Kinetics and mechanism of the thermal gas-phase reaction between bis(trifluoromethyl)trioxide, CF3O3CF3, and 1,1-difluoroethylene, CF2CH2

Abstract

The thermal addition of CF₃O₃CF₃ to CF₂CH₂ has been investigated between 315.2 and 332.9 K. The initial pressure of CF₃O₃CF₃(T) was varied between 15 and 100 Torr and that of CF₂CH₂(E) between 5 and 580 Torr. Several products of formula CF₃O(E)_nO₂CF₃ are formed, where n= 1–12. The sum of the products corresponds to the amount of T consumed and its distribution depends on the pressure of E. The reaction is homogeneous and its rate is not affected by the total pressure or the presence of inert gas. It is a free-radical telomerization represented by the basic steps: thermal formation of radicals CF₃O and CF₃ O₂, chain initiation by addition of the CF₃O radical to olefin, telomeric radical formation by successive additions to another molecule of alkene and termination of telomeric radicals. Their respective rate constants are designated by k₁, k_i, k_g and k_t.

The olefin consumption rate is well represented by: –d[E]/dt=k₁[T] [graphic omitted] where k^′_i=(k_ti/k^1/2_t)/(k_gi/k^1/2_t) attains its limiting value k^′_∞ at k^′₅. Within the experimental temperature and pressure range the mean chain length of telomerization n=(d[E]/dt)/k₁[T] increases from 1.2 to 10. The estimated value of the rate constant for the addition of telomeric radicals to alkene is: k_g= 6 ± 3 × 10⁵ exp (–9.2 ± 2.5 kJ mol^–1/RT) dm³ mol^–1 s^–1 and E_g= 9.2 ± 2.5 kJ mol^–1. At 342.7 K the reaction turns into an explosion.