Coumarin-6-carboxylic acid

51690-26-7

7734-80-7

The general procedure for the synthesis of 2-oxo-2H-benzopyran-6-carboxylic acid from 2-oxo-2H-benzopyran-6-carboxaldehyde was as follows: a mixture of 6-methylcoumarin (25 g, 0.156 mol) and chlorobenzene (25 ml) was slowly added dropwise to a solution of 62.5% sulfuric acid (152 ml containing 35 g, 0.4026 mol), followed by dropwise addition of 62.5% sulfuric acid (20 ml). The reaction was continued at 80-90°C for 1 hour. After completion of the reaction, the reaction system was cooled to room temperature and water (150 ml) was added. Under ice bath conditions, 25% ammonia (43 ml) was added slowly and dropwise, followed by the addition of EtOAc (50 ml) and butanone (100 ml), extraction was carried out twice (20 ml each time), the organic layers were combined and the ketone solvents were removed by steam. DMSO (15 ml) and HCl (10 ml) were added to the system and the residue was reintroduced into the reaction mixture. 25% sodium chlorite (55 ml) was added slowly and dropwise at 15-40°C. The mixture was stirred at this temperature for 30 min, followed by stirring at 74-80°C for 15 min. After completion of the reaction, the mixture was cooled to room temperature and the organic layer was separated. Water (125 ml) was added to the organic layer and 25% ammonia (20 ml) was added dropwise at 30-40°C until the pH of the solution reached 10 and the aqueous layer was separated. DMSO (70 ml) was added to the aqueous layer and HCl (16 ml) was added dropwise at 30-40°C and the temperature was raised to 65-75°C by adding HCl (15 ml) dropwise. The mixture was stirred at the same temperature for 30 min. Finally 14.8 g of yellow solid product was obtained in 50% yield.