Reactions involving fluoride ion. Part VII. Reactions of polyfluoroethylenes with pentafluoropyridine and tetrafluoropyridazine

Abstract

Reactions induced by fluoride ion of the olefins CF₂CFX (X = Cl, Br, or H) with pentafluoropyridine (I) and with tetrafluoropyridazine (VII) are described. With chlorotrifluoroethylene, pentafluoroethyl and chlorotetrafluoroethyl derivatives were obtained. A pseudo-S_N2′ process, involving attack of fluoride ion at the aromatic ring, is proposed as the mechanism for the displacement of chloride ion. This was confirmed by a reaction involving cyanuric fluoride. Reaction with bromotrifluoroethylene led to pentafluoroethyl derivatives in the case of the pyridazine (VII), via polyfluoroalkylation, but a more complex exchange reaction occurred with the pyridine (I). Reactions with trifluoroethylene gave mainly tars, although a small amount of a product arising from proton abstraction was isolated. Reactions with 1,1-dichlorodifluoroethylene gave products similar to those obtained with chlorotrifluoroethylene in the case of the pyridazine (VII) but no reaction occurred with the pyridine (I).