqueous sodium hydroxide (73 mL, 73 mmol). The reaction mixture was heated to reflux for 18 hours and subsequently cooled to room temperature. The reaction solution was acidified with 1 M hydrochloric acid (100 mL) and concentrated to near dryness. The residue was extracted with ethyl acetate (3 x 100 mL), the organic phases were combined, dried over anhydrous sodium sulfate, and concentrated to give 4-methylpyrazole-3-carboxylic acid (1.90 g, 99% yield). The product was confirmed by NMR hydrogen spectrum (DMSO-d6, 400 MHz): δ 13.00 (broad single peak, 2H), 7.50 (single peak, 1H), 2.19 (single peak, 3H).
