Kinetic Study of the Reactions of Cl Atoms with CF₃CH₂CH₂OH, CF₃CF₂CH₂OH,\nCHF₂CF₂CH₂OH, and CF₃CHFCF₂CH₂OH

Abstract

The reaction kinetics of chlorine atoms with a series of partially fluorinated straight-chain alcohols, CF₃CH₂CH₂OH (<b>1</b>), CF₃CF₂CH₂OH (<b>2</b>), CHF₂CF₂CH₂OH (<b>3</b>), and CF₃CHFCF₂CH₂OH (<b>4</b>), were studied in the\ngas phase over the temperature range of 273−363 K by using very low-pressure reactor mass spectrometry.\nThe absolute rate coefficients were given by the expressions (in cm³ molecule^-1 s^-1): <i>k</i>₁ = (4.42 ± 0.48) ×\n10^-11 exp(−255 ± 20/T); <i>k</i>₁(303) = (1.90 ± 0.17) × 10^-11, <i>k</i>₂ = (2.23 ± 0.31) × 10^-11 exp(−1065 ± 106/\nT); <i>k</i>₂(303) = (6.78 ± 0.63) × 10^-13, <i>k</i>₃ = (8.51 ± 0.62) × 10^-12 exp(−681 ± 72/<i>T</i>); <i>k</i>₃(303) = (9.00 ±\n0.82) × 10^-13 and <i>k</i>₄ = (6.18 ± 0.84) × 10^-12 exp(−736 ± 42/<i>T</i>); <i>k</i>₄(303) = (5.36 ± 0.51) × 10^-13. The\nquoted 2σ uncertainties include the systematic errors. All title reactions proceed via a hydrogen atom metathesis\nmechanism leading to HCl. Moreover, the oxidation of the primarily produced radicals was investigated, and\nthe end products were the corresponding aldehydes (R_F−CHO; R_F = −CH₂CF₃, −CF₂CF₃, −CF₂CHF₂,\nand −CF₂CHFCF₃), providing a strong experimental indication that the primary reactions proceed mainly\nvia the abstraction of a methylenic hydrogen adjacent to a hydroxyl group. Finally, the bond strengths and\nionization potentials for the title compounds were determined by density functional theory calculations, which\nalso suggest that the α-methylenic hydrogen is mainly under abstraction by Cl atoms. The correlation of\nroom-temperature rate coefficients with ionization potentials for a set of 27 molecules, comprising fluorinated\nC2−C5 ethers and C2−C4 alcohols, is good with an average deviation of a factor of 2, and is given by the\nexpression log(<i>k</i>) (in cm³ molecule^-1 s^-1) = (5.8 ± 1.4) − (1.56 ± 0.13) × (ionization potential (in eV)).