Rotating sector study of the gas phase photochlorination of 2,2-dichloro-1,1,1-trifluoroethane

The rate constant for the combination of 2,2-dichloro-1,1,1-trifluoroethyl radicals has been measured by applying the rotating sector technique to the gas phase photochlorination of 2,2-dichloro-1,1,1-trifluoroethane at 315°K. The observed value is 6.89 × 10¹² cc/mole.sec. This value is in excellent agreement with measurements by Wampler and Kuntz which yielded a temperature-independent value of 6.6 × 10¹² cc/mole.sec. The measurement by Wampler and Kuntz was determined from the photochemical system (CF₃CCl₃ + C-C₆H₁₂ + hν). The Arrhenius parameters for the reaction CF₃CCl₂· + Cl₂ → CF₃CCl₃ + Cl were found to be given by the expression log k₃ = 12.10 ? 5830/2.3RT (units in mole, cc, and sec). This is a relatively high activation energy for a chlorination reaction and makes the reaction ever slower than the chlorination of chloroform.