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Chlorine in 3-chlorotetrafluoro-and 3,5-dichlorotrifluoro-pyridines is replaced by hydrogen, using hydrogen and a palladium catalyst. Similarly, reduction of pentafluoropyridine gives 2,3,5,6-tetrafluoropyridine, by replacement of fluorine. The hydro-compounds react readily with butyl-lithium in hexane and carbonation of the resultant lithio-derivatives yields perfluoronicotinic or -isonicotinic acids and, using hexane-tetrahydrofuran, trifluoropyridine-3,5-dicarboxylic acid. pK, values for the acids have been determined and are compared with the values for other acids.

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