The kinetics of the elimination of hydrogen fluoride from chemically activated 1,1,2-trifluoroethane and 1,1,2,2-tetrafluoroethane

Abstract

The rates of elimination of hydrogen fluoride have been compared with rates of stabilisation by collision for chemically activated 1,1,2-trifluoroethane and 1,1,2,2-tetrafluoroethane molecules over a range of pressure and temperature. The energised molecules have been produced by radical combination from (a) photolysis of 1,1,3,3-tetrafluoroacetone and (b) co-photolysis of 1,3-difluoroacetone and 1,1,3,3-tetrafluoroacetone. The ratios of k(elimination of hydrogen fluoride)/k(deactivation by collision) at room temperature are 0·1 cm. (CH₂F·CHF₂) and 0·0015 cm. (CHF₂·CHF₂). The classical Rice–Ramsperger–Kassel theory of unimolecular reactions is shown to give a quantitative description of the decomposition of the energised molecules. Reasonable values of the activation energies for the hydrogen fluoride elimination reaction are CH₂·CHF₂= total C₂H₂F₂+ HF 59 kcal. mole^–1, =cis-CHFCHF + HF 58 kcal. mole^–1, =trans-CHFCHF + HF 60–61 kcal. mole^–1, = CH₂CF₂+ HF 59 kcal. mole^–1, HF₂·CHF₂= CHFCF₂+ HF 63 kcal. mole^–1