Atmospheric Oxidation Mechanism and Kinetics of Hydrofluoroethers, CH₃OCF₃, CH₃OCHF₂, and CHF₂OCH₂CF₃, by OH Radical: A Theoretical Study

Abstract

In the present work, the reaction mechanism of two segregated hydrofluoroethers (HFEs), CHOCF (HFE-143a) and CHOCHF (HFE-152a), and a nonsegregated HFE, CHFOCHCF (HFE-245fa2), with OH radical is studied using electronic structure calculations. The initial reaction between HFE and OH radical is studied by considering two (three for CHFOCHCF) pathways, H-atom abstraction and C-O bond breaking, OH addition reaction and C-C bond breaking, and OH addition reaction, which leads to the formation of alkyl radical intermediate. The dominant atmospheric fate of initially formed alkyl radical intermediate is its reaction with O. The peroxy radicals thus formed exit through the reaction with HO radical and NO radical resulting in the formation of products, carbonyl fluoride (COF), trifluoromethylformate, trifluoro(hydroperoxymethoxy)methane, difluoro(hydroperoxy methoxy)methane, difluoromethylformate, 2-(difluoromethoxy)-1,1,1-trifluoro-2-hydroperoxyethane, and difluoromethyl ester. The rate constant is calculated for the initial H-atom abstraction reaction using canonical variational transition state theory with small curvature tunnelling corrections over the temperature range 272-350 K. The atmospheric lifetime and global warming potential of HFEs are obtained from the calculated reaction potential energy surface and rate constant. The results are discussed with respect to the atmospheric implications of CHOCF (HFE-143a), CHOCHF (HFE-152a), and CHFOCHCF (HFE-245fa2).

Theoretical Investigation on the Mechanism and Kinetics of Atmospheric Reaction of Methyldichloroacetate with Hydroxyl Radical

“…Under atmospheric condition, the reaction of energized alkyl radical intermediate with molecular oxygen is one of the important reactions in the atmosphere. As reported in previous studies − as well as our attempt for the reaction of a alkyl radical intermediate (I1) with O 2 , HO 2 , NO x ( x = 1, 2), it is shown that the reaction of alkyl radical intermediate with O 2 is more favorable than that with other atmospheric species. The reaction of alkyl radical intermediate I1 with O 2 molecule leads to the formation of a peroxy radical intermediate, I5.…”

The catalytic effects of H2O, basic and acidic catalysts on the gas‐phase hydrolysis mechanism of carbonyl fluoride (CF2O)

“…In recent times, oxygenated hydrofluorocarbons (HFOCs), such as hydrofluoroethers (HFEs) and hydrofluoroalcohols (HFAs) have potentially considered as CFCs, HFCs, and HCFCs alternatives because of free Cl atoms and shorter atmospheric lifetimes [7,8]. It is, therefore, the decomposition of HFOCs compounds in the atmosphere has been a matter of scientific research interest in the past few years and recently [8][9][10][11][12][13]. Carbonyl difluoride (CF 2 O) is the key atmospheric decomposition products of HFOCs compounds and an important fluorine-containing reservoir species that plays a significant role in the atmospheric environment [8][9][10][11][14][15][16][17][18].…”

“…It is, therefore, the decomposition of HFOCs compounds in the atmosphere has been a matter of scientific research interest in the past few years and recently [8][9][10][11][12][13]. Carbonyl difluoride (CF 2 O) is the key atmospheric decomposition products of HFOCs compounds and an important fluorine-containing reservoir species that plays a significant role in the atmospheric environment [8][9][10][11][14][15][16][17][18]. Furthermore, CF 2 O is an important compound that uses as a semiconductor etching gas, cleaning gas, and a chemical intermediate to prepare other fluorinated compounds [9,[19][20][21], that is, CF 2 O is used instead of phosgene to react with amines for isocyanides production [22,23].…”

Thermochemistry of Fluorinated Dimethyl and Ethyl Methyl Ethers and Corresponding Radical Species

“…They have increased reactivity compared to HFCs in the first step of atmospheric degradation and yield water and a corresponding ether-based radical . HFE’s reactions with hydroxyl radicals involve H-atom abstractions and either C–O or C–C bond breaking upon OH addition and have energy barriers of approximately 9 and 30 kcal mol –1 , respectively …”

“…The rate of this first step is dependent upon the bond dissociation energies and on the hydroxyl radical addition to fluorinated olefins, for example, which determines the atmospheric lifetime of the these compounds, their rate of removal from the atmosphere, their potential for further stratospheric ozone layer interactions, and their impact as potential greenhouse gases. − These environmental considerations are paramount and should be evaluated before their implementation.…”