NEW METHODS OF FREE-RADICAL PERFLUOROALKYLATION OF AROMATICS AND ALKENES - ABSOLUTE RATE CONSTANTS AND PARTIAL RATE FACTORS FOR THE HOMOLYTIC AROMATIC-SUBSTITUTION BY N-PERFLUOROBUTYL RADICAL

New methods of free-radical perfluoroalkylation of aromatics and alken es are reported, n-C4F9I has been utilized as source of C4F9. radical through iodine abstraction by phenyl or methyl radical, The reaction w ith alkenes, carried out in the presence of catalytic amount of Cu(OAc )(2), leads to substitution by a mechanism substantially identical to the aromatic substitution and not to the usual chain addition of perfl uoroalkyl group and iodine atom to the double bond, This has allowed t o measure for the first time the absolute rate constants and the parti al rate factors for the homolytic aromatic perfluoroalkylation by comp etition kinetics, The C4F9. radical shows a clear-cut electrophilic ch aracter in the aromatic substitution, as already reported for the addi tion to alkenes, but the low regio-and chemoselectivities suggest that the polar effect is not the main factor in determining the high react ivity of perfluoroalkyl radicals toward aromatics (10(5)-10(6) M-1 s(- 1), 2-3 orders of magnitude more reactive than alkyl radicals). The en thalpic factor, related to the involved bond energies, appears to be t he major cause of the increased reactivity. The polar effect; is consi dered as related more to the polarizability than to the polarity of a radical (the sigma-perfluoroalkyl radicals are considered less polariz able and hence less sensitive to polar effects than pi-radicals).