Hydroxy-containing ionic liquids as catalysts in the synthesis of organic carbonates from epoxides and CO2

Article abstract of DOI:10.1007/s11172-020-2941-1

Hydroxy-containing ionic liquids such as triethyl(3-hydroxypropyl)ammonium, 1-(3-hydroxypropyl)-3-methylimidazolium, 3-(2-hydroxyethyl)-1-methylimidazolium, and 1-(3-hydroxypropyl)pyridinium chlorides were used as catalysts for the addition of carbon diox

Full text of DOI:10.1007/s11172-020-2941-1

Russian Chemical Bulletin, International Edition, Vol. 69, No. 8, pp. 1598—1600, August, 2020
1598
Hydroxy-containing ionic liquids as catalysts in the synthesis
of organic carbonates from epoxides and CO2*
S. E. Lyubimov,а A. A. Zvinchuk,а B. Chowdhury,b and V. A. Davankova
аA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
E-mail: lssp452@mail.ru
bIndian Institute of Technology (Indian School of Mines),
826004 Dhanbad, India.
E-mail: biswajit72@iitism.ac.in
Hydroxy-containing ionic liquids such as triethyl(3-hydroxypropyl)ammonium, 1-(3-hydr-
oxypropyl)-3-methylimidazolium, 3-(2-hydroxyethyl)-1-methylimidazolium, and 1-(3-hydr-
oxypropyl)pyridinium chlorides were used as catalysts for the addition of carbon dioxide to
epoxides, which gives cyclic carbonates. The effect of CO2 pressure and reaction temperature
on the conversion of epoxides, as well as a promoting effect of inorganic substrates were studied.
Key words: cyclic compounds, carbonates, hydroxy-containing compounds, ionic liquids,
carbon dioxide.
The increase in CO2 concentration in the atmosphere,
lysts for the addition of carbon dioxide to epoxides and
describe the effect of CO2 pressure and temperature on
the outcome of this reaction, as well as a promoting effect
of inorganic substrates.
leading to an enhancement in the greenhouse effect, has
initiated studies aimed at the search of both the reduction
of CO2 emissions and its capture and conversion into
economically valuable products.1 Emissions of CO2 have
increased significantly since the start of the industrial
revolution and are estimated to be around 33.3 Gt in 2019,
making carbon dioxide one of the most available and re-
newable sources of carbon.2—4 One of the most efficient
and practical directions for using carbon dioxide is its
introduction into organic molecules to obtain the corre-
sponding carbonates.5,6 The latter are widely used as fuel
additives, electrolytes for lithium-ion batteries, polar
solvents, anti-caking agents, monomers for the synthesis
of polycarbonates and polyurethanes.7 Recently, the use
of carbon dioxide in the synthesis of organic compounds
is closely related to another "green" approach, namely, the
use of ionic liquids as a medium or catalysts.1,2,8 Ionic
liquids are characterized by low volatility, incombustibil-
ity, acceptable thermal stability, the possibility of wide
modification by introducing additional functional groups
and replacing counterions, as well as high polarity, which
can facilitate acceleration of chemical reactions.9 A simple
approach to the increase in polarity and decrease in vola-
tility of ionic liquids consists in the introduction of ad-
ditional hydroxy groups into their structure.10
Results and Discussion
Hydroxy-containing ionic liquids 1—3 were obtained
by quaternization of triethylamine, 1-methylimidazole,
and pyridine with 3-chloropropan-1-ol and 2-chloro-
ethan-1-ol (Scheme 1). It should be noted that we have
developed procedures for the synthesis of compounds 1—3
allowing us to obtain them within 1 h. The proposed pro-
cedures are among the most optimal currently known
Scheme 1
In the present work, we report the results of our stud-
ies of a series of hydroxy-containing ionic liquids as cata-
* Dedicated to Academician of the Russian Academy of Sciences
A. M. Muzafarov on the occasion of his 70th birthday.
2: n = 3 (a), 2 (b)
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1598—1600, August, 2020.
1066-5285/20/6908-1598 © 2020 Springer Science+Business Media LLC

Cyclic carbonates
Russ. Chem. Bull., Int. Ed., Vol. 69, No. 8, August, 2020
1599
Table 1. Addition of CO2 to cyclohexene oxide (4)
temperature (120 С) increased the conversion from 5 to
20% (see Table 1, cf. entries 7 and 8). An even greater
promotional effect was manifested by titanium and alu-
minum oxides (entries 9 and 10).
Entry Catalyst Additive T/С P/atm. Conversion
of 4b (%)
Ammonium salt 1 (0.5 mol%) was used to study the
addition of CO2 to different epoxides 6a—i at 130 С
(Scheme 3). In all the cases, the corresponding carbonates
7a—i were obtained in quantitative yields regardless of the
electronic and steric characteristics of the substrate.
1
2
3
4
5
6
7
8
1
2a
2b
3
1
2a
1
1
1
1
—
—
130
130
130
130
130
130
120
120
120
120
56
56
56
56
20
20
56
56
56
56
100
100
1
—
—
30
—
100
100
5
—
—
a
Scheme 3
SiO2
20
a
9
10
Al2O3
65
a
TiO2
68
a 10 wt.% (30 mg) of additive was used.
b The selectivity according to the 1H NMR spectroscopy data
is more than 99%.
Conversion 100%
Selectivity 99%
methods.11—16 Thus, compound 1 was obtained by heat-
ing an excess of triethylamine with 3-chloropropan-1-ol
in an autoclave at 130 С, while derivatives 2 and 3 were
prepared by heating equimolar neat mixtures of amines
and the corresponding chlorine-substituted alcohols for 1 h.
Initial testing of the catalytic activity of compounds
1—3 (0.5 mol.%) was carried out in the addition of CO2
(56 atm.) to cyclohexene oxide 4 with the formation of
bicyclic carbonate 5 at 130 С (Scheme 2). The conversion
of cyclohexene oxide 4 was quantitative when ionic liquids
1 and 2a were used (Table 1, entries 1 and 2). An increase
in the length of the methylene spacer in homologous
compounds 2a,b, which also presumably increases electron
donating properties and improves solubility of salts in
organic compounds, is crucial for achieving high conver-
sion (compare entries 2 and 3). In the case of ionic liquid
3, the conversion of substrate 4 was 30%, which can be
explained by the strong electron-withdrawing effect of the
pyridine fragment (entry 4). The study of the effect of CO2
pressure on the conversion of substrate 4 in reactions in-
volving 1 and 2a showed that a quantitative conversion
was achieved at 20 atm. (entries 5 and 6). When the tem-
perature was reduced to 120 С, the conversion of epoxide
4 was only 5% (cf. entries 1 and 7).
R = Me (a), CH2Cl (b), CH2F (c), CH2CF3 (d), CH2C6F5 (e),
CH2OPh (f), CH2NEt2 (g), piperidin-1-ylmethyl (h), Ph (i)
Reagents and conditions: 1 (0.5 mol.%), СO2 (56 atm.), 130 С, 24 h.
Bis-epoxide 8 treated with CO2 in the presence of salt 1
gave bis-carbonate 9 in quantitative yield (Scheme 4).
Carbonate 9 is widely used in the synthesis of high-mo-
lecular-weight compounds with enhanced thermal and
mechanical properties, highly resistant adhesive materials,
and hydrophilizing agents.20—22
Scheme 4
Scheme 2
Conversion 100%
Selectivity 99%
Reagents and conditions: 1 (0.5 mol.%), СO2 (56 atm.), 130 С, 24 h.
To conclude, we showed that hydroxy-containing ionic
liquids can efficiently catalyze the addition of carbon di-
oxide to epoxides. The catalytic efficiency of these salts
depends on the length of the methylene spacer separating
the ammonium nitrogen atom from the hydroxy group, as
well as on the nature of the nitrogen-containing cation
itself. Inorganic additives can accelerate the reaction. The
Cat is the catalyst.
Taking into account a potential promoting effect of
the support on the outcome of this reaction, we studied
the effect of a series of supports under catalysis with
salt 1.6,17—19 The use of silica gel additive at the same

Lyubimov et al.
1600
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process is highly sensitive to temperature, with the carbon
dioxide pressure having lower effect on its rate.
Experimental
1H, 13С, and 19F NMR spectra were recorded on a Bruker
Avance 400 instrument (400.13, 100.61, and 376.5 MHz, respec-
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gel (0.06—0.2 mm, 60 Å, Acros Organics), TiO2, Al2O3, triethyl-
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2-chloroethan-1-ol, 7-oxabicyclo[4.1.0]heptane (4), 2-methyl-
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a 10-mL flat-bottom flask, and the mixture was refluxed for 1 h
with stirring. Then benzene (2 mL) was added to the mixture to
extract impurities and unreacted starting compounds. The solvent
was decanted, the products were additionally washed with di-
ethyl ether (2×2 mL) and vacuum dried. The yields were 94—96%.
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was placed into a 10-mL autoclave, followed by the addition of
an epoxide (3 mmol). The autoclave was filled with CO2 (20 or
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Received March 13, 2020;
in revised form May 22, 2020;
accepted June 1, 2020