An Experimental and Theoretical Study on the Unexpected Catalytic Activity of Triethanolamine for the Carboxylative Cyclization of Propargylic Amines with CO2

Article abstract of DOI:10.1002/cssc.201700241

Chemical conversion of CO₂ under atmospheric pressure and metal-free conditions remains a great challenge. In this work, a series of alkanolamines, low-cost and biodegradable bases, were used to catalyze the carboxylative cyclization of proparg

Full text of DOI:10.1002/cssc.201700241

Accepted Article
Title: An Experimental and Theoretical Study on the Unexpected
Catalytic Activity of Triethanolamine for the Carboxylative
Cyclization of Propargylic Amines with CO2
Authors: Yuling Zhao, Jikuan Qiu, Zhiyong Li, Huiyong Wang,
Maohong Fan, and Jian Ji Wang
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An Experimental and Theoretical Study on the Unexpected
Catalytic Activity of Triethanolamine for the Carboxylative
Cyclization of Propargylic Amines with CO2
Yuling Zhao, [a] Jikuan Qiu, [a] Zhiyong Li, [a] Huiyong Wang, [a] Maohong Fan [b] and Jianji Wang*[a]
Abstract: The chemical conversion of CO2 under atmospheric
pressure and metal-free conditions remains a great challenge. In this
work, a series of alkylolamines, low-cost and biodegradable bases,
were used to catalyze the carboxylative cyclization of propargylic
amines with CO2. It was found that among these alkylolamines,
environment problems has gained more and more attentions
these days.
2-Oxazolidinones are important heterocyclic compounds
12]
used as building blocks for different synthetic purposes[11,
.
Synthesis of 2-oxazolidinones from cycloaddition of propargylic
amines with CO2 has attracted extensive attention in recent
years. Many investigations have been conducted for this
triethanolamine (TEOA) was shown to be
a highly efficient
organocatalyst for this important transformation at atmospheric
pressure, and a series of desired products were synthesized in good
to excellent yields. After the reactions, TEOA could be easily
recoveried and reused without obvious reduction in the efficiency.
Density functional theory studies reveal that TEOA may activate CO2
to form a ring-shaped carbonate intermediate which plays an
important role in the catalysis of the reaction. This finding provides
an effective and environmentally friendly alternative route for the
production of 2-oxazolidinones.
reaction in the presence of metal catalysts, such as Cu[13-15]
,
Pa[16, 17], Ag[18-23], Ru[24] and Au[25-27]. It is demonstrated that
those transition metals are good activator for the C≡C triple
bond, thus catalyzing the chemical transformation of substrates
with CO2. Although CO2 can be efficiently transformed using
these catalytic systems, the metal catalysts used in the reactions
are both expensive and toxic. Metal-free catalytic process can
reduce the cost and avoid the pollution caused by metals, and is
thus regarded as greener process.
In the past decades, a number of metal-free catalysts, such
as superbase[28,29], N-heterocyclic carbene[30] and ionic liquids[13,
31] had been reported to catalyze the carboxylative cyclization of
propargylic amines with CO2. The most exciting implication is
that these catalysts also shown high activity in comparison with
the transition-metal catalysts under comparable reaction
conditions. Nevertheless, these reaction systems still have
disadvantages such as the use of high pressure and tedious
process for the preparation of catalysts. Therefore, development
of new organocatalytic systems that can operate under the
conditions of low pressure, room temperature and low cost is an
urgent task.
Introduction
With increasing awareness of growing carbon dioxide (CO2)
levels in the atmosphere, great efforts have been made to
develop new strategies and technologies towards the reduction
of carbon emissions[1-3]. In fact, CO2 is usually considered as a
ubiquitous, non-toxic, and renewable carbon resource, and can
replace commonly used toxic C1 building blocks[4]. Thus, fixation
and conversion of CO2 hold great promise for the recycling of
CO2 into value-added products. At present, many useful organic
chemicals which are currently derived from fossil fuel-based
resources have been produced by using CO2 as a feed stock,
such as alcohols[5], cyclic carbonates[6,7], formamide[8] and
carboxylic acid derivatives[9,10]. However, only a small proportion
of the total abundance of CO2 is currently being consumed in
industry because to establish ecological and economical CO2
conversion processes is still a great challenge. Thus the
development of efficient green process to solve energy and
As a class of low-cost and biodegradable base, alkanolamines
have been used in a wide variety of industrially important
processes such as natural gas stripping, adhesives, acid
neutralization, paint stripping, surfactants and derivatives in drug
formulations[32-34]
.
It is known that as early as 1931,
alkanolamines had been utilized to capture carbon dioxide from
natural gas[35]
This gives us an inspiration: maybe
.
alkanolamines can strongly activate CO2 in CO2 conversion
process. At present, it is widely recognized that only superbase
and its derivatives can serve as single catalyst or can coordinate
with metal catalysts to catalyze the transformation of CO2 and
[a]
Dr. Y. Zhao, J. Qiu, Z. Li, Dr. H. Wang, Prof. J. Wang
Collaborative Innovation Center of Henan Province for Green
Manufacturing of Fine Chemicals, School of Chemistry and
Chemical Engineering, Key Laboratory of Green Chemical Media
and Reactions, Ministry of Education
Henan Normal University
Xinxiang, Henan 453007, P. R. China.
E-mail: jwang@htu.cn
Prof. M. Fan
Department of Chemical and Petroleum Engineering,
University of Wyoming,
Laramie, WY 82071, USA.
Supporting information for this article is given via a link at the end
of the document.
29,
propargylic amines[28,
31]. Is it possible for us to move
sideways and develop a new type of mild base catalyst for
efficient synthesis of 2-oxazolidinones?
Herein, we used a series of alkylolamines to catalyze this
important transformation reaction (Scheme 1). It was found that
several alkylolamines could be used as catalyst for the reactions
under solvent-free and atmospheric pressure conditions.
Unexpectedly, triethanolamine (TEOA) was shown to be a highly
efficient catalyst at ambient pressure, and a series of desired
products were synthesized in good to excellent yields. Moreover,
the catalyst could be easily recovered from the reaction system
[b]
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10.1002/cssc.201700241
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and then reused without obvious activity loss. A possible
reaction mechanism was proposed through a detailed density
functional theory (DFT) study.
typical experiment, the catalyst was reused four times in the
reaction between 1a and CO2, and the catalytic activity of the
catalyst remained unchanged. This indicates that the used
catalyst was recyclable for catalyzing the reaction of CO2 with
propargylic amine.
O
C
R4
TEOA, 1atm, solvent-free
O
N
HN R4
R3
R1
R3
CO2
+
H
R2
R1
R2
N
H2N
HO
HO
OH
OH
OH
DEA
OH
MEA
N
+ Atmospheric pressure
+ Metal-free and solvent-free condition
+ Friendly to environment
N
HO
OH
+ Commercially available, very cheap and recyclable catalyst
MDEA
TEOA
OH
Scheme 1. Carboxylative cyclization of propargylic amines with CO2 catalyzed
by TEOA.
HO
N
OH
Results and Discussion
TIPA
Figure 1. The structures of the substituted MEA alkylolamine derivatives
Screening of the catalyst
Since alcohol amines are cheap, commercially available
and recyclable compounds and their basicity can be tuned
conveniently by changing their chemical structure, a series of
such compounds (Figure 1) were used as homogeneous
catalysts in this work. First, the catalytic activity of these typical
bases for the reaction between N-butyl-1-phenylhex-1-yn-3-
amine (1a) and atmospheric CO2 was investigated at 90℃ for 10
h, and the results were listed in Table 1. It can be seen that in
the absence of a base, the reaction did not occur (Table 1, entry
1). Then different types of alkylolamines were tried for the
reaction. To our delight, high yield and good selectivity were
obtained for the desired product through tuning the basicity of
the alkylolamines. It was shown that the basicity decreased in
the sequence: MEA>DEA>MDEA>TIPA>TEOA, which is
consistent with the order of the catalytic activity of these bases
for the reaction (entries 2-6). Surprisingly, among these
screened bases, the polyhydric substituted alcohol amines were
found to be excellent catalysts and 97% yield (entry 6) was
obtained for the desired product by using TEOA. This
observation can possibly be rationalized by assuming that stable
carbamates were more prone to be formed from the reactions of
primary and secondary amines with CO2, which decreased the
base-catalytic ability. As a result of the steric hindrance imposed
by the substituent, TEOA exhibited better catalytic activity for the
reaction than TIPA. Additionally, traditional inorganic bases
NaOH and Cs2CO3 were also used to catalyze this reaction
(Table 1, entries 7 and 8). However, the yield was quite low and
it is very difficult to recover these bases after the reaction.
Based on the above results, TEOA was selected as the
catalyst for the reaction under atmospheric pressure of CO2 to
study the effects of reaction temperature, reaction time and
catalyst dosage on the yields (see ESI, Figures S1-S3). It was
shown that under the optimized conditions (90oC, 10h and 0.1
mmol of TEOA), the yield of the desired product could reach
97%. The recyclability of the catalyst TEOA was also
investigated, and the results were shown in Figure S4. In a
a
Table 1. Carboxylic cyclization of propargylic amines with CO2
O
HN
Catalyst
O
N
+
CO2
0.1 MPa, 90 oC, 10 h
Ph
2a
1a
Entry
Catalyst
---
pKa
---
Yield(%)b
1c
2
3
4
5
6
7
8
0
MEA
9.45
8.88
8.56
7.82
7.74
15.74
---
42
49
54
87
97
<1
<1
DEA
MDEA
TIPA
TEOA
NaOH
Cs2CO3
aReaction conditions: 1a (1.0 mmol), catalyst (0.1 mmol), CO2 (0.1 MPa),
90oC, 10 h. bThe yield was determined by 1H NMR spectroscopy using
anisole as an internal standard. cWithout catalyst
Versatility of the catalyst
With the optimized conditions established, we further
investigated the reaction scope using a variety of propargylic
amines as the substrates, and the results were given in Table 2.
It can be seen that both terminal and internal propargylic amines
performed smoothly to give the corresponding 2-oxazolidinones
in moderate to excellent yields (entries 1-5, 7-9). However, the
reaction activity depended strongly on the substitute groups of
propargylic amines. When the R2 and R3 groups were combined
into a cyclopentane group, no product was obtained (entry 6),
probably due to the steric hindrance (1f). In addition, propargylic
amines with different R1 and R4 groups were also studied (1g-1i),
and good yields were obtained for the corresponding 2-
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10.1002/cssc.201700241
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oxazolidinones (2g-2i). These results confirmed the versatility of
the new catalyst for the production of 2-oxazolidinones.
O
O
N
8
89c
HN
Table 2 Scope of the propargylic amine substrates for the reaction under
the optimized conditionsa
2h
O
O
R4
HN
R4
N
R2
1h
TEOA
O
R1
R2
R3
+
CO2
O
0.1 MPa, 90 oC, 10 h
R1
R3
9
71c
1
2
N
H
N
Yield(%)b
1i
Entry
Substrate
Product
O
2i
aReaction conditions: 1 (1.0 mmol), TEOA (0.1 mmol), CO2 (99.999%, 0.1
MPa), 10 h, 90˚C. bThe yield was determined by 1H NMR spectroscopy
using anisole as an internal standard. c1 MPa.
O
N
HN
1
97
2a
2b
Possible reaction mechanism
1a
To investigate the reaction mechanism catalyzed by TEOA
in detail, DFT calculations were performed. In the DFT
calculations, the simplest propargylic amine substrate 1c (see
Table 2) was used as the representative substrate molecule to
reduce the computing complexity. Before the computation
begins, we were interested in thought about the mechanistic
pathway of the reaction. Since the reaction of propargylic amine
substrates and CO2 did not occur in the absence of TEOA
catalyst, it is possible that both propargylic amines and CO2 may
be activated by TEOA. For propargylic amines, their amino
group is prone to be activated by TEOA base, and CO2 can also
be activated by TEOA to form zwitterionic ammonium carbonate
adduct[36-38]. Therefore, the mechanisms for amino-activated and
CO2-activated reaction pathways were investigated by DFT
calculations, respectively.
O
O
N
HN
2
99
1b
O
O
N
HN
3
4
5
99
80
74c
2c
1c
O
O
N
HN
O
OH
R4
R4
N
HN
R3
R2
O
H
R3
R1
2d
N
R1
R2
1d
1e
1f
1
4
OH
HO
O
HO
O
N
R4
HN
R4
R3
N
H
N
HO
O
N
OH
R1
R3
R2
R2
O
HO
2
2e
N
OH
H
R1
CO2
HO
TS3-4
O
HO
HO
O
N
O
N
HN
O
R4
6
0
OH
R4
H
N
N
H
OH
R1
R3
R2
HO
O
N
2f
HO
O
TS2-3
R1
R3
R2
O
3
O
N
Scheme 2. The amino-activated mechanism for the carboxylative cyclization
reactions of propargylic amines with CO2 catalyzed by TEOA.
HN
7
86c
2g
1g
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were regenerated in the followed intramolecular cyclization step
(via transition state TS3–4). It is clear from Figure 3 that the
intramolecular cyclization step was still the rate-determining step
which is the same as the amino-activated mechanism. In
addition, a Noesy experiment was performed in order to
examine the configuration of the product. As shown in the partial
assignment of the 1H NMR spectrum of the compound 2e
(Figure S5), the signal assigned to 1 only showed obvious
correlation with the signal of 2 in Noesy NMR spectrum, which
provided the evidence for the Z-isomer structure of the product.
This experimental result was in good agreement with our
calculation result.
Figure 2. Free energy profiles of the amino-activated pathway for the
carboxylative cyclization of propargylic amines with CO2 catalyzed by TEOA.
O
OH
R4
N
O
H
R3
N
R1
R2
CO2
The amino-activated mechanism and its free energy profiles
were illustrated in Scheme 2 and Figure 2, respectively. The
details for the optimized geometries of the transition states were
shown in supporting information. As a result of the amino group
being activated by TEOA, the electrophilic attack of CO2 on N
atom of the amino group was more favorable. In this case, a
lower free energy barrier of 36.0 kcal/mol was observed (via
transition state TS2–3). After this step, the zwitterionic
carbamate species was formed (Scheme 2, structure 3). In the
following intramolecular cyclization step, the attack of the O
atom and the proton transfer to the C≡C bond took place
simultaneously. The proton was transferred from the positively
charged N atom of TEOA to the C≡C bond with an energy
barrier of 57.6 kcal/mol (via transition state TS3–4).Then the
target Z-isomer product and TEOA were regenerated. In this
step, TEOA promoted the attack of O atom on the C atom of the
C≡C bond and made the proton transfer easier. It was also
found from Figure 2 that the intramolecular cyclization step was
the rate-determining step, and the overall energy barrier was
57.6 kcal/mol for the amino-activated mechanism.
OH
HO
4
OH
O
C
N
H
O
R4
R3
R2
O
HO
N
O
N
HO
O
5
R4
OH
H
HN
R3
R2
R1
R1
HO
TS3-4
OH
O
H
HO
N
O
C
HO
O
OH
R4
N
R4
H
N
HO
H
O
N
R1
R3
R2
O
R1
R3
R2
TS5-3
3
Scheme 3. The CO2-activated mechanism for the carboxylative cyclization
reactions of propargylic amines with CO2 catalyzed by TEOA.
Next, the CO2-activated mechanism and free energy profiles
were illustrated in Scheme 3 and Figure 3, respectively. It can
be seen that at the beginning, TEOA could capture CO2 and
then made CO2 active. Unlike primary and secondary amines,
tertiary amines did not form ammonium carbamates. The ring-
shaped zwitterionic ammonium carbonate intermediate (Scheme
3, structure 5) was only formed when CO2 was absorbed by
TEOA, and the three dimensional structures were shown in
Figure 4. Clearly, CO2 molecule was inserted in hydroxyl group
of TEOA to form carbonate intermediate, while the hydroxyl
hydrogen had a hydrogen bond interaction with N atom to make
its charge more positive. As the ammonium carbonate
intermediate was very unstable and the C atom of carbonate
was more positively charged, the attack of N atom of propargylic
amine on C atom of carbonate would be more favorable. In the
subsequent attack of N atom of propargylic amine on C atom of
carbonate, the H atom connected to N atom of propargylic
amine transferred to the hydroxyl oxygen atom of TEOA
synchronously. This corresponds to the transition state of TS5–3,
and the energy barrier of this step was 27.3 kcal/mol. After this
step, CO2 was moved from carbonate intermediate to
propargylic amine, and then the Z-isomer product and TEOA
Figure 3. Free energy profiles of the CO2-activated pathway for the
carboxylative cyclization of propargylic amines with CO2 catalyzed by TEOA.
Figure 4. Optimized geometry for the zwitterionic ammonium carbonate
adduct composed by CO2 and TEOA.
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By comparing the energy barrier of the both mechanisms, it
can be concluded that the CO2-activated mechanism had a
lower energy barrier in the first step, and thus was more
favorable than the amino-activated mechanism. This suggests
that the formation of ring-shaped carbonate intermediate could
decrease the activation energy for the formation of intermediate
3 , so that the reaction can proceed more easily. This made the
point that the formation of ring-shaped carbonate intermediate
might play an important role in the catalysis of the reaction. As
we known, primary and secondary amines can form ammonium
carbamates with CO2, which are more stable than carbonate.
This will potentially decrease the attack ability of N atom of
propargylic amine on carbamates and have a negative effect on
the reaction. Therefore, the catalytic activity of MEA and DEA for
this carboxylative cyclization reaction is lower than that of
tertiary amines, as shown in Table 1. When the TEOAs have
more hydroxyl groups and smaller steric hindrance, the best
catalytic activity has been found for the reaction among these
tertiary amines (Table 1).
oxazolidinone. The catalyst was recovered by drying under vacuum and
reused in the next run.
Characterization of the products
1H and 13C NMR analyses of the purified products were conducted in
CDCl3 on a Bruker Avance III HD 600 spectrometer (600 MHz for 1H
NMR and 150 MHz for 13C NMR), and the results are consistent with the
previous reported experimental results[15]
.
Compound 2a. Light yellow oil; 1H NMR (600 MHz, CDCl3): δ=7.581 (d,
J = 7.26 Hz, 2 H), 7.326 (t, J = 7.62 Hz, 2 H), 7.203 (t, J =7.44 Hz, 1 H),
5.465 (d, J = 1.74 Hz, 1 H), 4.524 (t, J = 1.8 Hz, 1 H), 3.633-3.582 (m, 1
H), 3.047-3.000 (m, 1 H), 1.886-1.826 (m, 1 H), 1.712−1.655 (m, 1 H),
1.622-1.520 (m, 2 H), 1.417-1.348 (m, 4 H), 0.958 (t, J = 7.32 Hz, 6 H)
ppm; 13C NMR (150 MHz, CDCl3): δ =155.17, 147.00, 133.62, 128.48,
128.28, 126.75, 102.32, 58.40, 41.13, 34.43, 29.26, 19.92, 15.84, 13.91,
13.68 ppm.
Compound 2b. Colorless oil; 1H NMR (600 MHz, CDCl3): δ=7.592 (d, J =
1.2 Hz, 1 H), 7.579 (s, 1 H), 7.341-7.315 (m, 2 H), 7.219-7.194 (m, 1 H),
5.462 (d, J = 1.74 Hz, 1 H), 4.559-4.543 (m, 1H), 3.641-3.590 (m, 1 H),
3.040-2.993 (m, 1 H), 1.962-1.913 (m, 1H), 1.771-1.729 (m, 1 H), 1.629-
1.529 (m, 3 H), 0.959 (t, J = 7.38Hz, 3 H), 0.902 (t, J = 7.32 Hz, 3 H) ppm;
13C NMR (150 MHz, CDCl3): δ= 155.29, 146.61, 133.62, 128.48, 128.28,
126.73, 102.35, 59.00, 41.06, 29.23, 24.90, 19.93, 13.68 ppm.
Compound 2c. Colorless oil; 1H NMR (400 MHz, CDCl3): δ=7.589 (d, J =
7.6 Hz, 2 H), 7.329 (t, J = 7.2 Hz, 2 H), 7.208 (t, J = 7.2Hz, 1 H), 5.476 (d,
J = 2.0 Hz, 1 H), 4.556-4.503 (m, 1 H), 3.583-3.507 (m, 1 H), 3.174-3.104
(m, 1 H), 1.645-1.512 (m, 2 H), 1.475 (d, J = 6.4 Hz, 3 H), 1.400-1.340 (m,
2 H), 0.960 (t, J = 7.2 Hz, 3 H), 0.902 (t, J = 7.32 Hz, 3 H) ppm; 13C NMR
(100 MHz, CDCl3): δ=154.80, 148.60,133.56, 128.49, 128.26, 126.80,
102.08, 54.65, 41.26, 29.36, 19.93, 19.74, 13.71 ppm.
Compound 2d. Colorless oil; 1H NMR (600 MHz, CDCl3): δ=7.591 (d, J =
7.56 Hz, 2 H), 7.328 (t, J = 7.44 Hz, 2 H), 7.210 (t, J =8.76 Hz, 1 H),
5.486 (s, 1 H), 4.306 (s, 1 H), 3.679-3.629 (m, 1 H), 3.075-3.030 (m, 1 H),
2.159-2.126 (m, 1 H), 1.631-1.538 (m, 2 H), 1.375-1.341 (m, 2 H), 1.099
(d, J = 6.96 Hz, 3 H), 0.955 (t, J = 7.26Hz, 3 H), 0.920 (d, J = 6.72 Hz, 3
H) ppm; 13C NMR (150 MHz, CDCl3): δ = 155.35, 145.02, 133.57, 128.47,
126.85, 104.20, 63.71, 41.37, 30.20, 29.18, 19.91, 17.52, 15.44, 13.68
ppm.
Compound 2e. Light yellow oil; 1H NMR (600 MHz, CDCl3): δ =7.594-
7.579 (m, 2 H), 7.335-7.309 (m, 2 H), 7.212-7.184 (m, 1 H), 5.452 (s, 1
H), 3.205 (t, J = 7.92 Hz, 2 H), 1.686-1.634 (m, 2 H), 1.493 (s, 6 H),
1.371-1.334 (m, 2 H), 0.958 (t, J = 7.38 Hz, 3 H)ppm; 13C NMR (150 MHz,
CDCl3): δ = 154.19, 153.51, 133.68, 128.46, 128.28, 126.71, 100.38,
62.17, 40.41, 31.52, 27.61, 20.24, 13.75 ppm.
Compound 2g. Colorless oil; 1H NMR (600 MHz, CDCl3): δ =7.480 (d, J
= 7.8 Hz, 2 H), 7.136 (d, J = 7.8 Hz, 2 H), 5.428 (d, J = 1.2 Hz, 1 H),
4.545-4.530 (m, 1 H), 3.635-3.585 (m, 1 H), 3.032-2.986 (m, 1 H), 2.334
(s, 3 H), 1.949-1.904 (m, 1 H), 1.754-1.712 (m, 1 H), 1.612-1.532 (m, 2
H), 1.398-1.347 (m, 2 H), 0.956 (t, J = 7.2 Hz, 3 H), 0.891 (t, J = 7.2 Hz, 3
H)ppm; 13C NMR (150 MHz, CDCl3): δ =155.44, 145.84, 136.56, 130.79,
129.18, 128.21, 102.29, 58.98, 41.05, 29.24, 24.92, 21.21, 19.94, 13.69,
6.49 ppm.
Compound 2h. Light yellow oil; 1H NMR (600 MHz, CDCl3): δ =7.589 (d,
J = 7.38 Hz, 2 H), 7.326 (t, J = 7.68 Hz, 2 H), 7.204 (t, J =14.82 Hz, 1 H),
5.466 (d, J = 1.68 Hz, 1 H), 4.531-4.516 (m, 1 H), 3.618-3.568 (m, 1 H),
3.042-2.996 (m, 1 H), 1.884-1.825 (m, 1 H), 1.712-1.655 (m, 1 H), 1.638-
1.588 (m, 1 H), 1.449-1.383 (m, 1 H), 1.349-1.310 (m, 7 H), 0.956 (t, J =
7.32 Hz, 3 H), 0.905-0.882 (m, 3H) ppm; 13C NMR (150 MHz, CDCl3): δ =
Conclusions
In summary, among the alkanolamines catalysts
investigated, TEOA was found to display the best catalytic
performance for the reactions of CO2 with propargylic amine,
and a series of desired products were synthesized in good to
excellent yields. Additionally, TEOA could be easily regenerated
and reused without obvious loss in its activity. The mechanistic
studies revealed that CO2 was activated by TEOA to form
unstable ring-shaped carbonate intermediate. This carbonate
intermediate could decrease the activation energy for the
formation of intermediate 3, so that the reaction can proceed
more easily. Considering the fact that TEOA is a cheap,
biodegradable, commercially available and recyclable catalyst,
we expect that more applications can be found for it in the
transformation of CO2 under mild conditions.
Experimental Section
Chemicals
CO2 was supplied by Beijing Analytical Instrument Factory with a purity of
99.999%. The deuterated solvents (DMSO-d6, CDCl3) were provided by
Cambridge Isotope Laboratories, Inc. All chemicals were of analytical
grade and used as received. The propargylic amine substrates were
synthesized by following the procedures described in literature[31]
.
General procedure for the synthesis of α-alkylidene cyclic
carbonates
In a 20 mL Schlenk flask, propargylic amine (1.0 mmol) and the indicated
amount of the catalyst were added. The air in the reactor was replaced
by bubbling of CO2. Then the reaction mixture was stirred at 90 °C for 12
h under the desired CO2 pressure. After the reaction was finished, the
product was extracted with n-hexane, leaving the catalyst alone in the
reactor. The crude mixture was purified by silica gel column
chromatography (EtOAc : petroleum ether = 1:20) to obtain the desired 2-
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Keywords: CO2 conversion • triethanolamine • propargylic
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Entry for the Table of Contents
FULL PAPER
O
Yuling Zhao, Jikuan Qiu , Zhiyong Li,
Huiyong Wang, Maohong Fan, Jianji
Wang*
C
R4
N
R3
TEOA, 1atm, solvent-free
O
HN R4
R3
R1
CO2
+
R2
R1
R2
+
+
+
+
Atmosphric pressure
Metal-free and solvent-free condition
Friendly to envirenment
Page No. – Page No.
An Experimental and Theoretical
Study on the Unexpected Catalytic
Activity of Triethanolamine for the
Carboxylative Cyclization of
Commercially available, very cheap and recyclable catalyst
Triethanolamine (TEOA), as a low-cost and biodegradable catalyst, could efficiently
promote the conversion of CO2 with propargylic amine at atmospheric pressure.
Propargylic Amines with CO2
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