[Mn]([O-])(=O)(=O)=O.[K+].[Cl:7][C:8]1[NH:9][C:10]2[C:15]([CH2:16][C:17]=1[CH:18]=[O:19])=[CH:14][C:13]([F:20])=[C:12]([F:21])[C:11]=2[F:22].S(S([O-])=O)([O-])=[O:24].[Na+].[Na+]>O.[OH-].[K+]>[Cl:7][C:8]1[C:17]([C:18]([OH:24])=[O:19])=[CH:16][C:15]2[C:10](=[C:11]([F:22])[C:12]([F:21])=[C:13]([F:20])[CH:14]=2)[N:9]=1A solution of potassium permanganate (69.65 g) in water (730 cc) is added in the course of 1 hour to a stirred suspension, cooled to approximately 10° C., of 2-chloro-6,7,8-trifluoro-3-formyl-1,4-dihydroquinoline (45.7 g) in N potassium hydroxide (585 cc), while the temperature is maintained at between 10° and 14° C. The mixture is left stirring for a further 30 minutes at approximately 10° C. Sodium dithionite (12 g) is added and the mixture is stirred for 10 minutes at a temperature in the region of 10° C., filtered through diatomaceous silica and washed with water (3×400 cc). The filtrate and washings are combined and treated with 35% strength aqueous hydrochloric acid solution (70 cc). The precipitate formed is extracted with ethyl acetate (3×500 cc). The combined organic extracts are dried over magnesium sulphate, filtered and concentrated under reduced pressure (20 kPa) at 50° C. The residue is taken up with a mixture of ethyl ether (100 cc) and isopropyl ether (100 cc), drained and washed with the same mixture (100 cc). 2-Chloro-6,7,8-trifluoro-3-quinolinecarboxylic acid (46.43 g) is obtained in the form of a colorless solid, decomposing at 225°-230° C., which is used without further purification for the subsequent steps.
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