Sulfuric Acid → 1-(Ethoxycarbonyl)-4-(4-fluoroanilino)piperidine-4-carboximidic acid

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Reaction Steps

127.5 parts of ethyl 4-cyano-4-(4-fluorophenylamino)-1-piperidinecarboxylate are added dropwise to 360 parts of concentrated sulfuric acid (exothermic reaction: temperature rises to 50° C.). Upon completion, the whole is stirred overnight at room temperature. The reaction mixture is poured onto crushed ice and 250 parts of water are added. The whole is alkalized with sodium hydroxide solution at a temperature of 40°-50° C., whereupon the product is precipitated. It is filtered off, washed with water and taken up in boiling trichloromethane. The latter is washed twice with water, dried and evaporated, yielding 82.1 parts of less pure ethyl 4-carbamoyl-4-(4-fluorophenylamino)-1-piperidinecarboxylate.

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