[O:1]=[C:2]1[C:14]2[CH:13]=[C:12]([C:15]([OH:17])=[O:16])[CH:11]=[CH:10][C:9]=2[C:8]2[C:3]1=[CH:4][C:5]([C:18]([OH:20])=[O:19])=[CH:6][CH:7]=2.[OH:21]O>S(=O)(=O)(O)O>[O:21]=[C:2]1[O:1][C:14]2[CH:13]=[C:12]([C:15]([OH:17])=[O:16])[CH:11]=[CH:10][C:9]=2[C:8]2[CH:7]=[CH:6][C:5]([C:18]([OH:20])=[O:19])=[CH:4][C:3]1=2A suspension of 12.0 g (0.045 mole) of 9-oxo-fluorene-2,7-dicarboxylic acid in 100 ml of concentrated sulfuric acid is slowly reacted with 12.0 ml of a 30% hydrogen peroxide solution. The reaction is strongly exothermic and is controlled by cooling the stirred reaction mixture in a water bath. The cooled reaction mixture is poured onto 500 ml of an ice water mixture, filtered and washed with water. The residue is resuspended in water, stirred, filtered and washed with a total of about 350 ml of deionized water, to yield 11.2 g of 6-oxo-6H-dibenzo[b,d] pyran-3,8-dicarboxylic acid having a m.p. greater than 300° C. EXAMPLE IV
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