Functional fluorocarbons via free radical additions to hexafluoropropene

Abstract

The effect of substituents on the carbon-hydrogen bond reactivity in free radical additions to hexaf1uoropropene has been investegated. Ethers, amines, amides, isocyanates and silanes all give Free radical adducts. The order of reactivity has been compiled. The reactivity of cyclic ethers, amines and amides is discussed in terms of the stereoelectronic effect. The reactivity of tetrahydrofuran and N-methylpyrrolidine towards hexaf1uoropropene under uninitiated conditions has also been demonstrated. The ease of hydrogen abstraction from the substrates was estimated using a method based on the thermal decomposition of ditertiarybutylperoxide. A correlation between the ease of hydrogen abstraction and free radical reactivity is demonstrated, although the reactivity of aldehydes is not simply explained. The adducts of ethers and amines can be dehydrofluorinated to give a variety of alkenes. Further reactions of aldehyde and isocyanate adducts has given good synthetic routes to other functionally substituted fluorocarbons. The amide adducts are also a useful source o-f fluorinated amines which cannot be obtained directly. An amine 1:1 adduct has been fully fluorinated over cobalt trifluoride at 440 C in good yield, although higher adducts give lower yields. Remarkably high yields of perfluorinated alkanes are produced by successive reaction with sulphur tetrafluoride and cobalt trifluoride.