Synthesis of Fluorinated Dialkyl Carbonates from Carbon Dioxide as a Carbonyl Source

Article abstract of DOI:10.1002/cssc.202000090

Fluorinated dialkyl carbonates (DACs), which serve as environmentally benign phosgene substitutes, were produced successfully from carbon dioxide either directly or indirectly. Nucleophilic addition of 2,2,2-trifluoroethanol to carbon dioxide and subsequent reaction with 2,2,2-trifluoroethyltriflate (3 a) afforded bis(2,2,2-trifluoroethyl) carbonate (1) in up to 79 % yield. Additionally, carbonate 1 was obtained through the stoichiometric reaction of 3 a and cesium carbonate. Although bis(1,1,1,3,3,3-hexafluoro-2-propyl) carbonate (4) was difficult to obtain by either of the above two methods, it could be synthesized through the transesterification of carbonate 1.

Full text of DOI:10.1002/cssc.202000090

Accepted Article
Title: Synthesis of Fluorinated Dialkyl Carbonates from Carbon Dioxide
as a Carbonyl Source
Authors: Masafumi Sugiyama, Midori Akiyama, Kohei Nishiyama,
Takashi Okazoe, and Kyoko Nozaki
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Synthesis of Fluorinated Dialkyl Carbonates from Carbon Dioxide
as a Carbonyl Source
[a]
[a]
[b]
[a,c]
Masafumi Sugiyama, Midori Akiyama, Kohei Nishiyama, Takashi Okazoe,* and Kyoko
Nozaki*[a]
[
a]
M. Sugiyama, Dr. M. Akiyama, Dr. T. Okazoe, Prof. Dr. K. Nozaki
Department of Chemistry and Biotechnology,
Graduate School of Engineering, The University of Tokyo
7-3-1 Hongo Bunkyo-ku, 113-8656, Tokyo(Japan)
E-mail: nozaki@chembio.t.u-tokyo.ac.jp
t-okazoe@chembio.t.u-tokyo.ac.jp
K. Nishiyama
Department of Chemistry and Biotechnology,
Faculty of Engineering, The University of Tokyo
[
b]
c]
7-3-1 Hongo, Bunkyo-ku, 113-8656, Tokyo(Japan)
[
Dr. T. Okazoe
Materials Integration Laboratories,
AGC Inc.
1150 Hazawa-cho, Kanagawa-ku, Yokohama 221-8755 (Japan)
Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate))
Abstract: Fluorinated dialkyl carbonates (DACs), which serve as
environmentally benign phosgene substitutes, were successfully
produced from carbon dioxide either directly or indirectly.
Nucleophilic addition of 2,2,2-trifluoroethanol to carbon dioxide and
subsequent reaction with 2,2,2-trifluoroethyltriflate (3a) afforded bis
of phosgene requires great cautions to handle. Triphosgene
and CDI are derived from highly toxic reagents such as chlorine
or phosgene.[4]
In this context, organic carbonates would be
environmentally benign carbonyl sources because they are less
toxic and produced without using harmful compounds. The
reactivity of each carbonate depends on the pKa value of the
corresponding alcohol:[5] Two representative examples are
dimethyl carbonate (DMC) and diphenyl carbonate (DPC)
(2,2,2-trifluoroethyl) carbonate (1) in up to 79%. Additionally,
carbonate 1 was obtained by the stoichiometric reaction of 3a and
cesium carbonate. Although bis(1,1,1,3,3,3-hexafluoro-2-propyl)
carbonate (4) was difficult to be obtained by either of the above two
methods, it could be synthesized by the transesterification of
carbonate 1.
(
Figure 1b). DMC represents moderate reactivity due to the low
acidity of methanol, which allows its usage as a carbonyl
source for precise synthesis of small molecules,[6] while its
reactivity is not enough for polymerization with bisphenol-A to
produce PC. On the other hand, DPC shows much higher
reactivity than DMC owing to the higher acidity of phenol than
methanol. Although DPC is too reactive to be used as a
carbonyl source for fine chemicals, it is suitable for the
synthesis of PC. A part of PC is industrially produced in the
Asahi Kasei process, which utilized melt polymerization of
bisphenol-A and DPC is carried out.[7] It is noteworthy that, in
this process, DPC is prepared via several steps from carbon
Introduction
Electrophilic carbonyl sources which are composed of
a
carbonyl moiety with two leaving groups are essential reactants
in organic chemistry (Figure 1a).[1] They can be converted to
various functional motifs like carbonate, carbamate, and urea,
which are valuable in material science and medicinal chemistry.
They also serve as a monomer for production of Polycarbonate
(
PC) by their reaction with bisphenol-A. Phosgene is the most
commonly and widely-used electrophilic carbonyl source in
industry. In laboratory synthesis, triphosgene, diphosgene, and
carbodiimidazole (CDI) are also used as substitutes for highly-
toxic phosgene.[2] Usually, phosgene and its derivatives are so
reactive that the desired carbonyl compounds are obtained with
extremely high efficiency. For example, the PC obtained from
phosgene exhibits very high molecular weight (Mw).[3] However,
there are some drawbacks: the carcinogenetic and toxic nature
dioxide (CO
2
). Nevertheless, there is a significant disadvantage
monomer: Phenol,
associated with utilizing DPC as
a
eliminated along with polymerization of bisphenol-A and DPC,
can hardly be removed from the reaction system due to its high
boiling point, to shift the equilibrium between the monomers
and PC.[7e] Therefore, the molecular weight of the obtained
1
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ChemSusChem
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polymer is lower than that produced from phosgene. As the
molecular weight decreases, melt and solution viscosities of the
polymer decrease. Since shock resistance of PC depends on
its viscosities, the polymer obtained from DPC is short of shock
resistance, which is one of the most important properties of
PC.[8]
work, we envisaged to synthesize to fluorinated DACs directly
from carbon dioxide.
Hence, fluorinated carbonates are gathering great
attention as environmentally benign alternative carbonyl
sources.[9] Owing to the high electron negativity of fluorine atom,
the corresponding fluorinated alcohols show low pKa values
compared to those of non-fluorinated alcohols. In particular,
bis(2,2,2-trifluoroethyl) carbonate (1) shows the middle
reactivity between DPC and DMC, as the order of pKa of the
eliminating alcohols.[5] It has been known that 1 is able to be
converted to carbamate and isocyanate.[10] Furthermore,
Bogolubsky et al. and other group reported that 1 was a
convenient condensation reagent for the selective synthesis of
unsymmetrical ureas,[5,11] which requires no special care to
prevent formation of side products. It is also possible to employ
1
as a monomer for production of polycarbonate because of its
high reactivity.[12] In addition, the boiling point of the 2,2,2-
trifluoroethanol is low enough to be removed from the reaction
system, which promotes the condensation of bisphenol-A and 1.
Thus, the molecular weight of the obtained PC reaches as high
as that of phosgene-derived PC (Figure 1b).
Figure 1. Intoroduction of fluorinated DACs. a) General usage of carbonyl
sources. b) Advantages of fluorinated DACs compared to conventional
organic carbonates. c) Previously reported synthetic methods and this work.
In spite of this potential, most of the reported methods to
Strategy
synthesize 1 still employ phosgene, either directly or generated
in situ.[13] Namely, we could not say that 1 is an actual
Aiming at the synthesis of fluorinated DAC 1, we examined
three methods I–III referring to the previously reported methods
phosgene-free carbonyl source. Recently, several patents on
synthesis of 1 from hexachloroacetone[14] or chloroform[15] were
for the synthesis of DACs from CO
2
as shown in Scheme
a.[17a,19]
1
published. Although these two are promising synthetic methods,
we considered that it would be better if 1 is synthesized from
carbon dioxide in order to develop a further environmentally
friendly synthetic method (Figure 1c).
I)
Dehydrative condensation of CO and two molecules of
2
alcohol.[22]
II) Three-component coupling of alcohol, CO
electrophile.[23]
III) Dialkylation of inorganic carbonate by electrophile.[24]
2
,
and
Carbon dioxide can be also considered as an electrophilic
carbonyl source. Since carbon dioxide is low in toxicity,
abundant, and inexpensive, the reactions employing carbon
dioxide as a raw material have been well developed, and they
Above three methods are classified by the method for
introduction of the two alkyl groups into the target molecules
(
Scheme 1b). In method I, DACs are obtained by nucleophilic
addition of two alcohols to CO and dehydration. Method II is a
nucleophilic addition of one alcohol to CO followed by trap of
are excellent synthetic methods from the viewpoint of green
chemistry.[16] For example, synthesis of polycarbonates from
2
2
carbon
dioxide
was
with
reported
by
the
alternating
epoxides[17]
the oxygen anion by one electrophilic alkylating reagent. In
method III, both two alkyl groups are introduced through
alkylation of the two oxygen anions of an inorganic carbonate.
copolymerization
or
condensation
polymerization with diols,[18] although the products are limited to
aliphatic ones. As for small molecules, dialkyl carbonates
DACs),[19] diaryl carbonates,[20] and aromatic carbamates[21]
DACs synthesized by method III is also regarded as CO
2
-
(
derived, because inorganic carbonates (M CO generate
2
3
)
can be synthesized directly from carbon dioxide. Here in this
2
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through the reaction of metal hydroxide (MOH) or metal oxide
cyanopyridine[22c,d] as a dehydrating agent, the desired reaction
hardly proceeded (see Supporting Information). This was
probably due to the lower nucleophilicity of TFEA comparing to
that of non-fluorinated alkyl alcohol. Another trial of the reaction
(
M
2
O) and CO
Comparing to the previously reported synthesis of non-
fluorinated DACs, synthesis of 1 is rather challenging (Scheme
c): the lower nucleophilicity of 2,2,2-trifluoroethanol (TFEA)
2
.
1
of TFEA and CO
2
in the presence of methanesulfonic
due to the high electron negativity of fluorine atom would be
problematic in methods I and II. Furthermore, alkylation by
nucleophilic substitution at an alpha position of the
trifluoromethyl group may be also problematic in methods II and
III due to the steric and electronic repulsion between
nucleophile and fluorine.[25] In this study, we found that 1 could
anhydrate as a dehydrating agent afforded a trace amount of 1.
According to the known procedure for synthesis of phenyl 1-
propyl carbonate from phenol and propan-1-ol,[26] we mixed
2
TFEA, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), CO , and
methanesulfonyl anhydrate in acetonitrile at −42 °C. For the
reaction of propan-1-ol with methanesulfonic anhydride under
be synthesized from CO
2
in a high yield by each of method II
CO
2
pressure, formation of sulfonyl carbonate of propan-1-ol
1
and III when using 2,2,2-trifluoroethyl triflate, which is a strong
electrophile.
was confirmed by H NMR analysis. Analogously, we assume
sulfonyl carbonate intermediate X likely existed at this stage.
Further addition of TFEA and pyridine to the mixture gave
compound 1, detected by GC in 2.4% yield from total TFEA
(
scheme 2). We concluded that it was difficult to obtain 1 in a
sufficient yield by dehydration condensation even with a strong
dehydrating reagent like methanesulfonic anhydrate.
Scheme 2. Dehydrative condensation (Method I)
Method II: Three-component coupling reaction
Secondly, three-component coupling reaction of TFEA, CO
2
and electrophile was investigated (method II). Equimolar
amount of TFEA and DBU were mixed in a 20 mL Schlenk flask,
2
and then atmospheric pressure of CO was introduced into the
Scheme 1. Strategy for the synthesis of bis(2,2,2-trifluoroethyl) carbonate (1)
vessel. The reaction mixture was homogeneous ionic liquid.
from carbon dioxide as
a carbonyl source. a) Reported methods to
synthesize non-fluorinated DAC from carbon dioxide. b) Relationships among
three methods. c) Difficulties to introduce a fluorinated alkyl group.
Under a similar reaction condition, Liu et al. confirmed the
adduct A is plausible.[27] After stirring
formation of TFEA–CO
2
the mixture at 0 C for 1 h, 2,2,2-trifluoroethyl triflate (3a) was
added to the mixture and the mixture was stirred for further 16 h
at 0 C to provide the desired compound 1 in 51% (Table 1,
Results and Discussion
entry 1). The yield of 1 was estimated by 19F NMR analysis.
When the reaction was conducted at higher temperature, the
Synthesis of Bis(2,2,2-trifluoroethyl) Carbonate (1)
yield of 1 decreased and that of bis(2,2,2-trifluoroethyl) ether (2)
increased (entry 2). When the pressure of CO
to 4.5 MPa, the generation of side products was suppressed
entry 3, see Supporting Information). Next, a suitable base for
2
was increased
Method I: Dehydration condensation
First of all, synthesis of bis(2,2,2-trifluoroethyl) carbonate (1)
was attempted by dehydration condensation (method I).
Various dehydrating agents have been reported to be
(
this reaction was surveyed (entry 4–9). With 1,1,3,3-
tetramethylguanidine (TMG), both the yield of 1 and the
conversion of 3a were lower than those with DBU (entry 4).
When 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) was
and alcohols,[22]
applicable to the synthesis of DACs from CO
2
thus we employed two of them for dehydration condensation of
,2,2-trifluoroethanol (TFEA) and CO When using 2-
2
2
.
3
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ChemSusChem
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FULL PAPER
used, the yield of 1 was almost the same as that with DBU
Table1. Optimization of the reaction condition for the synthesis of
bis(2,2,2-trifluoroethyl) carbonate (1) from TFEA, carbon dioxide and
electrophile.
(
entry 5). Moreover, the side product possibly resulted from the
reaction of the base and the electrophile hardly generated (see
Supporting information). With 1,5,7-triazabicyclo[4.4.0]dec-5-
ene (TBD) or phosphazene base P
1
-t-Bu-tris(tetramethylene)
(
BTPP), the yield of 1 decreased, which was probably because
they did not mix with TFEA (entry 6,7). When inorganic base
was employed in the absence of solvent, the base was
insoluble in TFEA and the desired compound was not obtained
(
entry 8,9). The use of DMF as a solvent solved the solubility
problem so that Cs CO gave the highest yield (79%) among
2
3
the bases examined in this study (entry 10). Electrophiles were
also investigated, but no reaction occurred with either 2,2,2-
trifluoroethyl tosylate (3b) or 1,1,1-trifluoro-2-iodoethane (3c)
Yield (%)[d]
Conv.
(
Entry
1[a,e]
Base
Electrophile
Solv.
(
entry 11,12). Although alkyl iodides and alkyl tosylates are
%)[d]
1
51
11
44
10
52
1.1
30
0
2
1.0
40
1.8
0
generally used as good electrophilic alkylating reagents, their
electrophilicities were not sufficient in this case.[28] Nucleophilic
DBU
DBU
DBU
TMG
MTBD
TBD
CF
3
CF
3
CF
3
CF
3
CF
3
CF
3
CF
3
CF
3
CF
3
CF
3
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
2
OTf
2
OTf
2
OTf
2
OTf
2
OTf
2
OTf
2
OTf
2
OTf
2
OTf
2
OTf
None
None
None
None
None
None
None
None
None
DMF
DMF
DMF
None
63
100
48
13
69
32
69
0
2[b,e]
substitution at alpha position of the trifluoromethyl group is
known to be difficult due to the steric and electronic repulsion
between lone pairs of fluorine atoms and nucleophiles, and thus,
a strong electrophile like 3a was required for this reaction.[25a]
Finally, the large scale synthesis and isolation of compound 1
was accomplished in 27% yield (entry 13). Although the yield of
3[c]
4[c]
5[c]
0
6[c]
0
1
was not so high, solvent-free procedures (Entry 3,13) were
7[c,e]
BTPP
NaH
0
better than the others in the viewpoint of greenness and
sustainability.
8[c]
0
9[c]
Cs
Cs
CO
CO
0
0
0
2
3
A plausible reaction mechanism is shown in Scheme 3.
First, deprotonation of TFEA proceeds and the ion pair B
generates. This equilibrium is considered to shift toward ion pair
B with stronger organic bases. This nicely explains why 1 was
obtained in higher yield with DBU (pKBH = 24.2 in MeCN) or
MTBD (pKBH = 25.5 in MeCN) than with TMG (pKBH = 20.8 in
1 [
0
c]
86
0
79
0
0
2
3
11[c]
2
Cs CO3
CF CH I
3
2
0
1 [
2
c]
0
0
0
2
Cs CO
3
3
CF CH
2
OTs
1 [
3
f]
DBU
n.d.
27[g]
n.d.
3
CF CH
2
OTf
MeCN).[29] Afterward, TFEA–CO
nucleophilic addition of B to CO
(confirmed by in situ IR).[27] In
[a] 0 C, 0.1 MPa [b] 50 C, 0.1 MPa [c] 0 C, 4.5 MPa [d] Based on
electrophile, determined by 1H and F NMR, except for entry 13. [e] 1.0
mmol of TFEA, DBU, and 3a was used. [f] 43.1 mmol of TFEA, DBU, and
2
adduct
A
generates by
19
2
3a was used. [g] isolated yield.
the last step, A reacts with 3a to afford 1. On the other hand,
ether 2 is formed if B reacts with 3a.[30] Liu et al. reported that
the reaction between A and B is reversible: Compound A was
converted back to B either under N
This result is in good agreement with our results that desired
bubbling or by heating.[27]
2
compound 1 was selectively obtained over 2 under higher CO
2
pressure at lower temperature.
Scheme 3. Plausible reaction mechanism of three-component coupling with
DBU as a base.
Method III: Dialkylation of inorganic carbonate
Subsequently to the three-component coupling (method II,
Scheme 1a) described above, another method to synthesize 1
4
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was investigated: dialkylation of inorganic carbonate. First, 10
mmol of 2,2,2-trifluroethyl triflate (3a) and Cs
were mixed under 4.5 MPa of CO pressure in various solvents
Table 2, entry 1–3). After stirred for 16 h at 50 C, the reaction
2 3
CO (0.5 equiv.)
2
Table 2. Optimization of the reaction condition for the synthesis of bis(2,2,2-
trifluoroethyl) carbonate (1) by dialkylation of inorganic carbonates.
(
mixture was analyzed by H and 19F NMR spectroscopy. When
the reaction was conducted in N,N-dimethyl formamide (DMF)
or dimethyl sulfoxide (DMSO), which are commonly used
aprotic polar solvents, the desired compound 1 was observed
together with side products 2 and TFEA (entry 1,2).[24a] With
1
1
,3-dimethyl-2-imidazolidinone (DMI), 1 was observed in a
Yield (%)[a]
M
2
CO
3
Conv.
(%)[a]
moderate yield (54%) and good selectivity of 1 (entry 3). In
addition to the typical polar solvents above-mentioned,
biodegradable sugar-derived polar solvents like Cyrene and
dimethyl isosorbide (DMIS) were investigated (entry 4,5).
Unfortunately, 1 was not obtained with either two solvents due
Entry
X
Solv.
(equiv.)
1
2
TFEA
1
2
3
4
5
6
7
8
9
Cs CO3
2
OTf
OTf
OTf
OTf
OTf
I
DMF
DMSO
DMI
72
100
58
47
10
0
36
Trace
11
(0.5)
Cs
2
CO
3
3
3
3
3
3
3
14
54
0
3.5
68
0.6
1.3
Trace
0
(0.5)
2 3
to the low solubility of Cs CO .
Cs
2
CO
2.5
Next, alkylating agents were examined (entry 6,7). Same
as the result mentioned in Table 1, no reaction took place with
(0.5)
Cs
2
CO
Cyrene
DMIS
DMI
Trace
1,1,1-trifluoro-2-iodoethane (3c) or 2,2,2-trifluoroethyl tosylate
(0.5)
(
3b) (entry 6,7). By increasing the amount of Cs CO (1.0
2
3
Cs
(0.5)
2
CO
0
0
0
0
0
0
0
0
equiv.), the yield of 1 increased (entry 8). Inorganic carbonates
with different metals were also investigated (entry 9,10). Even
when using less expensive alkaline metal carbonates compared
Cs
2
CO
0
(0.5)
to Cs
selectivity decreased. In the previous studies on the synthesis
of non-fluorinated DACs, the higher yield with Cs CO than with
Na CO or K CO was also reported and it was explained by
2 3
CO , 1 was observed although the yield and the
Cs
2
CO
OTs
OTf
OTf
OTf
OTf
DMI
0
0
0
(0.5)
Cs
1.0)
2
CO
DMI
81
44
29
100
77
34
11
43
0.9
0.8
9.5
40
2
3
(
2
3
2
3
the order of nucleophilicity of each metal carbonate,[24e] which is
K
2
CO
3
DMI
(1.0)
known to increase as the radius of its counter cation becomes
larger. From these observations, the reaction in the presence of
10
Na
2
CO
3
DMI
(1.0)
1
eq. of 18-crown-6 ether was also attempted, however the
yield of 1 decreased and significant amount of TFEA generated
entry 11).
1 [
1
b]
Cs
(1.0)
DMI
2
CO
3
(
[
1
a] Based on electrophile, determined by 1H and 19F NMR. [b] 1.0 equiv. of
8-crown-6 ether was added.
The effect of CO
the absence of CO , no desired compound was observed and
instead, ether 2 and TFEA generated (Table 3, entry 1). When
the reaction was conducted under 0.1 MPa pressure of CO , 1
was obtained in 55% (entry 2). By increasing the pressure of
CO , the selectivity of carbonate 1 was improved at the
2
pressure was examined (Table 3). In
2
2
2
expense of the conversion (entry 2–4).
A plausible reaction mechanism is shown in scheme 4.
First, the reaction of one molecule of inorganic carbonate and
2
trifluoroethyl triflate 3a affords TFEA–CO adduct A’, which
then reacts with 3a to give 1. Meanwhile, if A’ and B’ are under
equilibrium, alkoxide B’ resulting from decarboxylation of A’
5
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ChemSusChem
10.1002/cssc.202000090
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reacts with 3a to give ether 2. Protonation of B’ by acidic work-
up affords TFEA. Under the higher CO
2
pressure, the
equilibrium shifts from B’ to A’ to cause the higher selectivity.
Table 3. Investigation of the effect of temperature and CO
2
pressure with
cesium carbonate.
Yield (%)[a]
P
MPa)
Conv.
(%)[a]
Entry
(
1
2
TFEA
1[b]
2[c]
3
0
100
100
95
Trace
34
40
Figure 2. Advantage of bis(1,1,1,3,3,3-hexafluoro-2-propyl) carbonate (4) for
polymerization. a) The general method to synthesize Polycarbonate (PC). b)
Advantages of carbonate 4 compared to other organic carbonates.
0.1
1.0
3.0
55
69
66
1.8
0
26
18
11
Method II and III
4
74
0
At first, method II was investigated (Scheme 5). Equimolar
amount of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and DBU
a] Based on electrophile, determined by H and 19F NMR. [b] 7 h [c] 6 h
1
[
2
were mixed in a 50 mL autoclave. CO gas was introduced into
the vessel at 4.5 MPa and stirred at 0 C for 20 min. Monitoring
this reaction by in situ IR, a new peak at 1750 cm was
1
observed after introduction of CO
C=O stretching of HFIP–CO
2
, which is assignable to the
2
adduct (see Supporting
C
Information). Thus, the mixture was treated with benzyl bromide
in order to convert C to an isolable form. As expected, the
reaction afforded carbonate 5, which strongly indicates the
generation of C (Scheme 5a). Notably, HFIP is one of the most
Scheme 4. Plausible reaction mechanism of dialkylation of inorganic
= 9.3 in water)[33a] due to the negative
acidic alcohols (pK
induction effect of the six fluorine atoms, and addition of HFIP
to CO has never been reported so far. Despite the formation of
C, the desired compound 4 was not obtained by adding
,1,1,3,3,3-hexafluoro-2-propyl nonaflate as an alkylating
a
carbonate (Method III)
2
1
Synthesis of Bis(1,1,1,3,3,3-hexafluoro-2-propyl) Carbonate
(
4)
reagent to the reaction mixture (Scheme 5b). The lower
reactivity of 1,1,1,3,3,3-hexafluoro-2-propyl nonaflate can be
attributed to the steric and electronic repulsion between the
hexafluoro-2-propyl moiety and the nucleophile. Actually,
nucleophilic substitution with electrophiles bearing a hexafluoro-
2-propyl group are limited to a few examples.[34]
Method II and III, by those 1 was successfully provided, were
next applied to synthesizing bis(1,1,1,3,3,3-hexafluoro-2-propyl)
carbonate (4). It was reported that Polycarbonate (PC) with
much higher molecular weight was obtained from 4[31] and
bisphenol-A when compared to other less toxic phosgene
substitutes such as 1[12] or diphenyl carbonate (DPC)[7] (Figure
2). This is because the eliminating 1,1,1,3,3,3-hexafluoro-2-
propanol (HFIP) possesses higher acidity than TFEA and lower
boiling point than phenol. Thus, we aimed at synthesis of 4 from
CO
2
.[32] It is notable that the introduction of a hexafluoro-2-
propyl moiety is considered to be far more challenging than that
of a trifluoroethyl group due to the low nucleophilicity of HFIP
and bulkiness of the hexafluoro-2-propyl group.
6
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ChemSusChem
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FULL PAPER
Scheme 5. Three-component coupling (Method II)
the mixture (Scheme 7). Because there are sufficient
temperature differences between boiling points of each
carbonate (4 : 97 C,[36] 1 : 118 C[37]), it is theoretically possible
In order to accelerate the difficult nucleophilic substitution
step, that is the reaction of C with the electrophile bearing a
hexafluoro-2-propyl moiety, we thought of elevating the reaction
temperature. For this purpose, method III is more favorable
since the reaction could be conducted at higher temperature
to isolate 4. Actually, distillation of the resulting mixture afforded
fractions with different composition ratio. Although it was
difficult to isolate 4 from the crude mixture by simple distillation
in a laboratory scale, 4 is assumed to be isolated by multistage
distillation (see Supporting Information for the details, such as
time course plot, fractional distillation, and control experiments).
than method II in the synthesis of 1 (vide supra). Thus, Cs
2
CO
3
(
1.3 mmol) and 1,1,1,3,3,3-hexafluro-2-propyl triflate (2.5 mmol)
were mixed under 3.0 MPa of CO
2
pressure in DMI. After stirred
1
for 16 h at 50 C, the reaction mixture was analyzed by H and
19F NMR spectroscopy. As a result, instead of the desired
compound 4, hydrated hexafluoroacetone and cesium
trifluoromethane sulfinate were obtained quantitively (Scheme
6a). This result can be explained by the mechanism shown in
Scheme 7. Transesterification (Method IV)
Scheme 6b. The proton of 1,1,1,3,3,3-hexafluro-2-propyl triflate
is predicted to be highly acidic because it is next to three
electron withdrawing groups: two trifluoromethyl groups and a
Conclusion
2 3
triflate moiety. This acidic proton can be abstracted by Cs CO
In summary, we achieved the synthesis of fluorinated DACs 1
to cause reduction of the sulfur atom affording hydrated
hexafluoroacetone and cesium trifluoromethane sulfinate.
2
and 4 from CO either directly or indirectly. Among all of the
methods we reported in this literature, three-component
coupling reaction using DBU (Table 1 entry 1–3, 13) was
considered to be the best procedure in the viewpoint of green
and sustainable chemistry. This is because the procedure is
solvent-free and scalable, moreover isolation of 1 has been
accomplished. However there still exists several issues to be
resolved.
1)
For environmentally benign synthesis, it is more desirable
to use a non-chlorine derived compound. In our procedure,
2,2,2-trifluoroethyl triflate (3a) was prepared from
Scheme 6. Dialkylation of inorganic carbonate (Method III)
trifluoromethanesulfonyl chloride. In order to prevent using
chlorine-derived chemicals, 3a should be produced from
Method IV
chlorine-free
trifluoromethanesulfonic
anhydride
Because it was difficult to obtain carbonate 4 either by method
II or III, we tried another method to synthesize 4:
transesterification of organic carbonate synthesized from
carbon dioxide. This transesterification strategy has been
employed in the industrial production of diphenyl carbonate
from DAC with phenol (pKa 10.0[35]) as a nucleophile. We
envisioned that even HFIP (pKa 9.3) could be introduced into
carbonate by this method. As mentioned above, fluorinated
instead.[38a] Actually, we also confirmed that 3a could be
synthesized by using trifluoromethanesulfonic anhydride.
Commercially available HFIP is produced from
hexachloroacetone, thus a chlorine-free production method
is more preferable, which has already been reported.[33b,c]
(
See Supporting Information, Scheme S3 for further
discussion on the greenness and sustainability of the
whole process).
carbonate 1 was successfully synthesized using CO
2
as a
2
)
The wastes generated through the process are also
problematic. Particularly, if the triflate salt of DBU could be
separated and reused, our method would be much better
in terms of atom-economy.
carbonyl source. Accordingly, conversion of 1 to 4 can be
2
considered as an indirect synthesis of 4 from CO as a carbonyl
source.
In the reaction of 1 and HFIP (45 equiv.) in the presence
CO (1.2 equiv.), existence of 4 (10% yield), 6 (32% yield),
and remaining 1 (38%) were confirmed by 19F NMR analysis of
Although these issues should be resolved for future
improvement, the reported synthesis of fluorinated DACs from
of Cs
2
3
7
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ChemSusChem
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FULL PAPER
CO
2
potentially lead to green and sustainable process for
Procedure for the synthesis of 2,2,2 trifluoroethyl trifluoromethane
sulfonate (3a)[38b]
production of PC and fine chemicals.
To the solution of 2,2,2-trifluoroethanol (11.7 ml, 163 mmol) and
triethylamine (22.8 mL, 163 mmol) in water (150 mL),
trifluoromethanesulfonyl chloride (25.0 g, 148 mmol) was added
dropwise at 0 °C. The reaction mixture was stirred for 8 h, and the lower
organic layer was separated. The layer was washed with 1N HCl aq. 3
Experimental Section
times and dried over Na
mmol). The product 3a is a known compound and the 1H and 19F NMR
2 4
SO to give the product in 63% (21.7 g, 93.5
General
shifts in CDCl
3
are identical to those given in the following literature.
) δ 4.71 (q, J = 7.3 Hz, 2H); 19F-NMR
3
376 MHz, CDCl ) δ −74.69 (t, J = 7.2 Hz, 3F), −74.48 (s, 3F).
All manipulations were carried out using standard Schlenk techniques
3 [
a
42]
1H-NMR (400 MHz, CDCl
3
2
under N purified by passing through a dry column (DC-L4, NIKKA
(
SEIKO CO., LTD.) and a gas clean column (GC-RX, NIKKA SEIKO CO.,
LTD.).
Representative procedure for the three-component coupling (Table
1)
Instrumentation
Table 1, Entry3
NMR spectra were recorded on JEOL JNM-ECZ400 ( H: 400 MHz, 13C:
1
01 MHz, 19F: 376 MHz). 1H NMR analyses were performed in
1,8-Diazabicyclo[5.4.0]undec-7-ene
(5.0
mmol)
and
2,2,2-
1
trifluoroethanol (5.0 mmol) were added to a 50 mL stainless autoclave
filled with nitrogen gas. The vessel was pressurized by CO (4.5 MPa)
and stirred at 0 °C for 1 hour. Afterwards, 2,2,2-trifluoroethyl triflate (5.0
mmol) was charged into the mixture and stirred under CO pressure (4.5
MPa) at 0 °C for 16 hours. After CO pressure was leaked, the yield of 1
chloroform-d with the number of FID's collected per sample of 8–128.
Chemical shift values for protons are referenced to the residual proton
2
resonance of chloroform-d (δ 7.26). 13C NMR analyses were performed
in chloroform-d with the number of FID's collected per sample of 1024–
2
2048. Chemical shift values for carbons are referenced to the carbon
2
and 2 and the conversion of 3a was determined by 1H and 19F NMR
resonance of chloroform-d (δ 77.16). 19F NMR analyses were performed
using benzotrifluoride as internal standard. Bis(2,2,2-trifluoroethyl)
with the number of FID's collected per sample of 16–60. Chemical shift
values for fluorine are referenced to the carbon resonance of α,α.α-
trifluorotoluene (δ –63.20). High-resolution mass (HRMS) spectra were
taken on a JEOL JMS-T100LP mass spectrometer with the electron
spray ionization time-of-flight (ESI-TOF) method. GC analysis was
performed by Agilent Technologies 7890B equipped with DB-1301
capillary column (0.250 ID, 1.00 μm df, 60 m). GC-TOFMS analysis was
performed by Agilent Technologies 7890A equipped with DB-5 capillary
column (30 m) and JEOL JMS-T100GC mass spectrometer with
electron ionization time-of-flight (EI-TOF) or chemical ionization time-of-
flight (CI-TOF) methods. In situ IR measurement was performed by
using Mettler Toledo ReactIR 45 and analyzed by icIR. Preparative
HPLC separation was carried out with a JAI NEXT (Japan Analytical
Industry Co. Ltd.) equipped with a GPC column (Japan Analytical
Industry Co. Ltd.; JAIGEL-2HR) by eluting with chloroform at room
temperature.
carbonate (1) was obtained in 44% yield (determined by 1H and 19
F
NMR). Optimization of the reaction condition was carried out by varying
the reaction temperature, time, and base (Entry 1–8). 1[40] 1H-NMR
(
400 MHz, CDCl
CDCl
) δ −74.69 (t, J = 7.9 Hz, 6F). 2[41] 1H-NMR (400 MHz, CDCl
.00 (q, J = 8.0 Hz, 4H); 19F-NMR (376 MHz, CDCl
) δ −75.13 (t, J = 8.3
Hz, 6F). 3a[42] 1H-NMR (400 MHz, CDCl
) δ 4.71 (q, J = 7.4 Hz, 4H);
) δ −74.70 (t, J = 7.2 Hz, 3F), −74.48 (s, 3F)
3
) δ 4.58 (q, J = 8.0 Hz, 4H); 19F-NMR (376 MHz,
) δ
3
3
4
3
3
19F-NMR (376 MHz, CDCl
3
Entry 10
Cesium carbonate (5 mmol), dehydrated N,N-dimethylformamide (13
mL), and trifluoroethanol (5 mmol) were added to a 50mL stainless
autoclave filled with nitrogen gas. The vessel was pressurized by CO
2
(4.5 MPa) and stirred at 0 °C for 1 hour. Afterwards, 2,2,2-trifluoroethyl
triflate (5 mmol) was charged into the mixture and stirred under CO
2
2
pressure (4.5 MPa) at 0 °C for 16 hours. After CO pressure was leaked,
Materials
crude mixture was submitted to NMR analysis directly. The yield of 1
and 2 and the conversion of 3a was determined by 19F NMR using
benzotrifluoride as internal standard. Bis(2,2,2-trifluoroethyl) carbonate
,2,2-Trifluoroethyl triflate,[38] 1,1,1,3,3,3-hexafluoro nonaflate[39] were
2
synthesized following the literature procedures. The authentic sample of
bis(1,1,1,3,3,3-hexafluoro-2-propyl) carbonate (4) was received from
AGC Inc. Carbon dioxide (>99.5 vol%) was purchased from Suzuki
Shokan Co.,Ltd. and used as received. Cerium Oxide was purchased
from Daiichi Kigenso Kagaku Kogyo Co., Ltd. Cyrene and DMIS were
(
1) was obtained in 79% yield (determined by 1H and 19F NMR).
Optimization of the reaction conditions was carried out by using 1,1,1-
trifluoro-2-iodoethane or 2,2,2-trifluoroethyl tosylate instead of 2,2,2-
trifluoroethyl triflate (Entry 11–12). 1[40] 19F-NMR (376 MHz, DMF) δ
−
=
3
75.10 (t, J = 8.6 Hz, 6F). 2[41] 19F-NMR (376 MHz, DMF) δ −75.71 (t, J
9.0 Hz, 6F). 3a[42] 19F-NMR (376 MHz, DMF) δ −75.32 (t, J = 8.3 Hz,
F), −75.94 (s, 3F)
dried over CaH
2
.
All other materials were purchased from Kanto
Chemical, FUJIFILM Wako Chemical, TCI, Aldrich and used as received.
8
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ChemSusChem
10.1002/cssc.202000090
FULL PAPER
Table 1, Entry 13
[
1]
2]
K. W. Jung, A. S. Nagle in Science of Synthesis, Vol. 18 (Eds.: K.
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1
,8-Diazabicyclo[5.4.0]undec-7-ene
trifluoroethanol (43.1 mmol) were added to a 50 mL stainless autoclave
filled with nitrogen gas. The vessel was pressurized by CO (4.5 MPa)
and stirred at 0 °C for 1 hour. Afterwards, 2,2,2-trifluoroethyl triflate
43.1 mmol) was charged into the mixture and stirred under CO
pressure (4.5 MPa) at 0 °C for 16 hours. After CO pressure was leaked,
(43.1
mmol)
and
2,2,2-
[
Triphosgene is often thought to be a safe substitute for highly-toxic
phosgene, however the following paper reported the toxcity of
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Dev. 2017, 21, 1439–1446.
2
(
2
2
obtained crude mixture was distilled to separate DBU and its salt. After
distillate was decompressed under 40 torr at 20 °C for 5 h to remove low
boiling point impurities, bis(2,2,2-trifluoroethyl) carbonate (1) was
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isolated in 27% yield (2.62 g, 11.6 mmol). The product 1 is a known
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compound and the H and 19F NMR shifts in CDCl
1
are identical to those
) δ 4.58
3
) δ −74.68 (t, J = 7.9 Hz,
3
given in the following literature. 1[40] 1H-NMR (400 MHz, CDCl
q, J = 8.1 Hz, 4H); 19F-NMR (376 MHz, CDCl
F).
3
(
6
Representative procedure for dialkylation of inorganic carbonates
Table 2, 3)
(
1
07–116; f) A. Tsuda (National University Corporation Kobe
Table 2 Entry 3
University, Mitsubishi Gas Chemical Co., Inc.), 2018,
WO2018211952A1.
Cesium carbonate (5 mmol), 2,2,2-trifluoroethyl triflate (10 mmol) and
dehydrated 1,3-dimethyl-2-imidazolidinone (13 mL) were added to a
[5]
a) A. V. Bogolubsky, Y. S. Moroz, P. K. Mykhailiuk, D. S. Granat, S.
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50mL stainless autoclave filled with nitrogen gas. The vessel was
pressurized by CO (4.5 MPa) and stirred at 50 °C for 16 hours.
2
Bis(2,2,2-trifluoroethyl) carbonate (1) was obtained in 54% yield
1
(
determined by H and 19F NMR). Optimization of the reaction conditions
was carried out by varying the reaction temperature, time, solvent,
43.
electrophile, an additive, and inorganic carbonate (Entry 1–11, Table 3).
1[40] 19F-NMR (376 MHz, DMI) δ −75.08 (t, J = 8.6 Hz, 6F). 2[41] 19F-NMR
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Procedure for transesterification (Scheme 7.)
A 15 mL glass vial was charged with cesium carbonate (0.25 mmol) and
2,2-bis(4-methylphenyl) hexafluoropropane (0.25 mmol, internal
standard). 1,1,1,3,3,3-Hexafluoro-2-propanol (1.17 mL, 45 equiv.),
bis(2,2,2-trifluoroethyl) carbonate (1) was added to the vial via syringe.
The reaction mixture was heated at 60 °C (thermostat bath temperature).
The resulting crude mixture was submitted to 19F NMR analysis to
determine the yield with an internal standard.
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8
Keywords: Carbon dioxide fixation • Sustainable Chemistry •
Phosgene free • Fluorinated carbonate • Polycarbonate
9
This article is protected by copyright. All rights reserved.

ChemSusChem
10.1002/cssc.202000090
FULL PAPER
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The product 1 is known compound and the 1H and 19F NMR shifts
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The product 2 is known compound and the 1H and 19F NMR shifts
3
in CDCl are identical to those given in the following literature. For
other solvents, 19F NMR shifts were confirmed by mesuring an
authentic sample in the corresponding solvents. S. Xu, J. S.
Boschen, A. Biswas, T. Kobayashi, M. Pruski, T. L. Windus, A. D.
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3a is known compound and the H and 19F NMR shifts in CDCl
1
are
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3
identical to those given in following literature. For other solvents,
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the corresponding solvents. H.-X. Song, S.-M. Wang, X.-Y. Wang,
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1
1
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ChemSusChem
10.1002/cssc.202000090
FULL PAPER
Entry for the Table of Contents
Fluorinated dialkyl carbonates were successfully produced from
carbon dioxide either directly or indirectly. They serve as
environmentally benign, less toxic and convenient phosgene
substitutes.
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1
2
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