The general procedure for the synthesis of 1,3-dioxo-1,3-dihydroisobenzofuran-5-carbonyl chloride from trimellitic anhydride was as follows: trimellitic anhydride (50 g) and cyclohexane (45 mL) were added to a reaction flask containing 4-dimethylaminopyridine (0.05 g), and heated to 90 °C. Subsequently, thionyl chloride (37.2 g, molar ratio of trimellitic anhydride to thionyl chloride 1:1.2) was added slowly and the reaction mixture was refluxed for 6 hours. Upon completion of the reaction, it was confirmed that no gas was produced. At the end of the reaction, the remaining cyclohexane and excess thionyl chloride were removed by distillation at 90 °C and the solution was recovered at -0.085 MPa. Next, the 180-190 °C fraction was collected by vacuum distillation (vacuum of 750 mmHg) to give trimellitic anhydride chloride (47.6 g). After cooling, the product was a white solid with a melting point of 67.5~68.8 °C, and the HPLC purity was 99.5% in 86.9% yield.
