Theoretical Kinetics Studies on the Reaction of CF₃CF═CF₂ with Hydroxyl Radical

Abstract

The potential energy surface for the reaction of hexafluoropropene with hydroxyl radical is explored by using BB1K density functional method. Single-point energy calculations are performed at CBS-Q level of theory. Semiclassical transition state theory and a modified strong collision/RRKM model are employed to calculate the thermal rate coefficients for the formation of major products as a function of temperature and pressure. It is revealed from the computed rate constants that the major product channels at low temperatures and high pressures are the formation of the primary adducts formed through OH addition to the double bond of CF3═CFCF2. At high temperatures and low pressures, however, many products arising from unimolecular decomposition of the chemically activated intermediates become important. P9A (CF3CFCOF + HF) and P7B (CF3COCF2 + HF) are dominant products at elevated temperatures. Semiclassical transition state theory is used to compute the overall high-pressure rate constants over the temperature range of 200-1500 K. The computed rate constants are in accordance with the available experimental data.

Kinetics and mechanism of the reaction of perfluoro propyl vinyl ether (PPVE, C3F7OCHCH2) with OH: assessment of its fate in the atmosphere

“…The energies obtained are in good agreement with analogous reactions described in the literature. [38][39][40][41]46 We predict a somewhat lower barrier for HF loss compared to earlier work on fluorinated methanol, 46 owing to the formation of a more stable vinoxy radical. As highlighted in Fig.…”

“…† The reaction of C 3 F 7 OCFQCF 2 with OH radicals is exothermic by 54 kcal mol À1 , leading to a b-hydroxy-alkyl radical, in agreement with literature data on other fluorinated alkenes. [38][39][40][41] The addition channel is significantly more exothermic than in analogous non-fluorinated compounds, e.g. for CH 3 OCHQCH 2 + OH the exothermicity is only B32 kcal mol À1 .…”

Theoretical study of the OH-initiated atmospheric oxidation mechanism of perfluoro methyl vinyl ether, CF3OCFCF2

“…CFOCFO was not observed in the case of OH-initiated oxidation of hexafluoropropene, CF 3 CFQCF 2 , at room temperature, 42,43 yielding CF 2 O and CF 3 OCFO as major products; this is supported by a recent theoretical kinetic study by Saheb and Pourhaghighi, 34 and others. [35][36][37]44 The ether functionality in CF 3 OCFQCF 2 thus appears responsible for an additional product channel, yet the proposed HF elimination route 8,9 is not expected to be dependent on the presence or absence of the oxygen atom.…”

“…The energies obtained for the above reactions are again in good agreement with analogous reactions described in the literature. 25,[34][35][36][37] The minor adduct, CF 3 OCF(OH)-C F 2 , has access to similar decomposition routes (see Fig. 3, see Fig.…”

Theoretical Kinetic and Mechanistic Studies on the Reactions of CF3CBrCH2 (2-BTP) with OH and H Radicals

“…For the average energy transferred per collision, <ΔE down >, there is no experimental date available for the target systems in the present work. Vahid et al [37] used a value of 129 cm −1 for CF 3 CF=CF 2 reacting with OH, and Zhang et al [38] used a value of 200 cm −1 in N 2 and 100 cm −1 in Ar for the reactions of CF 3 CH=CH 2 with OH. Considering a heavy Br atom in 2-BTP, we used a temperature-dependent form for this value, that is, <ΔE down > = ΔE 0 (T/300) n (ΔE 0 = 200, n = 0.85).…”