Methyl iodide (0.972 mL) was slowly added to a solution of DMF (8 mL) containing 3-mercaptobenzoic acid (601 mg, 3.9 mmol) and potassium carbonate (2.7 g, 19.5 mmol) under ice bath conditions. The reaction mixture was gradually warmed to room temperature and stirred continuously for 1 hour. After the reaction was completed, the reaction mixture was diluted with ethyl acetate, washed with water three times sequentially, and the organic phase was dried with anhydrous sodium sulfate, filtered and concentrated to give methyl 3-methylthiobenzoate (684 mg, 96%, yellow oil).1H NMR (CDCl3, δ ppm): 7.90 (s, 1H), 7.80 (d, 1H), 7.44 (d, 1H), 7.35 (t, 1H). 7.35 (t, 1H), 3.92 (s, 3H), 2.53 (s, 3H). Methyl 3-methylthiobenzoate (684 mg, 3.8 mmol) was dissolved in a mixed solvent of methanol (8 mL) and THF (8 mL), 1 N NaOH aqueous solution (5.6 mL, 5.6 mmol) was added, and the reaction was heated for 1 hr at 70 °C. After completion of the reaction, the reaction mixture was concentrated and the residue was diluted with water. After adjusting the pH to 2 with 1 N HCl, the aqueous phase was extracted with ethyl acetate, the organic phase was washed with water and saturated saline in turn, dried over anhydrous sodium sulfate, filtered and concentrated to give 3-methylthiobenzoic acid (616 mg, 97%, white solid).1H NMR (DMSO, δ ppm): 13.1 (bs, 1H), 7.76 (s, 1H), 7.70 (d, 1H ), 7.51 (d, 1H), 7.44 (t, 1H), 2.52 (s, 3H).
