Fluoro-olefin chemistry. Part 15. Thermal reaction of hexafluoropropene with hydrocarbon olefins

Abstract

The thermal reaction of hexafluoropropene with hydrocarbon olefins can give three different types of product, 1,1,2-trifluoro-2-trifluoromethylcyclobutanes, hexafluoroalkenes of the type R¹R²CCR³·CH₂·CHF·CF₂·CF₃, and 1,1,2-trifluoro-2-trifluoromethylcyclopentanes. The cyclobutanes are formed via diradical intermediates and the cyclopentanes via intermediate allyl-radical attack on the fluoro-olefin, while the hexafluoroalkenes arise via either of these radical intermediates or by the ‘ene’ reaction. With olefins of the type CH₂CHR (R = Me or Et), cyclobutanes are formed exclusively, while those such as CH₂CMeR (R = Et or Prⁱ) give both cyclobutanes and hexafluoroalkenes. However, the olefins CH₂CMe₂, CHMeCMe₂, and CMe₂CMe₂ afford all three types of product, but only with the alkene CHMeCMe₂ is cyclopentane-formation a major reaction (29% at 270 °C and 35% at 220 °C). Certain of the reactions are complicated by hydrocarbon-olefin isomerisation.