[Preparation of dimethyl 5-bromoisophthalate from 5-bromoisophthalic acid] To a 500 mL three-necked flask equipped with a mechanical stirrer and a Dimroth condenser, 110 g (0.45 mol) of 5-bromoisophthalic acid, 500 mL of anhydrous methanol, and 10 g of concentrated sulfuric acid were added sequentially. The reaction mixture was heated under reflux conditions with stirring for 6 hours. Upon completion of the reaction, the mixture was left to cool to room temperature, followed by slow dropwise addition to 1 L of distilled water. The mixture was centrifuged with 5 wt% aqueous sodium bicarbonate solution to pH 7-8. The precipitated white precipitate was collected by filtration and washed with 2 L of distilled water in two portions. The resulting white solid was placed in a vacuum drying oven and dried under reduced pressure at 50 °C for 48 h to give 109 g (0.4 mol) of dimethyl 5-bromoisophthalate in 89% yield.
