[F:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]([OH:10])=[O:9])=[CH:4][C:3]=1[N:11]1[C:15](=[O:16])[C:14]([CH3:17])=[C:13]([CH3:18])[C:12]1=[O:19].[N+:20]([O-])([OH:22])=[O:21]>S(=O)(=O)(O)O>[F:1][C:2]1[CH:7]=[C:6]([N+:20]([O-:22])=[O:21])[C:5]([C:8]([OH:10])=[O:9])=[CH:4][C:3]=1[N:11]1[C:15](=[O:16])[C:14]([CH3:17])=[C:13]([CH3:18])[C:12]1=[O:19]26.3 g of N-(2-fluoro-5-carboxyphenyl)-2,3-dimethylmaleic acid imide are introduced in portions, at 5°, into 230 ml of 96% sulphuric acid. There is then added dropwise to this mixture, while stirring vigorously at the same temperature, 5 ml of 100% nitric acid. The whole is further stirred overnight at room temperature and then poured into ice. The product which precipitates is filtered with suction, washed with water, dried and recrystallised from acetonitrile. 28 g of N-(2-fluoro-5-carboxy-4-nitrophenyl)-2,3-dimethylmaleic acid imide which has a melting point of 264°-265° is thus obtained.
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