Polyhalogenoallenes. Part VIII. Routes to tetrafluoroallene and tetra-fluoropropyne

Abstract

Pyrolysis of 1,3-dibromo-1,1,3,3-tetrafluoropropane, from dibromodifluoromethane and vinylidene fluoride, over activated charcoal gives 3-bromo-1,1,3,3-tetrafluoropropene. Free-radical bromination of the propene yields 1,2,3-tribromo-1,1,3,3-tetrafluoropropane, which provides 2,3-dibromo-1,1,3,3-tetrafluoropropene when treated with aqueous potash. Debromination of the 2,3-dibromopropene with magnesium in tetrahydrofuran yields tetrafluoroallene. Tetrafluoropropyne is obtained by debromination with zinc of 1,2-dibromo-1,3,3,3-tetrafluoropropene, prepared by reaction of its isomer 2,3-dibromo-1,1,3,3-tetrafluoropropene with aluminium bromide.

The n.m.r. spectra of tetrafluoroallene and tetrafluoropropyne are discussed.