Controllable Homogeneity/Heterogeneity Switch of Imidazolium Ionic Liquids for CO2 Utilization

Article abstract of DOI:10.1002/cctc.201801086

Imidazolium ionic liquids (IL) have been recognized as a promising platform for CO₂ capture and conversion owing to the structural designability through molecular combination of cationic substituents and counter anions. However, the conventiona

Full text of DOI:10.1002/cctc.201801086

Accepted Article
Title: Controllable Homogeneity/Heterogeneity Switch of Imidazolium
Ionic Liquids for CO2 Utilization
Authors: Jeehye Byun and Kai A. I. Zhang
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201801086
Link to VoR: http://dx.doi.org/10.1002/cctc.201801086
A Journal of
www.chemcatchem.org

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
Controllable Homogeneity/Heterogeneity Switch of Imidazolium
Ionic Liquids for CO
2
Utilization
[
a]
[a]
Jeehye Byun and Kai A. I. Zhang*
Abstract: Imidazolium ionic liquids (IL) have been recognized as a
reported in the literatures owing to their availability and high CO
2
[
8]
promising platform for CO
2
capture and conversion owing to the
solubility . The CO
2
solubility in the ILs is known to correlate
structural designability through molecular combination of cationic
substituents and counter anions. However, the conventional
homogeneous catalysis with ILs accompanies a laborious work-up
with the chemical nature of cations and anions. For instance,
functionalization of imidazolium cations with alkyl , hydroxyl[10],
[9]
fluorine[11], ether[12], nitrile[13] and amino[14] groups were found to
procedure to recycle the catalyst and purify product after the reaction, be effective for enhancing CO
2
solubility. The fluor anions on
-
-
and PF -
limiting the applicability of ILs. Herein, we optimize the molecular
structure of imidazolium ILs to mediate the cycloaddition of CO
imidazolium ILs, i.e., Tf
CO
The counter anions are further involving in catalytic cycles such
as CO cycloaddition with epoxides, resulting in 5-membered
cyclic carbonates[16]. The simple anion exchange of imidazolium
2
N , BF
4
6
, also exhibited high
solubility compared to the ILs without the fluor groups[15].
2
2
upon epoxides, in which the IL functions as a homogeneous catalyst
but exhibits heterogeneous separation capability. By varying the
length of alkyl substituent on the imidazolium ring, the conversion
efficiency of the epoxide into cyclic carbonate could be accelerated
owing to higher reactivity of anions with longer aliphatic chains. The
conversion efficiency was further optimized by having a proper type
of counter anions with suitable level of nucleophilicity. The long-
chain IL exhibited temperature-responsive phase transition behavior,
allowing a facile isolation of IL and products after the reaction. In
addition, with the high purity of obtained cyclic carbonates, non-
isocyanate poly(hydroxylurethane)s could be produced by
2
ILs allows a large window of catalytic applications for CO
2
[
17]
conversion, e.g. synthesis of oxazolidinone
and quinazoline-
2,4(1H,3H)-diones[ formylation of amine[19]
, , etc. Hence,
18]
various combinations of cations and anions have led to the
structural diversity of ILs for providing a great degree of control
for catalytic CO
2
utilization.
A remaining obstacle in exploiting ILs for CO
2
utilization
would be the recovery process after the homogeneous catalysis,
accompanying a tedious work-up process to recycle the ILs.
Whereupon, many have tried to incorporate ILs on
polyaddition of diamines, promoting the utilization of CO
chemical building block.
2
as a
[
20]
heterogeneous substrates such as silica structures , polymer
matrix[21], porous polymers[22], and metal organic frameworks
to facilitate the regeneration of materials. Nonetheless, the
embedment in substrates hinders the catalytic activity of ILs,
which requires high reaction pressure and temperature,
consequently resulting in inevitably higher cost. Therefore, there
[23]
Introduction
Large anthropogenic emission of carbon dioxide (CO
2
) is
revealed as a primary cause of global warming in the last
needs
heterogeneous separation of ILs for the efficient CO
Herein, we report a systematic design of imidazolium ILs
with controllable homogeneity/heterogeneity switch for CO
a
strategy to combine homogenous catalysis and
[
1]
decades . Due to prematurity of renewable energy technologies,
increasing energy demand depends on fossil fuels all the same,
so that the application of carbon capture and utilization (CCS)
2
utilization.
2
[
2]
technology has been ever highlighted . The direct CO
and conversion into valuable chemicals using well-designed
materials offer new opportunities to reduce CO emission into
the atmosphere as well as to use it as chemical feedstocks .
Thus, there have been tremendous attempts to develop
2
capture
utilization. By simply increasing alkyl chain length of the ILs to a
certain extent, the reactivity of counter anion and the solubility of
IL in epoxides could be gradually enhanced, thus affecting the
2
[
3]
2
CO conversion efficiency. The longer alkyl chain of ILs resulted
into the reversible solid/liquid phase transition behavior via
temperature swing, leading to easy heterogeneous separation of
the IL after the homogeneous catalytic reaction under a solvent-
materials for CO
frameworks[4] and porous organic polymers[5]. All these
advances, however, have to face challenge upon the
2
capture and conversion, such as metal organic
a
free condition. In order to enhance the chemical fixation of CO
2
imbalance between efficiency and cost of materials.
Ionic liquids (ILs) have drawn much attention for chemical
reactions due to their low vapor pressure, high thermal stability
with epoxide under atmospheric pressure, the effect of the
counter anions was also rationalized by altering their
nucleophilicity. Additionally, with high conversion efficiency of
epoxides, the obtained bis(cyclic carbonate) product was able to
be polymerized into poly(hydroxylurethane), demonstrating the
[
6]
and structural designability, also with an affordable price tag .
[
7]
After being first tested by Blanchard et al. , ILs have been
extensively studied for direct CO utilization. In particular,
imidazolium-based ILs are most widely investigated and
2
2
feasibility of CO utilization over imidazolium ILs a step forward.
Results and Discussion
[
a]
Dr. J. Byun, Dr. K. A. I. Zhang
Max Planck institute for Polymer Research, Ackermannweg 10,
The CO
2
cycloaddition upon epoxide is often conducted in
55128 Mainz, Germany
elevated temperature, and imidazolium IL plays a role as a
homogeneous catalyst in the reaction. Therefore, in order to
separate out cyclic carbonate product and recycle the IL catalyst,
energy-intensive methods have been utilized such as vacuum
E-mail: kai.zhang@mpip-mainz.mpg.de
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
distillation[24] and column chromatography[25], resulting in extra
cost. Basic idea of homogeneity/heterogeneity switch resides in
phase separation of IL catalyst by temperature change. When
the homogenous solution of reaction mixture is cooled down, the
IL is subjected to precipitation, thus enabling heterogeneous
isolation of the IL catalyst by a simple filtration (Scheme 1).
Therefore, structural design of imidazolium IL is a prerequisite
for accomplishing the controllable homogeneity/heterogeneity
switch of IL catalyst.
fully converted into respective cyclic carbonates in 24 h when
catalyzed with mimC
the rate-determining step of CO
nucleophilic ring-opening of epoxides by counter anion (Scheme
2b, step i)[26], mimC
[Br] having the same bromide anion might
n
[Br]s at the elevated temperature. Since
2
fixation upon epoxide is
n
exhibit the similar reactivity irrespective of alkyl chain length.
Scheme
1.
Schematic
illustration
of
temperature-assisted
homogeneity/heterogeneity switch of imidazolium IL to catalyze CO
cycloaddition on epoxide.
2
Figure 1. Time-dependent conversion of epoxide substrates (a) tert-butyl
glycidyl ether (tBGE) and (b) 1,2-epoxyoctane (EO) through cycloaddition of
CO
2 n
to form cyclic carbonates with mimC [Br]s (n = 3, 7, 12, and 18) as
catalysts. Inset of (a) shows the magnified view of the first 6 h of experiment
(
dotted frame). Reaction condition: mimC
n
[Br] (0.1 mmol, 1 mol%), epoxide
(< 1 bar), 110 oC for (a) and 130 C for (b).
o
Scheme 2. (a) Molecular design of imidazolium ionic liquid mimC
utilization. (b) Plausible mechanism of CO cycloaddition upon epoxide
substrates catalyzed by mimC [A].
n
[A] for CO
2
(10 mmol), CO
2
2
n
The magnified conversion kinetics, however, clearly
revealed the effect of alkyl chains on cation. As the alkyl chain
length on imidazolium ring became longer, the conversion of
epoxide into cyclic carbonate was faster in the first few hours. As
displayed in figure 1a, tBGE was converted into respective
cyclic carbonate upto 3.9 % and 35.3 % at the first 30 min of
reaction with mimC [Br] and mimC18[Br], respectively. The
3
conversion of EO substrate also exhibited the similar pattern,
showing 2.2 % and 38.4 % of conversion efficiency at 1 h of
The rational design of imidazolium ILs involves the change
of alkyl chain length on imidazolium cation and counter anions in
different combinations (Scheme 2a). Firstly, the length of alkyl
chain on imidazolium ring was varied from propane to
octadecane with bromide as a counter anion, giving a series of
ILs, namely mimC
heptane, dodecane, and octadecane-functionalized IL,
respectively). The mimC [Br]s were utilized to catalyze
cycloaddition of CO with epoxides, of which tert-butyl glycidyl
ether (tBGE) and 1,2-epoxyoctane (EO) were tested in a typical
condition of atmospheric CO pressure (Figure 1). Time-
dependent kinetics showed that the epoxide substrates were
n
[Br] (where n = 3, 7, 12, and 18, for propane,
n
reaction with mimC
3
[Br] and mimC18[Br], respectively (Figure
2
1b). The enhancement in conversion efficiency with respect to
the longer alkyl chain on imidazolium cation would be primarily
attributed to weaker electrostatic interaction between cation and
anion of ILs. The bulkiness of long-chain cation pushes the
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
bromide ion away, thus making the anion more nucleophilic to
attack epoxide ring[27]. Secondary reason for the increasing
efficiency would be originated from the improved solubility of ILs
in epoxide substrates with longer aliphatic chains, particularly for
solvent-free reaction. The longer chain IL is supposed to
The nucleophilicity of counter anions on mimC18[A]s could be
probed by experimental chemical shifts of protons on
imidazolium cation. The weakly acidic protons on imidazolium
ring can be affected by hydrogen bonding and inductive effect of
counter anions[29], in other words, the chemical shift of protons
on imidazolium ring moves to downfield with increasing
dissolve well in non-polar solvent than the shorter chain IL[28]
,
[
30]
1
therefore the mimC18[Br] could show enhanced catalytic
efficiency owing to the higher solubility in epoxide substrate.
Control experiment using inorganic LiBr salt as a catalyst
showed 3% conversion of EO substrate after 24 h, implying that
the solubility of catalyst in epoxide is indispensable for chemical
nucleophilicity of anions . As shown in Figure 2a, the
chemical shifts on 2-, 4-, and 5-position of imidazolium ring (H
, and H , respectively) exhibited obvious difference depending
H
2
,
H
4
5
on the type of anions (See Figure S1 for 1H NMR spectra of
mimC18[A]s). The 1H chemical shift for 2-position showed the
largest change than those for 4- and 5-position as the anions are
likely to be located at around 2-position on imidazolium cation[31].
2
fixation of CO upon epoxide.
Through
a
relative comparison of 1H chemical shift, the
-
nucleophilicity of anion was found to follow the order of [AcO] >
-
-
2 6
N] > [PF
]-, which would correlate to their
-
[
Br] ≥ [TfAcO] > [Tf
reactivity for CO conversion. As displayed in Figure 2b,
2
however, the conversion of tBGE was rather inconsistent with
the order of nucleophilicity, in which the conversion efficiency of
tBGE decreased in the following order of mimC18[Br]
>
mimC18[AcO] > mimC18[TfAcO] >> mimC18[Tf N] ≈ mimC18[PF ].
2
6
Despite the highest nucleophilicity, the IL with acetate anion
showed a moderate conversion of epoxide upto 76.7 % for 24 h,
while the IL with bromide anion resulted in 99 % of conversion
efficiency for 24 h. Though trifluoroacetate anion exhibited
similar level of nucleophilicity with bromide anion, mimC18[TfAcO]
showed 47 % of conversion efficiency for 24 h. Unexpected
behavior of mimC18[AcO] and mimC18[TfAcO] may be attributed
N
to thermal decomposition of ILs by S 2 nucleophilic substitution
of basic acetate anions upon methyl imidazolium ring[32]. In fact,
mimC18[AcO] and mimC18[TfAcO] could not be separated and
recycled after the first cycle of conversion experiment. Besides,
ILs with fluorinated anions showed no reactivity to convert
2
epoxides at the given atmospheric CO condition, probably due
to the relatively low nucleophilicity. The low nucleophilicity of
fluorinated counter anions may thus require high pressure (~2
MPa[33]) to facilitate the chemical fixation of CO
on epoxides.
2
Therefore, the structure of imidazolium ILs could be optimized
with long alkyl substituent on cation and bromide as a counter
anion.
Figure 2. (a) 1H NMR chemical shifts for C
imidazolium ring for mimC18[A]s with different counter anions. The chemical
shifts are relative to external TMS in CDCl . (b) Time-dependent conversion of
tBGE to cyclic carbonate with CO catalyzed by mimC18[A]s having different
2
4 5
-H, C -H, and C -H on the
3
2
anions. Reaction condition: mimC18[A] (0.1 mmol, 1 mol%), epoxide (10 mmol),
o
CO
2
(< 1 bar), 110 C.
Along with the longest alkyl chain, the influence of counter
anions on ILs was tested for CO conversion. Beside mimC18[Br],
2
four additional ILs were prepared by anion exchange of bromide
with common anions, giving mimC18[AcO], mimC18[TfAcO],
mimC18[Tf
bis(trifluoromethylsulfonyl)imide,
2
N], and mimC18[PF
6
], for acetate, trifluoroacetate,
and hexafluorophosphate,
respectively. Since the counter anions attack the electrophilic
carbon on epoxide ring, higher nucleophilicity of anions would
lead to the improved conversion of epoxide into cyclic carbonate.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
can be separated out from liquid products by lowering down the
temperature of reaction mixture e.g. to 0 oC. Therefore, the
temperature-responsive phase transition of mimC18[Br] enables
heterogeneous isolation of catalyst after the reaction as well as
homogeneous catalysis for CO
2
conversion.
The homogeneous catalysis
and heterogeneous
1
separation using mimC18[Br] could be monitored by H NMR
spectroscopy (Figure 4). Pristine catalyst mimC18[Br] (Figure 4a)
and epoxide substrate tBGE (Figure 4b) were mixed and heated
up to 110 oC in the absence of CO
substrate (Figure 4c). When blown with CO
, giving no change in the
, the epoxide
2
2
substrate was then able to be converted into respective cyclic
carbonate, showing clear chemical shifts at 4.74, 4.43, 4.34,
3.55, and 3.48 ppm for cyclic carbonate formation (Figure 4d).
The mimC18[Br] was separated out from reaction medium by
cooling the temperature down, and the recovered catalyst was
clean and intact with identical chemical shifts from the pristine
catalyst (Figure 4e).
Figure 3. (a) Temperature dependence of the total heat flow monitored during
the heating and cooling process for mimC18[Br]. (b) Phase transition of
mimC18[Br] in epoxide substrate (tBGE) via a consecutive temperature change.
The optimized mimC18[Br] exhibited phase transition
behavior upon temperature change. Figure 3a shows the
temperature-dependent total heat flow by heating and cooling
o
mimC18[Br]. As the temperature increased from -140 C, a large
o
endothermic peak appeared at 75 C, which corresponds to the
temperature for transition from crystalline solid to smectic phase
as a liquid crystal[34]. By the successive cooling of mimC18[Br],
the transition from smectic phase to solid phase was observed
o
at 48 C. The temperature range of phase transition from solid to
liquid coincides with the operation temperature of CO
2
Figure 4. Temperature-assisted separation of catalyst proven by 1H NMR
conversion reaction (Figure 3b). In other words, mimC18[Br]
solid at room temperature would not fully dissolve in target
epoxide substrates due to the long aliphatic chain. Once being
spectra in CDCl3.
pure substrate of tBGE before reaction, products recovered after the reaction
at 110 oC (c) without CO
and (d) with CO injection for 24 h (< 1 bar), and (e)
the separated catalyst through temperature swing after the reaction.
1
H NMR spectrum of (a) pristine catalyst mimC18[Br], (b)
2
2
o
heated over 75 C, mimC18[Br] is transformed into smectic liquid
crystals, becoming soluble in the epoxides to catalyze the CO
cycloaddition reaction. When the reaction is finished, mimC18[Br]
2
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
the separation of catalyst during the repeated cycle, the isolation
of mimC18[Br] was conducted in ethyl acetate solution (~20 mL).
There was no evidence of residual catalyst in product, confirmed
by the addition of AgNO
inset). The high efficiency and low cost of mimC18[Br] prompted
us to conduct in much larger scale of CO conversion.
3
solution after 5th cycle (Figure S3a
2
Epichlorohydrin 1a, one of the cheapest substrate among the
epoxides, was tested in 80 ml scale (1 mol) with 0.25 mol% of
mimC18[Br] (Figure 6a). The catalytic dose of mimC18[Br] was
optimized in a smaller scale as shown in Figure S3b. Large-
scale production of cyclic carbonate 2a was achieved after 70 h
of the reaction, leading to 99 % of conversion efficiency (Figure
6
b). The longer reaction time for the large-scale experiment
would be associated from the slower CO diffusion in the liquid
substrate. Nonetheless, the product aliquot obtained through
large-scale CO cycloaddition reaction under atmospheric
2
2
condition was clean after the separation of catalyst through a
temperature swing (Figure S4).
Figure 5. Substrate scope for generation of cyclic carbonates 2 by the
cycloaddition of CO
at 90 C. For 2b and 2f, at 110 C. For 2c-e and 2g-h, at 130 C.
2
on epoxides 1 (10 mmol). For 2a, the reaction was done
o
o
o
Temperature-assisted homogeneity/heterogeneity switch
of IL has been applied to epoxide substrates with a variety of
substituents (Figure 5). Regardless of the functionalities, the
tested substrates have shown quantitative conversion into cyclic
carbonates under atmospheric pressure of CO
mimC18[Br] comparable to efficient ILs reported recently
2
,
making
[
24, 35]
. By
virtue of thermal stability of mimC18[Br] (Figure S2), reaction
temperature could range from 90 oC to 130 oC to yield target
products 2a - 2h in 24 h (See NMR spectra of products in
supporting information). Depending on the type of products,
however, there was discrepancy in time to isolate the mimC18[Br]
after the reaction through lowering down the temperature. The
mimC18[Br] could be easily separated out from the reaction
mixture of 2a – 2c in ice bath, while there took few hours to
isolate the catalyst out of 2d and 2e mixture, maybe due to high
viscosity of resulting cyclic carbonates. In case of 2f – 2h, the
catalyst was separated by flash column chromatography as the
reaction mixtures were solidified in low temperature. When the
small amount of ethyl acetate was added into the crude reaction
mixtures, the temperature-controlled separation of catalyst could
be far accelerated under low temperature to afford the pure
products in few minutes (See a video clip in supporting
information).
Owing to the temperature-responsive separation behavior,
mimC18[Br] was able to be regenerated for the repeated use.
Figure 6. (a) Photograph of large-scale experiment set-up with ~80 mL of 1a
and mimC18[Br]. (b) Large-scale production of 2a catalyzed by mimC18[Br].
Repeating cycles of CO
2
cycloaddition on epoxide 1c in few
Reaction condition: mimC18[Br] (2.5 mmol, 0.25 mol%), epoxide 1a (1 mol),
o
CO
2
(< 1 bar), 90 C.
gram scale revealed that mimC18[Br] could catalyze the reaction
for repeated cycles, showing 98 % of conversion efficiency in 5th
cycle (Figure S3a). Each cycle only run for 6 h owing to the fast
conversion of 1c as described in Figure 1b. In order to facilitate
Cyclic carbonates are known as environmentally-friendly
precursor of non-isocyanate polyurethane (NIPU) by
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
polyaddition reaction with amine group[36]. The pure cyclic
1650 cm-1 also correspond to the formation of secondary amide
in the NIPUs. As being connected with different type of amines,
thermal properties of 3a and 3b could be largely altered. In
particular, the degree of freedom in chain fragments was verified
carbonate afforded from CO
applied to generate NIPU for proving the feasibility of CO
utilization process mediated by mimC18[Br]. Bis(cyclic carbonate)
was reacted with two different diamines to form
2
cycloaddition on epoxide was thus
2
2e
by glass transition temperature (T
3b showed -30 oC and 32 oC of T
Relatively low T of 3a resulted from structural flexibility with
alkyl chains of n-hexane, and 3b with harder segment of p-
xylene caused relatively higher T . In fact, 3a had sticky texture
g
) of NIPUs, in which 3a and
hydroxylurethane linkage at the elevated temperature, giving two
NIPUs 3a and 3b with high yields (Figure 7a). The resulting
NIPUs were insoluble in common organic solvents, probably due
to high molecular weight after polymerization (Figure S5a and
b). The fraction of NIPUs dissolved in 0.5% LiBr DMF solution at
g
, respectively (Figure 7c).
g
g
owing to the free aliphatic chains, on the other hand, 3b with
rigid aromatic ring was fine powder without adhesiveness. The
adhesive 3a could carry more than 50 g of mass when the 5 mg
of 3a was sandwiched between two glass plates and one side of
the plate was pulled with the mass (Figure S5c). The simple
o
-1
7
w
0 C showed molecular weight (M ) of 3320 g mol and 14166
-1
g mol for 3a and 3b, respectively. The formation of NIPU was
able to be simply observed by FTIR spectra (Figure 7b). A
distinct peak of 2e at 1780 cm-1 from C=O stretching vibration of
cyclic carbonate disappeared after the polymerization, while
broad peak was evolved at 3315 cm-1 for both 3a and 3b, which
is attributed to N-H and O-H stretching vibrations of amide and
hydroxyl group, respectively. The peaks appeared at around
change in monomeric composition thus allowed
a fine
adjustment in properties of NIPUs. Both NIPUs exhibited high
thermal stability, in which the first 5 % of mass loss occurred at
o
255 C (Figure 7d).
Figure 7. (a) Synthetic scheme of non-isocyanate polyurethanes 3a and 3b by polyaddition of bis(cyclic carbonate) 2e and diamines. (b) FTIR spectra of 2e, 3a
and 3b. (c) DSC and (d) TGA thermogram of 3a and 3b.
homogeneous catalysis at high temperature and the
heterogeneous separation of catalyst under low temperature
after the reaction. Low cost of the ILs facilitated large-scale
production of cyclic carbonate, and the IL was recyclable for the
Conclusions
repeated use. The obtained bis(cyclic carbonate) product could
be utilized to generate non-isocyanate polyurethane (NIPU) by
polyaddition with diamines under the elevated temperature,
In summary, we have optimized the structural composition of
imidazolium ILs by simply altering the length of alkyl substituent
on cation and type of counter anions to catalyze cycloaddition of
2
proving the feasibility of imidazolium IL for CO conversion. The
2
CO upon epoxides. When the IL bore long aliphatic chain of
resulting poly(hydroxylurethane) showed structural variation
based on the type of diamine linkage, further providing a room to
octadecane on imidazolium ring with bromide as a counter anion,
the complete conversion of epoxides into cyclic carbonates
2
explore the production of various NIPUs by CO utilization.
could be achieved under atmospheric pressure of CO
chain structure of IL exhibited temperature-responsive
solid/liquid phase transition behavior, enabling the
2
. The long
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
[
[
4]
5]
a) D. J. Darensbourg, W.-C. Chung, K. Wang, H.-C. Zhou, ACS Catal.
Experimental Section
2014, 4, 1511-1515; b) X.-H. Liu, J.-G. Ma, Z. Niu, G.-M. Yang, P.
Cheng, Angew. Chem. Int. Ed. 2015, 54, 988-991.
Synthesis of mimC18[Br]: In a typical set-up, 1-methylimidazole (1.1 mL,
a) O. Buyukcakir, S. H. Je, S. N. Talapaneni, D. Kim, A. Coskun, ACS
Appl. Mater. Interfaces 2017, 9, 7209-7216; b) S. Subramanian, J. Park,
J. Byun, Y. Jung, C. T. Yavuz, ACS Appl. Mater. Interfaces 2018, 10,
1
3.9 mmol) and 1-bromododecane (7.12 mL, 20.85 mmol) were
dispersed in absolute ethanol (7 mL). The mixture was heated at 80 oC
for 3 d under N atmosphere. After the reaction, the solvent was
2
9
478-9484; c) S. N. Talapaneni, O. Buyukcakir, S. H. Je, S. Srinivasan,
Y. Seo, K. Polychronopoulou, A. Coskun, Chem. Mater. 2015, 27,
818-6826; d) Y. Xie, T.-T. Wang, X.-H. Liu, K. Zou, W.-Q. Deng, Nat.
evaporated under the reduced pressure, resulting in off-white wax-like
solution. The crude product was dissolved in acetonitrile and
reprecipitated with ethyl acetate. The obtained precipitate was filtered
and dried in vacuo at 60 oC for overnight to afford white powder as a
product. The purified product was kept in moisture-free condition for
further use. Yield = 84.2 %. The other mimC [Br]s (n = 3, 7, and 12) with
n
shorter alkyl chains were produced with the similar procedure described
above.
6
Commun. 2013, 4, 1960; e) Z.-Z. Yang, H. Zhang, B. Yu, Y. Zhao, G. Ji,
Z. Liu, Chem. Commun. 2015, 51, 1271-1274.
[
6]
M. E. Boot-Handford, J. C. Abanades, E. J. Anthony, M. J. Blunt, S.
Brandani, N. Mac Dowell, J. R. Fernandez, M.-C. Ferrari, R. Gross, J. P.
Hallett, R. S. Haszeldine, P. Heptonstall, A. Lyngfelt, Z. Makuch, E.
Mangano, R. T. J. Porter, M. Pourkashanian, G. T. Rochelle, N. Shah, J.
G. Yao, P. S. Fennell, Energy Environ. Sci. 2014, 7, 130-189.
General procedure for synthesis of cyclic carbonate under
[
[
[
[
[
7]
8]
9]
L. A. Blanchard, D. Hancu, E. J. Beckman, J. F. Brennecke, Nature
atmospheric pressure of CO
substrate (10 mmol) were placed in a 20 mL screw-cap vial and purged
with CO for 10 min. The mixture was heated at the desired temperature
under CO atmosphere for 24 h, in which CO was injected through a
2
: Ionic liquid (0.1 mmol) and epoxide
1999, 399, 28.
C. Cadena, J. L. Anthony, J. K. Shah, T. I. Morrow, J. F. Brennecke, E.
J. Maginn, J. Am. Chem. Soc. 2004, 126, 5300-5308.
S. N. V. K. Aki, B. R. Mellein, E. M. Saurer, J. F. Brennecke, J. Phys.
Chem. B 2004, 108, 20355-20365.
2
2
2
Schlenk line with the pressure of ~1 bar. The reaction mixture was cooled
down to room temperature and the aliquot was diluted with
dichloromethane for GC-MS analysis to determine conversion efficiency.
10] D. Camper, J. E. Bara, D. L. Gin, R. D. Noble, Ind. Eng. Chem. Res.
008, 47, 8496-8498.
2
For the repeated use of the short-chain ionic liquids, mimC
n
[Br] (n = 3, 7,
11] a) E. J. Beckman, Chem. Commun. 2004, 1885-1888; b) M. J. Muldoon,
S. N. V. K. Aki, J. L. Anderson, J. K. Dixon, J. F. Brennecke, J. Phys.
Chem. B 2007, 111, 9001-9009.
12), the reaction mixture was purified through flash column
chromatography to isolate product. In the case of mimC18[Br],
temperature-assisted separation of catalyst was conducted. After the
reaction, the mixture was cooled down in ice bath, leading to precipitation
of the catalyst. Afterwards, the mixture was centrifuged at 3000 rpm for
[
[
[
[
[
[
[
[
[
12] J. E. Bara, C. J. Gabriel, S. Lessmann, T. K. Carlisle, A. Finotello, D. L.
Gin, R. D. Noble, Ind. Eng. Chem. Res. 2007, 46, 5380-5386.
13] T. K. Carlisle, J. E. Bara, C. J. Gabriel, R. D. Noble, D. L. Gin, Ind. Eng.
Chem. Res. 2008, 47, 7005-7012.
1
0 min under low temperature (~0 oC) to isolate the catalyst and afford
pure product as supernatant. For the cyclic experiment, the reaction
mixture was diluted with 20 mL of ethyl acetate and cooled down at 0 C
14] E. D. Bates, R. D. Mayton, I. Ntai, J. H. Davis, J. Am. Chem. Soc. 2002,
o
1
24, 926-927.
15] M. Ramdin, T. W. de Loos, T. J. H. Vlugt, Ind. Eng. Chem. Res. 2012,
1, 8149-8177.
to isolate mimC18[Br] in few minute. The solution was filtered while cold,
and the pure product was obtained after the evaporation of ethyl acetate.
The collected catalyst was gently washed with ether and dried for next
run. For the all tested substrates, the separation of catalyst from reaction
media could be accelerated by the addition of ethyl acetate.
5
16] D. Ballivet-Tkatchenko, A. Dibenedetto, in Carbon Dioxide as Chemical
Feedstock, Wiley-VCH Verlag GmbH & Co. KGaA, 2010, pp. 169-212.
17] Z.-Z. Yang, L.-N. He, S.-Y. Peng, A.-H. Liu, Green Chem. 2010, 12,
1
850-1854.
18] W. Lu, J. Ma, J. Hu, J. Song, Z. Zhang, G. Yang, B. Han, Green Chem.
014, 16, 221-225.
General procedure for production of poly(hydroxylurethane): Pure
bis(cyclic carbonate) 2e (1 mmol) and diamine (1.4 mmol) were placed in
a 40 mL screw-cap vial and dissolved in anhydrous DMF (1 mL). The
2
19] L. Hao, Y. Zhao, B. Yu, Z. Yang, H. Zhang, B. Han, X. Gao, Z. Liu, ACS
Catal. 2015, 5, 4989-4993.
mixture was heated at 130 oC under N
atmosphere for max. 2 d. The
2
obtained product was intensively washed with dichloromethane, and
20] a) A. S. Aquino, F. L. Bernard, J. V. Borges, L. Mafra, F. D. Vecchia, M.
O. Vieira, R. Ligabue, M. Seferin, V. V. Chaban, E. J. Cabrita, S. Einloft,
RSC Adv. 2015, 5, 64220-64227; b) L. Han, S.-W. Park, D.-W. Park,
Energy Environ. Sci. 2009, 2, 1286-1292; c) Y. Xie, K. Ding, Z. Liu, J. Li,
G. An, R. Tao, Z. Sun, Z. Yang, Chem. Eur. J. 2010, 16, 6687-6692.
21] Y. Xie, Z. Zhang, T. Jiang, J. He, B. Han, T. Wu, K. Ding, Angew. Chem.
Int. Ed. 2007, 46, 7255-7258.
o
dried at 80 C for further characterization.
Acknowledgements
[
[
J. B. thanks the Alexander von Humboldt Foundation for the
postdoctoral research fellowship. K. A. I. Z. acknowledges the
Max Planck Society for financial support.
22] a) W. Wang, C. Li, L. Yan, Y. Wang, M. Jiang, Y. Ding, ACS Catal.
2016, 6, 6091-6100; b) Y. Zhang, S. Yin, S. Luo, C. T. Au, Ind. Eng.
Chem. Res. 2012, 51, 3951-3957.
[
[
23] M. Ding, H.-L. Jiang, ACS Catal. 2018, 3194-3201.
24] P. Goodrich, H. Q. N. Gunaratne, J. Jacquemin, L. Jin, Y. Lei, K. R.
Seddon, ACS Sustain. Chem. Eng. 2017, 5, 5635-5641.
2
Keywords: CO utilization • Ionic liquid • Cyclic carbonate •
Homogeneity/heterogeneity switch • Polyhydroxylurethane.
[
25] S. Wu, Y. Zhang, B. Wang, E. H. M. Elageed, L. Ji, H. Wu, G. Gao, Eur.
J. Org. Chem. 2017, 2017, 753-759.
[
1]
a) R. Monastersky, Nature 2013, 497, 13-14; b) S. Solomon, G. K.
Plattner, R. Knutti, P. Friedlingstein, Proc. Natl. Acad. Sci. U.S.A. 2009,
[26] M. Buaki-Sogo, H. Garcia, C. Aprile, Catal. Sci. Technol. 2015, 5, 1222-
1230.
1
06, 1704-1709.
[27] a) V. Caló, A. Nacci, A. Monopoli, A. Fanizzi, Org. Lett. 2002, 4, 2561-
2563; b) E.-H. Lee, J.-Y. Ahn, M. M. Dharman, D.-W. Park, S.-W. Park,
I. Kim, Catal. Today 2008, 131, 130-134.
[
[
2]
3]
H. A. Patel, J. Byun, C. T. Yavuz, ChemSusChem 2017, 10, 1303-1317.
a) M. Aresta, in Carbon Dioxide as Chemical Feedstock, Wiley-VCH
Verlag GmbH & Co. KGaA, 2010, pp. 1-13; b) Z. Yuan, M. R. Eden, R.
Gani, Ind. Eng. Chem. Res. 2016, 55, 3383-3419.
[28] U. Domańska, in Pure and Applied Chemistry, Vol. 77, 2005, p. 543.
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
[
29] S. Cha, M. Ao, W. Sung, B. Moon, B. Ahlstrom, P. Johansson, Y. Ouchi,
D. Kim, Phys. Chem. Chem. Phys. 2014, 16, 9591-9601.
b) T. Wang, D. Zheng, J. Zhang, B. Fan, Y. Ma, T. Ren, L. Wang, J.
Zhang, ACS Sustain. Chem. Eng. 2018, 6, 2574-2582; c) Y. Ma, C.
Chen, T. Wang, J. Zhang, J. Wu, X. Liu, T. Ren, L. Wang, J. Zhang,
Appl. Cat., A. 2017, 547, 265-273; d) C. Yue, D. Su, X. Zhang, W. Wu,
L. Xiao, Catal. Lett. 2014, 144, 1313-1321; e) T. Wang, D. Zheng, Y.
[
[
30] R. Lungwitz, S. Spange, New J. Chem. 2008, 32, 392-394.
31] H. Tokuda, S. Tsuzuki, M. A. B. H. Susan, K. Hayamizu, M. Watanabe,
J. Phys. Chem. B 2006, 110, 19593-19600.
[
32] M. T. Clough, K. Geyer, P. A. Hunt, J. Mertes, T. Welton, Phys. Chem.
Chem. Phys. 2013, 15, 20480-20495.
2
Ma, J. Guo, Z. He, B. Ma, L. Liu, T. Ren, L. Wang, J. Zhang, J. CO Util.
2017, 22, 44-52; f) J.-Q. Wang, W.-G. Cheng, J. Sun, T.-Y. Shi, X.-P.
Zhang, S.-J. Zhang, RSC Adv. 2014, 4, 2360-2367.
[
[
33] J. Peng, Y. Deng, New J. Chem. 2001, 25, 639-641.
34] Y. Nozaki, K. Yamaguchi, K. Tomida, N. Taniguchi, H. Hara, Y.
Takikawa, K. Sadakane, K. Nakamura, T. Konishi, K. Fukao, J. Phys.
Chem. B 2016, 120, 5291-5300.
[36] a) M. Blain, L. Jean-Gerard, R. Auvergne, D. Benazet, S. Caillol, B.
Andrioletti, Green Chem. 2014, 16, 4286-4291; b) O. Lamarzelle, P.-L.
Durand, A.-L. Wirotius, G. Chollet, E. Grau, H. Cramail, Poly. Chem.
2016, 7, 1439-1451.
[
35] a) F. D. Bobbink, D. Vasilyev, M. Hulla, S. Chamam, F. Menoud, G.
Laurenczy, S. Katsyuba, P. J. Dyson, ACS Catal. 2018, 8, 2589-2594;
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.201801086
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Settling ionic liquid: Long-chain
imidazolium ionic liquid exhibited
temperature-dependent phase
transition behavior, thus enabling
heterogeneous isolation of catalyst
after the reaction as well as
J. Byun, K. A. I. Zhang*
Page No. – Page No.
Controllable
Homogeneity/Heterogeneity Switch of
Imidazolium Ionic Liquids for CO
Utilization
2
homogeneous catalysis for CO
conversion.
2
This article is protected by copyright. All rights reserved.