Chemical Physics Letters 439 (2007) 18 22
`
`www.elsevier.com/locate/cplett
`
`Atmospheric chemistry of CF3CF@CH2: Kinetics and mechanisms
`of gas-phase reactions with Cl atoms, OH radicals, and O3
`
`O.J. Nielsen a,*, M.S. Javadi a, M.P. Sulbaek Andersen a, M.D. Hurley b,
`T.J. Wallington b,*, R. Singh c
`
`a Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK 2100 Copenhagen, Denmark
`b Physical and Environmental Sciences Department, Ford Motor Company, Mail Drop SRL 3083, Dearborn, MI 48121, USA
`c Honeywell International Inc., 101 Columbia Road, Morristown, NJ 07962, USA
`
`Received 31 January 2007; in final form 6 March 2007
`Available online 21 March 2007
`
`Abstract
`
`techniques were used to determine k(Cl + CF3CF CH2) = (7.03 ± 0.59) · 1011,
`Long path length FTIR smog chamber
`k(OH + CF3CF CH2) = (1.05 ± 0.17) · 1012, and k(O3 + CF3CF CH2) = (2.77 ± 0.21) · 1021 cm3 molecule1 s1 in 700 Torr of
`N2, N2/O2, or air diluent at 296 K. CF3CF CH2 has an atmospheric lifetime of approximately 11 days and a global warming potential
`(100 yr time horizon) of four. CF3CF CH2 has a negligible global warming potential and will not make any significant contribution to
`radiative forcing of climate change.
`Ó 2007 Elsevier B.V. All rights reserved.
`
`1. Introduction
`
`impact of
`Recognition of the adverse environmental
`chlorofluorocarbon (CFC) release into the atmosphere
`[1,2] has led to an international effort to replace these com-
`pounds with environmentally acceptable alternatives.
`Unsaturated fluorinated hydrocarbons are a class of com-
`pounds which have been developed to replace CFCs and
`saturated hydrofluorocarbons in air conditioning units.
`Prior to their large-scale industrial use an assessment of
`the atmospheric chemistry, and hence environmental
`impact, of these compounds is needed. To address this need
`the atmospheric chemistry of CF3CF@CH2 was investi-
`gated. Smog chamber/FTIR techniques were used to deter-
`mine the following properties for this compound:
`(i)
`kinetics of its reaction with chlorine atoms, (ii) kinetics of
`its reaction with hydroxyl radicals, (iii) kinetics of its reac-
`
`tion with ozone and (iv) atmospheric implications. Results
`are reported herein.
`
`2. Experimental
`
`Experiments were performed in a 140-liter Pyrex reactor
`interfaced to a Mattson Sirus 100 FTIR spectrometer [3].
`The reactor was surrounded by 22 fluorescent blacklamps
`(GE F15T8-BL), which were used to photochemically initi-
`ate the experiments. Chlorine atoms were produced by
`photolysis of molecular chlorine.
`ð1Þ
`Cl2 þ hv ! Cl þ Cl
`OH radicals were produced by photolysis of CH3ONO in
`the presence of NO in air.
`CH3ONO þ hv ! CH3O þ NO
`CH3O þ O2 ! HO2 þ HCHO
`HO2 þ NO ! OH þ NO2
`
`ð2Þ
`ð3Þ
`ð4Þ
`
`* Corresponding authors.
`E mail addresses: ojn@kiku.dk (O.J. Nielsen), twalling@ford.com
`(T.J. Wallington).
`
`In the relative rate experiments the following reactions take
`place.
`
`0009 2614/$ see front matter Ó 2007 Elsevier B.V. All rights reserved.
`doi:10.1016/j.cplett.2007.03.053
`
`Arkema Exhibit 1099
`
`1 of 5
`
`

`
`OJ. Nielsen et al. I Otemical Physics Letters 439 (2007) I8 22
`
`19
`
`C1 + Reactant —> products
`
`C1 + Reference —> products
`
`OH + Reactant —> products
`
`OH + Reference —> products
`
`It can be shown that
`
`R
`m
`R f
`L, m = kn --uL,, l°i°°l~
`[Reactant],
`kR,f...,.,,,
`[Reference],
`
`(5)
`
`(6)
`
`(7)
`
`(8)
`
`(9,
`
`where [Reactant],9, [Reactant}, [Reference],o, and [Refer-
`ence} are the concentrations of reactant and reference at
`times to and t, and kncamm and kR¢fa-aw: are the rate
`constants for the reactant and the reference. Plots of
`
`vs. Ln([Reference],0/[Refer-
`Ln[Reactant],u/[Reactant],)
`ence}) should be linear, pass through the origin, and have
`a slope of k.;,,,,,.,,.,,/k;;,,r.=,.=,,.,.,. The kinetics of the O3 reac-
`tion were studied using an absolute rate method in which
`the pseudo first-order loss of CF3CF=CH2 was measured
`in the presence of excess 03.
`03 was produced from 02 via silent electrical discharge
`using a commercial O3 ozonizer. CH3ONO was synthesized
`by the drop wise addition of concentrated sulfuric acid to a
`saturated solution of NaNO2 in methanol. Other reagents
`were obtained from commercial sources. Experiments were
`conducted in 700 Torr total pressure of N2, or N;/O2 dilu-
`ent at 296 3: 1 K.
`
`Concentrations of reactants and products were moni-
`tored by FTIR spectroscopy. IR spectra were derived from
`32 coadded interferograrns with a spectral resolution of
`0.25 cm ' and an analytical path length of 27.1 m. To
`check for unwanted loss of reactants and reference com-
`
`reaction mixtures
`pounds via heterogeneous reactions,
`were left to stand in the chamber for 60min. There was
`
`no observable (<2%) loss of any of the reactants or prod-
`ucts in the present work. Unless stated otherwise, quoted
`uncertainties are two standard deviations from least
`
`squares regressions.
`
`3. Results and discussion
`
`3.1. Kinetics‘ of the C1 + CF3CF=CH2 reaction
`
`The rate of reaction (10) was measured relative to reac-
`tions (11) and (12):
`
`C1 + CF3CF=CH2 —» products
`
`C1 + C21-I4 —» products
`
`C1 + C2112 —» products
`
`(10)
`
`(1 1)
`
`(12)
`
`3.5
`
`5*’c
`
`N01
`
`Nc
`
`A U’!
`
`Ln([CF3CF=CH2]m/[CF3CF=CH2],) 8
`
`0.0
`
`0.5
`
`1.0
`
`1.5
`
`2.0
`
`2.5
`
`Ln ([Reference],,,l[Reference],)
`
`Fig. 1. Decay of CF,CF=CH2 vs. C2H4 and C2H2 in the presence of Cl
`atoms in 700 Torr of either air (open symbols) or N2 (filled symbols) at
`296 2|: 2 K.
`
`1 g.‘/CS kldkn
`
`0.76 i 0.04 and km/
`
`to the data in
`kn
`1.38 i 0.06.
`Using It"
`(9.29:b 0.51) x 10 " [4] and kn (5.07 :t
`0.34) x 10 " [4]
`(700 Torr, 295 K) gives km (7.06 :t
`0.54) x 10 " and (7.00 :L0.56)x10 " cm3 molecule ‘s ‘.
`We choose to cite a final value which is the average of the
`individual determinations together with error limits which
`encompass the extremes of the determinations, hence
`km (7.03 :l: 0.59) x 10 " cm3 molecule ' s '. While there
`have been no previous studies of km, we can compare our
`result with k(Cl + CH3CH=CH2)
`2.4 x 10 '° [5], lo(Cl +
`CF3CH=CH2)
`(9.07 :l: l.08)x 10 "
`[6],
`lo(Cl +
`C4F,CH=CH2)
`(8.9:I: l.0)x 10 "[71, k(Cl+C6F,3CH=
`CH2)
`(9.1 :I:l.0)x 10 "
`[7],
`and
`Io(Cl + CF3CF=
`CF2)
`(2.7 :l:0.3)x 10 " an’ molecule ' s ‘
`[81
`The
`reaction of Cl atoms with propene proceeds via electro-
`philic addition to the >C=C< double bond. The presence
`of electron withdrawing fluorine substituents is expected
`to lead to decreased reactivity with Cl atoms. Consistent
`with expectations, the reactivity of CF3CF=CH2 reported
`here lies between those of CF3CH=CH2 and CF3CF=CF2
`reported previously.
`
`3.2. Kinetics of the OH + CF3CI"'=CH2 reaction
`
`Reaction mixtures
`
`consisted of
`
`19.1 26.2 mTorr of
`
`104 133 mTorr C12, and either 4.33
`CF3CF=CH2,
`30.2 mTorr C2H4, or 2.35 8.5 mTorr C2H2, in 700 Torr
`of air, or N2, diluent. The observed loss of CF3CF=CH2
`vs. those of the reference compounds is plotted in Fig 1.
`As seen from Fig. 1, there was no discemable difference be-
`tween the results obtained in N2, or air, diluent. A linear
`least squares fit (unweighted, not forced through the origin)
`
`The rate of reaction (13) was measured relative to reac-
`tions (14) and (15):
`
`OH + CF3CF=CH2 —» products
`
`OH + C2H4 —+ products
`
`OH + C2H2 —> products
`
`(13)
`
`(14)
`
`(15)
`
`Initial reaction mixtures consisted of 17.6 18.1 mTorr of
`
`CF3CF=CH2, 110 200 mTorr CH3ONO, and 3.38 mTorr
`
`2of5
`
`

`
`20
`
`0..I. Nielsen el al. I Chemical Physics Letters 439 (2007) I8 22
`
`reactivity of CF3CF=CF2 appears to be anomalously high.
`A computational study of the reaction of OH radicals with
`CF3CF=CF2 would be of interest to shed further light on
`the mechanism of these reactions.
`
`3.3. Absolute Rate Study of k( 03 + CF3CF=CH2)
`
`The kinetics of reaction (16) were studied by observing
`the decay of CF3CF=CH2 when exposed to ozone in the
`reaction chamber. Reaction mixtures consisted of 14
`
`28 mTorr CF3CF=CH2, 30 46mTorr cyclohexane, and
`180 1890 mTorr O3 in 700 Torr of air diluent. Cyclohexane
`was added to avoid potential problems associated with the
`loss of CF3CF=CH2 via reaction with OH radicals formed
`in
`reaction
`(16). Variation of
`the
`[cyclohexanell
`[CF3CF=CH2] ratio over the range 1 3 had no discemable
`effect on the observed decay of CF3CF=CH2 suggesting
`that loss via reaction with OH radicals is not a significant
`complication. The loss of CF3CF=CH2 followed pseudo
`first-order kinetics in all experiments (see insert in Fig. 3).
`Fig. 3 shows a plot of the pseudo first-order loss of
`CF3CF=CH2 vs. 03 concentration. The line through the
`data gives km (2.77:t0.2l)xl0 2' cm’ molecule 's '.
`
`CF3CF=CH2 + 03 —> products
`
`(16)
`
`It is of interest to compare this result with the reported
`reactivity of ozone towards other fluoroalkenes and alk-
`enes. The reported rate constants for reactions of 03 with
`propene, 1-butene, 1-pentene , 1-hexene, 1-heptene, 1-oe-
`tene, and 1-decene are indistinguishable and are approxi-
`mately l.0xl0 '7 cm3 molecule '
`s '
`[9], The rate
`constants for reactions of 03 with CF3CF=CF2 and
`CF3CH=CH2
`are
`(6.2 d: 1.5) x 10 22
`[14]
`and
`
`
`
`' 0.0
`
`0.5
`
`1.0
`
`1.5
`
`2.0
`
`Ln ([Reference]ml[Reference],)
`
`Fig. 2. Decay of CF3CF=CH2 vs. CzH4 and C211; in the presence of OH
`radicals in 700 Torr of air at 296i 2 K.
`
`QH4 or 3.09 mTorr QH2 in 700 Torr total pressure of air
`diluent. Fig. 2 shows the loss of CF3CF=CH2 plotted ver-
`sus loss of the reference compounds. Linear least squares
`analysis
`glVCS
`k]3/[C14
`:i:
`and k]3/[C15
`1.21 2!: 0.09.
`
`(8.52 :t 1.28) x 10 '2 [9] (atmospheric pres-
`Using k...
`sure, 298 K) and k.5
`(8.45 :t 0.85) x 10 '3 [10] gives
`k];
`(1.07 i0.l7)x 10 '2 and (l.02i0.l3) x 10 '2 cm’
`molecule ' s ‘.
`Indistinguishable
`values of k1;
`are
`obtained using the two different references. We choose to
`cite a final value which is the average of the individual
`determinations together with error limits which encompax
`the extremes of the determinations, hence kl;
`(1.05 :l:
`0.17) x 10 '2 cm’ molecule ' s '.
`It is of interest to compare our result with the reactivity
`of propene and fluorinated propenes reported in the litera-
`ture. The reaction of OH radicals with propene proceeds
`via electrophilic addition to the >C=C< double bond with
`a rate constant of 2.6x 10 " cm3 molecule ls '
`in one
`
`atmosphere of air at 298 K [9]. Measurements of
`k(OH + CF3CH=CH2) by Orkin et al. [11] and Sulbaek
`Andersen et al. [6] are in good agreement, taking an aver-
`age from the two studies gives k(OH +CF3CH=CH2)
`1.45 x 10 '2 em’ molecule ' s '. Mcllroy and Tully [12],
`Dubey et al. [13], Orkin et al. [11], and Mashino et al. [8]
`studied the reaction of OH radicals with CF3CF=CF2.
`The results at ambient temperature from the four studies
`were in good agreement; the average from the studies is
`k(OH + CF3CH=CH2)
`24 x 10 '2em3 molecule ' s '.
`In contrast to Cl atoms, the reactivity of OH radicals with
`CH3CH=CH2,
`CF3CH=CH2,
`CF3CF=CH2,
`and
`CF3CF=CF2 does not follow the trend expected assuming
`a simple electrophilic addition mechanism. Specifically, the
`
`3of5
`
`33
`x"0ll
`'6
`5g -0u
`lIL
`9..IL
`
`I0l
`
`0$c_l
`
`3 .
`
`5
`
`[03] (10"‘molecu|e cm"°')
`
`Fig. 3. Pseudo first order loss of CF3CF=CH2 versus 03 concentration.
`The insert shows typical decay plots for CF3CF=CH2 when exposed to
`I80 mTorr (circles), 585 mTorr (triangles), or I890 mTorr (squares) of 0,.
`
`

`
`O.J. Nielsen et al. / Chemical Physics Letters 439 (2007) 18 22
`
`21
`
`01234
`
`Cross Section (10-18 cm2 molecule-1)
`
`800
`
`1000
`
`1200
`1400
`1600
`Wavenumber (cm-1)
`
`1800
`
`2000
`
`Fig. 4. IR spectrum of CF3CF@CH2.
`
`global warming potential, HGWP [20], for CF3CF@CH2
`
`
`
`
`(relative to CFC-11) can then be estimated using the
`expression:
`
`
`sCF3CF@CH2M CFC11
`HGWPCF3CF@CH2 ¼ IFCF3CF@CH2
`sCFC11M CF3CF@CH2
`IFCFC11
` 1 expðt=sCF3CF@CH2Þ
`1 expðt=sCFC11Þ
`IFCF3CF@CH2 ,
`where
`IFCFC 11, MCF3CF@CH2 , MCFC 11,
`sCF3CF@CH2 , and sCFC 11 are the instantaneous forcings,
`molecular weights,
`and
`atmospheric
`lifetimes
`of
`CF3CF@CH2 and CFC-11, and t is the time horizon over
`which the forcing is integrated. Using s(CF3CF@CH2)
`11 days and sCFC 11
`45 years [21] we estimate that the
`HGWP of CF3CF@CH2 relative to CFC-11 is 1.9 · 10 3
`for a 20 yr horizon and 7.6 · 10 4 for a 100 yr time hori-
`zon, respectively. Relative to CO2, the GWP of CFC-11
`on 20 and 100 yr time horizons are 6300 and 4600 [21].
`Hence, relative to CO2, the GWP of CF3CF@CH2 is
`approximately 12 for a 20 yr horizon and 4 for a 100 yr
`time horizon, respectively. CF3CF@CH2 has a negligible
`global warming potential and will not make any significant
`contribution to radiative forcing of climate change.
`
`Acknowledgements
`
`O.J.N., M.S.J., and M.P.S.A. acknowledge financial
`support from the Danish Natural Science Research Coun-
`cil for the Copenhagen Center for Atmospheric Research
`(CCAR). All statements, information, and data given here-
`in are presented without guaranty, warranty, or responsi-
`bility of any kind, expressed or implied, for Honeywell
`International Inc.
`
`References
`
`[1] M.J. Molina, F.S. Rowland, Nature 249 (1974) 810.
`
`(3.5 ± 0.3) · 10 19 cm3 molecule 1 s 1[6], respectively. The
`reactivity of fluorinated propenes towards ozone follows
`trend expected (CH3CH@CH2 > CF3CH@CH2 >
`the
`CF3CF@CH2 > CF3CF@CF2) for reaction proceeding via
`electrophilic addition of ozone to the >C@C< double
`bond. In its reaction with O3, CF3CF@CH2 is less reactive
`than its non-fluorinated counterpart by a factor of 3600.
`When compared to Cl atoms and OH radicals, O3 has
`the lowest reactivity and hence its rate of reaction with
`the compounds considered above is most sensitive to the
`presence of the electron withdrawing fluorine substituents.
`Finally, it is worth noting that while reactions of O3, Cl,
`and OH proceed via electrophilic addition to the >C@C<
`double bond there are differences in mechanism with O3
`adding across the double bond and Cl atoms and OH rad-
`icals adding to one of the carbon atoms.
`
`4. Atmospheric lifetime and global warming potential
`
`CF3CF@CH2 will not undergo photolysis [11] and is not
`expected to be removed effectively by either wet or dry
`deposition. Cl atoms are not present in the atmosphere in
`sufficient quantity to impact the lifetime of CF3CF@CH2.
`Reaction with OH and O3 are expected to be loss
`mechanisms for CF3CF@CH2. The value of k(OH +
`CF3CF@CH2) measured in the present work can be used
`to provide an estimate of the atmospheric lifetime of
`CF3CF@CH2. Using a global weighted-average OH con-
`centration of 1.0 · 106 molecules cm 3 [15] leads to an esti-
`mated lifetime of CF3CF@CH2 with respect to reaction
`with OH radicals of 11 days. In a similar fashion our value
`of k(O3 + CF3CF@CH2) can be combined with the global
`background O3 concentration of approximately 35 ppb [16]
`to provide an estimated lifetime with respect to reaction
`with ozone of 13 years. We conclude that the atmospheric
`lifetime of CF3CF@CH2 is determined by its reaction with
`OH and is approximately 11 days. The approximate nature
`of this lifetime estimate should be stressed; the average
`daily concentration of OH radicals varies significantly with
`both location and season [17]. The quoted lifetime is a glo-
`bal average, the local lifetimes could be significantly shorter
`or longer.
`The IR spectrum of CF3CF@CH2 measured in the pres-
`ent work is shown in Fig. 4. CF3CF@CH2 has an inte-
`grated IR absorption cross section (800 2000 cm 1) of
`(1.63 ± 0.09) · 10 16 cm molecule 1. The quoted uncer-
`tainty (±5%) is comprised of the following components:
`sample concentration (±2%), path length (±1.5%), residual
`baseline offset after
`subtraction of
`the background
`(±0.5%), and spectrometer accuracy (±1%) [18]. There
`are no literature IR data for CF3CF@CH2 to compare with
`our result.
`Using the method outlined by Pinnock et al. [18], the IR
`spectrum of CF3CF@CH2 shown in Fig. 4, and the IR
`spectrum of CFC-11 [19] we calculate instantaneous forc-
`for CF3CF@CH2
`and CFC-11 of
`0.22
`and
`ings
`0.26 W m 2 ppb 1, respectively. Values of the halocarbon
`
`4 of 5
`
`

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`22
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`O.J. Nielsen et al. / Chemical Physics Letters 439 (2007) 18 22
`
`[2] J.D. Farman, B.G. Gardiner, J.D. Shanklin, Nature 315 (1985) 207.
`[3] T.J. Wallington, S.M. Japar, J. Atmos. Chem. 9 (1989) 399.
`[4] T.J. Wallington, J.M. Andino, I.M. Lorkovic, E.W. Kaiser, G.
`Marston, J. Phys. Chem. 94 (1990) 3644.
`[5] R. Atkinson et al., Atmos. Chem. Phys. Discuss. 5 (2005) 6295.
`[6] M.P. Sulbaek Andersen et al., J. Photochem. Photobiol. A: Chem.
`176 (2005) 124.
`[7] E. Ve´sine, V. Bossoutrot, A. Mellouki, G. Le Bras, J. Wenger, H.
`Sidebottom, J. Phys. Chem. A. 104 (2000) 8512.
`[8] M. Mashino, Y. Ninomiya, M. Kawasaki, T.J. Wallington, M.D.
`Hurley, J. Phys. Chem. A. 104 (2000) 7255.
`[9] J.G. Calvert, R. Atkinson, J.A. Kerr, S. Madronich, G.K. Moortgat,
`T.J. Wallington, G. Yarwood, The Mechanisms of Atmospheric
`Oxidation of the Alkenes, Oxford University Press, Oxford, 2000.
`[10] M. Sørensen, E.W. Kaiser, M.D. Hurley, T.J. Wallington, O.J.
`Nielsen, Int. J. Chem. Kinet. 35 (2003) 191.
`[11] V. L Orkin, R.E. Huie, M.J. Kurylo, J. Phys. Chem. A. 101 (1997)
`9118.
`[12] A. McIlroy, F.P. Tully, J. Phys. Chem. 97 (1993) 610.
`
`[13] M.K. Dubey, T.F. Hanisco, P.O. Wennberg, J.G. Anderson,
`Geophys. Res. Lett. 23 (1996) 321.
`[14] G. Acerboni, J.A. Beukes, N.R. Jensen, J. Hjorth, G. Myhre, C.J.
`Nielsen, J.K. Sundet, Atmos. Environ. 35 (2001) 4113.
`[15] R.G. Prinn et al., Science 292 (2001) 1882.
`[16] B.J. Finlayson Pitts, J.N. Pitts Jr., Chemistry of the Upper and Lower
`Atmosphere, Academic Press, London, 2000.
`[17] G. Klecka et al., Evaluation of Persistence and Long Range Trans
`port of Organic Chemicals in the Environment, SETAC Press,
`Pensacola, 2000.
`[18] S. Pinnock, M.D. Hurley, K.P. Shine, T.J. Wallington, T.J. Smyth, J.
`Geophys. Res. 100 (1995) 23227.
`[19] Y. Ninomiya, M. Kawasaki, A. Gushin, L.T. Molina, M. Molina,
`T.J. Wallington, Environ. Sci. Technol. 34 (2000) 2973.
`[20] D.A. Fisher, C.H. Hales, W. Wang, M.K.W. Ko, N.D. Sze, Nature
`344 (1990) 513.
`[21] J.T. Houghton et al. (Eds.), Climate Change 2001: The Scientific
`Basis, Cambridge University Press, 2001.
`
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