[OH:1][C:2]1[C:7]([C:8]([OH:10])=[O:9])=[CH:6][N:5]=[C:4]([CH3:11])[CH:3]=1.[Br:12]Br>C(O)(=O)C.O>[Br:12][C:3]1[C:4]([CH3:11])=[N:5][CH:6]=[C:7]([C:2]=1[OH:1])[C:8]([OH:10])=[O:9]4-Hydroxy-6-methylnicotinic acid 19 (95.6 g, 0.625 mol) was dissolved in acetic acid (950 ml) and water (190 ml), and bromine (39 ml, 0.750 mol) was added over 15 minutes. After the solution was stirred at 60° C. for 5 hours, the solvent was distilled off under reduced pressure, methanol (200 ml) was added and, crystals were collected by filtration. The solution was distilled off under reduced pressure, methanol was added again to the residue, and crystalls were collected by filtration. A total of 142.2 g (98%) of 5-bromo-4-hydroxy-6-methylnicotinic acid 20 was obtained as a colorless crystal.
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