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

摘要

Ionic and free radical addition of halogen systems were carried out with perfluoroheptene-I (1), octafluorocyclopentene (2), IH,lH,2H- perfluorooctene-I (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 I 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 C12, Br2, BrCl, and ICI from ring-opening of the halonium ions at the ten-ninal carbon. Disubstituted perfluoroalkenes 2 and 4 did not react tonically with C12, Br2, BrCl, or ICI. Free radical reactions of C12, Br2, BrCl, and ICI 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.