[NH2:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[C:4]([F:11])[CH:3]=1.[C:12](OC(=O)C)(=[O:14])[CH3:13]>C(O)(=O)C.O>[C:12]([NH:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[C:4]([F:11])[CH:3]=1)(=[O:14])[CH3:13]A mixture of 4-amino-2-fluoro-benzoic acid (5.61 g, 36.2 mmol) and acetic anhydride (5.13 mL, 54.3 mmol) in 60 mL acetic acid was stirred at 60° C. overnight. The mixture was taken up in 250 mL water and stirred for 30 min. The precipitate was filtered and washed with water. The filtrate was washed with ethyl acetate. The organic phase was neutralized with sat. K2CO3 (aq) and concentrated i.vac. The precipitate was filtered and combined with the first isolated precipitate.
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