Free radical addition to olefins. Part 5.—Addition of difluorobromomethyl radicals to trifluoroethylene and ethylene

Abstract

The photochemical reaction of CF₂Br₂ with CHFCF₂ and CH₂CH₂ has been examined in a series of gas-phase experiments. A mechanism for the radical chain addition which takes place is proposed. The variation in the rate of formation of the termination products, CF₂BrCF₂Br and CF₂BrCHFCF₂Br, with reactant concentration is explained if five important termination reactions are taken into account and a long-lived excited state of the CF₂Br₂ is accepted. Arrhenius parameters for the addition of CF₂Br· radicals to the olefins have been derived : CF₂Br·+ E → CF₂BrE·(2), CF₂Br·+ CF₂Br·→ CF₂BrCF₂Br (4), k₂/k^½₄(addition to CHF)=(1.2 ± 0.3)× 10² exp (–3300 ± 200/RT), k₂/k^½₄(addition to CF₂)=(2.0 ± 0.3)× 10² exp (–4400 ± 200/RT), k₂/k^½₄(addition to CH₂)=(2.5 ± 0.5) exp (–1000/RT). A factors are in 1.^½ mol^–½ s^–½; activation energies in kcal/mol; R= 1.99 cal deg.^–1 mol^–1; 1 cal = 4.184 J.