Thionyl chloride (1.3 mL, 17.8 mmol) was added slowly and dropwise to a stirred mixed solution of 4-methoxy-2-methylbenzoic acid (1.0 g, 6 mmol) and methanol (50 mL) at room temperature and under nitrogen protection. The reaction mixture was heated to reflux and maintained for 3 hours. Upon completion of the reaction, the mixture was cooled to room temperature and concentrated under reduced pressure to give a light yellow crude product. The crude product was purified by silica gel column chromatography with the eluent of petroleum ether: ethyl acetate (9:1, v/v) to afford methyl 4-methoxy-2-methylbenzoate (1.11 g, 100% yield) in colorless liquid form. The product was characterized by 1H NMR (400 MHz, DMSO-d6) and ESI-MS: 1H NMR δ 7.81 (d, J = 9 Hz, 1H), 6.86 (d, J = 3 Hz, 1H), 6.83 (dd, J = 9, 3 Hz, 1H), 3.78 (s, 3H), 3.75 (s, 3H), 2.49 (s, 3H); ESI -MS m/z 181 ([M+H]+).
