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 pe rfluoroheptene-1 (1), octafluorocyclopentene (2), 1H,1H,2H-perfluorooctene- 1 (3) and perfluoro-4-methyl-2-pentene (4). The terminal alkene 1 was treat ed with chlorine in tert-butyl alcohol as solvent with mercury catalyst und er reaction conditions that assure an ionic pathway. Bromine did not react with 1 under similar conditions. Chlorine monofluoride reacts with 1 in met hylene chloride to give 2-chloroperfluoroheptane, Alkene 3 is more reactive and gives products with electrophiles Cl-2, Br-2, BrCl, and ICl from ring- opening of the halonium ions at the terminal carbon. Disubstituted perfluor oalkenes 2 and 4 did not react ionically with Cl-2, Br-2, BrCl, or ICl. Fre e radical reactions of Cl-2, Br-2, BrCl, and ICl give good yields of dihalo products with 1 and 3. Yields are poor for the photochemical bromination of disubstituted perfluoroalkenes 2 and 4 since the dibromoproducts are in ph otochemical equilibrium with the alkene. (C) 2000 Elsevier Science S.A. All rights reserved.