Methyl isothiazole-5-carboxylate (0.50 g, 3.49 mmol) was dissolved in a THF/MeOH solvent mixture (20 mL/5 mL) at room temperature, followed by slow addition of 1N NaOH solution (5.24 mL, 5.24 mmol). The reaction mixture was stirred continuously for 16 h at room temperature and the completion of the reaction was confirmed by thin layer chromatography (TLC) monitoring. Upon completion of the reaction, the reaction mixture was acidified to pH 2 with 1N HCl solution, at which point a precipitate was observed to be generated. The precipitate was separated by filtration and dried to afford the target product isothiazole-5-carboxylic acid (Compound 2) as a beige solid in a yield of 0.35 g (76% yield). The structure of the product was confirmed by 1H-NMR (400 MHz, DMSO-d6) with chemical shifts of δ 8.69 (d, 1H) and 7.85 (d, 1H), respectively.
