Full Papers
Experimental Section
Table 3. Cycloaddition of CO
cidol and TBAB as catalytic system (epoxide=71.5 mmol, glycidol=
mol%, TBAB=1 mol%, CO2 =1.0 MPa, T=608C, t=24 h, neat).
2
to various epoxides in the presence of gly-
Materials and methods
1
P
Glycidol (Sigma–Aldrich) was distilled under reduced pressure prior
to use. All other reagents were used as-received (Sigma–Aldrich or
TCI Europe). Deuterated solvents were purchased from Euriso-Top
or Sigma–Aldrich and used as received. NMR spectra were collect-
ed on Bruker Avance spectrometers (600, 400, 300, or 250 MHz for
1
[a]
H NMR): the chemical shifts were referenced to tetramethylsilane
Entry
Epoxide
Conversion [%]
(TMS) as external reference, using the residual protio signal of the
[
b]
deuterated solvents.
1
2
3
26 (12)
31 (21)
83 (65)
General procedure for CO /glycidol coupling to glycerol car-
bonate
2
[c]
A 60 mL stainless steel pressure reactor equipped with a magnetic
stirring bar was charged with TBAB (0.754 mmol, 0.2430 g). Three
cycles of pressurization-depressurization were carried out and gly-
cidol (5.0 mL, 75.4 mmol) was introduced in the reactor. The reac-
[
d]
4
5
6
85 (45)
57 (42)
76 (66)
tion mixture was pressurized with CO at 1.0 MPa and stirred at
2
8
08C for 1 h. The reactor was cooled with ice, the CO released,
2
[
e]
tetrachloroethane (0.8 mL, 7.54 mmol) was added as an internal
1
standard and the mixture was analyzed by H NMR spectroscopy
using CDCl as solvent. Conversion: 85%.
3
[
d,e]
7
19 (6)
General procedure for CO /propylene oxide coupling to pro-
pylene carbonate
2
1
[
a] Determined by H NMR using mesitylene as internal standard, the ob-
served selectivity was always >99%. The values in brackets are the con-
versions in absence of glycidol. [b] PCO2 =balloon. [c] Glycidol=5 mol%,
TBAB=5 mol%, t=3 h. [d] Glycidol=5 mol%, TBAB=5 mol%. [e] Methyl
ethyl ketone (MEK)=10 mL.
A 60 mL stainless steel pressure reactor equipped with a magnetic
stirring bar was charged with TBAB (0.715 mmol, 0.2303 g) and gly-
cidol (47 mL, 0.715 mmol). Three cycles of pressurization–depressu-
rization were carried out and propylene oxide (5.0 mL, 71.4 mmol)
was introduced in the reactor. The reaction mixture was pressur-
ized with CO at 1.0 MPa and stirred at 808C for 24 h. The reactor
substrate and catalyst in this reaction, allowing the synthesis
of GC under metal-free, solvent-free, and rather mild reaction
conditions (T=60–808C, PCO2 =0.1–1 MPa) and short times (t=
2
was cooled with ice, the CO released. Unreacted epoxide was re-
2
moved under vacuum. The residue was dissolved in methylene
chloride, filtered over silica and the solvent removed under
vacuum. Isolated yield: 85%.
1–3 h).
The mechanism of the reaction was studied using density
functional theory (DFT). The nucleophilic attack by the bro-
mide anion was revealed to be the rate determining step. The
hydroxyl group of glycerol, acting as a hydrogen-bond donor,
serves to activate the epoxide for the ring opening and to sta-
bilize the two negatively charged intermediates, and is thus es-
sential for reaction rate. Analysis of the hydrogen-bond net-
work revealed that the intermolecular hydrogen-bond interac-
tions are particularly effective in facilitating the reaction path-
way for the conversion of glycerol to GC. To extend the applic-
Typical procedure for CO /epoxide coupling to the corre-
sponding cyclic carbonate
2
The procedure for 1,2-epoxyhexane is as reported: A 60 mL stain-
less steel pressure reactor equipped with a magnetic stirring bar
was charged with TBAB (3.57 mmol, 1.15 g) and glycidol (237 mL,
3.57 mmol). Three cycles of pressurization–depressurization were
carried out and 1,2-epoxyhexane (8.6 mL, 71.4 mmol) was intro-
duced in the reactor. The reaction mixture was pressurized with
CO2 at 1.0 MPa and stirred at 608C for 24 h. The reactor was
ability of this substrate in the field of the CO fixation reaction,
2
cooled with ice, the CO released, mesitylene (1.0 mL, 7.14 mmol)
2
we explored the possibility of using glycerol as a co-catalyst
for the TBAB-catalyzed cycloaddition. Actually, the binary
system glycidol/TBAB can act as efficient organocatalyst for
the conversion of diverse epoxides into the corresponding
cyclic carbonates in high-to-excellent yields under very mild
conditions (T=60–808C, PCO2 =0.1–1 MPa). Finally the low cata-
lyst loading and the fact that the glycidol is also converted to
the corresponding carbonate render the recovery of the cata-
lyst superfluous for most applications making this catalytic
system sustainable from both the environmental and economi-
cal point of views.
was added as an internal standard, and the mixture was analyzed
1
by H NMR spectroscopy using CDCl as solvent. Conversion: 93%.
3
For other epoxides a similar procedure was employed.
Typical procedure for CO /epoxide coupling to the corre-
2
sponding cyclic carbonate at low pressure
The procedure for 1,2-epoxyhexane is as reported: A 50 mL three-
neck round-bottom flask equipped with a magnetic stirring bar
and a condenser was charged with TBAB (3.57 mmol, 1.15 g) and
glycidol (237 mL, 3.57 mmol). The flask was flushed with CO and
2
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ChemSusChem 2016, 9, 1 – 9
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