General procedure for the synthesis of 2-(acetyloxy)benzoic anhydride from acetylsalicylic acid:
1. prepare a suspension of 2-acetoxybenzoic acid (5.0 g, 28 mmol) in 30 mL of dichloromethane.
2. a solution of N,N'-dicyclohexylcarbodiimide (DCC, 2.9 g, 13.9 mmol) in 10 mL of dichloromethane was added to the above suspension.
3. The reaction mixture was stirred at room temperature overnight.
4. After completion of the reaction, the by-product dicyclohexylurea (DCU) was filtered through a glass filter and washed with a small amount of dichloromethane.
5. The solvent was evaporated and the resulting residue was dissolved in ethyl acetate.
6. The resulting suspension was filtered through a glass filter to remove residual DCU.
7. The filtrate was evaporated to give 2-(acetyloxy)benzoic anhydride as a clear thick oil, which solidified after storage at -20 °C.
Yield: 4.6 g (quantitative).
1H NMR (CDCl3, 400 MHz): δ 8.08 (d, 2H, J = 7.9 Hz), 7.70 (t, 2H, J = 7.8 Hz), 7.40 (t, 2H, J = 7.7 Hz), 7.19 (d, 2H, J = 8.1 Hz), 2.31 (s, 6H).
13C NMR (CDCl3, 100 MHz): δ 169.42, 159.29, 151.83, 135.54, 132.24, 126.29, 124.42, 121.69, 20.89.
IR (KBr) νmax (cm-1): 3570 (w), 3491 (w), 3445 (w), 3332 (br), 3205 (w), 3100 (s, CH), 2932 (s, CH), 2855 (w), 2409 (w), 2032 (w), 1789 (br, C=O), 1728 (br, C=O) , 1603 (s, C=C), 1581 (s), 1484 (s), 1451 (s), 1369 (s), 916 (s), 506 (s).
HRMS m/z Calcd. for C18H14Na7O6: (M + Na)+ 365.0637. Found: 365.0638.
Melting point: 80-85°C.
