Free radical addition to olefins. Part XV. Addition of bromoform and carbon tetrabromide to fluoroethylenes

Abstract

The peroxide-initiated addition of carbon tetrabromide and bromoform to ethylene, vinyl fluoride, 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene has been investigated in sealed tube experiments at 150°. With carbon tetrabromide the major products were adducts involving tribromomethyl radicals while in experiments with bromoform both dibromomethyl and tribromomethyl radicals were found to be important chain-carrying species. Telomers were formed, and the extent of telomer formation increased with increasing fluorine content of the alkene. The relative rates of addition of tribromomethyl and dibromomethyl radicals to the alkenes were estimated, and the orientation ratio for addition of each radical to vinyl fluoride and trifluoroethylene was obtained. The orientation ratios of radicals with any unsymmetrical alkene show significant correlations with the size and polarity of the radicals so that the orientation of radical addition appears to be governed by a complex interplay of factors in which steric and polar effects are of major importance.