To a suspension of phthalic anhydride (1) (22 g, 148.5 mmol, 1.0 eq.) in water (150 mL) was slowly added sodium hydroxide (12 g, 300.0 mmol, 2.0 eq.) and pure bromine (8.5 mL, 165.9 mmol, 1.1 eq.). The reaction mixture was stirred at 90 °C for 12 hours. Upon completion of the reaction, the mixture was cooled to 0 °C and filtered to collect a pale yellow solid. After washing the solid with cold water (50 mL), it was dissolved in sulfur dioxide (60 mL) and the mixture was heated to reflux for 5 hours. The reaction mixture was concentrated and dichloromethane (200 mL) was added to the residue and stirred at room temperature for 2 hours. After filtration, the filtrate was concentrated to give 5-bromoisobenzofuran-1,3-dione (2) (20 g, 71% yield) as a yellow solid.1H NMR (400 MHz, CDCl3) δ 8.16-8.17 (m, 1H), 8.06-8.07 (m, 1H), 7.89-7.90 (m, 1H).
