Step 1: 3-hydroxy-2-methylbenzoic acid (5 g, 33 mmol) and concentrated sulfuric acid (500 μl) were dissolved in methanol (20 mL) and heated to reflux for 15 hours. Upon completion of the reaction, the mixture was cooled to room temperature and subsequently partitioned between water and ethyl acetate. The aqueous phase was extracted with ethyl acetate, the organic phases were combined, washed sequentially with saturated sodium bicarbonate solution and brine, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to give methyl 3-hydroxy-2-methylbenzoate (5.46 g, 100% yield). The product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 9.71 (s, 1H), 7.20-7.17 (m, 1H), 7.11-7.07 (m, 1H), 7.01-6.97 (m, 1H), 3.79 (s, 3H), 2.28 (s, 3H). Mass spectrometry (EI) analysis showed the molecular ion peak m/z 166 (MH+, C9H10O3).
Step 2: 3-Hydroxy-2-methylbenzoic acid (5 g, 33 mmol) and concentrated sulfuric acid (3 mL) were dissolved in methanol (300 mL) and heated with reflux stirring for 48 hours. After completion of the reaction, it was cooled to room temperature and the pH was adjusted with solid sodium bicarbonate to 7. After partial evaporation of methanol, the residue was partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. The organic phase was washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated to give methyl 3-hydroxy-2-methylbenzoate (5.3 g, 32 mmol, 97% yield). The product was confirmed by 1H NMR (400 MHz, CDCl3): δ 7.41 (d, 1H), 7.13-7.09 (m, 1H), 6.94 (d, 1H), 3.89 (s, 3H), 2.46 (s, 3H). Mass spectrometry (EI) analysis showed the molecular ion peak m/z 167 (MH+, C9H10O3).
