C([O:3][C:4]([C:6]1[CH:7]=[N:8][C:9]2[C:14]([C:15]=1[OH:16])=[CH:13][C:12]([Br:17])=[CH:11][CH:10]=2)=[O:5])C>[OH-].[K+].O>[Br:17][C:12]1[CH:13]=[C:14]2[C:9](=[CH:10][CH:11]=1)[N:8]=[CH:7][C:6]([C:4]([OH:5])=[O:3])=[C:15]2[OH:16]A suspension of 6-bromo-4-hydroxy-quinoline-3-carboxylic acid ethyl ester (102.59 g, 337.7 mmol) in 10% potassium hydroxide in water (689 mL) was heated to reflux for 5 h to afford a light brown solution. After cooling to room temperature, the undissolved solid particles were removed by filtration and the filtrate was extracted with dichloromethane to remove any neutral impurities. The aqueous layer was neutralized with 3.0N hydrochloric acid to afford a white precipitate. Then, the solids were collected by filtration and washed with water. After drying in air, 91 g (98% yield) of 6-bromo-4-hydroxy-quinoline-3-carboxylic acid was isolated as a white solid: EI-HRMS m/e calcd for C10H6BrNO3 (M+) 266.9531, found 266.9521.
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