Addition of some unreactive fluoroalkanes to tetrafluoroethylene.: Direct catalytic synthesis of F-butene-2

Condensation of trifluoromethanes, CF3X (X = H, Cl, Br, I), with tetrafluorethylene to form the corresponding F-n-propyl adducts have been carried out with aluminum chlorofluoride as catalyst. Yields of C3F7I and C3F7Br are especially good, making these useful perfluoropropyl intermediates readily available. Details of the reactions, especially the presence of low percentages of perfluoroisopropyl iodide and bromide in the products, are accounted for by proposed mechanisms involving halonium intermediates. Longer-chain primary iodides can also be added to tetrafluoroethylene, but the final products are predominantly fluoroolefins, with pentafluoroethyl iodide as a byproduct. In the case of the addition of C2F5I to tetrafluoroethylene, conditions for an efficient, low temperature dimerization of terafluoroethylene to F-butene-2 catalyzed by a combination of C2F5I/aluminum chlorofluoride have been defined. Evidence for an unusual transfer of I+ from the iodonium derivative of F-butene-2 to tetrafluoroethylene is presented.