The general procedure for the synthesis of 3-bromo-5-methoxybenzoic acid from 2-amino-5-bromo-3-methoxybenzoic acid was as follows: 2-amino-5-bromo-3-methoxybenzoic acid (4 g, 16.3 mmol) was dissolved in water (20 mL) at 0 °C. Subsequently, concentrated hydrochloric acid (7.5 mL, 90 mmol) and tetrahydrofuran (20 mL) were added to this solution. The reaction mixture was stirred for 30 minutes and then sodium nitrite (3.16 g, 45.8 mmol) was added. After continued stirring for 2 h, hypophosphorous acid (5.1 g, 76 mmol, 50% aqueous solution) was added to the reaction system. The mixture was stirred at room temperature for 16 hours. Upon completion of the reaction, the precipitate was collected by filtration, washed with water and dried under vacuum to afford the target product 3-bromo-5-methoxybenzoic acid (3.2 g, 85% yield). The product was analyzed by ESI-MS, m/z: 229.2 [M-H]
