4576-90-3

693-92-5

4576-90-3

The general procedure for the synthesis of isothiazole-3-carboxylic acid using 3-methylisothiazole as starting material was as follows: chromium(IV) oxide (9.00 mmol) was added batchwise to a solution of 3-methylisothiazole (3.03 mmol) dissolved in fuming sulphuric acid (10 mL) under the condition of ice bath at 0°C. The reaction mixture was gradually warmed to room temperature and the reaction was stirred at this temperature for 16 hours. Upon completion of the reaction, the mixture was diluted with ice water (100 mL) followed by multiple extractions with ether (6 x 200 mL). All organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. The resulting crude product was purified by preparative high performance liquid chromatography (HPLC) to give isothiazole-3-carboxylic acid in 13% yield as a white solid. The structure of the product was confirmed by 1H-NMR (400 MHz, DMSO-d6) and LC/MS: 1H-NMR δ 3.43 (s, 1H), 9.17 (d, 1H), 7.80 (d, 1H), 3.43 (s, 1H); LC/MS (ESI) m/z [M + 1]+ 128.