Kinetics of the decomposition of chemically activated 1,1-difluoroethane, 1,1-difluoropropane, and 2,2-difluoropropane

Abstract

The rates of elimination of hydrogen fluoride have been compared with the rates of stabilization by collision for chemically activated 1,1-difluoroethane, 1,1-difluoropropane, and 2,2-difluoropropane molecules over a range of temperature and pressure. Activated 1,1-difluoroethane has been produced by radical combination from (a) the co-photolysis of acetone and 1,1,3,3-tetrafluoroacetone, and (b) the hydrogen-abstraction by methylene from difluoromethane. Activated difluoropropanes were produced by the reaction of methylene with 1,1-difluoroethane. The ratios k(elimination of hydrogen fluoride)/k(decativation by collision) at room temperature are 20 cm. (CH₃CHF₂), 1·2 cm. (CH₃CH₂CF₂H), and 30 cm. (CH₃CF₂CH₃). The classical Rice–Ramsperger–Kassel theory of unimolecular reactions is shown to give a quantitative description of the decomposition of the energized molecules. Reasonable values of the activation energies for hydrogen fluoride elimination reaction are 47–48 (CH₃CHF₂), 48–49 (CH₃CF₂CH₃), and 54 kcal, mole^–1(CH₃CH₂CHF₂).