Environmentally Benign Processes for Making Useful Fluorocarbons: Nickel- or Copper(I) Iodide-Catalyzed Reaction of Highly Fluorinated Epoxides with Halogens in the Absence of Solvent and Thermal Addition of CF2I 2 to Olefins

Article abstract of DOI:10.1021/jo0354488

Highly fluorinated epoxides react with halogens in the presence of nickel powder or CuI at elevated temperatures to provide a useful and general synthesis of dihalodifluoromethanes (CF₂X₂) and fluoroacyl fluorides (R_FCOF) in the absence of solvent. At 185 °C, hexafluoropropylene oxide and halogens produce CF₂X ₂ (X = I, Br) in 68-90% isolated yields, along with small amounts of X(CF₂)_nX, (n = 2, 3). With interhalogens I-X (X = Cl, Br), a mixture of CF₂I₂, CF₂XI, and CF ₂X₂ was obtained. The fluorinated epoxides substituted with perfluorophenyl, fluorosulfonyl, and chlorofluoroalkyl groups also react cleanly with iodine to give CF₂I₂ and the corresponding fluorinated acyl fluorides in good yields. The reaction probably involves an oxidative addition of fluorinated epoxides into metal surfaces to form an oxametallacycle, followed by rapid decomposition to difluorocarbene-metal surfaces, which alters the reactivity of the difluorocarbene carbon from electrophilic to nucleophilic. The increase of nucleophilicity of difluorocarbene facilitates the reaction with electrophilic halogens. CF ₂I₂ reacted with olefins thermally to give 1,3-diiodofluoropropane derivatives. Both fluorinated and nonfluorinated alkenes gave good yields of the adducts. Reaction with ethylene, propylene, perfluoroalkylethylene, vinylidene fluoride, and trifluoroethylene provided the corresponding adducts in 58-86% yields. With tetrafluoroethylene, a 1:1 adduct was predominantly formed along with small amounts of higher homologues. In contrast to perfluoroalkyl iodides, CF₂I₂ also readily adds to perfluorovinyl ethers to give 1,3-diiodoperfluoro ethers.