C([O:3][C:4]([C:6]1[O:7][C:8]2[C:13]([C:14](=[O:16])[CH:15]=1)=[CH:12][CH:11]=[C:10]([OH:17])[CH:9]=2)=[O:5])C.C(=O)([O-])[O-].[Na+].[Na+].Cl>C(O)C.O>[CH:11]1[C:10]([OH:17])=[CH:9][C:8]2[O:7][C:6]([C:4]([OH:5])=[O:3])=[CH:15][C:14](=[O:16])[C:13]=2[CH:12]=12-Ethoxycarbonyl-7-hydroxychromone (14.5 g, 62 mmol) is initially introduced dissolved in ethanol (400 ml) at 50° C., and sodium carbonate (20 g, 190 mmol) dissolved in deionised H2O (200 ml) is added dropwise. The mixture is refluxed at 80° C. for 3 hours with stirring. After cooling, the mixture is acidified using 2N HCl. The precipitated white solid is filtered off with suction, washed until neutral and dried.
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