Thermal Decomposition of Some Perfluoro- and Polyfluorodiacyl Peroxides

Article abstract of DOI:10.1021/jo00132a007

Seven polyfluoroacyl peroxides were synthesized, some of them by a new procedure involving the direct interaction of an acyl fluoride with hydrogen peroxide.In the temperature range of 20-40 deg C, all these peroxides undergo first-order decomposition in dilute 1,1,2-trichloro-1,2,2-trifluoroethane (Freon-113) solutions (<0.02 M.).The major decomposition products were separated and characterized as the coupling products of the corresponding radicals, R_F-R^F.Differing from other perfluoro or polyfluoro radicals, the perfluoro-α-isopropoxyethyl radicals (10) undergo substantial β scission to form perfluoroisopropyl radicals (11) during their lifetime.The ΔH_exc. values for the perfluoroacyl peroxides are about 24 kcal mol^-1, or about 5 kcal lower than that of the nonfluorinated diacyl peroxides (ca. 29 kcal mol^-1).Apparently, the higher relative rates for 3 and 7 are caused by different factors.The latter peroxide (7) decomposes with a more favorable ΔS_exc. term, whereas the former (3) decomposes with lower values of both ΔH_exc. and ΔS_exc..Thus, weakening of the peroxide bond by H bonding of the peroxide oxygen atom with the acidic ω-hydrogen atom seems to be implicated in the decomposition of 3.With a half-life of 81 min at 20 deg C, 3 may become a useful low-temperature initiator for free-radical reactions and polymerization.