Photochemistry of Anhydrides: Part 2.—Photolysis of Perfluoropropionic Anhydride : A New Source of C2F5 Radicals

Abstract

The photolysis of the vapour of (C2F5CO)2O in the temperature range 20–213°C is described quantitatively by the overall reaction (C2F5CO)2O +hν→ CO + CO2+ n-C4F10, with the effective primary process being (C2F5CO)2O +hν→ CO + CO2+ 2C2F5. The anhydride was photolyzed in the presence of both CH4 and cyclohexane and the following reactions occur: C2F5+ CH4→ C2F5H + CH3(7), C2F5+ c-C6H12→ C2F5H + c-C6H11(8), C2F5+ C2F5→ C4F10. (4) For these reactions, log(k7/k½c)/(cm[fraction three-over-two] mol–½ s–½)=(5.01 ± 0.28)–(11490 ± 560)/θ, log(k8/k½c)/(cm[fraction three-over-two] mol–½ s–½)=(5.68 ± 0.25)–(6440 ± 380)/θ, where θ= 2.303 RT/cal mol–1 and kc is the rate constant for reaction (4). It is concluded that Arrhenius parameters for abstraction of H from a given RH by CF3, C2F5 and n-C3F7 radicals are almost identical. When (C2F5CO)2O is photolyzed with cyclohexene both H-abstraction (kH) and addition to the double bond (kadd) occur with log(kH/kadd)=(0.67 ± 0.07)–(2530 ± 120)/θ.