[OH:1][C:2]1[C:11]2[N:10]=[CH:9][CH:8]=[CH:7][C:6]=2[C:5]([C:12]([OH:14])=[O:13])=[CH:4][CH:3]=1.S(=O)(=O)(O)O.[CH3:20]O>>[OH:1][C:2]1[C:11]2[N:10]=[CH:9][CH:8]=[CH:7][C:6]=2[C:5]([C:12]([O:14][CH3:20])=[O:13])=[CH:4][CH:3]=116.25 g (86 mmol) of 8-hydroxy-5-quinolinecarboxylic acid were dissolved in 70 ml of methanol, 3 ml of concentrated sulfuric acid were added and the mixture was heated under reflux for 25 hours. The solvent was then removed and the residue was taken up in ice-water, adjusted to a pH of 8 using sodium carbonate solution and filtered hot. The residue was extracted with methyl-tert-butyl ether for 7 hours on a jacketed Soxhlet extractor, and the solvent was subsequently removed from the extract. This gave 6.8 g of a brown powder;
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