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Add <strong>[21617-16-3]5-chloro-4-oxo-2,3-dihydroquinoline</strong> (0.01 mol) to a 25 ml reaction flask, add 15 ml of acetonitrile, concentrated sulfuric acid (0.02 mol), stir for 20 minutes, and slowly add potassium permanganate. (0.02 mol), the reaction was stirred at 85 C, the progress of the reaction was monitored by TLC, and the reaction was stopped after 5 hours. After the reaction solution is cooled to room temperature, it is poured into 50 ml of water, stirred and filtered to obtain a crude 5-chloro-4-hydroxyquinoline, which is separated by silica gel column chromatography (column chromatography silica gel 100-200 mesh, eluent oil) Ether: ethyl acetate = 1:4). The eluent was concentrated to give the product. The yield was 87%, and the purity was 98%