[NH2:1][C:2]1[C:11]([F:12])=[C:10]([F:13])[C:9]([F:14])=[C:8]2[C:3]=1[C:4](=[O:23])[C:5]([C:18]([O:20]CC)=[O:19])=[CH:6][N:7]2[CH:15]1[CH2:17][CH2:16]1.C(O)(=O)C.S(=O)(=O)(O)O>O>[NH2:1][C:2]1[C:11]([F:12])=[C:10]([F:13])[C:9]([F:14])=[C:8]2[C:3]=1[C:4](=[O:23])[C:5]([C:18]([OH:20])=[O:19])=[CH:6][N:7]2[CH:15]1[CH2:16][CH2:17]128.7 g of ethyl 5-amino-1-cyclopropyl-6,7,8-trifluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylate (0.088 mol), 160 ml of acetic acid, and a mixture of 100 ml of water and 18 ml of concentrated sulfuric acid were stirred at 100-110° C. for 40 minutes. The reacting mixture was cooled and filtered. The precipitate was recrystallized from chloroform-ethanol to give 25.6 g 5-amino-1-cyclopropyl-6,7,8-trifluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid (Sparcarboxylic acid, 0.086 mol), mp. 293-295C., in 98.0% yield.
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