Homolytic reactions of polyfluoroaromatic compounds. Part 16. Competitive phenylation of polyfluorobenzenes

Abstract

Pairs of polyfluorobenzenes were allowed to complete for phenyl radicals generated by the thermolysis of benzoyl peroxide at 80°. From the relative yields of biaryl, and the yields of each biaryl formed upon arylation of each arene individually, the relative rates of attack of each site in each arene were deduced. Neither iron(III) benzoate nor trichloroacetic acid uniformly improved yields of biaryl, although in some cases the isomer distribution altered, when decomposition of benzoyl peroxide was carried out in the presence of such additives, to favour products of aryldehydrogenation or of aryldefluorination, respectively. Competition did not usually affect the distribution of attack of a particular arene, except when hexafluoro-benzene was used, in which case greater selectivity of attack of the second arene occurred. This suggested the formation of a ‘stabilised’ phenyl radical, and supported an earlier suggestion of species such as [C₆F₆,Ph˙]; other evidence also supported the postulate.