Electrophilic versus free radical reactions of halogens and halogen systems with perfluoroalkenes and a perfluoroalkylethylene

Ionic and free radical addition of halogen systems were carried out with perfluoroheptene-1 (1), octafluorocyclopentene (2), 1H,1H,2H-perfluorooctene-1 (3) and perfluoro-4-methyl-2-pentene (4). The terminal alkene 1 was treated with chlorine in tert-butyl alcohol as solvent with mercury catalyst under reaction conditions that assure an ionic pathway. Bromine did not react with 1 under similar conditions. Chlorine monofluoride reacts with 1 in methylene chloride to give 2-chloroperfluoroheptane. Alkene 3 is more reactive and gives products with electrophiles Cl2, Br2, BrCl, and ICl from ring-opening of the halonium ions at the terminal carbon. Disubstituted perfluoroalkenes 2 and 4 did not react ionically with Cl2, Br2, BrCl, or ICl. Free radical reactions of Cl2, Br2, BrCl, and ICl give good yields of dihaloproducts with 1 and 3. Yields are poor for the photochemical bromination of disubstituted perfluoroalkenes 2 and 4 since the dibromoproducts are in photochemical equilibrium with the alkene.