[F:1][C:2]1[CH:10]=[CH:9][C:8]([N+:11]([O-:13])=[O:12])=[CH:7][C:3]=1[C:4]([OH:6])=[O:5].S(=O)(=O)(O)O.[CH3:19]O>>[F:1][C:2]1[CH:10]=[CH:9][C:8]([N+:11]([O-:13])=[O:12])=[CH:7][C:3]=1[C:4]([O:6][CH3:19])=[O:5]A solution of 2-fluoro-5-nitro-benzoic acid (3.702 g, 20 mmol) in anhydrous methanol (10.00 mL) was treated with 98% sulphuric acid and the solution was heated to reflux for 4 hours. The solvent was removed under vacuum and the residue was dissolved in ethyl acetate (50 mL). The solution was washed with saturated aqueous sodium bicarbonate (3×10 mL), brine until neutrality ant then water, and dried over anhydrous sodium sulphate. The solvent was removed under vacuum to afford a thick oil that started to crystallize. After adding n-hexane (3 mL) the crude was stored for 2 days in the fridge. The crystalline compound was filtered and washed with n-hexane to yield 3.147 g of the pure compound. By concentrating the mother liquors a second crop was obtained (390 mg) (y=89%).
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