Kinetics and mechanism of atmospheric reactions of partially fluorinated alcohols

Abstract

Gas-phase reactions typical of the Earth’s atmosphere have been studied for a number of partially fluorinated alcohols (PFAs). The rate constants of the reactions of CF₃CH₂OH, CH₂FCH₂OH, and CHF₂CH₂OH with fluorine atoms have been determined by the relative measurement method. The rate constant for CF₃CH₂OH has been measured in the temperature range 258–358 K (k = (3.4 ± 2.0) × 10¹³exp(−E/RT) cm³ mol⁻¹ s⁻¹, where E = −(1.5 ± 1.3) kJ/mol). The rate constants for CH₂FCH₂OH and CHF₂CH₂OH have been determined at room temperature to be (8.3 ± 2.9) × 10¹³ (T = 295 K) and (6.4 ± 0.6) × 10¹³ (T = 296 K) cm³ mol⁻¹ s⁻¹, respectively. The rate constants of the reactions between dioxygen and primary radicals resulting from PFA + F reactions have been determined by the relative measurement method. The reaction between O₂ and the radicals of the general formula C₂H₂F₃O (CF₃CH₂Ȯ and CF₃ĊHOH) have been investigated in the temperature range 258–358 K to obtain k = (3.8 ± 2.0) × 10⁸exp(−E/RT) cm³ mol⁻¹ s⁻¹, where E = −(10.2 ± 1.5) kJ/mol. For the reaction between O₂ and the radicals of the general formula C₂H₄FO (Ċ HFCH₂O, CH₂FĊHOH, and CH₂FCH₂Ȯ) at T = 258–358 K, k = (1.3 ± 0.6) × 10¹¹exp(−E/RT) cm³ mol⁻¹ s⁻¹, where E = −(5.3 ± 1.4) kJ/mol. The rate constant of the reaction between O₂ and the radicals with the general formula C₂H₃F₂O (ĊF₂CH₂O, CHF₂ĊHOH, and CHF₂CH₂Ȯ) at T = 300 K is k = 1.32 × 10¹¹ cm³ mol⁻¹ s⁻¹. For the reaction between NO and the primary radicals with the general formula C₂H₂F₃O (CF₃CH₂Ȯ and CF₃ĊHOH), which result from the reaction CF₃CH₂OH + F, the rate constant at 298 K is k = 9.7 × 10⁹ cm³ mol⁻¹ s⁻¹. The experiments were carried out in a flow reactor, and the reaction mixture was analyzed mass-spectrometrically. A mechanism based on the results of our studies and on the literature data has been suggested for the atmospheric degradation of PFAs.