Synthesis of cyclic carbonates with carbon dioxide and cesium carbonate

Article abstract of DOI:10.1039/c3gc40790j

Cyclic carbonates are important compounds for the synthesis of biocompatible polymers and linear dialkyl carbonates, as well as solvents and electrolytes. We report here the synthesis of such compounds from easily accessible starting materials with carbon dioxide as a C1 source and caesium carbonate as the base. This new methodology is able to yield 5- and 6-membered cyclic carbonates very efficiently in a green manner.

Full text of DOI:10.1039/c3gc40790j

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Synthesis of cyclic carbonates with carbon dioxide and
cesium carbonate
Cite this: DOI: 10.1039/c3gc40790j
Received 26th April 2013,
Accepted 2nd June 2013
Michael R. Reithofer, Yin Ngai Sum and Yugen Zhang*
DOI: 10.1039/c3gc40790j
www.rsc.org/greenchem
Cyclic carbonates are important compounds for the synthesis of When oxetane is used, trimethyl carbonate (TMC) analogs can
biocompatible polymers and linear dialkyl carbonates, as well as be obtained; again, the substrate scope is very limited.12 As a
solvents and electrolytes. We report here the synthesis of such result, the methodology has less impact on the modern syn-
compounds from easily accessible starting materials with carbon thetic laboratory. Obviously, the simultaneous conversion of
dioxide as a C1 source and caesium carbonate as the base. This CO2 and diols into cyclic carbonates is highly desirable, in
new methodology is able to yield 5- and 6-membered cyclic car- which water is the only byproduct and the process is highly
bonates very efficiently in a green manner.
atom-efficient. However, this ideal reaction is both thermo-
dynamically and kinetically not favored.13 Some heterogeneous
and homogeneous catalysts have been developed to accelerate
this reaction. However, the overall conversion of diols is very
low (∼5%).14 The limiting factor for this chemical equilibrium
is the water by-product; accordingly, dehydrating agents,
such as triphenylphosphine–diethyl azodicarboxylate, were
introduced into this reaction system but the efficiency of the
reaction was still unsatisfactory.14,15 Furthermore, this
methodology was only successful in the synthesis of ethylene
carbonates. Alternatively, halohydrin has also been used in the
synthesis of ethylene carbonates and related five-membered
cyclic carbonates under catalytic and pressurized conditions.16
Although methods have also been developed for the synthesis
of organic carbonates by using alkyl halides and alcohols, this
protocol has never been used for the synthesis of any cyclic
carbonates other than ethylene carbonates.17
We have been interested in utilizing carbon dioxide as a
feedstock for organic synthesis over the last few years.18
However, the activation and reaction of carbon dioxide under
mild conditions still remains a challenge in synthetic organic
chemistry. Here, we report a convenient and robust method for
the synthesis of 5- and 6-membered cyclic carbonates from
commercially available and easily accessible starting materials
using mild reaction conditions. The intermolecular ring
closing reaction proceeds in the presence of 1 atm CO2 and
Cs2CO3 very efficiently, thus providing an environmentally
benign method for the synthesis of cyclic carbonates.
Introduction
In recent years, cyclic carbonates have attracted increasing
attention as a versatile monomer for the synthesis of bio-
compatible polymers,1 as polar aprotic solvents and degreaser,2
as electrolytes and as intermediates for linear dialkyl carbonate
synthesis.3 In light of increased interest in biocompatible
materials, the synthesis of cyclic carbonates in a safe, reliable
and environmentally benign way has become important. Tra-
ditionally, cyclic carbonates are synthesized by the reaction of
phosgene or the coupling of halo formates with diols.4
However, these methods involving toxic materials are not environ-
mentally satisfactory. Recent developments have aimed to
replace phosgene with the relatively safer triphosgene or oxalyl-
choride.5 Several novel synthetic strategies for the synthesis of
cyclic carbonates were also developed recently which include
carbon dioxide insertion in epoxides2,4,6 and oxetane,7 trans-
esterification of diols with urea8 and oxidative carbonylation of
diols using carbon monoxide, with the aid of a transition
metal catalyst,9 and catalytic reaction from specific precursors
such as propargyl alcohols.10 However, these methods still rely
on specific precursors and have limited substrate scope.
The use of carbon dioxide for the formation of cyclic car-
bonates has been very successfully employed for the conver-
sion of epoxides into ethylene carbonate (EC) analogs.2,4,6,11
However, the reaction is quite limited in the substrate scope,
and only 5-membered cyclic carbonates can be obtained.
Results and discussion
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, The Nanos,
Singapore 138669, Singapore. E-mail: ygzhang@ibn.a-star.edu.sg;
Fax: (+65)-6478-9080; Tel: (+65)-6824-7162
In our initial efforts to synthesize cyclic carbonates in a green
manner without the use of a transition metal catalyst, we used
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the more general halo-alcohols as starting materials. The
We further looked at the influence of the catalyst on the
potential problem here is the production of a large amount of reaction and, thus, we replaced TBD with imidazolium based
polycarbonate with low selectivity for the desired cyclic carbon- catalysts to activate CO2.21 When 1,3-(2,6-diisopropylphenyl)-
ate.17 In our initial study, the reaction was carried out with imidazolium (IPr) was used, no change in yield was observed;
3-chloro-1-propanol and CO2 in the presence of K2CO3 and a however, the use of 1,3-(2,6-dimethylphenyl)-imidazolinimum
catalytic amount of triazabicyclodecene (TBD) (Table 1) in (SMes) resulted in a slight decrease in yield (92%).
DMF. At 60 °C, trimethyl carbonate (TMC, compound 1) could
Since only minor changes in the yield were observed with
be detected in 58% yield by NMR spectroscopy, whereas a different catalysts but large changes in the yield were observed
small decrease in yield was observed when the reaction was with different bases, the role of the catalyst in the reaction was
carried out at 40 °C. Interestingly, we only observed minor further investigated. When standard conditions were applied
polymeric side products of compound 1 even though TBD was (40 °C, 1 atm CO2, 1.1 equiv. Cs2CO3, 15 h reaction time) in
used as an additive.19 It has to be mentioned here that even the absence of a catalyst, the same NMR yield (95%) of com-
sparteine, a weaker base than TBD, is able to polymerize TMC pound 1 was observed. We therefore concluded that the
in minutes.20 This is the first example demonstrating that a addition of a catalyst for the activation of CO2 is not needed in
6-membered cyclic carbonate can be synthesized directly from order to form TMC.
CO2 without using any transition metal or toxic agents, such
Furthermore, the role of Cs2CO3 was investigated. When
as phosgene or CO.4,9 We do believe that the CO2 present in a substoichiometric amount of Cs2CO3 was used, incomplete
the reaction is able to act as an inhibitor by binding to TBD, conversion was observed. Instead, the yield of compound
thus preventing the polymerization of the newly formed com- 1 correlated with the amount of Cs2CO3 used, which indicates
pound 1.
An increase in the yield of compound 1 was observed when
that Cs2CO3 does not act as a catalyst in this reaction.
In order to prove that CO2 is essential for the reaction,
K2CO3 was replaced with Cs2CO3. At 60 °C, compound 1 was we carried out the experiment in the absence of CO2.
formed with up to 77% NMR yield, whereas almost quantitat- As expected, compound 1 could not be observed after the
ive formation of compound 1 was detected by lowering the reaction was quenched. Other polar volatile solvents, namely
temperature to 40 °C. However, employing the stronger base THF and acetonitrile, were also tested, but no successful
KOtBu resulted in a significant decrease in yield and only 20% reaction could be observed. In addition, when the reaction was
of compound 1 could be detected by NMR.
performed using water as a solvent, no product could be
detected.
Based on the above results, we postulate the following reac-
tion mechanism (Fig. 1). In the initial step, Cs2CO3 deproto-
nates the alcohol, resulting in the formation of cesium
alkoxide, which subsequently reacts with CO2 to form a car-
bonate. In the final step, TMC is formed by an intramolecular
ring closing reaction, affording CsCl as the side product.17 To
prove our postulated reaction mechanism and the formation
of CsCl, we performed a reaction using a substoichiometric
amount of Cs2CO3 and collected the solids after 15 h reaction
time. To verify the presence of Cl−, a small amount of solid
was dissolved in water and nitric acid was added to remove
residual Cs2CO3. The test for Cl− was positive using AgNO3 for
qualitative verification.
Table 1 Influence of the base on TMC formation
Entry
Base
T/°C
Yielda/%
1
2
3
4
K2CO3
K2CO3
Cs2CO3
Cs2CO3
KOtBu
Cs2CO3
60
40
60
40
40
40
58
54
77
95
20
95
5
The substrate scope of the reaction was then investigated.
We first looked into changing the chloride to other halides;
2-bromo-1-ethanol as well as 2-iodo-1-ethanol afforded the
expected product 2 in 92% yield by NMR spectroscopy. Since
6b
a Yield was determined by 1H-NMR using mesitylene as the internal
standard. b No TBD added.
Fig. 1 Proposed reaction mechanism for the formation of TMC using 3-chloro-1-propanol as the starting material and Cs2CO3 as the base.
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the accessibility of halide alcohols is limited, the possibility of
using tosylate as the leaving group was explored. Tosylates are
Experimental section
very easily accessible by reaction of tosyl chloride with the All reactions were set up in an Innovative Technologies Glove-
respective alcohols in the presence of a base. This synthetic box equipped with nitrogen gas. Chemicals were purchased
strategy would allow the conversion of diols in two reaction from commercial sources and used as received without further
steps into cyclic carbonates.
purification. Anhydrous solvents were purchased in Sure-seal
Reaction of 2-tosyl-1-ethanol with CO2 in the presence of packaging from Sigma-Aldrich and were used as received. CO2
1.1 equivalents of Cs2CO3 in DMF yielded ethylene carbonate was supplied by SOXAL. 1H and 13C NMR spectra were
in comparable yield to the product obtained from 2-bromo- recorded on a Bruker AV-400 (400 MHz) instrument. Reaction
1-ethanol. The selectivity of the reaction to form five-mem- temperatures refer to the temperatures of the heating blocks.
bered rings over six-membered rings was also investigated Mono-tosylated diols were synthesised according to previously
using ( )-3-chloro-1,2-propanediol. After 15 h reaction time, reported standard tosylation reaction conditions.23 With the
( )-3-chloro-1,2-propanediol was converted exclusively into gly- exception of compound 7, all cyclic carbonates reported herein
ceryl carbonate (3), a versatile chemical.22 The exclusive for- have been previously prepared by other methods and charac-
mation of the five-membered ring demonstrates the high terized by NMR spectroscopy: 1,3-dioxan-2-one (1),24 ethylene
selectivity of the reaction to yield the thermodynamically more carbonate (2),5,24a 4-(hydroxymethyl)-1,3-dioxolan-2-one (3),9,25
stable compound.
4-phenyl-1,3-dioxolan-2-one (4),26 5,5-dimethyl-1,3-dioxan-
To further expand the substrate scope, we looked into the 2-one (5),24a and 4,6-dimethyl-1,3-dioxan-2-one (6).27
possibility of forming 7- and 8-membered rings. When 4-chloro-
butan-1-ol was reacted with CO2 in the presence of 1.1 equi-
General reaction procedure
valents of Cs2CO3 in DMF, no product could be observed by 1H
and 13C NMR spectroscopy. The same holds true when 5-bromo- In a nitrogen filled glove box, a 20 mL crimp top vial was
pentan-1-ol was used as the starting material. This is not charged with 1 mmol starting material and dissolved in 3 mL
unexpected taking into account that 7- and 8-membered rings DMF; 1.1 mmol (1.1. equiv.) Cs2CO3 was then added immedi-
are kinetically not favored. In addition, the CvO bond distorts ately. The vial was closed with a crimp cap, brought out of the
the ring which most likely decreases the thermodynamic glove box and CO2 was bubbled through the solution for about
stability.
1 minute. The vial was placed on a 40 °C heat block and
A number of substrates yielding 5- and 6-membered stirred for 15 h under 1 atm of CO2 using a CO2 filled balloon.
rings were screened and the results are shown in Table 2. The reaction was quenched by adding 15 mL DCM. The result-
Residues R1, R2 and R3 were either a methyl, a phenyl or a ing suspension was filtered over Celite; the solvent was first
CH2OH group respectively. While no significant difference in removed on a rotary evaporator and DMF was later on removed
yield was observed when only one residue was substituted, on an oil vacuum pump. After 6 h, the residue was resus-
a slight drop in yield could be detected when R1 and R3 were pended in DCM and filtered over cotton wool to remove all salt
a methyl group. This may be attributed to steric hindrance traces. The solvent was removed and the product was dried on
as well as a decrease in nucleophilicity. In general, both an oil vacuum pump.
1
5- and 6-membered rings could be formed in moderate to
excellent yield.
1,3-Dioxan-2-one (1). Yield: 95%; H-NMR (CDCl3): δ = 4.45
3
3
(t, 4H, JHH = 5.8 Hz, O–CH2), 2.14 (quintet, 2H, JHH = 5.8 Hz,
CH2) ppm; 13C-NMR (CDCl3): δ = 148.5 (CvO), 68.1 (O–CH2),
21.8 (CH2) ppm.
Ethylene carbonate (2). Yield: 75%; 1H-NMR (CDCl3): δ =
4.48 (s, 4H, CH2) ppm; 13C-NMR (CDCl3): 155.7 (CvO),
64.8 (CH2) ppm.
Table 2 Scope of cyclic carbonate formation with CO2
4-(Hydroxymethyl)-1,3-dioxolan-2-one
(3). Yield:
92%;
1H-NMR (CDCl3): δ = 4.81 (m, 1H), 4.55–4.43 (m, 2H), 3.98 (dd,
3
2
3
1H, JHH = 12.9 Hz, JHH = 3.0 Hz), 3.71 (dd, 1H, JHH
=
12.9 Hz, JHH = 3.4 Hz), 2.40 (bs, 1H, OH) ppm; 13C-NMR
(CDCl3): 155.5 (CvO), 76.8 (CH), 65.9 (CH2), 61.8
(CH2) ppm.
2
δ
=
4-Phenyl-1,3-dioxolan-2-one (4). Yield: 76%; 1H-NMR
(CDCl3): δ = 7.49–7.41 (m, 3H, Ph), 7.39–7.34 (m, 2H, Ph), 5.66
Compound
X
n
R1
R2
R3
Yield [%]
3
3
(t, 1H, JHH = 8.0 Hz, CH), 4.80 (t, 1H, JHH = 8.4 Hz, CH2),
1
2
3
4
5
6
7
Cl
Br
Cl
OTs
OTs
OTs
OTs
1
0
0
0
1
1
1
H
H
H
H
H
H
H
H
Me
H
95
75
92
77
71
65
95
3
4.35 (t, 1H, JHH = 8.4 Hz, CH2) ppm; 13C-NMR (CDCl3): δ =
N.A.
N.A.
N.A.
(CH3)2
H
CH2OH
Ph
H
Me
H
154.9 (CvO), 136.0 (Cq), 129.9 (CH, Ph), 129.4 (CH, Ph), 126.0
(CH, Ph), 78.1 (CH–Ph), 71.3 (CH2) ppm.
5,5-Dimethyl-1,3-dioxan-2-one (5). Yield: 71%; 1H-NMR
(CDCl3): δ = 4.07 (s, 4H, CH2), 1.12 (s, 6H, CH3) ppm; 13C-NMR
Ph
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(CDCl3): δ = 148.4 (CvO), 77.6 (CH2), 28.6 (C(CH3)2), 21.3
(CH3) ppm.
44, 1755; (d) A. G. Davies, P. Hua-De and J. A. A. Hawari, J.
Organomet. Chem., 1983, 256, 251.
4,6-Dimethyl-1,3-dioxan-2-one (6). Yield: 65%; 1H-NMR
(CDCl3): δ = 4.53 (m, 2H), 2.04 (m, 1H), 1.54 (m, 1H), 1.34
(m, 6H) ppm. 13C-NMR (CDCl3): δ = 149.6 (CvO), 75.4 (CH),
36.4 (CH2), 21.2 (CH3) ppm.
6 (a) T. Sakakura and K. Kohno, Chem. Commun., 2009, 1312;
(b) J. Song, Z. Zhang, S. Hu, T. Wu, T. Jiang and B. Han,
Green Chem., 2009, 11, 1031; (c) W. Clegg,
R. W. Harrington, M. North and R. Pasquale, Chem.–Eur. J.,
2010, 16, 6828; (d) A. Decortes, M. M. Belmonte, J. Benet-
Buchholz and A. W. Kleij, Chem. Commun., 2010, 46, 4580;
(e) K. Motokura, S. Itagaki, Y. Iwasawa, A. Miyaji and
T. Baba, Green Chem., 2009, 11, 1876; (f) Y. Tsutsumi,
K. Yamakawa, M. Yoshida, T. Ema and T. Sakai, Org. Lett.,
2010, 12, 5728; (g) H. Zhou, Y.-M. Wang, W.-Z. Zhang,
J.-P. Qu and X.-B. Lu, Green Chem., 2011, 13, 644;
(h) L. Han, H.-J. Choi, S.-J. Choi, B. Liu and D.-W. Park,
Green Chem., 2011, 13, 1023; (i) T. Aida and S. Inoue, J. Am.
Chem. Soc., 1983, 105, 1304; ( j) W. J. Kruper and
D. V. Dellar, J. Org. Chem., 1995, 60, 725; (k) R. L. Paddock,
Y. Hiyama, J. M. McKay and S. T. Nguyen, Tetrahedron Lett.,
2004, 45, 2023; (l) R. Srivastava, T. H. Bennur and
D. Srinivas, J. Mol. Catal. A: Chem., 2005, 226, 199;
(m) J. Qu, C.-Y. Cao, Z.-F. Dou, H. Liu, Y. Yu, P. Li and
W.-G. Song, ChemSusChem, 2012, 5, 652.
7 D. J. Darensbourg and A. I. Moncada, Macromolecules,
2010, 43, 5996.
8 (a) B. M. Bhanage, S.-I. Fujita, Y. Ikushima and M. Arai,
Green Chem., 2003, 5, 429; (b) Q. Li, W. Zhang, N. Zhao,
W. Wei and Y. Sun, Catal. Today, 2006, 115, 111.
9 (a) P. Giannoccaro, D. Cornacchia, S. Doronzo, E. Mesto,
E. Quaranta and M. Aresta, Organometallics, 2006, 25, 2872;
(b) D. M. Pearson, N. R. Conley and R. M. Waymouth, Adv.
Synth. Catal., 2011, 353, 3007; (c) B. Gabriele, R. Mancuso,
G. Salerno, L. Veltri, M. Costa and A. Dibenedetto, Chem-
SusChem, 2011, 4, 1778.
10 (a) T. Kimura, K. Kamata and N. Mizuno, Angew. Chem., Int.
Ed., 2012, 51, 6700; (b) W. Yamada, Y. Sugawara,
H. M. Cheng, T. Ikeno and T. Yamada, Eur. J. Org. Chem.,
2007, 2604.
1
5-Phenyl-1,3-dioxan-2-one (7). Yield: 95%; H-NMR (CDCl3):
δ = 7.42–7.31 (m, 3H, Ph), 7.23 (m, 2H, Ph), 4.61–4.49 (m, 4H,
O–CH2), 3.49 (m, 1H, CH) ppm; 13C (CDCl3): δ = 148.3 (CvO),
134.2 (CH–C), 129.5 (CH on bottom), 128.7 (CH in the middle),
127.6 (CH on the top next to Cq), 72.2 (O–CH2), 37.7
(CH) ppm.
Conclusions
In conclusion, a new method for the green synthesis of cyclic
carbonates is presented. This novel synthetic approach does
not require any transition metal or organo catalyst; only
Cs2CO3 base and CO2 are required. The reaction proceeds very
efficiently at 40 °C under 1 atm CO2, yielding 5- and 6-mem-
bered cyclic carbonates in good to excellent yield. We could
further prove that the reaction is very robust, yielding the
expected product when chloride, bromide, iodide or tosyl is
used as the leaving group.
Acknowledgements
This work was funded by the Institute of Bioengineering and
Nanotechnology (Biomedical Research Council, Agency for
Science, Technology and Research, Singapore). M.R.R. would
like to thank Karen Xuetong Liu for help with the initial
screening of the reaction conditions.
Notes and references
1 G. Rokicki, Prog. Polym. Sci., 2000, 25, 259.
11 (a) K. M. Tomczyk, P. A. Gunka, P. G. Parzuchowski,
J. Zachara and G. Rokicki, Green Chem., 2012, 14, 1749;
(b) S.-H. Pyo and R. Hatti-Kaul, Adv. Synth. Catal., 2012,
354, 797; (c) M. Aresta, A. Dibenedetto, F. Nocito and
C. Pastore, J. Mol. Catal. A: Chem., 2006, 257, 149.
2 A.-A. G. Shaikh and S. Sivaram, Chem. Rev., 1996, 96, 95.
3 (a) J. S. Tian, C. X. Miao, J. Q. Wang, F. Cai, Y. Du, Y. Zhao
and L. N. He, Green Chem., 2007, 9, 566; (b) J. H. Clements,
Ind. Eng. Chem. Res., 2003, 42, 663–674.
4 (a) X. B. Lu and D. J. Darensbourg, Chem. Soc. Rev., 2012, 12 D. J. Darensbourg, A. Horn Jr. and A. I. Moncada, Green
41, 1462; (b) A. Decortes, A. M. Castilla, A. W. Kleiji, Chem., 2010, 12, 1376–1379.
J. Georgea, Y. Patel, S. M. Pillai and P. Munshic, J. Mol. 13 J. Ma, J. Song, H. Liu, J. Liu, Z. Zhang, T. Jiang, H. Fan and
Catal. A: Chem., 2009, 304, 9822, 2010, 49; (c) G. W. Coates B. Han, Green Chem., 2012, 14, 1743.
and D. R. Moore, Angew. Chem., Int. Ed., 2004, 43, 6618; 14 (a) J. Hu, J. Li, Y. Gu, Z. Guan, W. Mo, Y. Ni, T. Li and G. Li,
(d) M. R. Kember, A. Buchard and C. K. Williams, Chem.
Commun., 2011, 47, 141; (e) S. Klaus, M. W. Lehenmeier,
C. E. Anderson and B. Rieger, Coord. Chem. Rev., 2011, 255,
Appl. Catal., A, 2010, 386, 188; (b) M. Aresta,
A. Dibenedetto, F. Nocito and C. Pastore, J. Mol. Catal. A:
Chem., 2006, 257, 149.
1460; (f) M. North, R. Pasquale and C. Young, Green Chem., 15 (a) J.-I. Kadokawa, H. Hideyuki, S. Fukamachi, M. Karasu,
2010, 12, 1514.
H. Tagaya and K. Chiba, J. Chem. Soc., Perkin Trans. 1, 1999,
2205; (b) J. Georgea, Y. Patel, S. M. Pillai and P. Munshic,
J. Mol. Catal. A: Chem., 2009, 304, 1.
5 (a) W. A. Hoffman, J. Org. Chem., 1982, 47, 5209;
(b) P. Brignou, M. P. Gil, O. Casagrande, J.-F. Carpentier
and S. M. Guillaume, Macromolecules, 2010, 43, 8007; 16 (a) J. R. Ochoa-Gomeza, O. Gomez-Jimenez-Aberasturia,
(c) X. Zhang, Z. Zhong and R. Zhuo, Macromolecules, 2011,
C. A. Ramirez-Lopeza, J. NietoMestrea, B. Maestro-
Green Chem.
This journal is © The Royal Society of Chemistry 2013

View Article Online
Green Chemistry
Communication
Madurgaa and M. Belsuea, Chem.–Eng. J., 2011, 175, 505; 21 (a) J. D. Holbrey, W. M. Reichert, I. Tkatchenko,
(b) J.-L. Wang, L.-N. He, X.-Y. Dou and F. Wu,
Aust. J. Chem., 2009, 62, 917.
17 (a) S. Oi, K. Nemoto, S. Matsuno and Y. Inoue, Macromol.
Rapid Commun., 1994, 15, 133; (b) S.-I. Kim, F. Chu,
E. E. Dueno and K. W. Jung, J. Org. Chem., 1999, 64,
4578; (c) J. A. Cella and S. W. Bacon, J. Org. Chem., 1984,
E. Bouajila, O. Walter, I. Tommasi and R. D. Rogers, Chem.
Commun., 2003, 28; (b) S. N. Riduan, Y. Zhang and
J. Y. Ying, Angew. Chem., Int. Ed., 2009, 48, 3322;
(c) Y. G. Zhang and J. Y. G. Chan, Energy Environ. Sci., 2010,
3, 408; (d) D. Yu, M. X. Tan and Y. Zhang, Adv. Synth.
Catal., 2012, 354, 969.
49, 1122; (d) M. Shi and Y.-M. Shen, Molecules, 2002, 7, 22 (a) A. Behr, J. Eilting, K. Irawadi, J. Leschinski and
386.
F. Lindner, Green Chem., 2008, 10, 13; (b) J. Hu, J. Li, Y. Gu,
Z. Guan, W. Mo, Y. Ni, T. Li and G. Li, Appl. Catal., A, 2010,
386, 188; (c) F. Doro, P. Winnertz, W. Leitner, A. Prokofieva
and T. E. Muller, Green Chem., 2011, 13, 292.
18 (a) S. N. Riduan and Y. G. Zhang, Dalton Trans., 2010, 39,
3347; (b) Y G. Zhang and S. N. Riduan, Angew. Chem., Int.
Ed., 2011, 50, 6210; (c) D. Yu and Y. G. Zhang, Proc. Natl.
Acad. Sci. U. S. A., 2010, 107, 20184; (d) L. Gu and 23 C. Kim, J. E. Keum, S. H. Yu and S. Y. Ko, Bull. Korean
Y. G. Zhang, J. Am. Chem. Soc., 2010, 132, 914; (e) D. Yu and Chem. Soc., 2009, 30, 1671.
Y. G. Zhang, Green Chem., 2011, 13, 1275; (f) S. N. Riduan, 24 (a) B. A. Sweileh, Y. M. A-Hiari and K. M. Aiedeh, J. Appl.
J. Y. Ying and Y. G. Zhang, Org. Lett., 2012, 14, 1780;
(g) S. N. Riduan, J. Y. Ying and Y. G. Zhang, ChemCatChem,
2013, 5, 1490.
Polym. Sci., 2008, 110, 2278; (b) E. Castellanos, B. Kopsch
and H. J. Neumann, Fuel Sci. Technol. Int., 1993, 11, 1759.
25 G. Rokicki, W. Kuran and B. Pogorzelska-Marciniak,
Monatsh. Chem./Chem. Mon., 1984, 115, 205.
19 H. Mutlu, J. Ruiz, S. C. Solleder and M. A. R. Meier, Green
Chem., 2012, 14, 1728.
26 R. C. White and S. Ma, J. Chem. Educ., 1988, 65, 827.
20 S. Tempelaar, L. Mespouille, P. Dubois and A. P. Dove, 27 K. Matsumoto, Y. Sato, M. Shimojo and M. Hatanaka, Tetra-
Macromolecules, 2011, 44, 2084.
hedron: Asymmetry, 2000, 11, 1965.
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