Highly efficient synthesis of alkylidene cyclic carbonates from low concentration CO2using hydroxyl and azolate dual functionalized ionic liquids

Article abstract of DOI:10.1039/d0gc03510f

A highly efficient catalytic system was developed for the reaction between CO2 and propargylic alcohols for alkylidene cyclic carbonates. Ionic liquids (ILs) with different anions and cations were designed as cocatalysts, in order to find out the effect of the cation and the anion on this reaction. The results indicated that the effect of the cation was significant, especially the hydroxyl group on the cation played an important role due to the presence of a hydrogen bond. It was also found that the basicity of the anion was important for its catalytic activity, where the anion with moderate basicity gave the best activity. Moreover, this hydroxyl and azolate dual functionalized catalytic system showed excellent reusability and generality. It is worth mentioning that at a low concentration of CO2, this dual functionalized catalytic system showed excellent catalytic activity even in a gram-scale reaction, indicating its potential in carbon capture and utilization processes.

Full text of DOI:10.1039/d0gc03510f

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DOI: 10.1039/D0GC03510F
ARTICLE
Highly Efficient Synthesis of Alkylidene Cyclic Carbonates from
Low Concentration CO using Hydroxyl and Azolate Dual
Functionalized Ionic Liquids
2
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
*,a
DOI: 10.1039/x0xx00000x
Guiling Shi, Ran Zhai, Haoran Li, and Congmin Wang
2
A highly efficient catalytic system was developed for the reaction between CO and progargylic acohols for alkylidene cyclic
carbonates. Ionic liquids (ILs) with different anions and cations were designed as cocatalysts, in order to find out the effect
of the cation and the anion on this reaction. The results indicated that the effect of the cation was significant, especially,
hydroxyl group on the cation played an important role due to the presence of hydrogen bond. It was also found that the
basicity of anion was important to its catalytic activity, where the anion with moderate basicity gave the best activity.
Moreover, this hydroxyl and azolate dual functionalized catalystic system showed excellent reusability and generality. It
2
was worth mentioning that under low concentration of CO , this dual functionalized catalytic system showed excellent
catalytic activity even on a gram-scale reaction, which indicating the potential in carbon capture and utilization process.
Recently, carbonates have drawn much attention because of
their potential bioactivities and widespread applications in Li ion
Introduction
3
9-40
batteries and pharmaceutical industry.
of green and sustainable chemistry, the carboxylative cyclization of
propargylic alcohols and CO is a promising route to reach α-
Based on the principles
CO
past decades, because CO
environmentally friendly C1 synthon, which was widely used for the
2
capture and utilization (CCU) has evoked great interest in the
2
can be regarded as an abundant, cheap,
2
4
1-42
alkylidene cyclic carbonates.
heterogeneous catalysts have been reported for this reaction,
most of them were suffered from harsh reaction conditions
including high CO pressure, excessive catalysts loading and poor
Up to now, although numerous
1
-6
synthesis of many fine chemicals. Unfortunately, because of its
inherent thermodynamic stability and kinetic inertness, CCU
processes usually require high energy input (including high
temperature, high pressure) and the addition of metal catalysts or
4
3-57
2
reusability of catalysts, which can be ascribed to the poor activity or
low stability of catalysts. How to realise this processes efficiently
7
,8
excessive strong base. In addition, compared with other CO
sources, fixation CO from flue gas, one of the major CO sources, is
still a severe challenge due to its low CO concentration ( ~10 vol.%
2
2
2
under low concentration of CO
researchers.
2
(such as 10%) is still a puzzle for
2
9
-11
).
Thus, effective catalysts are still urgently desired for CO
2
upgrading under low concentration.
Herein, we developed a highly efficient catalytic system used for
the reaction between CO and progargylic acohols. ILs with different
anions and cations were used as cocatalysts (Figure 1), in order to
2
Ionic liquid (IL) is a promising and eco-friendly candidate as CO
2
absorbent, because of their unique properties, such as high thermal
stability, negligible vapor pressure, and tunable structures. By finely
tuning of ILs structures and properties, significant achievements
1
2-25
could be achieved in designing ILs with impressive CO
At the same time, thanks to their tunable structures and superior
CO absorption ability, ILs have the ability to realize CCU processes
even under mild conditions.
2
capacity.
2
2
6-33
There have been many systematical
reports focusing on the influence of anions in ILs, where the anion
played a key role on CCU processes due to its dual roles as
3
4-38
absorbent and catalyst.
However, few work could be realized
the important role of the cation in CCU processes such as the
synthesis of alkylidene cyclic carbonates.
a. Department of Chemistry, State Key Laboratory of Chemical Engineering, Zhejiang
University, Hangzhou 310027, China.
Electronic Supplementary Information (ESI) available: NMR, Table S1, Table S2. See
DOI:10.1039/b000000x/
Figure 1. Structures of the cation and anion of the IL used in this
work
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find out the effect of ILs on this reaction. The results indicated that
The effect of the cation on catalytic activity wasVieinwvAertsictliegOatnelinde,
both the cation and anion played a key role. Therefore, dual which was seen in Table 1. At first, the reactDioOnI:c1o0u.1l0d3n9o/Dt0tGakCe03p5la10ceF
functionalized IL with hydroxyl and azolate group [Ch][Triz] was with no IL as cocatalyst (entry 1). When a protic IL ([DBU][Tri]) was
designed, which exhibited excellent activity and good reversibility in used as the cocatalyst, the reaction did not occur. It was clear that
this reaction. It was worth mentioning that under 10% of CO
2
, the the type of IL made a big difference. Then, a series of aprotic ILs
catalytic system (AgNO /[Ch][Tri]) showed excellent catalytic with different kinds of cation were designed and prepared for the
3
activity even on a gram-scale reaction.
reaction. It was illustrated that the chain length of the cation
affected its catalyst activity significantly. When aprotic ILs,
[N1111][Tri], [N2222][Tri] and[N4444][Tri],were used as the cocatalyst,
the yields of 81%, 69% and 67% were obtained (Table 1, entry 3-5),
respectively. In other word, the cation with shorter chain length
gave higher yield of 2a in this reaction. We could come to a similar
conclusion by comparing entry 5 and entry 6. Besides, [N4444][Tri]
and [P4444][Tri] resulted in comparable yields of 67% and 64% (Table
Experimental
Materials and methods
All chemicals used in this work were purchased from commercial
and used without further purification unless otherwise stated.3-
Methyl-1-pentyn-3-ol, 2-Phenyl-3-butyn-2-ol and 1-Ethynyl-
cyclopentanol were purchased from J&K Scientific Ltd. 2-Methyl-3-
butyn-2-ol were purchased from Aladdin Ind. Co., Ltd. 1H-Tetrazole
1
, entry 4 and 5), which indicated that the impact of central atom of
the cation was weak.
(
(
(
Tetz), 1H-Benzotriazole (Bentri), 1,2,4-Triazole (Triz), Benzimidazole
BenIm), Tetrabutylammonium hydroxide ([N4444][OH]), Imidazole
Considering that hydrogen bond played an important role in
([N2222][OH]), some CCU processes, a hydroxyl functionalized aprotic IL [Ch][Tri]
Im),
Tetraethylammonium
hydroxide
Tetramethylammonium hydroxide ([N1111][OH]), choline (Ch) and 1- was designed, prepared, and used in this reaction. To be excited,
Ethynyl-1-cyclohexanolwere purchased from Energy-Chemistry Co., the conversion and yield could be improved to 99% and 93% (Table
2 2 2
Ltd. CO (99.99%), CO (10%) and N (99.99%) were purchased from 1, entry 8), respectively. These results indicated that hydroxyl group
1
13
Hangzhou Jingong Special Gas Co., Ltd. H NMR and C NMR of the cation could promote this reaction well. As a controlled
spectra were recorded on a Bruker spectrometer (400 MHz) in experiment, no reaction was proceeded without AgNO (Table 1,
3
6
3
DMSO-d , which was obtained from Adamas-beta, with DMSO as entry 9). Clearly, both of AgNO and base (also called co-catalyst)
the standard.
were indispensable for this reaction.
The synthesis of functionalized ILs
To investigate the influence of the basicity of the anion, the
reaction was carried out using the ILs with various basic anions, and
the results were listed in Table 2. When [Ch][Cl] was used, only a 4%
yield of the product was obtained, which implied that the basicity
was also significant for this reaction. By tuning the basicity of the
anion, it was obvious that this reaction was affected by the strength
of the base, where higher conversion was achieved when stronger
basic IL was used. As for the anion with weak basicity, like [Tetz]
and [BenTri], the reaction was not complete within 24 hours,
implying for poor catalytic activity (entry 2, 3). To our delight, [Tri],
These functionalized ILs were easily prepared by the neutralization
of superbases or the solution of [N1111]OH , [N2222]OH , [N4444]OH,
[
P4444]OH or choline with azole compound. In a typical example, the
o
reaction mixture was stirred at 50 C for 6 h and then applying the
evacuum-rotary evaporation procedure to remove most of water.
After that, ILs were dried under vacuum at 80 C for more than 24
hours to reduce possible traces of water. Before use, the water
content of ILs was determined with a Karl Fisher titration and found
to be less than 0.1 wt%.
o
a
whose pK was 18.6, could improve the conversion and yield to 99%
General procedure for the synthesis of alkylidene carbonates
Table 1. The effect of the cation on catalytic activity[a]
As a typical example, the procedure using 2-Methyl-3-butyn-2-ol
(1a) as a typical substrate was described. AgNO
3
(0.066 g, 0.4
mmol), [Ch][Triz] (0.138 g, 0.8 mmol), and 1a (0.336 g, 8 mmol) was
added into a Schlenk flask, connecting with a CO
CO
2
balloon filled with
(99.99%). Then the reaction mixture was stirred at 30 C for 24
o
2
h. The conversion and yield of product 1b were quantitatively
analyzed by gas chromatography (GC) with biphenyl as the internal
standard. When the reusability of the catalyst system was
investigated, the reaction mixture was extracted with n-hexane (4 ×
Entry
Ionic liquid Conversion [%][b] Yield [%][b]
1
2
3
4
5
6
7
8
-
-
<1
<1
81
69
67
64
59
59
<1
[DBU][Tri]
[N1111][Tri]
[N2222][ Tri]
[N4444][Tri]
[P4444] [Tri]
[P66614][Tri]
[P66614][Tri]
[Ch][Tri]
4
1
5 mL). The upper layer was collected and removed the solvent to
90
82
77
75
70
70
<1
obtain the product, and the lower layer, composed of AgNO
3
and
o
[
Ch][Triz], can be dried in the vacuum at 60 C for next cycle.
Results and discussion
At first, various catalysts were applied to the reaction, the results
were listed in Table S1. It was seen that the effect of different metal
9[
c]
catalysts on this reaction was obvious, where AgNO
3
and AgOAc [a] Reaction conditions: 1a (4 mmol), AgNO
3
(0.4 mmol),
o
catalyst displayed better catalytic reactivity. Considering the base (0.8 mmol) and CO
2
(1 bar) for 24 h at 30 C. [b]
basicity of AgOAc may affect the catalytic reactivity of ILs, we chose Determined by GC using internal standard method. [c]
Without AgNO
3
AgNO for further research.
3
2
| J. Name., 2012, 00, 1-3
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Table 2. The effect of different basic anion on catalytic
View Article Online
DOI: 10.1039/D0GC03510F
activity[a]
pK
anions[
1.8
a
of
Conversion
Entry Ionic liquid
Yield[%][c]
b]
[c]
[%]
1
2
3
4
5
6
[Ch][Cl]
[Ch][Tetz]
[Ch][BenTri]
[Ch][Tri]
15
23
67
99
97
99
4
8.2
17
11.9
13.9
18.2
18.9
64
93
67
3
Figure 3. Recycling experiments using AgNO as the catalyst
[Ch][BenIm]
[Ch][Im]
and [Ch][Triz] as the cocatalyst.
64
Table 3. The synthesis of alkylidene carbonates from CO
2
[
a] Reaction conditions: 1a (4 mmol), AgNO
3
o
(0.4 mmol),
using [Ch][Tri].[
a]
2
base (0.8 mmol) and CO (1 bar) for 24 h at 30 C. [b] Values
in DMSO. [c] Determined by GC using internal standard
method.
and 93% (entry 4), respectively. However, strongly basic ILs,
[
Ch][BenIm] and [Ch][Im], resulted in much lower yields of
product than [Ch][Tri], due to the decreased selectivity (entry
,6). Therefore, dual functionalized IL with hydroxyl group and
moderately basicity [Ch][Tri] exhibited the best catalytic
activity. Besides, compared with other AgNO -based systems,
AgNO /[Ch][Tri] exhibited excellent performance for CO2
Yield
[
Entry substrate
R
1
R
2
T [h]
%][b]
5
1
2
3
4
5
6
7
1a
1a[c]
1a[d]
Me
Me
Me
Me
Me
Me
Me
Me
Et
24
48
48
24
36
36
30
93
85
87
92
3
3
utilization (Table S4).
1b
1c
1d
1f
2 2
Compared with other CO sources, capturing CO from flue
95 (87)[c]
Ph
gas was a severe challenge due to its low concentration (~10
vol.%). Therefore, to further evaluate its practicability, the
reaction was also carried out under low concentration CO
-
2
(CH )
5
-
92
89
2
of
-(CH ) -
2 4
1
0%. To our delight, after extending the reaction time to 48
[
3
a] Reaction conditions: substrate (4 mmol), AgNO (0.4
hours, this catalytic system composed of AgNO
gave 2a in a yield of 90% after bubbling CO
3
and [Ch][Tri]
o
mmol), [Ch][Tri] (0.8mmol) and CO
Determined by NMR using internal standard method. [c]
0 vol.% of CO . [d]15 vol.% of CO . [e] Isolated yield.
2
(1 bar) at 30 C. [b]
2
at 0.1 bar under
o
3
0 C, even at a gram-scale (Figure 2).
The reusability of the catalystic system was a critical
property for CO utilization, which had a direct impact on the
1
2
2
2
obtained. With an ethyl group, 2b was given in a yield of 92% (entry
). By extending the reaction time, substrate with a large
cost because it determined the frequency of the replacement
of catalyst. Therefore, we investigated the recycling
performance of AgNO and [Ch][Tri] catalytic system under the
3
optimized reaction conditions. The results for 8 cycles were
shown in Figure 3. It was found that good catalytic activity was
well-maintained during the 8 cycles.
4
substituent group could also convert totally. The reactivity of
phenyl substituted propargylic alcohol was investigated, and a 95%
yield of 2c was provided (entry 5). In addition, the reaction of 1d
and 1f was found to occur smoothly with yields of 92% and 89%,
respectively, which means this dual functionalized IL also has a good
The substrate scope and generality of this reaction were
investigated by using this dual functionalized catalytic system. catalytic activity on propargylic alcohol with a cycloalkane group.
As illustrated in Table 3, all of these substrates could react
On the basis of experimental results and previous literature
with CO
were
2
under mild conditions, and good to excellent yields
reports, we proposed a plausible mechanism for this reaction
Figure 4). Firstly, the carbon-carbon triple bond on the substrate 1a
could be activated by silver ions (AgNO ). Meanwhile, [Tri] had a
(
3
sufficiently basicity to extract the proton from hydroxyl group on 1a
to form intermediate I, and the hydroxyl group on [Ch] could
stabilize the intermediate I through intermolecular hydrogen
bonding. Subsequently, intermediate II was obtained by
Figure 2. A gram-scale reaction under low concentration of intermediate I nucleophilic attacked CO , which was captured by
2
2 3
CO using AgNO as the catalyst and [Ch][Triz] as the cocatalyst.
[
Tri]. Finally, 2a was generated through an intramolecular ring-
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J. Name., 2013, 00, 1-3 | 3
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closing reaction in II, and silver ions and [Ch][Tri] were regenerated.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We acknowledge the support of the National Natural Science
Foundation of China (21776239), the Zhejiang Provincial
Natural Science Foundation of China (LZ17B060001), and the
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