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1.
Díaz-de-Mera Y Aranda A Bravo I Rodríguez D Rodríguez A Moreno E 《Environmental science and pollution research international》2008,15(7):584-591
Background, aim, and scope The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort
to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated
alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number
of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve
our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation
of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase.
Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present
work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF3CF2CF2OCH3) (1) and its isomer CF3CF2CF2CH2OH (2).
Materials and methods Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr
of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order
kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K
for reactions of HFE-7000 and CF3CF2CF2CH2OH, respectively.
Results The measured room temperature rate constants were k(Cl+CF3CF2CF2OCH3) = (1.24 ± 0.28) × 10−13 cm3 molecule−1 s−1and k(Cl+CF3CF2CF2CH2OH) = (8.35 ± 1.63) × 10−13 cm3 molecule−1 s−1 (errors are 2σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k
1(266–333 K) = (6.1 ± 3.8) × 10−13exp[−(445 ± 186)/T] cm3 molecule−1 s−1 and k
2(298–353 K) = (1.9 ± 0.7) × 10−12exp[−(244 ± 125)/T] cm3 molecule−1 s−1 (errors are 2σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl
radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2σ) were obtained for CF3CF2CF2OCH3 and CF3CF2CF2CH2OH, respectively.
Discussion The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into
account the error limits. Comparing the obtained results at room temperature, k
1 and k
2, HFE-7000 is significantly less reactive than its isomer C3F7CH2OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers
with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and
alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF2– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties
for a given application by changing the number of –CF2– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated
and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C3H7CH2OH, respectively.
Conclusions The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average
contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the
marine boundary layer, τ
Cl values as low as 2.5 and 0.4 years for HFE-7000 and C3H7CH2OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes
under such conditions may constitute a relevant sink. In the case of CF3CF2CF2OCH3, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would
result in underestimations of lifetimes and GWPs.
Recommendations and perspectives The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge
of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development
of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject
to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature
dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate
lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution
is still required. 相似文献
2.
《Atmospheric environment (Oxford, England : 1994)》1999,33(18):2893-2905
Products of the gas-phase reactions of OH radicals (in the presence of NO) and O3 with the biogenic organic compound 2-methyl-3-buten-2-ol have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography–mass spectrometry (GC-MS), gas chromatography with Fourier transform infrared detection (GC-FTIR), in situ FT-IR spectroscopy and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS/MS). Formaldehyde, 2-hydroxy-2-methylpropanal and acetone were identified from both the OH radical and O3 reactions, glycolaldehyde and organic nitrate (s) were also observed from the OH radical reaction, and the OH radical formation yield from the O3 reaction was measured. The formaldehyde, 2-hydroxy-2-methylpropanal, glycolaldehyde, acetone and organic nitrate yields from the OH radical reaction were 0.29±0.03, 0.19±0.07, 0.61±0.09, 0.58±0.04 and 0.05±0.02, respectively, and the formaldehyde, 2-hydroxy-2-methylpropanal and OH radical formation yields from the O3 reaction were 0.29±0.03, 0.30±0.06 (0.47 from FT-IR measurements) and 0.19 (uncertain to a factor of 1.5), respectively. Acetone was also observed from the O3 reaction, but appeared to be formed from secondary reactions. Reaction mechanisms are presented and discussed. 相似文献
3.
T.J. Wallington M.P. Sulbaek Andersen O.J. Nielsen 《Atmospheric environment (Oxford, England : 1994)》2010,44(11):1478-1481
The photochemical ozone creation potentials (POCPs) for CF3CFCH2 and other commercially significant hydrofluoroolefins have been estimated for the first time. CF3CFCH2 (HFO-1234yf) has a POCP of 7.0 which is less than that for ethane (12.3) and greater than for methane (0.6). Methane and ethane have sufficiently low POCPs that they are usually considered unreactive with respect to ozone formation in urban areas and accordingly are exempt from volatile organic compound (VOC) emission regulations. Estimated POCPs for other hydrofluoroolefins are: CH2CF2, 18.0; CF2CF2, 12.5; CH2CHCF3, 10.7; CF2CFCF3, 5.4; Z-CHFCFCF3, 5.6; E-CHFCFCF3, 7.3; CH2CHCF2CF3, 6.6; and t-CHFCHCF3, 6.4. 相似文献
4.
Hans Peter H. Arp Kai-Uwe Goss 《Atmospheric environment (Oxford, England : 1994)》2009,43(22-23):3654-3655
5.
María B. Blanco Iustinian Bejan Ian Barnes Peter Wiesen Mariano A. Teruel 《Environmental science and pollution research international》2009,16(6):641-648
Background, aim, and scope
Unsaturated esters are emitted to the atmosphere from biogenic and anthropogenic sources, including those from the polymer industry. Little information exists concerning the atmospheric degradation of unsaturated esters, which are mainly initiated by OH radicals. Limited information is available on the degradation of alkenes by Cl atoms and almost no data exists for the reactions of unsaturated esters with Cl atoms. This data is necessary to assess the impact of such reactions in maritime environments where, under circumstances, OH radical- and Cl atom-initiated oxidation of the compounds can be important. Rate coefficients for the reactions of chlorine atoms with vinyl acetate, allyl acetate, and n-butyl acrylate have been determined at 298 ± 3 K and atmospheric pressure. The kinetic data have been used in combination with that for structurally similar compounds to infer the kinetic contributions from the possible reaction channels to the overall reaction rate. 相似文献6.
《Atmospheric environment (Oxford, England : 1994)》2007,41(8):1792-1802
Gas-phase rate coefficients for the atmospherically important reactions of NO3, OH and O3 are predicted for 55 α,β-unsaturated esters and ketones. The rate coefficients were calculated using a correlation described previously [Pfrang, C., King, M.D., C. E. Canosa-Mas, C.E., Wayne, R.P., 2006. Atmospheric Environment 40, 1170–1179]. These rate coefficients were used to extend structure–activity relations for predicting the rate coefficients for the reactions of NO3, OH or O3 with alkenes to include α,β-unsaturated esters and ketones. Conjugation of an alkene with an α,β-keto or α,β-ester group will reduce the value of a rate coefficient by a factor of ∼110, ∼2.5 and ∼12 for reaction with NO3, OH or O3, respectively. The actual identity of the alkyl group, R, in −C(O)R or −C(O)OR has only a small influence. An assessment of the reliability of the SAR is given that demonstrates that it is useful for reactions involving NO3 and OH, but less valuable for those of O3 or peroxy nitrate esters. 相似文献
7.
《Atmospheric environment (Oxford, England : 1994)》2007,41(8):1652-1662
The night-time tropospheric chemistry of two stress-induced volatile organic compounds (VOCs), (Z)-pent-2-en-1-ol and pent-1-en-3-ol, has been studied at room temperature. Rate coefficients for reactions of the nitrate radical (NO3) with these pentenols were measured using the discharge-flow technique. Because of the relatively low volatility of these compounds, we employed off-axis continuous-wave cavity-enhanced absorption spectroscopy for detection of NO3 in order to be able to work in pseudo first-order conditions with the pentenols in large excess over NO3. The rate coefficients were determined to be (1.53±0.23)×10−13 and (1.39±0.19)×10−14 cm3 molecule−1 s−1 for reactions of NO3 with (Z)-pent-2-en-1-ol and pent-1-en-3-ol. An attempt to study the kinetics of these reactions with a relative-rate technique, using N2O5 as source of NO3 resulted in significantly higher apparent rate coefficients. Performing relative-rate experiments in known excesses of NO2 allowed us to determine the rate coefficients for the N2O5 reactions to be (5.0±2.8)×10−19 cm3 molecule−1 s−1 for (Z)-pent-2-en-1-ol, and (9.1±5.8)×10−19 cm3 molecule−1 s−1 for pent-1-en-3-ol. We show that these relatively slow reactions can indeed interfere with rate determinations in conventional relative-rate experiments. 相似文献
8.
E. Merian 《Chemosphere》1981,10(1):N13-N14