One-pot conversion of carbon dioxide, ethylene oxide, and amines to 3-aryl-2-oxazolidinones catalyzed with binary ionic liquids

Article abstract of DOI:10.1002/cctc.201300801

An effective one-pot method for the conversion of carbon dioxide, ethylene oxide, and amines to 3-aryl-2-oxazolidinones has been developed. This one-pot method consists of two parallel reactions and a subsequent cascade reaction between the two products of the corresponding parallel reactions. Notably, the binary ionic liquids of 1-butyl-3-methyl-imidazolium bromide and 1-butyl-3-methyl-imidazolium acetate demonstrate a synergistic catalytic effect on this new strategy. 1-Butyl-3-methyl-imidazolium bromide is essential in two parallel reactions owing to the good nucleophilicity and leaving ability of bromide, and 1-butyl-3-methyl-imidazolium acetate plays a dominant role in the subsequent cascade reaction owing to the strong basicity of acetate. In addition, the binary ionic liquids can be used thrice without significant loss of catalytic activity. Copyright

Full text of DOI:10.1002/cctc.201300801

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DOI: 10.1002/cctc.201300801
One-Pot Conversion of Carbon Dioxide, Ethylene Oxide,
and Amines to 3-Aryl-2-oxazolidinones Catalyzed with
Binary Ionic Liquids
Binshen Wang, Elnazeer H. M. Elageed, Dawei Zhang, Sijuan Yang, Shi Wu, Guirong Zhang,
and Guohua Gao*[a]
An effective one-pot method for the conversion of carbon di-
oxide, ethylene oxide, and amines to 3-aryl-2-oxazolidinones
has been developed. This one-pot method consists of two par-
allel reactions and a subsequent cascade reaction between the
two products of the corresponding parallel reactions. Notably,
the binary ionic liquids of 1-butyl-3-methyl-imidazolium bro-
mide and 1-butyl-3-methyl-imidazolium acetate demonstrate
a synergistic catalytic effect on this new strategy. 1-Butyl-3-
methyl-imidazolium bromide is essential in two parallel reac-
tions owing to the good nucleophilicity and leaving ability of
bromide, and 1-butyl-3-methyl-imidazolium acetate plays
a dominant role in the subsequent cascade reaction owing to
the strong basicity of acetate. In addition, the binary ionic liq-
uids can be used thrice without significant loss of catalytic
activity.
Introduction
Carbon dioxide originating from the combustion of fossil fuel
is regarded as the main greenhouse gas.[1] With the growth of
world population, it is apparent that atmospheric CO2 concen-
tration will continue to increase monotonically for the foresee-
able future owing to the energy demand. The projected global
CO2 emissions are 36 billion metric tons by 2020 and 45 billion
metric tons by 2040.[2] However, CO2 is an abundant, economi-
cal, and nontoxic biorenewable carbon resource.[3] Thus, in the
last decade, a growing number of studies have been conduct-
ed on the fixation of CO2 to valuable chemicals.[4] To overcome
the thermodynamic stability of CO2 molecules, the fixation pro-
cesses typically require harsh reaction conditions (high temper-
ature and high pressure) or high-energy substances such as
small-ring compounds, hydrogen, unsaturated compounds,
and metal organic compounds.[5]
though several studies on the transformation of CO2 to value-
added chemicals have been performed with epoxides as cou-
pling agents, the products are limited to carbonates, such as
glycerol carbonate,[8] dimethyl carbonate,[5a,9] and diethyl car-
bonate.[10]
3-Aryl-2-oxazolidinones are important heterocyclic com-
pounds that have attracted much attention owing to their bio-
activity. They can serve as reversible monoamine oxidase inhib-
itors, HIV-1 protease inhibitors, and antimicrobial agents.[11] The
conventional conversions to oxazolidinones are through the re-
action of phosgene and 2-alkamine[12] and the reaction of ep-
oxide and isocyanate,[13] which are considered nongreen as
toxic starting materials are used. The alternative synthetic con-
versions through the reaction of CO2 and aziridines are also re-
ported.[14] In another study, we developed a strategy for the
ionic liquid-catalyzed formation of 3-aryl-2-oxazolidinones from
cyclic carbonates and aromatic amines (Scheme 1a).[15] Herein,
we report a new approach for the straightforward conversion
of CO2 to 3-aryl-2-oxazolidinones via the high-energy molecule
of EO catalyzed with binary ionic liquids (Scheme 1b). The
binary ionic liquids of 1-butyl-3-methyl-imidazolium bromide
As a small-ring compound, ethylene oxide (EO; the annual
worldwide production of which is approximately 19 million
metric tons) is used mainly to produce ethylene glycol (EG)
through hydrolysis in the conventional chemical industry.[6]
This hydrolysis process, however, does not take full advantage
of the inherent high energy of EO.[7] Therefore, it would be
practically useful to maintain downstream EG unchanged as
well as to utilize the high-energy molecule of EO to fix CO2. Al-
[a] B. Wang, E. H. M. Elageed, D. Zhang, S. Yang, S. Wu, Dr. G. Zhang,
Prof. Dr. G. Gao
Shanghai Key Laboratory of Green Chemistry and Chemical Processes
Department of Chemistry
East China Normal University
North Zhongshan Road 3663, Shanghai (P.R. China)
Fax: (+86)21-62233323
E-mail: ghgao@chem.ecnu.edu.cn
Scheme 1. a) Synthesis of 3-aryl-2-oxazolidinones from cyclic carbonate and
aromatic amines and b) the present approach for the straightforward con-
version of CO2 to 3-aryl-2-oxazolidinones.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300801.
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(BmimBr) and 1-butyl-3-methyl-imidazolium acetate (Bmi-
mOAc) demonstrate a synergistic catalytic effect on the one-
pot conversion.
creasing the catalyst amount, reaction time, temperature, or
CO2 pressure led to lower yields (entries 12–15). Furthermore,
an equal amount of 3-phenyl-2-oxazolidinone and EG was gen-
erated under optimal reaction conditions (entry 7) as deter-
mined from 1H NMR analysis of the reaction mixture (Fig-
ure S1).
Results and Discussion
Reaction of CO2, EO, and aniline catalyzed with ionic liquids
under various conditions
Reaction mechanism studies
During the reaction under optimal conditions (entry 7), a small
amount of 2-(phenylamino)ethanol was detected in 1 h and EG
was obtained as a byproduct after the completion of the reac-
tion. 2-(Phenylamino)ethanol was probably the intermediate in
this one-pot conversion of CO2 to 3-phenyl-2-oxazolidinone.
Hence, a reaction mechanism was proposed (Scheme 2): EO as
a high-energy molecule is used to fix CO2 to ethylene
The reaction of CO2, EO, and aniline was performed under vari-
ous conditions to optimize reaction parameters. The effects of
a single ionic liquid, binary ionic liquids, the ratio of binary
ionic liquids, the amount of ionic liquids, reaction time, tem-
perature, and CO2 pressure were investigated, and the results
are summarized in Table 1.
carbonate [reaction (1)]. At the same time, EO reacts
with aniline to form the intermediate 2-(phenylami-
Table 1. Optimization of reaction conditions for the conversion of CO2 to 3-phenyl-2-
no)ethanol [reaction (2)]. Then, 2-(phenylamino)etha-
nol reacts with ethylene carbonate to yield 3-phenyl-
2-oxazolidinone and EG [reaction (3)]. Notably, two
reactions [reactions (1) and (2)] proceed in parallel,
followed by a cascade reaction [reaction (3)] between
the two products of the corresponding parallel reac-
tions. Notably, the binary ionic liquids of BmimBr and
BmimOAc synergistically catalyze this one-pot con-
version: BmimBr is essential in the parallel reactions
involving EO [reactions (1) and (2)] because bromide
promotes ring opening of epoxides owing to its
good nucleophilicity and leaving ability,[5c,9f,16] and
BmimOAc plays a dominant role in the subsequent
cascade reaction of 2-(phenylamino)ethanol and eth-
ylene carbonate [reaction (3)], in which the strong
basicity of acetate results in increase of nucleophilici-
ty of 2-(phenylamino)ethanol.
oxazolidinone.[a]
Entry
Ionic liquid
Mol[b]
[%]
t
[h]
T
[8C]
P
Yield (Conversion)[c]
[%]
[MPa]
1[d]
2[d]
3[d]
4
BmimBF4
BmimBr
BmimCl
BmimOAc
20
20
20
20
10+10
10+10
10+10
15+5
5+15
10+10
15+15
5+5
9
9
9
9
9
9
9
9
9
12
12
12
6
9
9
140
140
140
140
140
140
140
140
140
140
140
140
140
130
140
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2
2 (>99)
24 (>99)
45 (>99)
70 (>99)
33 (>99)
74 (>99)
94 (>99)
84 (>99)
81 (>99)
94 (>99)
94 (>99)
70 (>99)
83 (>99)
72 (>99)
81 (>99)
5[d]
6
BmimBF4 +BmimOAc
BmimCl+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
BmimBr+BmimOAc
7
8
9
10
11
12
13
14
15
10+10
10+10
10+10
[a] Reaction conditions: aniline (2 mmol), EO (2 mL); [b] Based on aniline; [c] GC yield
of 3-phenyl-2-oxazolidinone and conversion of aniline; [d] A mixture of 2-(phenyl-
amino)ethanol and its oligomers was detected.
To validate the proposed reaction mechanism, the
following experiments and calculations were per-
formed. First, in the presence of BmimBr or BmimOAc
Under different reaction conditions, the conversion of aniline
was extremely high (>99%); however, the yield of 3-phenyl-2-
oxazolidinone changed considerably. Upon using 20 mol% of
1-butyl-3-methyl-imidazolium tetrafluoroborate (BmimBF4),
BmimBr, 1-butyl-3-methyl-imidazolium chloride (BmimCl), or
BmimOAc alone, we obtained 3-phenyl-2-oxazolidinone in 2,
24, 45, and 70% yields, respectively (Table 1, entries 1–4). Then,
binary ionic liquids were investigated. The mixture of BmimBF4
and BmimOAc and the mixture of BmimCl and BmimOAc af-
forded the product in 33 and 74% yields, respectively (en-
tries 5 and 6). Notably, the mixture of 10 mol% of BmimBr and
10 mol% of BmimOAc afforded the product in approximately
94% yield, which revealed a synergistic catalytic effect of
binary ionic liquids (entry 7). By varying ratios of BmimBr and
BmimOAc, no improvement in the yields was achieved (en-
tries 8 and 9). In addition, increasing the reaction time or cata-
lyst amount did not improve the yield (entries 10 and 11). De-
Scheme 2. The proposed reaction mechanism.
alone, the reaction of EO and CO2 [Scheme 2, reaction (1)] af-
forded ethylene carbonate in 77 and 23% yields, respectively
(Scheme 3). This finding indicated that BmimBr was more ef-
fective than BmimOAc in the cycloaddition of CO2 and EO
[Scheme 2, reaction (1)]. Second, the enthalpy changes calcu-
lated by using DFT indicated that 2-(phenylamino)ethanol was
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Scheme 3. Reaction of CO2 and EO.
Scheme 6. Reaction of ethylene carbonate and 2-(phenylamino)ethanol.
favorably formed through the reaction of aniline and EO
[DH1 =À27.7 kcalmolÀ1; Scheme 2, reaction (2)] rather than
through the reaction of aniline and ethylene carbonate (DH2 =
À17.3 kcalmolÀ1) (Scheme S1). However, the use of BmimBr in
the reaction of aniline and EO [Scheme 2, reaction (2)] gave
only a mixture of oligomers. These oligomers could be due to
the further reaction of 2-(phenylamino)ethanol with EO.[17] In
contrast, the use of BmimOAc gave the lower conversions of
aniline (>99% vs. 83% at 1408C; 96% vs. 73% at 1008C),
which indicated that BmimBr was more effective than Bmi-
mOAc for the ring-opening reaction of EO [Scheme 2, reac-
tion (2); Scheme 4]. Adding ethylene carbonate and EO to
(5:1:1) affording an equal amount of 3-phenyl-2-oxazolidinone
and EG (90% yields) also testified the proposed reaction mech-
anism (Scheme 7).
Scheme 7. Reaction of ethylene carbonate, EO, and aniline.
Reusability of binary ionic liquids
To investigate their reusability, the binary ionic liquids of
BmimBr and BmimOAc were recycled after the reaction of CO2,
EO, and aniline.
The binary ionic liquids could be recovered easily through
simple extraction with water from chloroform and desiccation
under vacuum. As shown in Figure 1, the yields of the first
three cycles were constant whereas the yield of the fourth
cycle decreased. After the fourth cycle, the ionic liquids were
decomposed partially as determined from 1H NMR analysis
(Figure S2); this decomposition was probably due to the volati-
lization of acetic acid during the desiccation of ionic liquids
under vacuum at 1308C.[18] Another reason for the decrease in
Scheme 4. Reaction of aniline and EO.
2-(phenylamino)ethanol (5:5:1) simultaneously afforded
3-phenyl-2-oxazolidinone (major product, in 70% yield) instead
of the above-mentioned oligomers (Scheme 5). These results
revealed that the 2-(phenylamino)ethanol intermediate could
react with ethylene carbonate more efficiently and favorably
than EO. Third, with use of different ionic liquids in the reac-
Scheme 5. Reaction of ethylene carbonate, EO, and 2-(phenylamino)ethanol.
tion of ethylene carbonate and 2-(phenylamino)ethanol to pro-
duce 3-phenyl-2-oxazolidinone [Scheme 2, reaction (3)], the
catalytic activity followed the order BmimOAc>BmimCl>
BmimBr>BmimBF4, which was consistent with the order of
the basicity of anions of ionic liquids (Scheme 6).[15] This finding
indicated that BmimOAc played the dominant role in this reac-
tion owing to the strong basicity of acetate. Finally, as a supple-
ment, the reaction of ethylene carbonate, EO, and aniline
Figure 1. Reusability of binary ionic liquids. Reaction conditions: aniline
(4 mmol), EO (4 mL), BmimBr (0.4 mmol), BmimOAc (0.4 mmol), 9 h, 1408C,
2.5 MPa CO2 pressure.
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the yield could be that EG was not removed completely under
the above recycling conditions. The residue EG could hinder
the reaction of 2-(phenylamino)ethanol and ethylene carbon-
ate [Scheme 2, reaction (3)]. Instead, 2-(phenylamino)ethanol
was converted to its oligomers. A control experiment was per-
formed to demonstrate the prohibiting effect of EG: After
adding 1 equiv. of EG, the model reaction of CO2, EO, and ani-
line under optimal reaction conditions afforded 3-phenyl-2-ox-
azolidinone in only 48% yield. In addition, with the desiccation
of ionic liquids under vacuum at 708C (water can be removed;
however, EG was removed with difficulty under these condi-
tions), the yields of the second and third cycles decreased con-
siderably to 74 and 28%, respectively.
Table 2. Conversion of CO2 to various 3-substituted-2-oxazolidinones cat-
alyzed with binary ionic liquids.[a]
Entry
1
Amine
Product
Yield[b] [%]
>99
2
3
>99
96
4
>99
Reaction of CO2, EO, and other amines catalyzed with binary
ionic liquids of BmimBr and BmimOAc
5
6
>99
To investigate the generalities of this method, the reactions of
CO2, EO, and other amines catalyzed with binary ionic liquids
of BmimBr and BmimOAc were performed (Table 2). p-Chloro-
aniline (1a) and m-chloroaniline (1b) gave the corresponding
3-aryl-2-oxazolidinones 2a and 2b in >99% yields (entries 1
and 2). In contrast, o-chloroaniline (1c) afforded the product
2c in a slightly lower yield (96%) owing to the steric effect
(entry 3). Aromatic amines with electron-withdrawing substitu-
ents (such as halides) 1a–e gave the desired products 2a–e in
quantitative yields (entries 1–5). However, aromatic amines
with electron-donating substituents (such as alkyl or alkoxy
species) 1 f–h provided target products 2 f–h in 63–77% yields
and N,N-(dihydroxyethyl)amines in 11–17% yields (entries 6–8).
The formation of byproducts could be attributed to the in-
creased electronegativity of amidos. In addition, naphthalen-1-
ylamine (1i) could be converted to 2i in an excellent yield
(entry 9). Aliphatic amines that possess stronger electronega-
tivity, such as benzylamine (1j) and cyclohexylamine (1k), were
tolerated, which afforded 3-substituted-2-oxazolidinones 2j
and 2k in 31 and 29% yields, respectively (entries 10 and 11).
The reaction of CO2, propylene oxide, and aniline afforded 5-
methyl-3-phenyl-oxazolidin-2-one (2l) in 31% yield (entry 12).
77
7
8
9
63
75
>99
10
31
11
29
31
12[c]
[a] Reaction conditions: amine (2 mmol), EO (2 mL), BmimBr (0.2 mmol),
BmimOAc (0.2 mmol), 9 h, 1408C, 2.5 MPa CO2 pressure; [b] GC yield;
[c] Propylene oxide (40 mmol).
Conclusions
We have developed an effective strategy for the direct conver-
sion of CO2 to a series of 3-aryl-2-oxazolidinones via the high-
energy molecule of ethylene oxide catalyzed with binary ionic Experimental Section
liquids. This one-pot method consists of two parallel reactions
General
and a subsequent cascade reaction between the two products
of the corresponding parallel reactions. The binary ionic liquids
of 1-butyl-3-methyl-imidazolium bromide (BmimBr) and
1-butyl-3-methyl-imidazolium acetate (BmimOAc) demonstrate
a synergistic catalytic effect on this process. BmimBr promotes
two parallel reactions owing to the good nucleophilicity and
leaving ability of bromide, and BmimOAc accelerates the sub-
sequent cascade reaction owing to the strong basicity of ace-
tate. Furthermore, the binary ionic liquids of BmimBr and Bmi-
mOAc can be recycled by using the simple extraction method
and used thrice without significant loss of catalytic activity.
CO2 with a purity of 99.995% was commercially available. All ionic
liquids were supplied by the Centre for Green Chemistry and Catal-
ysis, LICP, CAS. 2-(Phenylamino)ethanol was supplied by TCI. Ethyl-
ene carbonate was supplied by Sigma–Aldrich. The other com-
pounds were supplied by Sinopharm. All chemicals were used
without further purification.
GC analysis was performed by using a Shimadzu GC-14B equipped
with
a capillary column DM-1701 (30 mꢁ0.32 mmꢁ0.25 mm)
equipped with a flame ionization detector. The NMR spectra were
recorded by using a Bruker Ascend 400 and Bruker DRX500 MHz
NMR spectrometers with tetramethylsilane as the internal standard.
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1
3-Benzyl-oxazolidin-2-one (2j): H NMR (500 MHz, CDCl3, TMS): d=
Typical method for the reaction of CO2, EO, and aniline cata-
lyzed with binary ionic liquids of BmimBr and BmimOAc
7.29–7.40 (m, 5H), 4.46 (s, 2H), 4.33 (t, J=8.0 Hz, 2H), 3.45 ppm (t,
J=8.0 Hz, 2H).
In a typical experiment, BmimBr (0.044 g, 0.2 mmol), BmimOAc
(0.040 g, 0.2 mmol), aniline (0.186 g, 2.0 mmol), and EO (2 mL,
40 mmol) were added to a stainless steel autoclave reactor with an
inner volume of 25 mL. The reactor was pressurized with approxi-
mately 1 MPa of CO2 pressure at ambient temperature. Then, the
reactor was heated to 1408C and the CO2 pressure was adjusted to
2.5 MPa for 9 h. After the completion of the reaction, the autoclave
was cooled to RT, followed by slow venting of the remaining CO2.
The reaction mixture (0.07 g) was taken out for NMR analysis. Next,
chloroform (7 mL) was added to the reaction mixture. The organic
phase was washed with water (3ꢁ7 mL) to remove ionic liquids
and EG and then analyzed by using GC with n-dodecane as the in-
ternal standard. The pure 3-phenyl-2-oxazolidinone was obtained
by using chromatography on silica gel and structurally character-
ized by using NMR spectroscopy.
To investigate the reusability of binary ionic liquids, chloroform
(14 mL) was added to the reaction mixture after slow venting of
the remaining CO2. The organic phase was extracted with water
(5ꢁ14 mL) and then analyzed by using GC with n-dodecane as the
internal standard. The ionic liquids were recovered after the aque-
ous phase was evaporated under vacuum at 1308C for 10 h to
remove water and EG. The same method was repeated for the
next cycle.
1
3-Cyclohexyl-oxazolidin-2-one (2k): H NMR (500 MHz, CDCl3, TMS):
d=4.31 (t, J=8.0 Hz, 2H), 3.66–3.70 (m, 1H), 3.53 (t, J=8.0 Hz,
2H), 1.65–1.85 (m, 4H), 1.68 (d, J=13.5 Hz, 1H), 1.34–1.39 (m, 4H),
1.08–1.13 ppm (m, 1H).
5-Methyl-3-phenyl-oxazolidin-2-one (2l): 1H NMR (400 MHz, CDCl3,
TMS): d=7.53 (d, J=7.2 Hz, 2H), 7.37 (t, J=7.2 Hz, 2H), 7.13 (t, J=
7.2 Hz, 1H), 4.75–4.83 (m, 1H), 4.11 (m, 1H), 3.62 (m, 1H), 1.53 ppm
(d, J=6.4 Hz, 3H).
Acknowledgements
We thank the National Natural Science Foundation of China
(grant number 20873041 and 21273078) and Shanghai Leading
Academic Discipline Project (project number B409) for financial
support.
Keywords: 3-aryl-2-oxazolidinones · carbon dioxide fixation ·
ethylene oxide · ionic liquids · one-pot reaction
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3-(3,5-Dichloro-phenyl)-oxazolidin-2-one (2d): 1H NMR (500 MHz,
CDCl3, TMS): d=7.52 (s, 2H), 7.15 (s, 1H), 4.53 (t, J=8.0 Hz, 2H),
4.05 ppm (t, J=8.0 Hz, 2H).
1
3-(4-Bromo-phenyl)-oxazolidin-2-one (2e): H NMR (500 MHz, CDCl3,
TMS): d=7.45–7.51 (m, 4H), 4.49–4.52 (m, 2H), 4.05 ppm (t, J=
8.0 Hz, 2H).
1
3-p-Tolyl-oxazolidin-2-one (2 f): H NMR (400 MHz, CDCl3, TMS): d=
7.42 (d, J=8.4 Hz, 2H), 7.18 (d, J=8.4 Hz, 2H), 4.48 (t, J=8.0 Hz,
2H), 4.04 (t, J=8.0 Hz, 2H), 2.33 ppm (s, 3H).
3-(4-Methoxy-phenyl)-oxazolidin-2-one (2g): 1H NMR (400 MHz,
CDCl3, TMS): d=7.43 (d, J=9.2 Hz, 2H), 6.91 (d, J=9.2 Hz, 2H),
4.46 (t, J=8.0 Hz, 2H), 4.02 (t, J=8.0 Hz, 2H), 3.79 ppm (s, 3H).
3-(4-Ethoxy-phenyl)-oxazolidin-2-one (2h): 1H NMR (500 MHz,
CDCl3, TMS): d=7.42–7.44 (m, 2H), 6.90–6.92 (m, 2H), 4.45–4.48
(m, 2H), 4.00–4.04 (m, 4H), 1.41 ppm (t, J=7.0 Hz, 3H).
3-Naphthalen-1-yl-oxazolidin-2-one (2i): 1H NMR (400 MHz, CDCl3,
TMS): d=7.85–7.87 (m, 3H), 7.47–7.59 (m, 4H), 4.64 (t, J=8.0 Hz,
2H), 4.09 ppm (t, J=8.0 Hz, 2H).
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Received: September 20, 2013
Published online on December 5, 2013
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ChemCatChem 2014, 6, 278 – 283 283