[F:1][C:2]1[CH:20]=[C:19]([F:21])[CH:18]=[CH:17][C:3]=1[O:4][C:5]1[CH:6]=[C:7]([CH:11]=[CH:12][C:13]=1[N+:14]([O-:16])=[O:15])[C:8]([OH:10])=[O:9].[CH2:22](O)[CH3:23]>S(=O)(=O)(O)O>[F:1][C:2]1[CH:20]=[C:19]([F:21])[CH:18]=[CH:17][C:3]=1[O:4][C:5]1[CH:6]=[C:7]([CH:11]=[CH:12][C:13]=1[N+:14]([O-:16])=[O:15])[C:8]([O:10][CH2:22][CH3:23])=[O:9]A mixture of 3-(2,4-difluorophenoxy)-4-nitrobenzoic acid (1.0 g) and sulfuric acid (3 drops) in ethanol (5 ml) was refluxed for 8 hours. Ethanol was evaporated under reduced pressure, and the residue was dissolved in ethyl acetate, washed with a saturated aqueous solution of sodium bicarbonate, dried over magnesium sulfate, and concentrated to give pale brown needles of ethyl 3-(2,4-difluorophenoxy)-4-nitrobenzoate (1.1 g).
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