General procedure for the synthesis of 4-chloro-7-hydroxyquinoline using 4-chloro-7-methoxyquinoline as starting material: 4-chloro-7-methoxyquinoline (3.86 g, 20 mmol), 40% hydrobromic acid (30 mL) and acetic anhydride (20 mL) were mixed and heated to reflux, and the progress of the reaction was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture was cooled to room temperature. Subsequently, 100 mL of water was added to the reaction mixture and the pH was adjusted to 6.0 with 20% sodium hydroxide solution, at which point a large amount of solid precipitated. After filtration, washing and drying, an off-white solid product (3.53 g, 98.6% yield) was obtained.
