Choline-based ionic liquids for CO2 capture and conversion

Article abstract of DOI:10.1007/s11426-018-9358-6

Choline-based ionic liquids (Ch-ILs) with anions possessing interacting sites to attract CO₂ were designed, which could capture CO₂ with capacity >1.0 mol CO₂ per molar IL under ambient conditions. Moreover, this kind of ILs combining with CuCl could catalyze the formylation of amines with CO₂/H₂ at 120 °C. Especially, choline imidazolate showed the best performance, affording a series of N-formamides in excellent yields. It was demonstrated that the IL activated CO₂ and the synergistic effect between the IL and CuCl resulted in the high activity for catalysing the formylation of amines with CO₂/H₂.

Full text of DOI:10.1007/s11426-018-9358-6

SCIENCE CHINA
Chemistry
•ARTICLES•
https://doi.org/10.1007/s11426-018-9358-6
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Choline-based ionic liquids for CO2 capture and conversion
Ruipeng Li1, Yanfei Zhao2, Zhiyong Li1, Yunyan Wu2, Jianji Wang1* & Zhimin Liu2*
1Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering,
Henan Normal University, Xinxiang 453007, China;
2Beijing National Laboratory for Molecular Sciences, Key Laboratory of Colloid, Interface and Thermodynamics, CAS Research/Education
Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Received August 24, 2018; accepted September 6, 2018; published online November 9, 2018
Choline-based ionic liquids (Ch-ILs) with anions possessing interacting sites to attract CO2 were designed, which could capture
CO2 with capacity >1.0 mol CO2 per molar IL under ambient conditions. Moreover, this kind of ILs combining with CuCl could
catalyze the formylation of amines with CO2/H2 at 120 °C. Especially, choline imidazolate showed the best performance,
affording a series of N-formamides in excellent yields. It was demonstrated that the IL activated CO2 and the synergistic effect
between the IL and CuCl resulted in the high activity for catalysing the formylation of amines with CO2/H2.
choline, ionic liquid, N-formylation, CO2, H2
Citation:
Li R, Zhao Y, Li Z, Wu Y, Wang J, Liu Z. Choline-based ionic liquids for CO2 capture and conversion. Sci China Chem, 2018, 61, https://doi.org/
10.1007/s11426-018-9358-6
1 Introduction
saturated groups [14]. Though some progress has been made,
it is still highly desirable to develop a simple and green
catalyst or catalytic system with high efficiency for N-for-
mylation of amines with CO2/H2.
The capture and utilization of carbon dioxide (CO2) have
been paid much attention due to the requirements of sus-
tainable development in recent years. As a cheap, abundant,
green and renewable C1 resource, CO2 has been widely
applied in the synthesis of chemicals [1–13]. For example, it
is an alternative of formylated reagents for synthesis of
formamides [14,15]. The reductive N-formylation of amines
with CO2/H2 is an environment-friendly route to produce N-
formamides, which have been achieved over various cata-
lysts [16]. The reported catalysts mainly focus on the noble
metals such as Pd [8,9,17,18], Ru [13,15,16,19–22], Au [23]
and Ir [24], while cheap transition-metal catalysts are seldom
reported [25,26]. In a recent work, Cu(OAc)2 with the as-
sistance of 4-dimethylaminopyridine realized the reductive
formylation of amines containing unsaturated groups using
CO2/H2, producing corresponding N-formamides with un-
Ionic liquids (ILs), composing of organic cations and in-
organic/organic anions, can be designed with specific prop-
erties via choosing cations and anions, which therefore have
promising applications in many areas. Especially, in chemi-
cal reactions, ILs can be used as the solvents and/or catalysts,
displaying unique performances for reactions [5,27–32]. ILs
can dissolve metal salts, and the specific interactions among
the ionic species can offer new properties to the ILs solution,
thus showing new functions. For example, 1-butyl-3-methyl
imidazolium acetate ([Bmim][OAc]) in combination with
AgCl was efficient for the synthesis of asymmetrical organic
carbonates from CO2 and propargylic alchols [33]. The IL,
1,8-diazabicydo-[5,4,0]-7-undecenium
trifluoroethanol,
containing CuI worked well for the carboxylative cyclization
of propargylic alcohols with CO2 at ambient pressures [34].
Task-specific ILs with interacting sites to attract CO2 have
*Corresponding authors (email: jwang@htu.cn; liuzm@iccas.ac.cn)
© Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018
chem.scichina.com link.springer.com

2
Li et al. Sci China Chem
been presented for efficient CO2 capture via forming car-
bamates and/or carbonates, which changes the form of CO2
and reduces its activation energy, facilitating its subsequent
transformation [35–38]. These CO2-reactive ILs combining
with low-cost metal salts are expected to be capable of cat-
alyzing CO2 chemical conversion with high efficiency.
ILs with choline cation have recently attracted consider-
able attention because of their easy availability, low toxicity
and excellent biodegradability [39]. The hydroxyl group in
choline cation in cooperation with appropriate anions may
offer new opportunities for addressing the challenge of CO2
activation and subsequent transformation, which is both
environmentally and practically attractive but seldom re-
ported [40]. To explore the applications of ILs in CO2 capture
and further conversion, in this work a series of choline-based
ILs (Ch-ILs) as shown in Scheme 1 were synthesized via the
reactions of choline hydroxide with proton donors. Their
capacities to absorb CO2 were examined, and the interaction
between CO2 and ILs was investigated by NMR and FTIR
analyses. Moreover, these Ch-ILs were applied in the re-
ductive N-formylation of amines with CO2/H2, and com-
bining with CuCl they were found to be very effective for
this N-formylation.
Scheme 1 Chemical structures of cation and anions of Ch-ILs.
using a Karl Fisher titration and found to be less than
0.1 wt%. The as-synthesized ILs were characterized by
NMR spectroscopy to verify their chemical structures.
2.3 Characterization
1H and 13C NMR analyses were performed on a Bruker
Avance III NMR spectrometer (400 MHz; Germany). The
Fourier transform infrared spectroscopy (FT-IR) analysis
was conducted on a Bruker TENSON-27 FT-IR spectro-
meter. The water content of the ILs was measured with an
851 Titrando Karl Fischer Coulometer. The density of the ILs
was determined by means of Anton paar DMA 2000 density
meter (shown in Figure S1, Supporting Information online)
and their dynamic viscosity was obtained by using a
Brookfield DV-C digital rotational viscometer (Figure S1).
The decomposition temperature (Td) of these ILs was tested
on a PerkinElmer TGA 4000 thermal gravimetric analyser
(USA). The 1H and 13C NMR data and the Td of the resultant
Ch-ILs are as follows.
2 Experimental
2.1 Materials
CO2 (99.99%) and H2 (99.999%) were provided by Beijing
Analytical Instrument Company (China). Amine substrates
were purchased from J&K Scientific Ltd. and Alfa Aesar
(China), and CuCl was from Sinopharm Chemical Reagent
Beijing Co., Ltd. (China). The solvents were provided by
Beijing Chemical Company (China), and the deuterated
solvents (dimethyl sulfoxide (DMSO), D2O, CDCl3) were by
J&K Scientific Ltd. (China). All reagents were used without
further purification.
[Ch][Im]: 1H NMR (400 MHz, DMSO-d6) δ, 7.12 (s, 1H),
6.69 (s, 2H), 3.84 (dd, 2H), 3.59–3.30 (m, 2H), 3.10 (s, 9H)
ppm. 13C NMR (101 MHz, DMSO-d6) δ, 141.67, 124.22,
67.39–67.34, 54.65, 53.15–53.08 ppm. Td=135 °C.
1
[Ch][2-MIm]: H NMR (400 MHz, DMSO-d6) δ, 6.54 (s,
2H), 3.85 (dd, 2H), 3.37–3.36 (m, 2H), 3.11 (s, 9H) ppm.13C
NMR (101 MHz, DMSO-d6) δ, 148.04, 123.59, 67.42, 53.13,
53.08, 15.81 ppm. Td=136 °C.
2.2 Procedures to synthesis of Ch-ILs
The ILs as illustrated in Scheme 1, including [Ch][Im], [Ch]-
[2-MIm], [Ch][4-MIm], [Ch][2,4-DMIm], [Ch][PhO] and
[Ch][2-OP], were synthesized by neutralization of choline
hydroxide ([Ch][OH]) with the corresponding proton donors
(i.e., imidazole, 2-methyl imidazole, 4-methyl imidazole,
2,4-dimethyl imidazole, phenol, and 2-methyl phenol), re-
spectively. In a typical experiment to synthesize [Ch][Im], an
ethanol solution of [Ch][OH] was mixed with equimolar
imidazole, and was then stirred at room temperature for 24 h.
Subsequently, ethanol and water were distilled off at 70 °C
under reduced pressure. The obtained [Ch][Im] was dried in
high vacuum for 24 h at 70 °C to remove possible trace of
water. The water content of these ILs was determined by
1
[Ch][4-MIm]: H NMR (400 MHz, DMSO-d6) δ, 7.09 (s,
1H), 6.47 (s, 1H), 3.84 (dd, 2H), 3.31–3.30 (m, 2H), 3.05–
3.01 (s, 9H), 2.13 (s, 3H) ppm.13C NMR (101 MHz, DMSO-
d6) δ, 140.58, 132.13, 121.55, 67.46, 54.66, 53.15–53.08,
13.58 ppm. Td=223 °C.
[Ch][2,4-DMIm]: 1H NMR (400 MHz, DMSO-d6) δ, 6.29
(s, 1H), 3.83 (dd, 2H), 3.29 (m, 2H), 3.06 (s, 9H), 2.14 (s,
3H), 2.04 (s, 3H) ppm. 13C NMR (101 MHz, DMSO-d6) δ,
147.80, 131.81, 121.03, 68.07, 53.64, 53.56, 17.21,
13.58 ppm. Td=131 °C.
[Ch][PhO]: 1H NMR (400 MHz, D2O-d2) δ, 7.33–7.12 (m,
2H), 6.68 (dd, 8.0 Hz, 2H), 4.18–4.03 (m, 2H), 3.51 (dd, 1H),

3
Li et al. Sci China Chem
3.20 (s, 9H) ppm. 13C NMR (101 MHz, DMSO-d6) δ,
167.03, 131.42, 120.23, 116.47, 69.02–68.96, 57.15,
55.47 ppm. Td=149 °C.
(ppm): 7.89 (s, 1H), 3.38–3.35 (t, 2H), 3.22–3.19 (t, 2H),
1.61–1.55 (m, 2H), 1.50–1.40 (m, 4H). 13C NMR (101 MHz,
CDCl3), δ (ppm): 160.77, 46.77, 40.55, 26.51, 25.02, 24.62.
N-formylpyrrolidine. 1H NMR (400 MHz, CDCl3), δ
(ppm): 8.13 (s, 1H), 3.44–3.11(m, 4H), 1.86–1.81 (m, 4H).
[Ch][2-OP]: 1H NMR (400 MHz, D2O-d2) δ, 7.65 (s, 1H),
7.55 (s, 1H), 6.62–6.39 (m, 2H), 4.01 (t, 2H), 3.45 (m, 2H),
3.15 (s, 9H) ppm. 13C NMR (101 MHz, DMSO-d6) δ,
171.99, 147.16, 136.70, 113.87, 105.80, 67.46, 55.05,
53.13 ppm. Td=148 °C.
13C NMR (101 MHz, CDCl3) δ (ppm): 160.67, 45.80, 44.16,
24.56, 24.14.
1-Formyl-4-methylpiperazine. 1H NMR (400 MHz,
CDCl3), δ (ppm): 7.88 (s, 1H), 3.47–3.44 (m, 2H), 3.32–3.29
(m, 2H), 2.34–2.32 (t, 2H), 2.30–2.27 (t, 2H), 2.21 (s, 3H).
2.4 Absorption of CO2 by Ch-ILs
13C NMR (101 MHz, CDCl3), δ (ppm): 162.12, 55.40, 54.32,
Typically, 0.3 g of Ch-IL was loaded into a 10 mL round
bottom flask equipped with a magnetic stirrer. After the air
inside was removed via being vacuumed, CO2 was charged
into the flask using a balloon of CO2 at 0.1 MPa. The mass of
the flask was detected by an analytical balance with an ac-
curacy of ±0.0001 g. Until its mass remained unchanged, the
absorption was considered to reach equilibrium, and the
amount of CO2 absorbed by IL was calculated based on the
mass changes of the flask containing IL. To obtain the so-
lubility of CO2 at different pressures, the partial pressure of
CO2 passing through a surge flask was diluted with N2 by
changing the flow rate ratio of CO2 and N2, and the above
CO2 balloon was replaced with the balloon filled with the
fully mixed gases.
48.52, 48.33, 40.19.
N-formylhexamethyleneimine. 1H NMR (400 MHz,
CDCl3), δ (ppm): 1.56 (s, 4H), 1.69–1.72 (m, 4H), 3.35 (t,
2H), 3.43 (t, 2H), 8.06 (s, 1H). 13C NMR (101 MHz, CDCl3)
δ(ppm): 162.81, 47.64, 43.35, 30.21, 27.89, 26.91, 26.81.
1
2-Methylpiperidine-1-carbaldehyde. H NMR (400 MHz,
CDCl3), δ (ppm): 8.08 (s, 1H), 7.95 (s, 1H), 4.68 (t, 1H), 3.94
(d, 1H), 3.76–3.75 (m, 1H), 3.35 (dd, 1H), 3.22–3.16 (m,
1H), 3.06–2.99 (m, 1H), 1.70–1.63 (m, 8H), 1.55–1.54 (m,
2H), 1.42–1.39 (m, 2H), 1.28 (d, 3H), 1.17 (d, 3H). 13C NMR
(101 MHz, CDCl3), δ (ppm): 161.0, 160.5, 50.5, 42.8, 42.1,
36.6, 31.7, 29.5, 26.5, 25.2, 20.2, 19.3, 17.8, 15.6.
3-Methylpiperidine-1-carbaldehyde. 1H NMR (400 MHz,
CDCl3), δ (ppm): 8.01 (d, 1H), 4.22 (dd, 1H), 3.48 (dd, 1H),
3.07–2.96 (m, 1H), 2.74–2.64 (m, 1H), 2.32 (dd, 1H), 1.86
(dd, 3.8 Hz, 1H), 1.79–1.65 (m, 1H), 1.63–1.36 (m, 2H),
1.31–1.13 (m, 2H), 0.98–0.86 (m, 3H). 13C NMR (101 MHz,
CDCl3), δ (ppm): 160.80, 160.72, 56.97, 53.30, 47.02, 46.37,
40.17, 34.65, 33.23, 33.16, 31.92, 31.55, 30.64, 29.59, 28.98,
25.98, 24.27, 18.86, 18.60, 18.54.
2.5 Procedures for N-formylation of amines with CO2/
H2
The reaction of N-formylation of amines with CO2/H2 was
performed in a 25 mL stainless steel autoclave with a Teflon
tube. Typically, 1.0 mmol of amine, 0.5 mmol of Ch-IL, and
CuCl (e.g., 50 mg) were loaded in sequence into the reactor.
After being sealed, the autoclave was charged with CO2 up to
3 MPa, followed by charging H2 up to 8 MPa at room tem-
perature. The reactor was then moved into an oil-bath of
desired temperature (e.g., 120 °C) and stirred. After the de-
sired reaction time, the reactor was cooled to room tem-
perature, and the gas inside the autoclave was released. As an
internal standard n-dodecane was added to the reaction so-
lution for determining the amine conversion and product
yield by gas chromatography with a FID detector and a
nonpolar capillary column (GC, DB-5, 30 m×0.25 mm×
0.25 μm; Agilent 7890B, USA).
1
N,N-dipropylformamide. H NMR (400 MHz, CDCl3), δ
(ppm): 7.90 (s, 1H), 3.11–3.08 (t, 2H), 3.04–3.00 (t, 2H),
1.46–1.36 (m, 4H), 0.76–0.72 (m, 6H). 13C NMR (101 MHz,
CDCl3), δ (ppm): 162.63, 48.99, 43.59, 21.69, 20.40, 11.16,
10.8.
N-methylformanilide: 1H NMR (400 MHz, CDCl3), δ
(ppm): 8.48 (s, 1H), 7.42 (t, 2H), 7.28 (t, 1H), 7.18 (d, 2H),
3.33 (s, 3H). 13C NMR (101 MHz, CDCl3), δ (ppm): 162.37,
142.19, 129.65, 126.42, 122.37, 32.06.
3 Results and discussion
The reaction solutions were examined by 1H and 13C NMR
1
analysis on a Bruker Avance NMR (400 MHz). The H and
3.1 Absorption of CO2 by the Ch-ILs
13C NMR data of the resultant compounds are listed as fol-
The resultant Ch-ILs were applied in the CO2 capture, and
their CO2 absorption capacities are shown in Table 1. Ob-
viously, each Ch-IL has CO2 absorption capacity higher than
1.0 mol per mol IL, suggesting the strong interaction be-
tween the IL and CO2, which probably originated from the
chemical absorption by the IL. In contrast, the CO2 capacity
of each Ch-IL was significantly greater than that of triethy-
lows.
N-formylmorpholine. 1H NMR (400 MHz, CDCl3), δ
(ppm): 8.05 (s, 1H), 3.70–3.63 (m, 4H), 3.58–3.55 (t, 2H),
3.40–3.37 (t, 2H). 13C NMR (101 MHz, CDCl3), δ (ppm):
161.52, 67.94, 67.05, 45.80, 40.63.
N-formylpiperidine. 1H NMR (400 MHz, CDCl3), δ

4
Li et al. Sci China Chem
Table 1 CO2 absorption capacity of the Ch-ILs at 30 °C and atmospheric
pressure
value of CO2 absorption capacity should be 3.0 mol per mol.
However, the experimental value was much lower than the
theoretic one. It was observed that the IL became more and
more viscous as CO2 molecules were absorbed by the IL. The
high viscosity of the IL-CO2 solution may prevent more CO2
molecules from contacting with the interacting sites of the
IL, thus resulting in an experimental capacity much lower
than the theoretic value.
Ch-ILs
[Ch][Im]
CO2 capacity (mol/mol)
1.17
1.18
1.63
1.50
1.71
1.88
0.14
[Ch][2-MIm]
[Ch][4-MIm]
[Ch][2,4-DMIm]
[Ch][PhO]
The IR analysis supports the 13C NMR results. In the
spectrum of [Ch][Im] exposed to CO2 (Figure 2), the bands at
1651 and 1628 cm−1, can be attributed to the formation of
carbamate group in N–C=O and carbonic acid O–COOH,
respectively. These results indicate that the IL chemically
absorb CO2 via forming carbamate with anion and forming
carbonic acid with the cation of the IL [40].
[Ch][2-OP]
Triethylene glycol dimethyl ether
lene glycol dimethyl ether (0.14 mol/mol). To explore the
influences of temperature and pressure on the CO2 capa-
cities, the CO2 adsorption capacities of these ILs were ex-
amined in the temperature range of 30–60 °C at 1 atm, and in
the pressure range of 0.3–1 atm at 30 °C, respectively, as
shown in Tables S1 and S2 (Supporting Information online).
It is obvious that both temperature and pressure have a little
influence on the CO2 adsorption capacity, deduced from the
facts that the CO2 absorption capacity decreased slightly with
the temperature, and increased slightly with the pressure
under the experimental conditions.
To further understand the CO2 absorption by the Ch-ILs,
NMR and IR analysis were performed on the Ch-ILs after
absorbing CO2. In the 13C NMR spectrum of [Ch][Im] ex-
posed to CO2, several new signals appeared compared to that
of [Ch][Im], which are assigned to the carbon atoms as re-
marked (Figure 1). These results indicate that both cation and
anion of the IL could chemically attract CO2 to form car-
bonic acid and/or carbamate, which are responsible for the
high CO2 absorption capacity of the resultant Ch-ILs. From
the NMR analysis, it seems that [Ch][Im] has three interac-
tion sites to bind with CO2, which implies that the theoretic
3.2 N-formylation of amines with CO2/H2
The resultant Ch-ILs could chemically absorb CO2 with high
capacity, and they are thus expected to be capable of cata-
lyzing the further conversion of CO2. In this work, these Ch-
ILs were applied in the N-formylation of amines with CO2
and H2, which is a green route to produce formamides. It was
indicated that these Ch-ILs could not individually catalyze
the N-fomylation of morpholine with CO2/H2, and CuCl only
showed low catalytic activity (Table 2, entries 1 and 2). In-
terestingly, the combination of Ch-IL with CuCl showed
high performance for catalyzing this reaction, as shown in
Table 2. Especially, [Ch][Im] in combination with CuCl
displayed the best performance compared to other Ch-ILs
under the similar conditions, affording a product yield of
>99.9%. These results indicate that Ch-ILs and CuCl coop-
erated and realized the formylation of amine with CO2/H2.
As described above, the Ch-ILs could chemically absorb
CO2 to form carbamates or carbonic acid, which may reduce
Figure 2 FT-IR spectra of [Ch][Im] and that exposed to CO2 (color on-
line).
Figure 1 13C NMR spectra of [Ch][Im] and that exposed to CO2.

5
Li et al. Sci China Chem
a)
Table 2 Reaction conditions optimization
b)
Yield
(%)
Tempera- Conversion
Entry
Ch-IL
CuCl (mg)
ture (°C)
(%)
1
2
[Ch][Im]
−
−
120
120
120
120
120
120
120
120
120
120
90
0
0
50
50
50
50
50
50
50
25
10
50
50
50
13.2
>99.9
>99.0
>99.0
90.8
58.2
32.4
87.2
67.9
58.0
67.9
82.5
11.9
>99.9
>99.0
>99.0
3
[Ch][Im]
4
[Ch][2-MIm]
[Ch][4-MIm]
[Ch][2,4-DMI]
[Ch][PhO]
[Ch][2-OP]
[Ch][Im]
5
6
90.2
57.7
31.6
85.8
66.3
56.3
64.1
82.3
Figure 3 Dependences of N-formylmorpholine yield on reaction time.
7
a)
Table 3 Results of N-formylation of amines
8
b)
9
Entry
1
Substrate
Product
Yield (%)
10
11
12
13
[Ch][Im]
99.9
96.5
[Ch][Im]
2
3
4
[Ch][Im]
100
110
[Ch][Im]
99.9
95.6
a) Reaction conditions: morpholine, 1.0 mmol; Ch-IL, 0.5 mmol; P(CO2)
=3 MPa, total pressure of 8 MPa after charging H2, 24 h. b) Determined by
GC analysis.
5
6
97.4
77.8
the activation energy of CO2, facilitating its further conver-
sion. Though the ILs [Ch][2-OP] and [Ch][PhO] had higher
CO2 capture capacities than [Ch][Im], they displayed lower
activity in the N-formylation reaction (Table 2, entries 3, 7
and 8), suggesting that the anion considerably affected the
catalytic activity of the CuCl-IL system. The good co-
ordination ability of imidazolate with CuCl may be re-
sponsible for its high activity [41]. Moreover, it was also
observed that the ILs with substituted imidazolate anions
exhibited similar activities to the IL with imidazolate anion
(Table 1, entries 3–6), suggesting the cooperation effect from
imidazolate anions and CuCl played the key role in cata-
lyzing the reaction.
In order to get the optimal reaction conditions, the influ-
ences of temperature, CuCl amount and reaction time on the
N-formylation of morpholine with CO2/H2 were in-
vestigated, and the results are displayed in Table 3 and Figure
3. Obviously, the N-formylmorpholine yield increased with
temperature in the range of 90–120 °C, reaching >99.9% at
120 °C. The amount of CuCl significantly influenced the
product yield, which increased with the CuCl amounts,
achieving a yield of >99.9% with 50 mg of CuCl. As for the
influence of reaction time, the N-formylmorpholine yield
rapidly increased to ~60% within initial 5 h, and gradually
increased to >99.9% as the time was prolonged to 24 h.
From the above experiments, the optimized conditions
were obtained as listed in the footnote of Table 3, and the
amine scope was explored, with results summarized in Table
7
8
90.3
91.2
9
31.2
a) Reaction conditions: amine, 1.0 mmol; IL, 0.5 mmol; CuCl,
50 mg; P(CO2)=3 MPa; P(H2)=5 MPa; 120 °C, 24 h. b) Yield determined
by H NMR.
1
3. All the tested cyclic secondary amines could react with
CO2/H2 well, producing the desired products in excellent
yields in most cases (Table 3, entries 1–7). Moreover, sec-
ondary amine, di-n-propylamine, also achieved excellent
product yield, while N-methylaniline exhibited poor re-
activity, affording product in a low yield (entries 8 and 9).
To test the reusability of the CuCl-[Ch][Im] catalytic
system for the formylation of morpholine with CO2/H2 under
the optimized conditions, the product was separated from the
reaction solution by extraction with ethyl acetate for three
times, and the left CuCl-[Ch][[Im] was reused for the next
run. After the CuCl-[Ch][[Im] catalytic system was reused
for five times, the product yield still remained a high value

6
Li et al. Sci China Chem
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4 Conclusions
In conclusion, Ch-ILs with anions that can attract CO2 che-
mically have been designed, which showed CO2 absorption
capacity >1.0 mol/mol. Moreover, these Ch-ILs combined
with CuCl showed high performance for catalyzing reductive
formylation of amines with CO2/H2 at 120 °C. Especially, the
[Ch][Im]-CuCl system displayed the best performance,
producing a series of formamides in excellent yields. This
work provides a simple and IL-based catalytic system with
high efficiency for reductive N-formylation of amines with
CO2/H2, which may have a great potential in application.
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Acknowledgements This work was supported by the Chinese Academy of
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