The general procedure for the synthesis of methyl 3-bromo-4-methyl-5-nitrobenzoate from methanol and 3-bromo-4-methyl-5-nitrobenzoic acid was as follows: 3-bromo-4-methyl-5-nitrobenzoic acid (7.10 g, 27.3 mmol) and methanol (100 mL) were added to a 250 mL single-necked flask, and dichlorosulfoxide (2.96 mL, 41.0 mmol) was added slowly and dropwise at 25°C. The synthesis was carried out using the following formula. 41.0 mmol). The reaction mixture was stirred at 0 °C for 12 hours. Upon completion of the reaction, the mixture was concentrated in vacuum to remove the solvent. Saturated sodium bicarbonate solution (200 mL) was added to the residue and extracted with ethyl acetate (100 mL x 2). The organic phases were combined, washed with saturated brine (100 mL), dried over anhydrous sodium sulfate, filtered and concentrated in vacuum. Finally, the residue was purified by silica gel column chromatography (eluent: ethyl acetate/petroleum ether, v/v=1/30) to afford methyl 3-bromo-4-methyl-5-nitrobenzoate as a light yellow solid (6.36 g, 85% yield).
