Kinetics of the photochemical fluorination of carbonyl fluoride

Abstract

The kinetics of the photochemical gas phase fluorination of CF 2O has been studied between 15 ° and 80 °C in cells of quartz and of aluminium. The only products formed are CF 3OF and the peroxide (CF 3O) 2. The reaction rate is proportional to the first power of the light intensity. The quantum efficiency of the CF 2O consumption, Φ cf 2 o , increases with increasing CF 2O pressure up to a maximum value of 2 mol/ hν and is independent of the total pressure and the fluorine pressure: ▪ The ratio (CF 3O) 2/CF 3OF, R, increases proportionally to P cf 2 o and is independent of P tot. and P f 2 . ▪ The F 2 consumption is independent of P f 2 but increases at low pressures rather rapidly with P cf 2 o , passing through a maximum and then decreasing slowly. Φ f 2 can reach values somewhat higher than 1 mol/ hν. ▪ A certain wall effect can be observed. Changing from the quartz to the aluminium cell Φ cf 2 o is slightly reduced, whereas the R values increase in a more pronounced way. O 2 has an inhibiting effect which increases with increasing P o 2 and decreases with increase of temperature. ▪ There are no chains, but the reaction is a very complex one. The experimental results can be explained with the following reaction scheme: ▪ Applying the stationary-state treatment this mechanism leads to eqns. (I) – (IV), resulting in k = k 7/ k 2; k′ = k 5/2 k 4 and k″ = k 9 k 8/ k 2 2 k′ 8. From the temperature coefficients of k, k′ and k″ and assuming that E 7 = 0; E 8 = 0 and E 9 ≊ 3 kcal, the following activation energies are obtained: E 2 = 6.2 kcal, E 5 — E 4 = 5 kcal and E 8 = 11 ± 3 kcal.