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/k^½_c)/(cm mol^–½ s^–½)=(5.01 ± 0.28)–(11490 ± 560)/θ, log(k₈/k^½_c)/(cm mol^–½ s^–½)=(5.68 ± 0.25)–(6440 ± 380)/θ, where θ= 2.303 RT/cal mol^–1 and k_c 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 (k_H) and addition to the double bond (k_add) occur with log(k_H/k_add)=(0.67 ± 0.07)–(2530 ± 120)/θ.