[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].[OH-].[K+].S(S([O-])=O)([O-])=[O:26].[Na+].[Na+]>O>[Cl:7][C:8]1[C:17]([C:18]([OH:26])=[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 69.65 g of potassium permanganate in 730 cm3 of water is added in the course of 1 hour, while keeping the temperature between 10° and 14° C., to a stirred suspension, cooled to about 10° C., of 45.7 g of 2-chloro-6,7,8-trifluoro-3-formyl-1,4-dihydroquinoline in 585 cm3 of N potassium hydroxide solution. The mixture is stirred for a further 30 minutes at about 10° C. 12 g of sodium dithionite are added and the mixture is stirred for 10 minutes at a temperature close to 10° C. and filtered through diatomaceous silica and the filter cake is washed with 3 times 400 cm3 of water. The filtrate and the washings are combined and 70 cm3 of a 35% aqueous solution of hydrochloric acid are added. The precipitate formed is extracted with 3 times 500 cm3 of ethyl acetate. 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 in a mixture of 100 cm3 of diethyl ether and 100 cm3 of diisopropyl ether, drained and washed with 100 cm3 of the same mixture. 46.43 g of 2-chloro-6,7,8-trifluoroquinoline-3-carboxylic acid are obtained in the form of a colourless solid which decomposes at 225°-230° C. and which is used for the subsequent steps without further purification.
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