MERCURY-PHOTOSENSITIZED DECOMPOSITIONS OF ETHYL FLUORIDE 1,1-DIFLUOROETHANE AND 1,1,1-TRIFLUOROETHANE

A study has been made of the mercury-photosensitized decomposition of ethyl fluoride, 1,1-difluoroethane, and 1,1,1-trifluoroethane alone and in the presence of hydrogen. The major products from ethyl fluoride were hydrogen and 2,3-difluorobutane, together with appreciable amounts of ethane and 2-fluorobutane. A deuterium-labeling study and the variation of product yields with light intensity and pressure showed that the C2H5• radicals were formed by the addition of hydrogen atoms to ethylene which arises from the elimination of HF from vibrationally excited ethyl fluoride molecules. The primary quenching process led to the formation of CH3CHF• radicals and hydrogen atoms, and a lower limit of φ = 0.77 was obtained for this reaction at infinite pressure, leading to an upper limit of 0.3 for the disproportionation/combination ratio for CH3CHF• radicals. The major products from 1,1-difluoroethane were hydrogen, 2,2,3,3-tetrafluorobutane, and 1,1-difluoroethylene, together with smaller quantities of 1,1,3,3-tetrafluorobutane and di- and trifluorobutanes. CH3CF2• radicals and hydrogen atoms are the major products of the primary quenching processes, but some CHF2CH2• radicals are also produced. Routes to other radicals again involve the elimination of HF from vibrationally excited species. 1,1,1-Trifluoroethane gave very small yields of 1,1,1,4,4,4-hexafluorobutane after prolonged irradiation. The quenching cross sections of the three fluoroethanes were estimated to be approximately equal with a value of σ2 = 0.45 Å2 based on σ2(N2O) = 18 Å2.