Polyfluorocyclopentadienes. Part II. The thermal dimer of perfluorocyclopentadiene: perfluoro(tricyclo[5,2,1,02,6]deca-3,8-diene)

Abstract

Perfluorocyclopentadiene dimerises readily to perfluoro(tricyclo[5,2,1,0^2,6]deca-3,8-diene), the structure of which was proved by chemical methods and by infrared, nuclear magnetic resonance, and mass spectroscopy. Pyrolysis of the dimer effects its breakdown by a retro-Diels–Alder cleavage to perfluorocyclopentadiene, accompanied by elimination of difluorocarbene and formation of tetrafluoroethylene and perfluoro(bicyclo[4,3,0]nona-2,4,7-triene). Pyrolysis of the last product over mild steel gives perfluoroindane and a compound believed to be perfluoroindene.

Dehalogenation with zinc dust of a trichloroheptafluorocyclopentane from the reaction of perchlorocyclopentadiene with cobalt trifluoride gives perfluorocyclopentadiene and 4-chloroheptafluorocyclopentene, oxidation of which affords β-chloropentafluoroglutaric acid. Direct fluorination of perchlorocyclopentadiene in 1,1,2-trichlorotrifluoroethane gives low yields of tetrachlorohexafluorocyclopentane and trichloroheptafluorocyclopentane.