Pentafluoropyridine, reduction

Pentafluoropyridine (292) is reduced440 in dry DMF at a mercury cathode to perfluoro-4,4 -bipyridyl (293) in the presence of hydroquinone as proton donor, 2,3,5,6-tetrafluoropyridine (294) is obtained [Eq. (150)]. Pentachloro-pyridine gives on reduction in dry DMF very little bipyridyl derivative, but tetrachloropyridine and bis(tetrachloropyridyl) mercury. 

Catalytic hydrogenation of pentafluoropyridine (16) gives a mixture of the tetrafluoropyridines (17)-(19), with reduction taking place most easily at the 4-position and to only a trace extent at the 3-position (equation 36). ... 

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