A theoretical investigation on the kinetics and reactivity of the gas-phase reactions of ethyl chlorodifluoroacetate with OH radical and Cl atom at 298 K (original) (raw)
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Journal of Fluorine Chemistry, 2014
A theoretical study on the mechanism and kinetics of the gas phase reactions of CF 3 CHFCF 2 OCH 2 CF 3 (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid modern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF 3 CHFCF 2 OCH 2 CF 3 and the most stable one is considered for detailed study. Reaction profiles for OHinitiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH 2 group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for C H bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250-450 K. The calculated rate constant values are found to be 9.10 × 10 −15 and 4.77 × 10 −17 cm 3 molecule −1 s −1 for reactions with OH radicals and Cl atom, respectively. At 298 K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years.
A DFT study on kinetics of the gas phase reactions of CH3CH2OCF3 with OH radicals and Cl atoms
Journal of Fluorine Chemistry, 2014
A theoretical study on the mechanism and kinetics of the gas phase reactions of CH 3 CH 2 OCF 3 (HFE-263) with the OH radicals and Cl atoms have been performed using meta-hybrid density functional MPWB1K method and 6-31+G(d,p) basis set. Energetics are further refined by calculating the energy of the species with a high level G2(MP2) method. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. The hydrogen abstraction from -CH 2 group is found to be the dominant reaction channel for reaction with OH radicals, whereas hydrogen abstraction from CH 3 group is the dominant channel for Cl atoms, especially at higher temperature. Using groupbalanced isodesmic reactions, the standard enthalpies of formation for CH 3 CH 2 OCF 3 and radicals generated by hydrogen abstraction, CH 3 CHOCF 3 and CH 2 CH 2 OCF 3 are reported for the first time. The calculated bond dissociation energies for C-H bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250-1000 K. The G2(MP2) calculated rate constant values are 0.52 Â 10 À13 and 0.77 Â 10 À12 cm 3 molecule À1 s À1 , respectively for reactions with OH radicals and Cl atoms at 298 K. ß
Chemical Physics Letters, 2009
Relative rate techniques were used to study the title reactions in 930-1200 mbar of N 2 diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k(Cl + CH 2 F 2 ) = 1.19 × 10 −17 T 2 exp(−1023/T ) cm 3 molecule −1 s −1 (253-553 K), k(Cl + CH 3 CCl 3 ) = 2.41 × 10 −12 exp(−1630/T ) cm 3 molecule −1 s −1 (253-313 K), and k(Cl + CF 3 CFH 2 ) = 1.27 × 10 −12 exp(−2019/T ) cm 3 molecule −1 s −1 (253-313 K). Results are discussed with respect to the literature data.
The Journal of Physical Chemistry A, 2007
The reaction kinetics of chlorine atoms with a series of partially fluorinated straight-chain alcohols, CF 3 -CH 2 CH 2 OH (1), CF 3 CF 2 CH 2 OH (2), CHF 2 CF 2 CH 2 OH (3), and CF 3 CHFCF 2 CH 2 OH (4), were studied in the gas phase over the temperature range of 273-363 K by using very low-pressure reactor mass spectrometry. The absolute rate coefficients were given by the expressions (in cm 3 molecule -1 s -1 ): k 1 ) (4.42 ( 0.48) × 10 -11 exp(-255 ( 20/T); k 1 (303) ) (1.90 ( 0.17) × 10 -11 , k 2 ) (2.23 ( 0.31) × 10 -11 exp(-1065 ( 106/ T); k 2 (303) ) (6.78 ( 0.63) × 10 -13 , k 3 ) (8.51 ( 0.62) × 10 -12 exp(-681 ( 72/T); k 3 (303) ) (9.00 ( 0.82) × 10 -13 and k 4 ) (6.18 ( 0.84) × 10 -12 exp(-736 ( 42/T); k 4 (303) ) (5.36 ( 0.51) × 10 -13 . The quoted 2σ uncertainties include the systematic errors. All title reactions proceed via a hydrogen atom metathesis mechanism leading to HCl. Moreover, the oxidation of the primarily produced radicals was investigated, and the end products were the corresponding aldehydes (R F -CHO; R F ) -CH 2 CF 3 , -CF 2 CF 3 , -CF 2 CHF 2 , and -CF 2 CHFCF 3 ), providing a strong experimental indication that the primary reactions proceed mainly via the abstraction of a methylenic hydrogen adjacent to a hydroxyl group. Finally, the bond strengths and ionization potentials for the title compounds were determined by density functional theory calculations, which also suggest that the R-methylenic hydrogen is mainly under abstraction by Cl atoms. The correlation of room-temperature rate coefficients with ionization potentials for a set of 27 molecules, comprising fluorinated C2-C5 ethers and C2-C4 alcohols, is good with an average deviation of a factor of 2, and is given by the expression log(k) (in cm 3 molecule -1 s -1 ) ) (5.8 ( 1.4) -(1.56 ( 0.13) × (ionization potential (in eV)).
RSC Advances, 2016
Rate coefficients as a function of temperature have been measured for the first time for the gas-phase reactions of chlorine atoms with methyl chlorodifluoracetate (k 1) and ethyl chlorodifluoroacetate (k 2) using the relative rate technique. The experiments were carried out in a 1080 L photoreactor over the temperature range 287-313 K at a total pressure of 1000 AE 10 mbar of synthetic air using in situ FTIR spectroscopy to monitor reactants and products. The following Arrhenius expressions were obtained: k (MCDFA+Cl) ¼ (9.6 AE 5.1) Â 10 À12 exp[À(1363 AE 79)/T] and k (ECDFA+Cl) ¼ (64.4 AE 29.7) Â 10 À12 exp [À(1110 AE 68)/T]. The kinetic results are compared with previous experimental and theoretical studies. In addition, a product study of the reactions of Cl with methyl chlorodifluoracetate and ethyl chlorodifluoroacetate is reported. The results indicate that in the absence of NO x the main fate of the alkoxy radicals formed after H-atom abstraction by Cl from the-CH 3 group in methyl chlorodifluoroacetate is reaction of the radical with O 2 to form the mixed anhydride CF 2 ClC(O)OC(O)H. In the case of ethyl chlorodifluoroacetate the main fate of the alkoxy formed via H-atom abstraction by Cl from the-CH 2entity in the ethyl group is a-ester rearrangement to produce chlorodifluoroacetic acid and the corresponding radical. The yields of chlorofluoracetic acid (CF 2 ClC(O)OH) obtained were as follows: (34 AE 5)% and (86 AE 8)% for the reactions of Cl with CF 2 ClC(O)OCH 3 and CF 2 ClC(O)OCH 2 CH 3 , respectively. The measured yields are rationalized in terms of mechanisms consisting of competitive reaction channels for the formed products in the oxidation, i.e. reaction with O 2 , a-ester rearrangement and a decomposition pathway. Atmospheric implications are discussed according to the rate coefficients obtained as a function of temperature and altitude, and regarding the formation of chlorofluorocarboxylic acid.
Journal of Molecular Modeling, 2013
Theoretical investigations are carried out on reaction mechanism of the reactions of CF 3 CH 2 NH 2 (TFEA) with the OH radical by means of ab initio and DFT methods. The electronic structure information on the potential energy surface for each reaction is obtained at MPWB1K/6-31+G(d,p) level and energetic information is further refined by calculating the energy of the species with a Gaussian-2 method, G2(MP2). The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation. Our calculation indicates that the H abstraction from-NH 2 group is the dominant reaction channel because of lower energy barrier. The rate constants of the reaction calculated using canonical transition state theory (CTST) utilizing the ab initio data. The agreement between the theoretical and experimental rate constants is good at the measured temperature. From the comparison with CH 3 CH 2 NH 2 , it is shown that the fluorine substution decreases the reactivity of the C-H bond.
Atmospheric Environment, 2011
The rate coefficients for the reactions of OH radicals with three fluoroalcohols, CF 3 CH 2 OH (k 1), CF 3 CF 2 CF 2 CH 2 OH (k 2), and CHF 2 CF 2 CH 2 OH (k 3), have been measured in the temperature range of 298e363 K, at a total pressure of w55 torr, using LP-LIF method. The kinetic parameters measured for CF 3 CH 2 OH, which is well studied, matches with the previous reports within error limits. The rate expression for k 2 is (1.54 AE 0.80) Â 10 À12 exp (À765 AE 170)/T), and for k 3 is (1.12 AE 0.26) Â 10 À12 exp (À560 AE 80)/T). Based on the above values of the rate coefficients, the tropospheric lifetimes with respect to removal by reaction with OH have been estimated to be 0.38 and 0.26 years for CF 3 CF 2 CF 2 CH 2 OH and CHF 2 CF 2 CH 2 OH respectively, supporting their potential use as HFC alternatives. The results are discussed along with the literature data on other fluoroalcohols. The present study is aimed to assess the effect of additional CF 2 groups and H atoms on tropospheric lifetime and global warming potential of fluoroalcohols. The results confirm that the rate coefficients at room temperature and activation energy parameters are independent of n, for the reaction of OH with fluoroalcohols of general formula CF 3 (CF 2) n CH 2 OH, which are potential CFC/HFC alternatives.
Computational and Theoretical Chemistry, 2013
Theoretical investigations were carried out on the mechanism, kinetics and thermochemistry of the gasphase reactions between CHF 2 CF 2 OCHF 2 and OH radical using the high level ab initio G2(MP2) and hybrid density functional MPWB1K/6-31+G(d,p) methods. Two most stable conformers of CHF 2 CF 2 OCHF 2 are identified and the energy difference between them is found to be only 0.3 kcal mol À1. Both of them are considered for rate coefficient calculations in our study and the contribution from each of the conformers is found to be quite significant in the temperature range of our study. The rate coefficients are determined for the first time in a wide range of temperature 250-1000 K. The calculated total rate coefficient value k OH = 1.01 Â 10 À15 cm 3 molecule À1 s À1 is in reasonably good agreement with the experimental value of k OH = 2.36 Â 10 À15 cm 3 molecule À1 s À1 at 298 K. The heats of formation for CHF 2 CF 2 OCHF 2 and CHF 2 CF 2-OCF 2 and CF 2 CF 2 OCHF 2 radicals are estimated to be À359.64, À305.43 and À306.88 kcal mol À1 , respectively. The bond dissociation energies of the two C-H bonds are CHF 2 CF 2 OC(-H)F 2 : 106.3 kcal mol À1 and C(-H)F 2 CF 2 OCHF 2 : 104.8 kcal mol À1. The atmospheric lifetime of CHF 2 OCF 2 CHF 2 is estimated to be around 35 years.