Fluoride-catalyzed hydroalkoxylation of hexafluoropropene with 2,2,2-trifluoroethanol

Article abstract of DOI:10.1016/j.jfluchem.2008.02.003

Trifluoroethoxylation of hexafluoropropene with 2,2,2-trifluoroethanol (TFE) were conducted using an alkali metal fluoride catalyst to produce CF₃CHFCF₂OCH₂CF₃. KF exhibited the highest yield and selectivity of CF₃CHFCF₂OCH₂CF₃, whereas LiF and NaF were inactive for the trifluoroethoxylation reaction. The same reaction also proceeded well in the presence of RbF or CsF, but yielded large amounts of olefinic and high molecular weight side products, implying that the size of alkali metal cation or the degree of MF dissociation plays an important role in determining the activity and the product composition. FT-IR and NMR experiments revealed that CsF interacts with TFE more strongly than KF through a hydrogen bonding. The experimental and spectroscopic results suggest that the degree of MF dissociation should be in the medium range for the selective production of CF₃CHFCF₂OCH₂CF₃ in high yield and selectivity.

Full text of DOI:10.1016/j.jfluchem.2008.02.003

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Journal of Fluorine Chemistry 129 (2008) 474–477
www.elsevier.com/locate/fluor
Fluoride-catalyzed hydroalkoxylation of hexafluoropropene
with 2,2,2-trifluoroethanol
Debby Natalia a, Dinh Quan Nguyen a, Ji Hee Oh a, Honggon Kim a,
Hyunjoo Lee a, , Hoon Sik Kim
*
b,**
a Energy & Environment Research Division, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Sungbuk-gu,
Seoul 136-791, Republic of Korea
b Department of Chemistry and Research Institute of Basic Sciences, Kyung Hee University, 1 Hoegi-dong, Dongdaemoon-gu,
Seoul 130-701, Republic of Korea
Received 16 January 2008; received in revised form 13 February 2008; accepted 13 February 2008
Available online 17 February 2008
Abstract
Trifluoroethoxylation of hexafluoropropene with 2,2,2-trifluoroethanol (TFE) were conducted using an alkali metal fluoride catalyst to produce
CF3CHFCF2OCH2CF3. KF exhibited the highest yield and selectivity of CF3CHFCF2OCH2CF3, whereas LiF and NaF were inactive for the
trifluoroethoxylation reaction. The same reaction also proceeded well in the presence of RbF or CsF, but yielded large amounts of olefinic and high
molecular weight side products, implying that the size of alkali metal cation or the degree of MF dissociation plays an important role in determining
the activity and the product composition. FT-IR and NMR experiments revealed that CsF interacts with TFE more strongly than KF through a
hydrogen bonding. The experimental and spectroscopic results suggest that the degree of MF dissociation should be in the medium range for the
selective production of CF3CHFCF2OCH2CF3 in high yield and selectivity.
# 2008 Published by Elsevier B.V.
Keywords: Hydrofluoroethers; CFC alternatives; Hydroalkoxylation; Alkali metal fluoride
1. Introduction
physical and chemical properties comparable to CFCs, such as
low surface tension, nonflammability, and excellent solvating
ability [10–12].
In spite of broad applications in various areas including
chemical, mechanical, and semiconductor industries, chloro-
fluorocarbons (CFCs) and chlorofluorohydrocarbons (HCFCs)
are doomed to be phased out due to their high ozone deleting
potential (ODP) and high global warming potential (GWP)
[1–4]. As the second generation of CFC alternatives,
hydrofluorocarbons (HFCs) were newly introduced, but soon
turned out to possess high GWP [5,6]. For this reason, a number
of silicone, nitrogen, and oxygen-containing molecules with
zero ODP and low GWP were proposed as the third generation
CFC alternatives [7–9]. Based on the theoretical and
experimental results reported so far, oxygen atom-containing
hydrofluoroethers (HFEs) seem to possess most favorable
Various HFEs were prepared by the alkylation of acyl
halides using a sulfonic acid ester as an alkylating agent in the
presence of anhydrous KF [13,14]. However, the alkylation
method suffered from the relatively high cost of raw material
and the difficulty in handling the toxic acyl fluorides. Recently,
Matsukawa et al. [15] reported that the hydroalkoxylation of
fluoroolefins in the presence of a Pd0 complex, [Pd(PPh3)4] was
highly active for producing HFEs in high yield and selectivity.
This is a great finding because the formation of commonly
observed olefinic side products can be completely suppressed,
but the use of an expensive Pd complex seems to be a major
obstacle in the commercial application of this process [14]. As a
more economical process, alkali metal fluoride-catalyzed
hydroalkoxylation, discovered by Dow Chemical Company,
is particularly attractive because the process required a small
amount of inexpensive catalyst [16]. However, detailed
investigation on the role of alkali metal fluoride (MF) was
never been attempted.
* Corresponding author. Tel.: +82 2 958 5868; fax: +82 2 955 5859.
** Corresponding author. Tel.: +82 2 961 0432; fax: +82 2 965 4408.
E-mail addresses: hjlee@kist.re.kr, u04623@naver.com (H. Lee),
khs2004@khu.ac.kr (H.S. Kim).
0022-1139/$ – see front matter # 2008 Published by Elsevier B.V.
doi:10.1016/j.jfluchem.2008.02.003

D. Natalia et al. / Journal of Fluorine Chemistry 129 (2008) 474–477
475
Scheme 1. Reaction scheme of hexafluoropropene (HFP) with 2,2,2-trifluoroethanol (TFE).
In this paper, we report our study on the role of metal
fluoride for the hydroalkoxylation of hexafluoropropylene
(HFP) with 2,2,2-trifluoroethanol (TFE) by means of FT-IR and
NMR spectroscopic methods.
means of a FT-IR spectroscopy. As shown in Fig. 1, the peak
at 3452 cmꢀ1 corresponds to the O–H stretching frequency of
TFE. Since KF is an active catalyst for the hydroalkoxylation
of TFE, KF was expected to interact with TFE through the
hydroxyl group. Contrary to our expectation, the O–H peak
remained unchanged when KF was added to a solution of TFE
in CH3CN, possibly due to the extremely low solubility of KF
in CH3CN. However, the O–H peak shifted to a lower
frequency from 3452 to 3447 cmꢀ1 upon interaction with CsF,
suggesting a strong interaction between CsF and HFE through
a hydrogen bond between hydroxyl group and Fꢀ [19]
(Fig. 1).
2. Results and discussion
The hydroalkoxylation of HFP with TFE was conducted in
the presence of MF. As shown in Table 1, LiF and NaF were
inactive for the hydroalkoxylation of HFP. On the contrary, the
use of RbF and CsF resulted in almost quantitative conversion
of TFE. Among MF tested, KF exhibited the highest selectivity
to the desired product, CF3CHFCF2OCH2CF3, but RbF and
CsF produced large amounts of side products. GC–mass and 1H
NMR analysis showed that the side products contained
three olefinic HFEs (cis/trans CF3CF CFOCH2CF3 and
CF2 CFCFOCH2CF3) and higher molecular weight HFEs,
which are believed to be produced by further hydroalkoxyla-
tion of olefinic HFEs with HFP as depicted in Scheme 1.
In general, the solubility and dissociation of alkali metal
fluoride in polar organic solvents increase with increasing size
of the cation, and therefore, the higher activity of MF with a
larger size of cation strongly suggests that the hydroalkoxyla-
tion proceeds in a homogeneous way. The formation of the side
product seems to be largely affected by the degree of
dissociation (or the nucleophilicity) of MF. This is supported
by an experiment using 18-crown-6-ether, which is known to
completely dissociate KF into K+ and Fꢀ [17]. When KF was
used together with 18-crown-6-ether, quantitative conversion
was obtained, but with the formation of large quantities of side
products.
The interaction of TFE with CsF can be more clearly seen in
1H NMR spectra in Fig. 2. The peak corresponding to the
hydroxyl group of TFE shifted slightly downfield by the
interaction with KF from 3.89 to 4.51 ppm at the molar ratio of
TFE/KF = 5. The peak shift was much more pronounced when
interacted with CsF. The degree of peak shift increased with
increasing amount of CsF.
Besides the interaction with TFE, MF is also known to
interact with HFP to form metal alkoxide and CF3CHFCF3 as
shown in Eq. (3). Thus formed metal akoxide is proposed as an
To have a better understanding of the role of MF, the
interaction of MF with TFE was investigated in CH3CN by
Table 1
Effect of MF on the hydroalkoxylation of TFE and HFPa
Entry
MF
Conversion
of TFE (%)
Yield
(%)b
Selectivity
(%)b
1
2
3
4
5
6
LiF
NaF
KF
KFc
RbF
CsF
–
–
–
Trace
85.3
96
Trace
83.2
79.4
75.8
71.1
Trace
97.2
79.7
81.5
71.1
93
100
a
Reaction conditions: CF3CH2OH (TFE, 50 mmol), CF3CF = CF2 (HFP,
100 mmol), solvent (CH3CN, 30 mL), MF (0.1 mmol), r.t., 1 h.
b
Yield and selectivity of CF3CHFCF2OCH2CF3.
Fig. 1. FT-IR spectra showing the interaction of metal fluoride with CF3CH2OH
(TFE).

476
D. Natalia et al. / Journal of Fluorine Chemistry 129 (2008) 474–477
Table 2
Effect of solvent for the hydroalkoxylation of TFE with HFPa
Entry
Solvent
Conversion
of TFE (%)
Yield
(%)b
Selectivity
(%)b
1
2
3
4
5
6
Toluene
Ethyl acetate
Acetone
CH3CN
DMF
4.5
5.7
2.3
3.8
–
1.9
91.4
85.3
100
74.1
83.2
83.6
71.5
81.0
97.2
83.6
71.5
DMSO
100
a
Reaction conditions: CF3CH2OH (TFE, 50 mmol), CF3CF = CF2 (HFP,
100 mmol), solvent (30 mL), catalyst (0.1 mmol), r.t., 1 h.
b
Yield and selectivity of CF3CHFCF2OCH2CF3.
Fig. 2. NMR spectra showing the interaction of MF with CF3CH2OH (TFE).
active species for the hydroalkoxylation [15,18].
CF3CF ¼ CF2ꢀ! ðCF3Þ CFꢀMþCF ꢀC!H OHCF3CHFCF3
MF
3
2
2
þ CF3CH2OꢀMþ
(3)
In fact, the formation of CF3CHFCF3 was also observed in
our experiment, implying that the interaction between MF and
HFP might play an important role in the catalysis. The
concentration of CF3CHFCF3 increased with increasing size of
the cation of MF.
Fig. 3. Effect of the amount of KF for the hydroalkoxylation of 2,2,2-trifluor-
oethanol (TFE) to hexafluoropropene (HFP). Reaction conditions: CF3CH2OH
(TFE, 50 mmol), CF3CF = CF2 (HFP, 100 mmol), solvent (30 mL), r.t., 1 h.
The hydroalkoxylation of HFP was significantly affected by
the polarity of solvent employed. As listed in Table 2, the
reaction in a less polar solvent such as toluene and ethyl acetate
gave poor TFE conversion, whereas the reaction in a polar
solvent like acetone, DMF, DMSO, and CH3CN showed much
higher conversion of TFE. Interestingly, the amount of side
products were higher in carbonyl or sulfoxide-containing
solvents such as acetone, DMF, and DMSO, implying that the
dissociation of KF can be facilitated through the interaction
with the functional groups, C O or S O.
the amount of KF up to 0.25 mol.% KF and then remained
constant on further increase of the catalyst concentration.
Interestingly, the selectivity of CF3CHFCF2OCH2CF3 was
maintained at approximately 96%, regardless of the catalyst
concentration.
On the basis of experimental and spectroscopic results, two
mechanistic pathways were proposed for the hydroalkoxylation
of HFP with TFE. The first mechanism is based on the
activation of TFE by MF as depicted in Scheme 2. TFE is likely
to be activated by either MF or Fꢀ. The MF-activated TFE
would then react with HFP to form a transient intermediate A,
To optimize the amount of the catalyst, the concentration of
KF was varied from 0.02 to 0.3 mol.% with respect to the amount
of TFE. As shown in Fig. 3, the conversion of TFE and yield of
CF3CHFCF2OCH2CF3 increased continuously with the increase
Scheme 2. Proposed mechanism for the production of saturated and unsaturated ether.

D. Natalia et al. / Journal of Fluorine Chemistry 129 (2008) 474–477
477
which in turn transforms into CF3CHFCF2OCH2CF3 with the
4.2. Hydroalkoxylation of HFP
regeneration of MF. Since the olefinic compounds were not
produced from the reaction of CF3CHFCF2OCH2CF3 with MF
in CH3CN at 80 8C in the absence of TFE and HFP, the
abstraction of H atom from CF3CHFCF2OCH2CF3 by MF is
unlikely. As an alternative, the activation of TFE by free Fꢀ can
be considered as the most plausible route to the formation of
olefinic side products. Fꢀ-activated TFE will then interact with
HFP to form an intermediate species, B. The abstraction of HF
from B will generate the anionic species, C. The subsequent
elimination of Fꢀ from C would produce olefinic compounds.
Alternatively, CF3CHFCF2OCH2CF3 can be produced
through a carbanionic mechanism involving the formation of
(CF3)2CFꢀM+, as described in the previous papers by Sekiya
et al. [15,18].
In a 100 mL stainless-steel reactor, TFE (50 mmol, 5 g), a
catalyst, dibutyl ether as an internal standard and a solvent were
placed. After purging the reactor with Ar (99.9%), HFP
(100 mmol, 15 g) was introduced and stirred for 1 h at room
temperature. After completion of the reaction, the product
mixture was analyzed using a Gas chromatograph equipped with
a FID detector and HP-FFAP column (OD = 0.32 mm,
L = 30 m). The identification of the product mixtures was
conducted using an Agilent 6890-5973 MSD GC–mass spectro-
meter and 1H NMR spectrometer (Varian 300 Unity plus).
1
4.3. FT-IR and H NMR studies
Even though the exact mechanism cannot be precisely
defined, each mechanism seems to be functioning in the
formation of CF3CHFCF2OCH2CF3. It is also obvious that MF
with higher dissociation constant produces larger amounts of
olefinic side products.
Samples for the IR measurements were prepared as follows:
MF was dissolved in TFE, and then 0.5 g of the resulting
solution was mixed with 3 mL of anhydrous CH3CN. In the
1
case of H NMR experiment, 0.05 g of MF–TFE mixture was
dissolved in 1 mL of CD3CN. FT-IR measurements were
performed on a PerkinElmer Spectrophotometer GX 1 using a
PerkinElmer Horizontal Attenuated Total Reflectance Acces-
3. Conclusions
1
sory. H NMR spectra were recorded on a Varian 300 Unity
plus.
Various alkali metal fluorides were tested as catalysts for the
hydroalkoxylation of HFP with TFE. The catalytic activity of
MF and the formation of side products were found to increase
with increasing size of M+. Spectroscopic and experimental
results showed that MF interacts with TFE through a hydrogen
bond. MF with larger sized M+ was found to interact more
strongly with the OH group of TFE and consequently produces
larger amounts of side products. Among the fluorides tested, KF
with a medium-sized cation exhibited the highest yield and
selectivity of CF3CHFCF2OCH2CF3. The formation of
CF3CHFCF3 was also observed, implying that the hydroalk-
oxylation reaction could proceed through a carbanionic
mechanism.
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