[OH:1][CH:2]([C:4]1[CH:5]=[C:6]2[C:11](=[CH:12][CH:13]=1)[O:10][CH:9]=[C:8]([C:14]1[NH:18][N:17]=[N:16][N:15]=1)[C:7]2=[O:19])[CH3:3].CC(C)=O.S(=O)(=O)(O)O>[O-2].[O-2].[O-2].[Cr+6].O>[C:2]([C:4]1[CH:5]=[C:6]2[C:11](=[CH:12][CH:13]=1)[O:10][CH:9]=[C:8]([C:14]1[NH:15][N:16]=[N:17][N:18]=1)[C:7]2=[O:19])(=[O:1])[CH3:3]To a solution of 2.58 parts of 6-(1-hydroxyethyl)-3-(1H-tetrazol-5-yl)chromone in 700 parts by volume of acetone kept at 9°-15° C there is added dropwise over a period of 30 minutes 4.5 parts by volume of a solution which is prepared from chromium trioxide, 97% sulfuric acid and water in a ratio of 6.0 parts: 3.6 parts by volume: 18 parts by volume. The reaction mixture is concentrated at a temperature lower than 30° C to a one-tenth volume and then admixed with 700 parts by volume of water to give precipitates. The precipitates are recovered by filtration and recrystallized from dimethylformamide. The procedure yields 1.70 parts of 6-acetyl-3-(1H-tetrazol-5-yl)chromone as colorless crystals.
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