Environ. Sci. Technol. 1997, 31, 1817-1821
OCF2OCF2CF2OCF2H, since the predicted degradation path-
Tropospheric Degradation Products
of Novel Hydrofluoropolyethers
way of this compound in the troposphere is by reaction with
OH radicals. Because the rates of reaction of the OH radical
with these halocarbons are generally very slow (3, 4), Cl atoms
instead of OH radicals were employed for the initial H atom
abstraction since they can be generated at higher concentra-
tion by Cl2 photolysis. The rate constants for the reaction of
Cl atoms with the above HFPEs were also measured in this
work using a relative rate method.
E R N E S T O C . T U A Z O N
Statewide Air Pollution Research Center, University of
California, Riverside, California 92521
Experimental Section
The Cl atom-initiated photooxidations of the hydrofluo-
ropolyethers (HFPEs) HCF OCF OCF CF OCF H, HCF OCF CF -
The irradiation experiments were carried out in a 5800-L
evacuable, thermostated, Teflon-coated chamber equipped
with a solar simulator that provided radiation from a 24-kW
xenon arc lamp (5). The chamber housed an in situ multiple-
reflection optical system interfaced to a Nicolet 7199 Fourier
transform infrared (FT-IR) absorption spectrometer equipped
with a liquid nitrogen-cooled HgCdTe detector.
2
2
2
2
2
2
2
2
OCF H, and HCF OCF OCF H in air produced C(O)F as the
2
2
2
2
2
only carbon-containing product, with observed average
C(O)F molar formation yields of 4.73, 3.77, and 2.82, respectively.
2
The C(O)F molar formation yields during the early stages
2
of the reactions were observed to be closer to the
number of C atoms in each parent HFPE. On the basis of
current knowledge concerning the degradation pathways
of hydrofluorocarbons and hydrochlorofluorocarbons, it is
The partial pressures of the HFPEs were measured into
calibrated 2-L Pyrex bulbs with a capacitance manometer
(MKS Baratron, 100-Torr sensor) and introduced into the
chamber filled with the diluent air by flushing with N2 gas.
Chlorine was measured and introduced into the chamber
both by the above procedure and by direct injection into the
chamber with the use of gas-tight, all-glass 100-mL syringes
(the latter procedure being used for the lesser quantities of
chlorine employed during the earlier experiments). The initial
concentrations (in units of 1013 molecule cm-3) employed
were as follows: for the product studies, HFPEs, 4.8-7.2, and
Cl2, 94-485; for the relative rate experiments, HFPEs, 4.8-
6.0, CF3CF2H, 7.2, and Cl2, 360-480. An experiment for the
infrared spectroscopic calibration of C(O)F2 employed the
photolysis in air of a mixture containing 9.6 × 1013 and 8.2
× 1014 molecule cm-3, respectively, of CHClF2 and Cl2.
The experiments were conducted at 298 ( 2 K and 740
Torr total pressure with irradiation times of 60-150 min. The
reactants and products were monitored by FT-IR absorption
spectroscopy, using a path length of 62.9 m and a full width
expected that C(O)F will also be produced with near unit
2
yield per C atom from the above HFPEs in the troposphere,
where loss processes would be initiated primarily by
reaction with OH radicals. The rate constants for reaction
with the Cl atom at 298 ( 2 K were determined for the
HFPEs by a relative rate method that employed CF CF H as
3
2
the reference compound [k(Cl + CF CF H) ) (2.4 ( 0.5)
3
2
× 10-16 cm3 molecule-1 s-1], with measured values of (in
units of 10-17 cm3 molecule-1 s-1) HCF OCF OCF CF -
2
2
2
2
OCF H, 3.6 ( 0.8; HCF OCF CF OCF H, 4.5 ( 1.0; and HCF -
2
2
2
2
2
2
OCF OCF H, 5.0 ( 1.1.
2
2
Introduction
Perfluorinated polyethers (PFPEs) are among the organo-
fluorine compounds that have found important industrial
applications. They are being employed as solvents, lubricants
in both delicate and heavy machinery, components of coatings
and a variety of polymer formulations, and contact fluids for
thermal testing of electronic components (1). However, in
response to environmental issues that encompass industrial
halocarbons in general, including their possible contributions
to stratospheric ozone depletion and global warming, per-
fluorinated ethers are also being redesigned to enhance their
degradability in the lower atmosphere. Thus, for example,
the polyethers HCF2O(CF2CF2O)m(CF2O)nCF2H, where m )
0-7 and n ) 0-5, represent a group of novel hydrofluo-
ropolyethers (HFPEs) being developed by Ausimont (2) as
replacements for the PFPEs as well as for chlorofluorocarbons
(CFCs). As for the hydrofluorocarbon (HFC) and hydrochlo-
rofluorocarbon (HCFC) substitutes for the CFCs (which have
been phased out of production in industrialized nations), the
presence of one or more carbon-hydrogen bonds in the
molecule enables the abstraction of hydrogen atoms by the
OH radical to be the initial step that facilitates the degradation
of these replacement compounds in the troposphere, thus
minimizing their transport into the stratosphere (3).
at half-maximum resolution of 0.7 cm-1
.
The samples of HCF2OCF2OCF2H, HCF2OCF2CF2OCF2H,
and HCF2OCF2OCF2CF2OCF2H were supplied by Ausimont.
Cl2 (99.9% minimum) and CHClF2 (99.8% minimum) were
from Matheson, and CF3CF2H (g99.5%) was from E. I. du
Pont de Nemours and Co., Inc. The diluent gas was synthetic
air (20% O2 + 80% N2) made of M.O.S.-grade O2 (99.995%,
Liquid Carbonic) and head gas from liquid N2 (Airco).
Results
Product Studies. HCF2OCF2OCF2CF2OCF2H. A quantitative
vapor-phase spectrum (700-1700 cm-1) of the HCF2OCF2-
OCF2CF2OCF2H sample, along with those obtained for HCF2-
OCF2CF2OCF2H and HCF2OCF2OCF2H, is presented in Figure
1. The gas chromatographic analysis provided by Ausimont
indicated a 95.24% purity for HCF2OCF2OCF2CF2OCF2H, with
the other sample constituents being 1.2% of a C4 homolog
and 3.4% of C6 homologs. In the following, the concentrations
and extent of reactions are reported first on the basis of a
100% pure C5 sample and later discussed in terms of the
above-measured composition.
Three irradiation experiments, each with 4.8 × 1013
molecule cm-3 initial concentration of the ether and 2.0 ×
1015, 3.6 × 1015, and 4.8 × 1015 molecule cm-3 of Cl2 (runs
EC-1628, EC-1629, and EC-1633, respectively), were carried
out. The respective consumptions of HCF2OCF2OCF2CF2-
OCF2H at the end of the experiments were 6.7% after 141 min
(EC-1628), 11.8% after 147 min (EC-1629), and 10.6% after
138 min (EC-1633).
To assess the environmental impact that may result in the
event of their widespread use, a knowledge of the identities
and yields of products from the atmospheric degradation
reactions of the HFPEs is required. In this work, experiments
were carried out to study the products generated from the
alkoxy radicals formed after the initial H atom abstraction
step from HCF2OCF2OCF2H, HCF2OCF2CF2OCF2H, and HCF2-
9
S0013-936X(96)01010-3 CCC: $14.00
1997 Am erican Chem ical Society
VOL. 31, NO. 6, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 1 8 1 7