[Br:1][C:2]1[CH:3]=[CH:4][C:5]2[C:9]3[CH:10]=[CH:11][CH:12]=[CH:13][C:8]=3[S:7](=[O:14])[C:6]=2[CH:15]=1.S(=O)(=O)(O)O.[N+:21]([O-])([OH:23])=[O:22]>C(O)(=O)C>[Br:1][C:2]1[CH:3]=[CH:4][C:5]2[C:9]3[CH:10]=[CH:11][C:12]([N+:21]([O-:23])=[O:22])=[CH:13][C:8]=3[S:7](=[O:14])[C:6]=2[CH:15]=1A flask equipped with a stirrer and a thermometer was charged with 69.8 g of glacial acetic acid and 27.9 g of 3-bromodibenzothiophene-5-oxide prepared in Example 1-1 in a nitrogen atmosphere, and cooled to 10° C. 239.8 g of concentrated sulfuric acid was added dropwise, and the resulting mixture was cooled to −2° C. Then 72.0 g of 70 wt % nitric acid was added dropwise at −2 to 8° C., and the resulting mixture was stirred at or below 5° C. for 2 hours. The reaction mass was poured into 1200 g of ice water to terminate the reaction, and stirred further. The reactant was filtered, washed with water, and dried. The resulting dry cake was washed with ethanol to obtain 31.9 g of 3-bromo-7-nitrodibenzothiophene-5-oxide. The product was subjected to elemental analysis, the results of which are as follows:
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