Product distribution in the Cl‐initiated photooxidation of CF₃C(O)OCH₂CF₃

Abstract

The product distribution and the mechanism of the reaction of Cl atoms with 2,2,2‐trifluoroethyl 2,2,2‐trifluoroacetate (TFETFA; CF3C(O)OCH2CF3) were investigated using a 1080 L environmental chamber with in situ Fourier transform infrared (FTIR) spectroscopy detection. The experiments were performed at (296 ± 2) K and atmospheric pressure (760 ± 10) Torr of synthetic air free of NOx. A yield of (45 ± 3)% was obtained for the CF3C(O)OC(O)CF3 formation. CF2O and CO were produced with estimated yields of 35 and 28%, respectively. No trifluoroacetic acid (TFA; CF3C(O)OH) was observed. The yields determined are rationalized in terms of the competitive reaction channels for the fluoroalcoxy radicals formed in the H‐abstraction process: (a) reaction with O2, (b) CC, CO, CH decomposition, and (c) a possible α‐ester rearrangement pathway. The negligible importance of the α‐ester channel, to produce TFA, was explained by the reduction of the stability of the five‐membered transition state of the α‐ester rearrangement. Atmospheric implications, particularly regarding the fluorocarboxylic acid formation, are discussed. Copyright © 2010 John Wiley & Sons, Ltd.

Theoretical investigation on mechanism and kinetics of the Cl-initiated hydrogen abstraction reactions of ethyl trifluoroacetate at 298 K

“…Therefore, it is necessary to understand the chemistry of fluorinated esters in the atmosphere in order to assess the environmental acceptability of HFEs as a plausible replacement for chlorofluorocarbons. The reaction mechanisms of FESs with atmospheric oxidants have been studied extensively both experimentally [20][21][22][23][24][25] and theoretically [26][27][28][29][30][31][32] and continue to receive considerable attention. FESs absorb strongly in the earthly infrared (IR) radiation region of 800-1,200 cm −1 .…”

Theoretical study on mechanism, kinetics, and thermochemistry of the gas phase reaction of 2,2,2-trifluoroethyl butyrate with OH radicals at 298 K

“…At first, the reaction enthalpies ( H • r 298 ) of the isodesmic reactions (9-10) are determined using the total energy of the species obtained at the M06-2X/6-311++G(d,p) level, including thermal correction to enthalpy estimated at the M06-2X/6-31+G(d,p) level. Since the H • r 298 value corresponds to the difference in the enthalpies of formation ( H • f 298 ) of the reactants and products, the ( H • f 298 ) values of the reactant species can be easily evaluated by combining them with the known enthalpies of formation of the reference compounds involved in the isodesmic reaction schemes mentioned above (9)(10) 44 The H • f 298 values for radicals P1, P2, P3, and P4 determined from the energy data obtained at M06-2X/6-311++G(d,p) are found to be -227.6, -233.9,-228.2 and -225.5 kcal mol −1 , whereas the same for M06-2X/6-31+G(d,p) are found to be -227.7, -234.1, -228.3 and -225.6 kcal mol −1 , respectively. These data are not available in the literature and can therefore be useful for further thermochemical and kinetic modeling of reaction involving these species.…”

“…Geometries of all the species involved in the isodesmic reactions (9)(10) were first optimized at the M06-2X/6-31+G(d,p) level. Energies were further refined with an extended basis set (6-311++G(d,p)) using the same functional.…”

“…Considerable attention has been paid in recent years to perform experimental and theoretical studies on the decomposition kinetics of FESs. [8][9][10][11][12][13][14][15][16][17][18][19] In this work, kinetic and mechanistic studies have been performed at 298 K for the reaction of 2,2,2-trifluoroethyl butyrate, CH 3 CH 2 CH 2 C(O)OCH 2 CF 3 (TFEB) with OH radicals. To the best of our knowledge, there is only one experimental study reported by Blanco et al 12 They studied the hydrogen abstraction reactions of OH radicals with TFEB using relative rate method at 298 K and reported a rate constant of (1.3 ± 0.3) × 10 −12 cm 3 molecule −1 s −1 .…”

Theoretical studies on mechanism and kinetics of the hydrogen-abstraction reaction of CF3C(O)OCH2CH3 with OH radicals

“…Recently, hydrofluoroethers (HFEs) [1,2] have been developed as the third generation alternatives for CFCs and used in various industrial applications for two reasons: one is these fluorine-containing compounds have zero ozone depletion [3][4][5][6], the other is they have little impact on climate change due to their relatively shorter atmospheric lifetimes in the troposphere than HFCs and HCFCs. The main degradation product of HFEs in the atmosphere is to form the corresponding hydrofluorinated esters (FESs) [7][8][9], which could be further photochemically oxidized in the troposphere by atmospheric oxidants, affording environmentally burdened products such as trifluoroacetic acid (TFA, CF 3 C(O)OH) and CO 2 et al [10,11]. Thus, to better assess the environmental impact of HFEs as candidates to replace CFCs, a complete understanding of the atmospheric chemistry of FESs is required.…”