Reactivity of carbon dioxide in hydrofluoroethers: A facile access to cyclic carbonates

Article abstract of DOI:10.1039/c5cc03896k

The high solubility of CO₂ in hydrofluoroethers led to various cyclic carbonates with excellent selectivities and yields. The fluorinated phase increased the amount of CO₂ in contact with the reagents. Reactions could be realized und

Full text of DOI:10.1039/c5cc03896k

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DOI: 10.1039/C5CC03896K
Journal Name
COMMUNICATION
Reactivity of Carbon Dioxide in Hydrofluoroethers: Facile Access
to Cyclic Carbonates
Received 00th January 20xx,
Accepted 00th January 20xx
Marius Mamone, Thierry Milcent, Benoit Crousse*
DOI: 10.1039/x0xx00000x
www.rsc.org/
The high solubility of CO in hydrofluoroethers led to various cyclic than the PFCs, the hydrofluoroethers (HFEs) bearing both
2
carbonates with excellent selectivities and yields. The fluorinated perfluorinated and hydrocarbon segments appeared as excellent
phase increased the amount of CO in contact with the reagents. substitute of PFCs. The HFEs display a combination of physical
2
Reactions could be realized in mild conditions at 80°C under properties such as low surface tension, low flammability, and low
atmospheric pressure or under 5 bar.
toxicity. In addition they have a good environmental profile because
they are considerably less persistent and have low global warming
potential.
7
Carbon dioxide (CO ), as the major greenhouse gas, accumulates in
2
the atmosphere at an alarming pace and is suspected to cause
global warming over the past several decades. The transformation
While the fluorinated solvents are known to dissolve high
1
5,8
quantity of CO2, surprisingly at our knowledge the fluorous phase
has never been exploited in the reactivity of carbon dioxide. By
against the very high solubility of compounds bearing
of CO is limited because of its inherent thermodynamic stability,
2
2
thus resulting in low reactivity. In this context, the key issue to
convert CO into useful chemicals under mild reaction conditions
2
perfluorinated chains in supercritical CO is well known and
2
9
will inevitably rely on its activation. Therefore, there is still a need
to search for new types of reactions that are capable of efficiently
reported. Faced with this lack we report here our study on the
synthesis of cyclic carbonates from CO2 gas and epoxides with
hydrofluoroethers, HFE-7200 and HFE-7500 (Fig. 1).
converting CO under very mild conditions. A reaction which is the
2
3
most operated, is the synthesis of cyclic carbonates which served
as electrolytes in secondary batteries, aprotic polar solvents,
monomers of polycarbonates and polyurethanes and raw materials
2,3
in various chemical reactions.
Generally these cycloaddition
reactions are either carried out under solvent-free conditions, or
3
either under ionic liquid as both solvent and catalyst. The use of
classical solvents is not always effective for the reaction between
4
CO and epoxides due to the low solubility of CO in these solvents.
2
2
Fig. 1 Formulas of Hydrofluoroethers 7200 and 7500.
However, some solvents reported in the literature by Rabai and
Horvath in 1994, are known having the distinction of dissolving a
5
large quantity of gases : the perfluorinated solvents. These solvents
which formed a third phase called the “Fluorous Phase” have been
largely exploited in organic synthesis due to their specific
First in order to show the efficiency of these perfluorinated
solvents and in comparison with other solvents, the cyclic
carbonate reaction was performed at room temperature and at
5
, 6
properties, and in particular to their capacity to solubilise oxygen.
8
0°C, and under 1 or 5 bar CO2 in the presence of
However the environmental persistence of perfluocarbons (PFCs)
such as perfluorohexane, perfluorocyclohexane, FC-75 for example,
detracts from their use on large scale in different reactions.
Conversely another family of perfluorinated solvents, less expensive
tetrabutylammonium iodide (TBAI) as catalyst, and the epoxide 1a.
Reactions were performed with vigorous stirring. Results are
reported in the Table 1.
a.
Univ Paris-Sud, BioCIS, CNRS, Faculté de Pharmacie, LabEx LERMIT, 5 rue J-B.
Clément, 92290 Châtenay-Malabry, FRANCE
E-mail: benoit.crousse@u-psud.fr
†
Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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Table 1. Cyclic carbonate reaction in HFEs and in organic phase at 1 or 5 bar.
only 3h for the HFE-7500 (entry 7). No degradation or formation of
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polymers are observed. The cyclic carbonate 2a was obtained with
DOI: 10.1039/C5CC03896K
an excellent selectivity. From this study, the mixture HFE-7500/MEK
(
7
1/1) is not at all effective (entry 17). The contribution of the HFE-
500 properties is lost. In addition, when reaction was performed
neat, the conversion was only 4% (entry 18). Furthermore It should
be noted that at higher pressure (10, 20, 50 bar), there was no
improvement at all.
Recognizing that the epoxide and the catalyst are slightly soluble in
the perfluorinated solvents, the reactions were heterogeneous. In
Entry
Solvent
P
T°C
Time
(h)
1a/
a
(bar)
2a
1
2
3
4
5
6
7
8
9
HFE-7200
HFE-7200
HFE-7200
HFE-7500
HFE-7500
HFE-7500
HFE-7500
1
5
5
1
1
5
5
1
5
5
1
1
1
1
1
5
1
rt
rt
24
24
5
79/21
77/23
0/100
64/36
8/92
this case, the hydrofluoroethers rich in CO , could facilitate the
2
delivery of the CO towards the reagents. Furthermore, the heating
2
80
rt
had to increase the exchange between the reagents and the CO2
dissolved in the perfluorinated solvent. We can assume that the
reaction took place at the interface of the fluorous phase and the
medium comprising the epoxide and the TBAI (Fig. 2).
24
24
24
3
80
rt
55/45
0/100
80
rt
b
CF
CF
CF
3
3
3
C
C
C
6
H
6
H
6
H
6
H
5
24
24
15
24
24
24
24
24
10
24
92/8
b
5
rt
91/9
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
5
80
rt
0/100
95/5
CF
3
-C
11
C
6
H
12
rt
98/2
AcOEt
rt
98/2
Acetone
MEK
rt
98/2
rt
93/7
MEK
80
rt
0/100
90/10
HFE-
500/MEK
7
Fig. 2. Reaction at the interface.
1
8
neat
1
rt
24
96/4
1
.
a.
Ratio determined by H NMR. b. Presence of side products.
We tried to improve the conditions by testing other different
catalysts such as tetrabutylammonium bromide (TBAB), KBr, NaI,
KI… Only the TBAB is efficient and led to the same result that the
TBAI. The other catalysts did not show improvement. In particular
with the counterion such as Na and K, a precipitate was observed,
and the reaction did not occur.
Knowing that very mild conditions (temperature close to room
temperature and low pressure) are always required, we first
oriented our studies on the previous very mild conditions (table 1,
Conventional organic solvents showed a very low efficiency. In
benzotrifluoride, partially fluorinated solvent, very small
conversion (8-9%) was observed at room temperature under 1 or 5
bar (entries 8, 9). The conversion is complete when reaction was
a
performed at 80°C under 5 bar after 15h (entry 10). In the CF3-
cyclohexane, only 5% of conversion was observed (entry 11). In
classical solvents such as cyclohexane, ethyl acetate, acetone, the
conversions after 24h were only of 2% (entries 12-14). In Methyl
Ethyl Keton (MEK) which is generally the solvent used for reactions
entries 4 and 5 : CO 1 bar, rt or 80°C, 5% TBAI, HFE-7500). Results
are summarized in the Table 2.
2
1
0
involving carbon dioxide gas led only 7% of cyclic carbonate (rt, 1
bar, entry 15), but the conversion was complete at 80°C under 5 bar
after 10h (entry 16). However without exception, all fluorinated
solvents shown a better efficiency in the cyclic carbonate reaction
with higher conversions after 24h. HFE-7200 and HFE-7500 led to a
conversion of 21% and 36% respectively at room temperature at 1
bar (entries 1 and 4). The higher pressure did not improve
considerably the conversion (23% for HFE-7200, entry 2 and 45% for
HFE-7500, entry 6). The conversion and the reaction time could be
upgraded at 80°C (entry 5). The best conditions are obtained under
Table2. Cyclic carbonate reaction in HFE-7500.
5
bar at 80°C. Reactions are faster : 5h for HFE-7200 (entry 3), and
2
| J. Name., 2012, 00, 1-3
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Journal Name
COMMUNICATION
a
Entry
Carbonate 2
T°C
rt
Time
55h
2 select.
Entry
1
Carbonate 2
Time
2 select. (yield)
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DOI: 10.1039/%C5CC03896K
b
(yield)
%
95 (91)
3h
3h
4h
>99 (96)
1
2
a
2
a
2
3
>99 (92)
>99 (98)
2
3
2a
80
rt
26h
48h
>99 (90)
>99 (89)
2
b
2
b
4
5
2b
80
rt
24h
49h
>99 (91)
>99 (92)
2
c
4
6h
>99 (91)
2
d
2
c
6
7
2c
80
rt
21h
24h
>99 (90)
20
5
6
3.5h
5h
>99 (90)
>99 (89)
a
2
e
2
d
a
8
2d
80
16h
50
1
a. % of conversion determined by H NMR. b. Isolated yields.
2
f
From epoxides 1a, 1b, 1c reasonable to complete conversions
are observed into cyclic carbonates at room temperature (entries 1,
7
5
h
>99 (98)
>99 (80)
3
, 5). Reactions required more or less 48-55 h with a complete
2
g
selectivity. Always under 1 bar but at 80°C, reaction times are
shorter (21-26 h, entries 2, 4, 6). Reactions were clean and with a
complete conversion and selectivity to carbonates without side
products. However for the less reactive epoxide 1d, conversion are
very low at room temperature and at 80°C, 20 and 50% respectively
8
9
6h
2
h
7
h
>99
(
entries 7, 8). It should be noted that at 80°C the medium is still
(85)
heterogeneous. Thus the heating must surely increase the exchange
between the CO dissolved in the perfluorinated solvent and the
2i
b
10
10h
9%
2
reagents.
2
j
Furthermore as previously observed (Table 1, entry 7), the
reaction time was extremely reduced when reaction was performed
at 80°C under 5 bar. This result encouraged us to use these
conditions (HFE-7500 / 5 bar / 80°C) for other less reactive
epoxides. The different results are reported in the Table 3.
1
a. Isolated yield. b. % conversion determined by H NMR.
For epoxides, conversion is complete and the selectivity into
cyclic carbonates is superior to 99%. No degradation or formation
of polymers are observed. It was demonstrated that terminal
epoxides with both electron-donating (entries 1, 3, 4, 6-9) and
electron-withdrawing groups (entries 2, 5) could be transformed to
the corresponding cyclic carbonates with excellent yields. We then
also investigated the use of more challenging internal epoxide.
Unfortunately, the cyclic epoxide 1j was only converted to a low
conversion into carbonates (entry 10).
Table 3. Cyclic carbonate reaction under 5 bar at 80°C.
At the end of the reaction, the cyclic carbonates and the HFE-
7
500 could be easily separated after addition of non miscible
solvent such as MeOH for example. In the case of 2a, 2d and 2f
which are solid, a simple filtration is required. The cyclic carbonates
could be obtained pure after flash chromatography. The HFE-7500
could be recovered and recycled for further reactions.
Conclusions
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Journal Name
8
(a) Organofluorine Chemistry, K. Uneyama EVdie.w, ABrtliaclcekOwnleinlel
In summary we demonstrated that the hydrofluoroethers
Publishing, 2006, p 7; (b) S. T. Cui, H. D. Cochran, P. T.
DOI: 10.1039/C5CC03896K
allowed the delivery of the CO towards the reagents and
2
Cummings, J. of Physical Chem. B, 01/1999; 103:4485; (c) U.
Gross, G. Papke, S. Rüdiger, J. Fluorine Chem., 1993, 61, 11;
favoured the reaction, in comparison to classical organic
solvents. For example these solvents and in particular the HFE-
500 were excellent for the synthesis of cyclic carbonates from
(
d) M.R.J. Dack, Technique of Chemistry, Vol. 8, Solutions and
7
Solubility, Part 1. Wiley, New York.
9
1
(a) Q.-W. Song, L.-N. He, J.-Q. Wang, H. Yasud, T. Sakakura
Green Chem., 2013, 15, 110; (b) Z.-Z. Yang, Y. Zhao, G. Ji, H.
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0 (a) C. J. Whiteoak, A. Nova, F. Maseras, A.W. Kleij,
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Whiteoak, E. Martin, E. Escudero-Adàn, A. W. Kleij, Angew.
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epoxides and CO . The conditions are very mild for reactive
2
epoxides (1 atm of CO /80°C and 5 bar/80°C), and did not
2
required supplementary co-catalyst. The combination Fluorous
Phase/Carbon Dioxide in other reactions is under investigation
in our laboratory.
Dr Julien Legros is gratefully acknowledged for having
improved the presentation of the paper. The authors thank Dr
Didier Desmaële for having lend us the autoclave, and Dr
Catherine Sol from 3M (Fluids & Gas Market Development, 3M
Electronics Materials Market, 3M France, Boulevard de l'Oise,
Cergy Pontoise Cedex 95006, France ) for the gift of HFE-7500
and HFE-7200.
Notes and references
1
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Environmental Chemistry: Organofluorines; Neilson, A. H.,
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(SNAP):
http://www.epa.gov/ozone/snap/regulations. html.
4
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