AgX@carbon (X = Br and I) as robust and efficient catalysts for the reaction of propargylic alcohols and CO2 to carbonates under ambient conditions

Article abstract of DOI:10.1039/c6ra05224j

Development of new efficient catalytic systems for chemical transformation of CO₂ is a very attractive topic in green chemistry. In this work, we studied the synthesis of α-alkylidene cyclic carbonates through the coupling reaction between propargylic alcohols and CO₂ with new silver catalysts. It was found that activated carbon supported AgX (X = Br and I) was a simple and efficient catalyst for the carboxylative cyclization of propargyl alcohols with CO₂ at atmospheric pressure and room temperature. Nearly 99% yield of the desired product was obtained, and the product could be simply separated through solvent extraction. Moreover, the catalyst could be easily recovered and reused at least ten times without a decrease in the catalytic activity and selectivity. These findings are useful for the development of an environmentally friendly chemical process for the production of α-alkylidene cyclic carbonates.

Full text of DOI:10.1039/c6ra05224j

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AgX@carbon (X ¼ Br and I) as robust and efficient
catalysts for the reaction of propargylic alcohols
and CO2 to carbonates under ambient conditions†
Cite this: RSC Adv., 2016, 6, 54020
*
Jikuan Qiu, Yuling Zhao, Huiyong Wang, Guokai Cui and Jianji Wang
Development of new efficient catalytic systems for chemical transformation of CO2 is a very attractive topic
in green chemistry. In this work, we studied the synthesis of a-alkylidene cyclic carbonates through the
coupling reaction between propargylic alcohols and CO2 with new silver catalysts. It was found that
activated carbon supported AgX (X ¼ Br and I) was a simple and efficient catalyst for the carboxylative
cyclization of propargyl alcohols with CO2 at atmospheric pressure and room temperature. Nearly 99%
yield of the desired product was obtained, and the product could be simply separated through solvent
extraction. Moreover, the catalyst could be easily recovered and reused at least ten times without
a decrease in the catalytic activity and selectivity. These findings are useful for the development of an
environmentally friendly chemical process for the production of a-alkylidene cyclic carbonates.
Received 27th February 2016
Accepted 25th May 2016
DOI: 10.1039/c6ra05224j
www.rsc.org/advances
reported catalyst systems required high reaction temperature
and/or high CO2 pressure. Therefore, the exploration of an
Introduction
efficient catalyst system which can work at atmospheric pres-
sure and room temperature is still a challenge.
As one of the major greenhouse gases, carbon dioxide has caused
serious environmental problems such as global warming and
climate change. However, carbon dioxide is a cheap, non-toxic,
and renewable C1 building block.1–4 Thus, how to capture and
utilize CO2 is a very important topic. Chemical xation is regarded
as an efficient route for the utilization of carbon dioxide. At
present, many useful organic chemicals have been produced by
using CO2 as a feed stock, such as methanol,5 urea,6 cyclic
carbonates,7 formamides,8 and alkynyl carboxylic acid derivatives.9
a-Alkylidene cyclic carbonates are important heterocyclic
compounds used as building blocks for different synthetic
purposes.10 The synthesis of these compounds through
coupling reaction between propargylic alcohols and CO2 is one
of the most important methods for the utilization of CO2. In the
past few years, many metal-free catalytic systems and transition-
metal catalysts had been developed for this reaction and
signicant results had been reported. The metal-free catalytic
systems mainly include tertiary phosphine,11 phosphorus
ylides,12 N-heterocyclic carbene (NHC)/CO2 13 and N-heterocyclic
olen/CO2 adducts,14 guanidines,15 and functionalized imida-
zolium betaines,16 while Pd,17 Ag,18–25 W,26 Co,27 Fe,28 Cu29,30 and
Zn31 are typical transition-metal catalysts. In general, the
Recently, great progress has been made in this area. Two types
of novel catalyst systems have been developed to catalyze the
carboxylative cyclization of propargyl alcohols with CO2 under
ambient condition. He et al.32 reported that [(Ph3P)2Ag]2CO3
catalyst could efficiently catalyze the reaction, but the recovery of
catalyst was difficult. Han and co-workers33 found that Ag
nanoparticles were able to catalyze the carboxylative cyclization
with high yields, and the target products could be obtained by
means of column chromatograph. Despite these signicant
advances, the example of CO2 utilization at atmospheric pressure
and room temperature is still seldom, and the recycling of
catalysts and separation of products also need to be improved.
Therefore, development of efficient, simple and recyclable cata-
lysts for the synthesis of a-alkylidene cyclic carbonates using CO2
under ambient conditions is highly desirable.
Herein, we demonstrate the rst example to use silver salt
supported on porous carbon material as a novel catalyst for the
reaction of propargylic alcohols with CO2 at room temperature
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; Fax: +86-373-3326445
† Electronic supplementary information (ESI) available: FT-IR spectra, FESEM
image, NMR spectra of the products and DFT calculations. See DOI:
10.1039/c6ra05224j
Scheme 1 Carboxylative cyclization of propargyl alcohols with CO2.
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and atmospheric pressure (Scheme 1). It is found that the catalyst
is robust and highly efficient, and it is stable to air and moisture,
and can be recovered and reused in the reaction. In addition, the
product can be easily separated by simple extraction.
Results and discussion
Characterization of the catalysts
Considering the fact that activated carbon (AC) is cheap, highly
stable and easy available, this carbon material was used as
a support to prepare heterogeneous silver catalysts in the present
Fig. 2 XRD patterns of AgI@C before (a) and after (b) the catalytic
work. The novel catalysts AgX@C (X ¼ Cl, Br and I) were prepared reaction.
by in situ sonication-assisted deposition–precipitation34 of AgX
nanoparticles on the surface of activated coconut-shell carbon
(100–200 mesh). Silver content in AgCl@C, AgBr@C and AgI@C
was found to be 19.8, 18.2 and 16.9 wt%, respectively, as deter-
mined from inductively coupled plasma mass spectrometry.
Meanwhile, other metal components were not detectable by X-ray
uorescence spectrometer in AgX@C samples, which indicates
high purity of AgX@C catalysts. IR spectrometry was used to
investigate the interactions between AgX and the support. It was
shown that no obvious change was observed in wavenumber of
the peaks between the pure activated carbon and the activated
carbon in the catalyst (Fig. S1, ESI†). This is an indicative that
interaction between AgX and the support was mainly physical.
X-ray diffraction (XRD) patterns of the as-prepared AgX/C
composites with different AgX contents were shown in Fig. 1.
Compared with the pure activated carbon, various diffraction
peaks were observed for AgX@C composites, which are
consistent with the standard diffraction peaks of AgCl cubic
crystal phase,34 AgBr cubic crystal phase,34 and AgI crystal
phase,35 respectively. From the XRD pattern shown in Fig. 2, it is
clear that the framework of AgI@C catalyst was well maintained
aer the catalytic reaction, indicating excellent stability of the
AgI@C catalyst. Similar results were obtained for AgCl@C and
AgBr@C catalysts.
Optimization of the reaction conditions
With the as-prepared catalysts in hand, we initiated our exper-
iments by using 2-methyl-3-butyn-2-ol as a model substrate,
acetonitrile as the solvent and AgI@C as the catalyst at atmo-
spheric pressure of CO2 and room temperature. As shown in
Table 1, the reaction did not occur in the absence of a base or
a silver catalyst (entries 1 and 2). However, it was surprising to
note that the product was obtained in a quantitative yield in the
presence of 3 mol% catalyst and 1 equivalent (equiv.) of DBU
(entry 3). Encouraged by this result, we investigated the effect of
base types and dosage on the yield of product. For this purpose,
different kinds of bases such as diisopropylethylamine (DIEA),
trimethylamine (TEA), K2CO3 and NaOH were used in the
reaction, but the yields were not satisfactory, and in some cases
the yields were very low (entries 4–7). This indicates that DBU
was a superior base for the direct carboxylic cyclization of
propargylic alcohols with CO2. Interestingly, a quantitative yield
was also obtained when the amount of DBU was deceased to 0.2
equiv. (entry 8). Therefore, the amount of the base used in our
catalyst system was lower than that reported in the previous
studies.14,16,19,26 Based on this result, we investigated the effect of
the catalyst amount on the reaction in the presence of 0.2 equiv.
DBU. It was shown that catalyst loading higher than 3 mol%
(5%, 10%) did not improve the yield further (entries 9 and 10),
whereas the loading lower than 3 mol% (say 2 mol%) decreased
the yield from 99% to 72% (entry 11).
For the sake of comparison, the Ag@C catalyst prepared by
the procedure (See ESI†) described in the literature36 was used
to catalyze the reaction, and the result was given in Table 1
(entry 15). It is clear that the yield of 2a was lower than that
catalysed by AgI@C, which indicates that the ability of Ag0 to
activate the C^C triple bond was weaker than AgI. In addition,
it was found that AgI, AgNO3 and Ag2CO3 without the support
signicantly decreased the conversion efficiency of propargylic
alcohols (entries 12–14). This could be understood from the fact
that the AgI on the support has excellent dispersibility and
stability in the reaction system, which efficiently increases the
contacting area of the catalyst with the reactants.
For a better understanding of the microscopic morphology
of AgX@C samples before and aer the reaction, eld emission
scanning electron microscope (FESEM) photographs were taken
for AgI@C as a model catalyst, and the results were shown in
Fig. S2 (ESI†). It is evident that the sample surface was quite
smooth, and no signicant morphology change was observed
before and aer the reaction. This result suggests that the AgX
was successfully loaded on activated carbon.
The effect of solvent on the yield of 2a was investigated and
the results were shown in Table 2. It can be seen that yield of
the product was strongly dependent on the reaction media,
for example, no product was obtained when the reaction was
Fig. 1 XRD patterns of (a) AC, (b) AgCl@C, (c) AgBr@C, and (d) AgI@C.
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a
Table 1 Carboxylic cyclization of propargylic alcohols with CO2
was identied as the most suitable medium for the formation
of 2a.
To study the effect of different supports and their specic
surface area on this reaction, other silver catalysts including
AgI@C (300 mesh), AgI@C (400 mesh), and AgI@C (carbon
black) were prepared under similar conditions. Their specic
surface area and catalytic performance for the cyclization
reaction were determined, and the results were listed in Table 3.
It can be seen that the yield increased with the increase of
specic surface area. Among these catalysts, the AgI@C (100–
200 mesh) with the maximum specic surface area was found to
give the best yield. This indicates that increase of the contacting
area of the catalysts with reactants can effectively improve the
interaction between the reactants and the well dispersed small
particles catalysts.
Next, we examined the effect of silver source on the reaction
under ambient temperature and pressure. It was found from
Table 4 that the use of AgBr@C and AgI@C could lead to
a quantitative yield of 2a, while AgCl@C only gave inferior
result. Also, the effect of reaction time on the yield of 2a was
investigated and the results were shown in Fig. 3. It is evident
that the maximum yield (97%) was obtained in 4 h of the
reaction. Moreover, we also studied the effect of the reaction
temperature and pressure on the yield of 2a (see ESI, Table S1†).
Entry Cat.
Cat. loading (mol%) Base
Yieldb (%)
c
1
AgI@C
3
—
3
3
3
3
3
3
5
—
0
0
>99
0
0
d
2
—
DBU (1.0 equiv.)
DBU (1.0 equiv.)
DIEA (1.0 equiv.)
TEA (1.0 equiv.)
K2CO3 (1.0 equiv.) 12
NaOH (1.0 equiv.) 15
DBU (0.2 equiv.)
DBU (0.2 equiv.)
DBU (0.2 equiv.)
DBU (0.2 equiv.)
DBU (0.2 equiv.)
DBU (0.2 equiv.)
DBU (0.2 equiv.)
DBU (0.2 equiv.)
3
4
5
6
7
8
9
AgI@C
AgI@C
AgI@C
AgI@C
AgI@C
AgI@C
AgI@C
>99
>99
>99
72
88
73
10
11
12
13
14
15
AgI@C 10
AgI@C
AgI
AgNO3
Ag2CO3
Ag@C
2
3
3
3
3
14
78
a
Reaction condition: 2-methyl-3-butyn-2-ol (1 mmol), catalyst (x mol%
b
based on Ag), CH3CN (2 mL), CO2 (99.999%, 0.1 MPa), 4 h, r.t. The
yields were determined by GC with naphthalene as internal standard.
c
Without base. d Without catalyst.
Table 3 The effect of specific surface area of catalyst on the reactiona
Entry
1
Catalyst
SABET/m2 gꢀ1
973.44
Yieldb
90
Table 2 Solvent effect in carboxylic cyclization of 2-methyl-3-butyn-
2-ola
AgI@C (100–200
mesh)
2
3
4
AgI@C (300 mesh)
AgI@C (400 mesh)
AgI@C (carbon black)
701.26
562.35
194.61
86
83
79
a
Reaction condition: 2-methyl-3-butyn-2-ol (1 mmol), catalyst (3 mol%
based on Ag), DBU (0.2 mmol), CH3CN (2 mL), CO2 (99.999%, 0.1 MPa),
b
3 h, r.t. Isolated yield.
Entry
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
THF
EtOH
H2O
Toluene
DMSO
Cyclohexane
Dichloromethane
CH3CN
0
0
0
51
65
96
97
>99
Table
4 Influence of the AgX@C catalysts on the carboxylic
cyclizationa
a
Reaction condition: 2-methyl-3-butyn-2-ol (1 mmol), catalyst (3 mol%
b
based on Ag), DBU (0.2 mmol), CO2 (99.999%, 0.1 MPa), 4 h, r.t. The
yields were determined by GC with naphthalene as internal standard.
Cat. (3
mol%)
Entry
Yieldb (%)
performed in THF, EtOH or H2O (entries 1–3), while the
reaction in toluene and DMSO gave a 51% and 65% yield,
respectively (entries 4 and 5). Great improvement was ach-
ieved when the reaction was conducted in cyclohexane (96%)
and dichloromethane (97%) (entries 6 and 7). Especially, an
almost quantitative yield (>99%) was observed by using
acetonitrile (CH3CN) as solvent (entry 8). Thus, acetonitrile
1
2
3
AgCl@C
AgBr@C
AgI@C
71
>99
>99
a
Reaction condition: 2-methyl-3-butyn-2-ol (1 mmol), catalyst (3 mol%
based on Ag), DBU (0.2 mmol), CH3CN (2 mL), CO2 (99.999%, 0.1 MPa),
b
4 h, r.t. The yields were determined by GC with naphthalene as
internal standard.
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Table 5 Scope of the propargylic alcohol substrates for the reaction
under optimized conditionsa
Entry
1
Substrate
Product
Yieldb (%)
>99
95d
>99
96d
2
3
Fig. 3 Effect of reaction time on the product yield over AgI@C.
Reaction conditions: 1 mmol of 2-methyl-3-butyn-2-ol, 0.3 mol% of
AgI@C (based on the substrate), 0.2 mmol of DBU, 2 mL of CH3CN, 0.1
MPa CO2, r.t. Yields were determined by GC using naphthalene as an
internal standard. The results were obtained from at least three
separate experiments.
>99
97d
>99
96d
It was found that the CO2 pressure had no effect on the reaction
within the pressure range investigated. However, the reaction
was affected by temperature, and the yield of the product
decreased with the increasing temperature, although the
structure of the by-product is not clear. Thus, the following
optimal reaction conditions were used for further investiga-
tions: AgBr@C or AgI@C as the catalyst (3 mol%), DBU as the
base (0.2 equiv.), and CH3CN as the solvent for 4 h reaction.
4
5
6
>99
98d
>99
96d
Scope of the substrates
The reaction of CO2 with a range of different substituted
propargylic alcohols were performed under the optimized
reaction conditions by using AgI@C as a representative catalyst,
and the yields of the target products were summarized in
Table 5. It was shown that propargyl alcohols with a variety of
alkyl substituents at the propargylic position were effective
substrates to give the corresponding carbonates in good to
excellent yields. The reaction time did not depend on the steric
hindrance effect of the substituted R2 and R3 groups. However,
different results were obtained for the catalysts reported in
literatures where the catalytic effect was signicantly affected by
the steric hindrance.20,31,32 In addition, although the reaction
was effectively catalyzed by our catalysts, the product was only
obtained in moderate yield in the case of the internal prop-
argylic alcohol. These results suggest that the catalyst system
reported here is more favorable for terminal propargylic alco-
hols than internal propargylic alcohols.
99
97d
7
8
97
94d
45
38d
9c
a
Reaction conditions: propargylic alcohols (1.0 mmol), catalyst (3
mol%, based on Ag), DBU (0.2 mmol), CH3CN (2 mL), CO2 (99.999%,
b
balloon), r.t.,
4
h.
The yields were determined by GC with
naphthalene as internal standard. 1 MPa of CO2. d Isolated yield.
c
Separation of the target products and recyclability of the
catalysts
Here, the products could be separated by solvent extraction
technique. Aer the reaction was nished, the catalyst was
rstly separated from the reaction mixture by centrifugation.
Then the target compound was extracted with n-hexane. The
combined organic layers were washed with saturated aqueous
NaCl solution and then dried with anhydrous Na2SO4. The
products were easily obtained aer removal of the solvent.
Compared with the product separation reported for a-alkyli-
dene cyclic carbonates in literatures,20,32,33 the strategy
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Table 6 The binding energy between 2 and different catalysts
developed in this work was simple, fast and efficient, which is
more favorable for industrial processes.
Catalyst
DE (kJ molꢀ1
)
As a heterogeneous catalyst, AgX@C was not only robust in
catalytic activity, but also easily separated from the reaction
system only by centrifugation. In a typical experiment, the
catalyst was reused 10 times in the reaction of 1a with CO2. In
each cycle, the heterogeneous catalyst was recovered by ltra-
tion and reused directly for the next run aer drying. As shown
in Fig. 4, the catalytic activity of the catalyst remained
unchanged even aer being reused 10 times. The leaching of Ag
during the reaction was also examined by ICP mass analysis of
the ltrates. It was found that the amount of Ag present in the
ltrate was less than 0.01% of the initial amount. The above
results indicate that the catalyst exhibited excellent activity and
stability due to the strong interaction of the activated carbon
with AgX nanoparticles.
AgCl
AgBr
AgI
ꢀ125.6
ꢀ120.3
ꢀ114.8
the presence of base promoters.21,33 It is reasonable to assume
that the reaction catalyzed by AgX@C should have a similar
mechanism (Scheme 2). Firstly, the alcohol reacts with CO2 to
generate a carbonate intermediate via base activated process.
Then, an intramolecular ring-closing reaction takes place on the
alkyne, which can be activated by AgX catalyst supported on the
activated carbon. Finally, the corresponding cyclic carbonate is
formed with the release of the catalyst.
Density functional theory (DFT) calculations were performed
to gain a deeper insight into structures of 2 and 3 (2-AgX) in
Scheme 2. These structures were optimized at B3LYP/BSI level,
where BSI (basis set LANL2DZ) was performed for Ag and I
atoms and basis set 6-31G* for other non-metal main group
atoms, and the results were included in Fig. S3 (ESI†). Based on
the optimized geometries, it was found that 2 and AgX catalyst
could be combined to form 3, which conrms the above
purposed mechanism. In addition, comparison was made for
the binding energy of 2 with three different catalysts in aceto-
nitrile calculated at B3LYP/BSI level, where basis set 6-311++G**
was employed for C, H and O atoms while basis set LANL2DZ
was employed for Ag and I atoms (Table 6). It is clearly indicated
that the interaction between 2 and AgCl was the strongest. This
suggests that in the case of AgCl, more energy was needed to
release the catalyst. Therefore, higher yields were observed by
the use of AgBr@C and AgI@C than that of AgCl@C catalyst,
which explains the reason why the catalytic activity of AgBr@C
and AgI@C was much higher than that of AgCl@C.
Possible reaction mechanism
The mechanism of the carboxylative cyclization of propargyl
alcohols with CO2 catalyzed by Ag(I) and Ag NPs was studied in
Fig. 4 Catalyst recycling for the carboxylation of 1a with CO2 (0.1 MPa)
at 25 ꢁC for 4 h. Yields were determined by GC using naphthalene as an
internal standard. The results were obtained from at least three
separate experiments.
Conclusions
In summary, we developed an efficient and cost-competitive
catalytic system for chemical xation of CO2 to produce
a-alkylidene cyclic carbonates. In this chemical reaction, the
heterogeneous catalysts AgX@C (X ¼ Br and I) exhibited high
activity and excellent stability, and they could be easily recov-
ered and reused without loss of activity. A range of propargylic
alcohols could undergo the coupling reaction with CO2 under
conditions of atmospheric pressure and room temperature, and
the yields of the desired products reached up to 99% under the
optimized condition. In addition, the product could be easily
separated by simple solvent extraction.
Experimental
Materials
CO2 was supplied by Beijing Analytical Instrument Factory with
a purity of 99.99%. All solvents were obtained commercially and
were used as received unless otherwise indicated. The
Scheme 2 The proposed mechanism for the carboxylative cyclization
of propargyl alcohols with CO2.
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Compound 2a. Colourless oil; 1H NMR (600 MHz, DMSO-d6)
d (ppm): 4.79 (d, J ¼ 3.6 Hz, 1H), 4.64 (d, J ¼ 4.2 Hz, 1H), 1.59 (s,
6H); 13C NMR (150 MHz, DMSO-d6) d (ppm): 158.7, 151.3, 85.9,
85.5, 27.4.
propargylic alcohols (purity >98%) and AgX were provided by J &
K Scientic Ltd. Activated carbon and DBU was purchased from
Aladdin Company. Other bases were analytical grade and were
supplied from Beijing Chemical Reagent Company. The
deuterated solvents (CDCl3 and DMSO-d6) were obtained from
Sigma-Aldrich Company.
Compound 2b. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 4.82 (d, J ¼ 3.6 Hz, 1H), 4.26 (d, J ¼ 3.6 Hz, 1H), 1.94–
1.88 (m, 1H), 1.79–1.73 (m, 1H), 1.59 (s, 3H), 0.99 (t, J ¼ 7.8 Hz,
3H); 13C NMR (150 MHz, CDCl3) d (ppm): 157.5, 151.6, 87.6,
85.6, 33.4, 26.0, 7.4.
Preparation of the supporter
To the aqueous solution of concentrated hydrochloric acid (12
mol Lꢀ1, 8 mL), nitric acid (16 mol Lꢀ1, 6 mL), water (400 mL)
and coconut shell carbon (100–200 mesh, 20 g) were added. The
mixture was stirred at room temperature for 24 h and then
ltered. Then, the solid was collected and dried at 110 ꢁC for 16
h under owing nitrogen gas. Thus obtained solid was
employed as supporter for the synthesis of catalyst.
Compound 2c. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 4.87 (d, J ¼ 3.6 Hz, 1H), 4.22 (d, J ¼ 3.6 Hz, 1H), 1.97–
1.91 (m, 4H), 1.75–1.69 (m, 4H), 0.98 (t, J ¼ 7.8 Hz, 6H); 13C NMR
(150 MHz, CDCl3) d (ppm): 155.8, 151.9, 90.8, 85.8, 31.9, 7.1.
Compound 2d. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 4.79 (d, J ¼ 4.2 Hz, 1H), 4.26 (d, J ¼ 4.2 Hz, 1H), 1.85–
1.79 (m, 2H), 1.68–1.64 (m, 1H), 1.58 (s, 3H), 0.98–0.96 (m, 6H);
13C NMR (150 MHz, CDCl3) d (ppm): 158.4, 151.5, 87.3, 85.6,
48.6, 27.0, 24.3, 24.0, 23.7.
Preparation of activated carbon supported AgX catalysts
Compound 2e. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 4.79 (d, J ¼ 4.2 Hz, 1H), 4.26 (d, J ¼ 3.6 Hz, 1H), 1.89–
1.83 (m, 1H), 1.72–1.67 (m, 1H), 1.58 (s, 3H), 1.42–1.25 (m, 8H),
0.88 (t, J ¼ 7.2 Hz, 6H); 13C NMR (150 MHz, CDCl3) d (ppm):
157.8, 151.6, 87.2, 85.4, 40.4, 31.6, 31.5, 28.9, 26.3, 22.9, 22.7,
22.5, 14.21, 14.0.
Typically, 0.7 g of the activated carbon was added into 50 mL of
deionized water and sonicated for 30 min. Next, 0.1 g mLꢀ1 of
aqueous AgNO3 solution (3 mL) was added dropwise to the
suspension. The mixture was stirred magnetically for 1 h to
allow adsorption of Ag+ ions on the surface of activated carbon.
Then, the respective aqueous solutions of sodium halides NaX
(X ¼ Cl, Br and I) were added dropwise into the suspension with
an excess amount of 10% to ensure that the amount of halide
ions from NaX was enough to precipitate Ag+ on the activated
carbon surface. Here, the dropwise addition of aqueous NaX
was necessary to avoid rapid nucleation of the Ag+ and Xꢀ on the
activated carbon. The resulting mixture was further stirred
vigorously at room temperature for 3 h. The product was ob-
tained by washing with ethanol and deionized water for three
Compound 2f. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 4.82 (s, 1H), 4.27 (s, 1H), 1.97–1.92 (m, 1H), 1.58 (s, 3H),
1.04–1.00 (m, 6H); 13C NMR (150 MHz, CDCl3) d (ppm): 157.2,
151.7, 89.8, 86.2, 37.0, 24.1, 16.4, 16.1.
Compound 2g. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 4.79 (d, J ¼ 3.6 Hz, 1H), 4.34 (d, J ¼ 3.6 Hz, 1H), 2.26–
2.22 (m, 2H), 1.95–1.83 (m, 6H); 13C NMR (150 MHz, CDCl3)
d (ppm): 157.8, 151.5, 94.2, 85.3, 40.7, 24.3.
Compound 2h. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 4.76 (d, J ¼ 3.6 Hz, 1H), 4.28 (d, J ¼ 4.2 Hz, 1H), 2.01 (d,
J ¼ 13.2 Hz, 2H), 1.78–1.59 (m, 8H); 13C NMR (150 MHz, CDCl3)
d (ppm): 158.8, 151.5, 86.4, 85.5, 36.5, 24.4, 21.6.
ꢁ
times and then dried at 70 C for 12 h.
The specic surface area of AgI@C was determined by N2
adsorption at 77 K using a Micromeritics ASAPꢁ 2010 system
aer the sample was degassed in vacuum at 130 C for 20 h.
Compound 2i. Colourless oil; 1H NMR (600 MHz, CDCl3)
d (ppm): 7.55–7.54 (m, 2H), 7.37–7.34 (m, 2H), 7.28–7.26 (m,
1H), 5.50 (s, 1H), 1.70 (s, 6H); 13C NMR (150 MHz, CDCl3)
d (ppm): 151.3, 150.7, 132.4, 128.7, 128.5, 127.6, 101.6, 85.5,
27.8.
General procedure for the carboxylation cyclization of
propargylic alcohol with CO2
In a 20 mL Schlenk ask, propargylic alcohol (1.0 mmol), DBU
(0.2 mmol), indicated amount of the catalyst, and CH3CN (3 mL)
were added. The ask was capped with a stopper and sealed.
Then the freeze–pump–thaw method was employed for gas
exchanging process. The reaction mixture was stirred at room
temperature for 4 h under CO2 atmosphere (balloon). Aer the
reaction was nished, the product was extracted with n-hexane.
The combined organic layers were washed with saturated
aqueous NaCl solution and then dried with anhydrous Na2SO4.
The organic phase was treated by reduced pressure distillation
to give the desired products. All of these compounds were
identied by NMR spectroscopy, which are consistent with the
previous reported experimental results.29,30
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant No. 21403060, 21133009) and
Program for Innovative Research Team in Science and Tech-
nology in University of Henan Province (16IRTSTHN002).
Notes and references
1 J. Louie, Curr. Org. Chem., 2005, 9, 605–623.
To test the reusability, the catalyst was separated from the
reaction mixture by centrifugation, washed with CH3CN for
three times (3 ꢂ 10 mL) and dried under vacuum for 24 h at
2 M. Cokoja, C. Bruckmeier, B. Rieger, W. A. Herrmann and
¨
F. E. Kuhn, Angew. Chem., Int. Ed., 2011, 50, 8510–8537.
3 L. J. Murphy, K. N. Robertson, R. A. Kemp, H. M. Tuononen
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ꢁ
30 C, and then was reused directly for the next run.
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