Atmospheric sink of methyl chlorodifluoroacetate and ethyl chlorodifluoroacetate: temperature dependent rate coefficients, product distribution of their reactions with Cl atoms and CF2ClC(O)OH formation

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 (k1) and ethyl chlorodifluoroacetate (k2) 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 ± 10 mbar of synthetic air using in situ FTIR spectroscopy to monitor reactants and products. The following Arrhenius expressions were obtained: k(MCDFA+Cl) = (9.6 ± 5.1) × 10−12 exp[−(1363 ± 79)/T] and k(ECDFA+Cl) = (64.4 ± 29.7) × 10−12 exp[−(1110 ± 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 NOx the main fate of the alkoxy radicals formed after H-atom abstraction by Cl from the –CH3 group in methyl chlorodifluoroacetate is reaction of the radical with O2 to form the mixed anhydride CF2ClC(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 –CH2– entity in the ethyl group is α-ester rearrangement to produce chlorodifluoroacetic acid and the corresponding radical. The yields of chlorofluoracetic acid (CF2ClC(O)OH) obtained were as follows: (34 ± 5)% and (86 ± 8)% for the reactions of Cl with CF2ClC(O)OCH3 and CF2ClC(O)OCH2CH3, 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 O2, α-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.

[1]  I. Barnes,et al.  Kinetics of the reactions of Cl atoms with CF3C(O)OCH3, CF3C(O)OCH2CH3, CF2HC(O)OCH3 in the temperature range of 287–313 K and 1 atm , 2015 .

[2]  D. Rodríguez,et al.  Atmospheric chemistry of HFE-7300 and HFE-7500: Temperature dependent kinetics, atmospheric lifetimes, infrared spectra and global warming potentials , 2014 .

[3]  B. Mishra,et al.  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 , 2014, Structural Chemistry.

[4]  B. Mishra,et al.  Theoretical investigation of the gas-phase reactions of CF2ClC(O)OCH3 with the hydroxyl radical and the chlorine atom at 298 K , 2013, Journal of Molecular Modeling.

[5]  J. D. de Gouw,et al.  Vertically resolved measurements of nighttime radical reservoirs in Los Angeles and their contribution to the urban radical budget. , 2012, Environmental science & technology.

[6]  J. Orlando,et al.  Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance. , 2012, Chemical Society reviews.

[7]  J. Lelieveld,et al.  Significant concentrations of nitryl chloride observed in rural continental Europe associated with the influence of sea salt chloride and anthropogenic emissions , 2012 .

[8]  C. Zetzsch,et al.  Radicals in the atmosphere: a changing world! , 2010, Chemphyschem : a European journal of chemical physics and physical chemistry.

[9]  J. Orlando,et al.  The atmospheric oxidation of ethyl formate and ethyl acetate over a range of temperatures and oxygen partial pressures , 2010 .

[10]  I. Barnes,et al.  Atmospheric photooxidation of fluoroacetates as a source of fluorocarboxylic acids. , 2010, Environmental science & technology.

[11]  J. Thornton,et al.  A large atomic chlorine source inferred from mid-continental reactive nitrogen chemistry , 2010, Nature.

[12]  I. Bravo,et al.  Atmospheric HFEs degradation in the gas phase: Reaction of HFE-7500 with Cl atoms at low temperatures , 2009 .

[13]  T. Wallington,et al.  Kinetics of the reactions of chlorine atoms with a series of acetates , 2009 .

[14]  A. Ravishankara,et al.  High levels of nitryl chloride in the polluted subtropical marine boundary layer , 2008 .

[15]  M. B. Blanco,et al.  Rate constants of the reactions of CF2ClC(O)OCH3 and CF2ClC(O)OCH2CH3 with OH radicals and Cl atoms at atmospheric pressure , 2007 .

[16]  D. Rodríguez,et al.  Atmospheric HFEs degradation in the gas phase: reactions of HFE-7100 and HFE-7200 with Cl atoms at low temperatures. , 2006, Environmental science & technology.

[17]  J. Codnia,et al.  Rate Measurement of the Reaction of CF2Cl Radicals with O2 , 2006, Photochemistry and photobiology.

[18]  K. Tokuhashi,et al.  Henry's law constants of 2,2,2-trifluoroethyl formate, ethyl trifluoroacetate, and non-fluorinated analogous esters , 2005 .

[19]  O. Nielsen,et al.  Atmospheric chemistry of CF3OCF2CF2H and CF3OC(CF3)2H: reaction with Cl atoms and OH radicals, degradation mechanism, global warming potentials, and empirical relationship between k(OH) and k(Cl) for organic compounds. , 2005, The journal of physical chemistry. A.

[20]  Wen-Tien Tsai,et al.  Environmental risk assessment of hydrofluoroethers (HFEs). , 2005, Journal of hazardous materials.

[21]  S. R. Sellevåg,et al.  Study of the OH and Cl-initiated oxidation, IR absorption cross-section, radiative forcing, and global warming potential of four C4-hydrofluoroethers. , 2004, Environmental science & technology.

[22]  K. Solomon,et al.  Haloacetic acids in the aquatic environment. Part I: macrophyte toxicity. , 2004, Environmental pollution.

[23]  K. Tokuhashi,et al.  Henry's law constants and hydrolysis rate constants of 2,2,2-trifluoroethyl acetate and methyl trifluoroacetate , 2004 .

[24]  R. Peters.  Chloroacetic acids in European soils and vegetation. , 2003, Journal of environmental monitoring : JEM.

[25]  E. Galán,et al.  Estimation of fluorine and chlorine emissions from Spanish structural ceramic industries. The case study of the Bailén area, Southern Spain , 2002 .

[26]  J. Doussin,et al.  FTIR spectroscopic study of the OH-induced oxidation of two linear acetates: ethyl and n-propyl acetates , 2001 .

[27]  Akira Sekiya,et al.  The potential of hydrofluoroethers to replace CFCs, HCFCs and PFCs , 2000 .

[28]  S. Mabury,et al.  Detection of Chlorodifluoroacetic Acid in Precipitation: A Possible Product of Fluorocarbon Degradation , 2000 .

[29]  B. Finlayson‐Pitts,et al.  Unexpectedly high concentrations of molecular chlorine in coastal air , 1998, Nature.

[30]  S. Hashimoto,et al.  Distribution, sources, and stability of haloacetic acids in Tokyo Bay, Japan , 1998 .

[31]  W. Carter,et al.  The Reactions of Selected Acetates with the OH Radical in the Presence of NO: Novel Rearrangement of Alkoxy Radicals of Structure RC(O)OCH(Ȯ)Ŕ , 1998 .

[32]  P. Brimblecombe,et al.  The Henry's Law Constants of the Haloacetic Acids , 1998 .

[33]  M. K. Kubo,et al.  Hydrocarbon and halocarbon measurements as photochemical and dynamical indicators of atmospheric hydroxyl, atomic chlorine, and vertical mixing obtained during Lagrangian flights , 1996 .

[34]  N. Mihalopoulos,et al.  An FTIR product study of the photooxidation of dimethyl disulfide , 1994 .

[35]  A. Becke.  Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[36]  B. Finlayson‐Pitts.  Chlorine atoms as a potential tropospheric oxidant in the marine boundary layer , 1993 .

[37]  D. Burton,et al.  Generation of trifluoromethylcopper from chlorodifluoroacetate , 1991 .

[38]  Hermann Stoll,et al.  Results obtained with the correlation energy density functionals of becke and Lee, Yang and Parr , 1989 .

[39]  Parr,et al.  Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. , 1988, Physical review. B, Condensed matter.

[40]  M. A. Pereira,et al.  The carcinogenicity of trichloroethylene and its metabolites, trichloroacetic acid and dichloroacetic acid, in mouse liver. , 1987, Toxicology and applied pharmacology.

[41]  Joseph L. Walter,et al.  The Infrared Spectra of Complex Molecules , 1982 .

[42]  R. L. Redington,et al.  Infrared spectra of trifluoroacetic acid and trifluoroacetic anhydride , 1971 .

[43]  L. J. Bellamy.  The infra-red spectra of complex molecules , 1962 .

[44]  C. Eckart.  The Penetration of a Potential Barrier by Electrons , 1930 .