926. Polyfluoroheterocyclic compounds. Part V. Catalytic reduction of perfluoro- and chlorofluoro-pyridines and the preparation of polyfluoropyridinecarboxylic acids

Abstract

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.

Organic Fluorine Chemistry

“…Similarly, in pentafluoropyridine, mainly fluorine in position 4 (para to nitrogen) is replaced by hydrogen to give tetrafluoropyridine. In 3-chlorotetrafluoropyridine, catalytic hydrogenation preferentially replaces chlorine, whereas lithium aluminum hydride reduction preferentially replaces fluorine in position 4 [Equation (l52)1 [289). 30% 5% trace…”

New polyfluorinated aromatic and aza-aromatic diselenides, selenyl chlorides, non-symmetric selenides and selenoxides

“…Selected bond lengths (Å ), bond and torsion angles ( @ ): Compound 3: C-Se 1.899(5) and 1.907(5), Se-Se 2.3385(12); C-Se-Se 101.8(2) and 100.45 (19); C-Se-Se-C À106.52. Compound 5: C-Se 1.914(4) and 1.911(4), Se-Se 2.3192(8); C-Se-Se 99.71 (12) and 100.13 (12); C-Se-Se-C À79.44 (17). solutions in CDCl 3 unless otherwise indicated.…”

“…Starting 2,3,5,6-tetrafluoro-1-chlorobenzene [14], 2,3,5,6-tetrafluoroanisole [15], N,N-dimethyl-2,3,5,6-tetrafluoroaniline [16], 2,4,6-trifluoropyridine and 2,3,4,6-tetrafluoropyridine [17], and pentafluoropyridine [18] were described before.…”

Polychloroheteroaromatic Compounds

“…Likewise, 4,5,6-trichloro-2-trichloromethylpyridine is reduced by hydriodic acid to 5-chloro-2-trichloromethylpyridine [349]. The J3-chlorine atoms in 3-chlorotetrafluoro-and 3,5-dichlorotrifluoro-pyridine are replaced, however, on catalytic hydrogenation over a palladium catalyst [350]. This probably reflects the fact that chlorine is more readily reduced than fluorine under these conditions.…”