[OH:1][CH:2]([C:4]1[CH:5]=[CH:6][C:7]2[O:12][CH:11]=[C:10]([C:13]#[N:14])[C:9](=[O:15])[C:8]=2[CH:16]=1)[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]=[CH:6][C:7]2[O:12][CH:11]=[C:10]([C:13]#[N:14])[C:9](=[O:15])[C:8]=2[CH:16]=1)(=[O:1])[CH3:3]To a solution of 0.645 part of 6-(1-hydroxyethyl)-4-oxo-4H-1-benzopyran-3-carbonitrile in 20 parts by volume of acetone under stirring at room temperature is added dropwise over a period of 1 hour 1.0 part 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 dark-green resins precipitated in the flask bottom is separated from the reaction mixture by decantation, and the solution is concentrated at room temperature to a one-third volume and then admixed with water to give precipitates. The precipitates collected by filtration is washed with water and recrystallized from ethyl acetate. The procedure yields 0.440 part of 6-acetyl-4-oxo-4H-1-benzopyran-3-carbonitrile as colorless crystals. Melting point: 170°-172° C
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