7
0
X.-F. Liu et al. / Catalysis Today 263 (2016) 69–74
O
Tianjin Guangfu Fine Chemical Research Institute. All reagents were
used without further purification. Carbon dioxide with a purity
of 99.99% was commercially available. The products were charac-
terized by NMR, FT-IR and HRMS. 1H NMR spectra was recorded
cat.
O
+
CO2
O
O
R
R
on 400 MHz spectrometers using CDCl as solvent referenced to
3
CDCl3 (7.26 ppm). 13C NMR was recorded at 100.6 MHz in CDCl3
Scheme 1. Cycloaddition of CO2 with epoxide.
(
77.00 ppm). Multiplets were assigned as singlet, doublet, triplet,
doublet of doublet, multiplet and broad singlet. Gas chromatograph
Shimadzu 2014 chromatographer) is equipped with a RTX-5 cap-
illary column (30 m × 0.25 mm) using a flame ionization detector
FID). Infrared (IR) spectra were recorded on a Bruker Tensor 27
(
(
FT-IR spectrophotometer with KBr pellets. High-resolution mass
spectrometry (HRMS) was conducted using an Ionspec 7.0 T spec-
trometer.
Scheme 2. EDTA, TMEDA and EDTA-3Na used in this study.
2.2. General procedure for the cycloaddition reaction of epoxides
and CO2
catalytic system was developed even at atmospheric pressure of
CO2 and room temperature to prepare cyclic carbonates [26].
However, the complicated procedure is required for the catalyst
preparation.
As a kind of HBD, carboxylic acids are alternatives to alco-
hols and phenolic compounds. This could be understandable
because carboxylic group could coordinate with oxygen atom in
the epoxide through hydrogen bonding interaction, thus facilitat-
ing ring-opening of the epoxide. In this aspect, Han et al. employed
betaine-based salts bearing with carboxyl group as catalysts for
The cycloaddition reaction of epoxides and CO2 was conducted
in a stainless steel autoclave (50 mL inner volumes). In a typical
reaction, the reactor was charged with EDTA (73.1 mg, 0.25 mmol),
TBAB (80.6 mg, 0.25 mmol) and styrene oxide (0.6008 g, 5 mmol)
successively at room temperature. Then, CO2 was introduced into
◦
the reactor and pressure was adjusted to 5 bar at 70 C. The auto-
clave was heated at this temperature for 18 h, and the pressure
was kept constant during the reaction. After the reaction was com-
◦
pleted, the reactor was cooled to 0 C in ice-water bath, and then
the excess of CO2 was carefully vented. An aliquot of the sample
was taken from the resultant mixture and dissolved in ethyl acetate
the synthesis of cyclic carbonates from epoxides and CO . As a
2
result, the reaction could proceed smoothly under 8 MPa CO2 and
1
for H NMR analysis. The conversion of epoxide and yield of cyclic
◦
at 140 C [27]. Subsequently, milder reaction conditions (2 MPa,
carbonate were determined by 1,3,5-trimethyoxybenzene as the
◦
1
25 C) was realized for the cycloaddition of epoxides with CO cat-
2
internal standard in CDCl . The residue was purified by column
3
alyzed by bifunctional carboxylic-functionalized ionic liquids [28].
Inspiringly, CO2 pressure could reduce to 1 MPa when amino acid
chromatography with ethyl acetate–petroleum ether as the eluent
to afford the desired product. Spectral data for the products (2a–f)
are as follows:
◦
ionic liquids were applied as catalysts at 120 C [29]. Although sig-
nificant advances have been made, performing the cycloaddition
of epoxides and CO2 under mild reaction conditions especially at
low pressure (ideally at 1 bar) could be desirable and still remains
a challenge.
2
.2.1. 4-Phenyl-1,3-dioxolan-2-one (2a)
1
White solid; H NMR (CDCl , 400 MHz) ı (ppm) 4.31 (t,
3
3
3
3
J = 8.4 Hz, 1H), 4.78 (t, J = 8.4 Hz, 1H), 5.66 (t, J = 8.0 Hz, 1H),
Ethylenediaminetetraacetic acid (EDTA, Scheme 2) is commonly
used as a complexing agent in analytical and environmental chem-
istry due to the advantageous characters of being nontoxic, cheap
and commercially available [30,31]. EDTA with carboxylic group
could be potentially used as an excellent hydrogen-bonding donor.
Furthermore, we envisioned that multiple carboxylic groups in one
molecule, e.g. four carboxylic groups in one EDTA molecule, could
more effectively activate the epoxide through multi-site hydro-
gen bonding compared with single-site hydrogen bonding, and
thereby greatly promote the cycloaddition of epoxides with CO2.
Herein, we would like to disclose an efficient process for the syn-
thesis of cyclic carbonates from epoxides and CO2 by employing
EDTA/TBAB (tetrabutylammonium bromide) as dual-component
bifunctional catalyst system. Notably, the catalyst system with
EDTA/TBAB worked well for the coupling reactions under mild reac-
13
7
.34–7.44 (m, 5H); C NMR (CDCl , 100.6 MHz) ı (ppm) 71.25,
3
7
1
8.09, 125.99, 129.24, 129.74, 135.87, 155.02. IR (KBr): 1779, 1162,
−1
046, 756, 688 cm . HRMS (EI) calc. for [C H O ]: 164.0473,
9
8
3
found: 164.0474.
2
.2.2. 4-Methyl-1,3-dioxolan-2-one (2b)
Colorless liquid; 1H NMR (CDCl , 400 MHz) ı (ppm) 1.50 (d,
3
3
3
3
J = 6.0 Hz, 3H), 4.04 (t, J = 8.4 Hz, 1H), 4.58 (t, J = 8.4 Hz, 1H), 4.88
13
(m, 1H); C NMR (CDCl , 100.6 MHz) ı (ppm) 19.35, 70.71, 73.65,
3
−1
1
55.12. IR (KBr): 1791, 1184, 1120, 1076, 1052, 776 cm . HRMS
(
EI) calc. for [C H O ]: 102.0317, found: 102.0315.
4 6 3
2
.2.3. 4-Phenoxymethyl-1,3-dioxolan-2-one (2c)
1
White solid; H NMR (CDCl , 400 MHz) ı (ppm) 4.16 (dd,
3
3
2
3
2
J = 4.4 Hz, J = 10.8 Hz, 1H), 4.24 (dd, J = 3.6 Hz, J = 10.8 Hz, 1H),
◦
tion conditions (5 bar, 70 C) and cyclic carbonates were gained in
.55 (dd, 3J = 8.4 Hz, J = 6 Hz, 1H), 4.62 (t, J = 8.4 Hz, 1H), 5.03
2
3
4
good yields and high selectivity.
m, 1H), 6.91 (d, J = 8.0 Hz, 2H), 7.02 (t, 3J = 7.4 Hz, 2H), 7.31
3
(
(
3
13
t, J = 8.0 Hz, 2H); C NMR (CDCl , 100.6 MHz) ␦ (ppm) 66.26,
3
2
. Experimental
66.94, 74.05, 114.66, 122.05,129.72, 157.78. IR (KBr): 2927, 1783,
−
1
1
600, 1490, 1396, 1161, 1081, 1009 cm . HRMS (FAB) calc. for
2.1. General information
[C10H10O ]: 194.0517, found: 194.0515.
4
Propylene oxide and epichlorohydrin were purchased from
2.2.4. 4-n-Butyl-1,3-dioxolan-2-one (2d)
Alfa Aesar, other epoxides and EDTA (ethylenediaminetetraacetic
acid), TMEDA (tetramethylethylenediamine), EDTA-3Na (ethylene-
diaminetetraacetic acid trisodium salt), were of analytical grade
and obtained from Aladdin. TBAB, TBAI and KBr were from
Colorless liquid; 1H NMR (CDCl , 400 MHz) ı (ppm) 0.93 (t,
3
3
J = 7.2 Hz, 3H), 1.26–1.48 (m, 4H), 1.64–1.87 (m, 2H), 4.08 (dd,
3
J = 7.3 Hz, J = 8.0 Hz, 1H), 4.54 (t, 3J = 8.0 Hz, 1H), 4.68–4.75 (m,
2
1H); 13C NMR (CDCl , 100.6 MHz) ı (ppm) 13.81, 22.26, 26.44,
3