Functionalized quaternary ammonium salt ionic liquids (FQAILs) as an economic and efficient catalyst for synthesis of glycerol carbonate from glycerol and dimethyl carbonate

Article abstract of DOI:10.1016/j.mcat.2019.02.005

A series of functionalized quaternary ammonium salt ionic liquids (FQAILs) with different functional groups, such as hydroxyl, carboxyl, ether group, and amino, were prepared and used as a catalyst for the synthesis of glycerol carbonate from transesterification of glycerol and dimethyl carbonate without any additional organic solvent and co-catalyst. The effects of functional groups, anions (Cl^?, Br^?, I^?, OH^?), and reaction parameters were investigated in detail. It is found that both the cation and anion of FQAILs display an important effect on its catalytic activity. Among these FQAILs, hydroxyl functionalized ionic liquid, [HPTPA]OH possesses the highest activity because there are the strong interactions between hydroxyl and dimethyl carbonate molecular and between anion OH^? and glycerol molecular, which were shown by FTIR spectra. The glycerol conversion of 96.2% and glycerol carbonate yield of 87.6% can be obtained over [HPTPA]OH under moderate conditions of reaction temperature of 80 °C, reaction time of 90 min, dimethyl carbonate/glycerol molar ratio of 3, and catalyst amount of 0.9 mol% based on glycerol amount. The [HPTPA]OH catalyst can be reused at least three cycles without significant reduction in its catalytic activity. Finally, a possible reaction mechanism for the synthesis of glycerol carbonate is also proposed.

Full text of DOI:10.1016/j.mcat.2019.02.005

Molecular Catalysis 468 (2019) 19–28
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Functionalized quaternary ammonium salt ionic liquids (FQAILs) as an
economic and efficient catalyst for synthesis of glycerol carbonate from
glycerol and dimethyl carbonate
Elrasheed Elhaj , Huajun Wanga,b,⁎, Yanlong Gua,b,⁎
a,c
a
Key Laboratory for Material Chemistry for Energy Conversion and Storage, Ministry of Education, Wuhan, 430074, PR China
Hubei Key Laboratory of Material Chemistry & Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan,
b
4
30074, PR China
c
Chemical Engineering Department, Faculty of Engineering and Technical Studies, University of Elimam Elmahdi, Kusti, P.O. Box 209, Sudan
A R T I C L E I N F O
A B S T R A C T
Keywords:
Glycerol carbonate
Ionic liquid
Glycerol
Transesterification
Quaternary ammonium salt
A series of functionalized quaternary ammonium salt ionic liquids (FQAILs) with different functional groups,
such as hydroxyl, carboxyl, ether group, and amino, were prepared and used as a catalyst for the synthesis of
glycerol carbonate from transesterification of glycerol and dimethyl carbonate without any additional organic
−
−
−
−
solvent and co-catalyst. The effects of functional groups, anions (Cl , Br , I , OH ), and reaction parameters
were investigated in detail. It is found that both the cation and anion of FQAILs display an important effect on its
catalytic activity. Among these FQAILs, hydroxyl functionalized ionic liquid, [HPTPA]OH possesses the highest
activity because there are the strong interactions between hydroxyl and dimethyl carbonate molecular and
−
between anion OH and glycerol molecular, which were shown by FTIR spectra. The glycerol conversion of
96.2% and glycerol carbonate yield of 87.6% can be obtained over [HPTPA]OH under moderate conditions of
reaction temperature of 80 °C, reaction time of 90 min, dimethyl carbonate/glycerol molar ratio of 3, and
catalyst amount of 0.9 mol% based on glycerol amount. The [HPTPA]OH catalyst can be reused at least three
cycles without significant reduction in its catalytic activity. Finally, a possible reaction mechanism for the
synthesis of glycerol carbonate is also proposed.
1. Introduction
intermediate for many kinds of polymers. In addition, GLC also can be
utilized as components for gas separation membranes [9–13].
In the last couple of decades, with the continuous reduction in fossil
Several approaches have been employed for upgrading GL into GLC,
fuel resources and increasing concern about climate change, the pro-
duction of renewable and clean fuel, such as biodiesel, has attracted
much attention from the industrial and academic circles [1–4]. Gen-
erally, biodiesel is produced by transesterification of vegetable or an-
imal oil with methanol, where the glycerol (GL) is also yielded as an
undesired by-product (about 100 g/kg biodisel) [5,6]. The rapidly in-
crease of biodiesel production has resulted in huge amounts of surplus
GL and therefore, in order to promote the development of biodiesel
industry, it is necessary to convert GL into value-added chemicals [7,8].
Among the derivatives of GL, glycerol carbonate (GLC) is a promising
one due to its physical properties and potential uses. GLC is a nontoxic,
readily biodegradable, water-soluble, not flammable (fp 165.9 °C) and
viscous liquid with a very low evaporation rate (bp 353.9 °C at
including (ⅰ) the reaction of GL with phosgene [14]; (ⅱ) the direct GL
carboxylation with CO [15–17]; (ⅲ) the carbonylation of GL with urea
2
[18–21]; (ⅳ) the GL transesterification with dimethyl carbonate (DMC),
propylene carbonate (PC), ethylene carbonate (EC), or diethyl carbo-
nate (DEC) [22–26]. However, in these methods, the route of GL car-
bonation with phosgene is not suitable for the industrial production of
GLC due to the highly toxic and corrosive nature of phosgene. Some
catalysts, such as basic ion-exchange resin, 13X zeolite, CeO
2 2
and Bu SnO were used for the direct GL carboxylation with CO , but a
2
/NbO
5
,
n
very low GLC yield was obtained under harsh conditions of pressure of
5 MPa and temperature of 180 °C for this reaction is severely limited by
thermodynamics [17,27]. Alternatively, carbonylation of GL with urea
has better potential of commercialization. However, in this method, the
removal of ammonia under reduced pressure become inevitable to drive
the reaction equilibrium to the product side [28]. The
101.325 kPa). All these features make GLC a green chemical that can be
used as a polar high boiling solvent, a surfactant component, an
⁎
Corresponding authors at: School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China.
E-mail addresses: wanghuajun@mail.hust.edu.cn (H. Wang), klgyl@hust.edu.cn (Y. Gu).
https://doi.org/10.1016/j.mcat.2019.02.005
Received 6 December 2018; Received in revised form 5 February 2019; Accepted 7 February 2019
2468-8231/ © 2019 Elsevier B.V. All rights reserved.

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Scheme 1. Synthesis of GLC from transesterification of GL
with DMC.
transesterification of GL with ethylene carbonate or propylene carbo-
nate was also used; however, this procedure consumed high energy for
product purification because the boiling point of the by-product,
ethylene glycol (bp 197 °C at 101.325 kPa) or propanediol (bp 188 °C at
parameterswere also investigated in detail. Finally, based on the cur-
rent results and FTIR characterization, a possible reaction mechanism
was proposed for the synthesis of GLC.
101.325 kPa) is very high. Briefly, the transesterification of GL with
2. Experimental
dimethyl carbonate (DMC) is the most attractive method due to the
constitution of non-toxic raw material, mild operation condition, high
yield, and simple purification of GLC, which collectively offers an en-
vironmentally benign route for synthesizing GLC (Scheme 1) [29].
Up to now, a series of catalysts were developed to catalyze the re-
action of GL with DMC. The homogeneous catalysts, such as K CO ,
2 3
NaOH, and KOH, showed high catalytic activity [30]. However, it was
difficult to separate and reuse these catalysts. The heterogeneous cat-
2.1. Chemicals
Tripentylamine (TPA) (97%), 3-bromo-1-propanol (97%), methyl-4-
bromobutanoate (98%), 1-methylimidazole (99%), 3-chloropropionic
acid (98%), 1-bromopropane (99%), GL (99%), glycidol (GD) (97%),
and GLC (90%) were purchased from Shanghai SaEn Chemical
Technology Co. Ltd., Shanghai, China. 3-Bromopropylamine hydro-
bromide (98%) and 1-bromo-3-methoxypropane (98%) were provided
by Aladdin Industrial Corporation. Tetraethylene glycol (99%) and
DMC (99%) were provided by Tianjin Guangfu Fine Chemical Research
Institute, China. Methanol and n-butanol with 99% purity were pur-
chased from Shanghai Zhan Yun Chemical Co., Ltd., Shanghai, China.
The DMF, THF, anhydrous diethyl ether, and ethanol solvents have
purity of 99%.
alysts, such as metal salts or oxides (CaO, KNO
3 2 3
/CaO, K CO /MgO,
Mg1+xCa1-x
O
2
, MgO-La , Li-La ), hydrotalcite (LDHx, HT-M), Na-
2
O
3
2 3
O
Based Zeolite, and so on [31–34], were also discovered to possess high
activities for the transesterification of GL with DMC to produce GLC.
However, some drawbacks are associated with heterogeneous catalyst,
including easily deactivation, leaching of catalyst active sites, and large
energy consumption due to calcination step needed in their preparation
and regeneration process. Several lipases, like Novozym 435 and As-
pergillus niger, were also used as heterogeneous catalyst for the reac-
tion of GL with DMC [35,36]. Unfortunately, these catalysts are suf-
fering many drawbacks, such as high cost, poor activity, large DMC/GL
molar ratio, and long reaction time (˜25 h). In addition, some solvents,
such as THF (tetrahydrofuran) and DMF (dimethyl formamide), are
often added in the reaction system to overcome the resistance of mass
transfer due to the insolubility of GL with DMC, which further make it
difficult to purify the product [29].
2.2. Preparation of FQAILs
The FQAILs were prepared according to the previous methods
[41,42] and the TPA was used as starting materials. In a typical pro-
cedure for the preparation of Hydroxypropyl-tripentylammonium hy-
droxide ([HPTPA]OH), 4.55 g of TPA (20 mmol) and 45 mL of THF
were firstly mixed in a round bottom flask equipped with a reflux
condenser, and then, 2.77 g of 3-bromo-1-propanol (20 mmol) was
added to the reaction mixture. After stirred at 80 °C for 24 h with
protection of nitrogen current, the reaction mixture was cooled to room
temperature. The resulting reaction mixture became two phases and the
yellow viscous liquid was obtained by removing the solvent phase. The
yellow viscous liquid was further washed with anhydrous diethyl ether
three times (20 mL × 3) to remove any impurities. The resulting yellow
concentrated liquid was dried under vacuum at 50 °C for 18 h, pro-
viding Hydroxypropyl-tripentylammonium bromide ([HPTPA]Br).
Then, 3.31 g of [HPTPA]Br (0.01 mol) was added into the solution of
KOH (0.85 g, 0.015 mol) in ethanol (35 mL), and the resulting mixture
was stirred at room temperature for 2 h to complete the anion exchange
process. During the process, the KBr white precipitate was formed and
then removed by filtration. After concentrating the filtrate by removing
the solvent and impurities, 2.74 g of clear yellow liquid was obtained.
Then it was further dried under vacuum at 50 °C for 18 h to give
[HPTPA]OH.
Ionic liquid (IL) is a kind of new solvent and catalyst with many
unique properties, such as negligible vapor pressure, good thermal
stability, excellent tunability, and high solubility [37]. Furthermore, it
is easy to adjust IL’s acid-base property by changing its cation-anion
pairing. These properties make the IL widely available as a catalyst for
2
cycloaddition of propylene oxide with CO , Knoevenagal-Michael re-
action, direct aldol reactions, aza-Michael reaction and so on [38–40].
Meanwhile, its dual function, namely strong solubility and catalytic
activity, often results in an increase in rate and reactivity for the
transesterification reaction, compared with other catalysts that need
additional solvent to overcome the resistance of mass transfer. In ad-
dition, some basic groups, such as hydroxyl (−OH), carboxyl
(
2
−COOH), and amino (-NH ), can be easily attached on the alkyl arms
of ILs to produce functionalized ILs, which reflect additional advantages
such as alterable polarity, low viscosity, higher solubility, and im-
mobilization potential [41,42]. Compared with imidazole ILs, qua-
ternary ammonium salts ILs are more suitable catalyst in industrial
processes owing to simpler preparation process, cheaper cost, and less
toxicity.
Aminopropyl-tripentylammonium
Methoxypropyl-tripentylammonium
hydroxide
hydroxide
([APTPA]OH),
([MPTPA]OH),
Tripentylammonium hydroxide ([TPA]OH), and Propyl-tripenty-
lammonium Hydroxide ([PTPA]OH) were prepared by the same process
with [HPTPA]OH using 3-bromopropylamine hydrobromide, 1-bromo-
3-methoxypropane, hydrobromic acid, and 1-bromopropane instead of
3-bromo-1-propanol, respectively. The same process with [HPTPA]OH
was also used to prepare 1-Hydroxypropyl-3-methylimidazolium hy-
droxide ([HPMIM]OH) by using 1-methylimidazole instead of TPA.
Hydroxypropyl-tripentylammonium chloride ([HPTPA]Cl) was pre-
pared by the reaction of [HPTPA]OH with hydrochloric acid while
Hydroxypropyl-tripentylammonium iodide ([HPTPA]I) was prepared
by the reaction of [HPTPA]OH with hydroiodic acid.
To the best of our knowledge, there are few reports about the
synthesis of GLC form GL and DMC by using functionalized quaternary
ammonium salts ILs (FQAILs) as a catalyst. Moreover, the role of both
functional group and anion of the ILs for activation of the reactant
molecules in the GLC synthesis process is also not understood clearly. In
the present work, a series of FQAILs with different functional groups,
such as hydroxyl, carboxyl, ether group, and amino, were prepared and
then used as a catalyst for the synthesis of GLC from transesterification
of GL and DMC without any additional organic solvent or co-catalyst.
−
−
−
−
The effects of cations, anions (Cl , Br , I , OH ), and reaction
20

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Carboxypropyl-tripentylammonium hydroxide ([CPTPA]OH) was
300 rpm. After that, the reaction mixture was cooled to the room
temperature. In order to recover the catalyst, 15.0 mL of anhydrous
diethyl ether was added into the reaction mixture to make two phases.
The upper phase (product phase) consists of the product, the residual
reactants, and anhydrous diethyl ether, while the lower phase (catalyst
phase) mainly consists of the catalyst. After the two phases were se-
parated by separating funnel, the upper phase was sampled to analyze
while the lower phase was evaporated by rotary evaporator to further
purify the catalyst. The recovery catalyst was dried in a vacuum drier at
60 °C and 24 h and then used in the recycled experiment.
prepared by the following procedure: 4.55 g of TPA (20 mmol) was
mixed with 3.65 g of methyl-4-bromobutanoate (20 mmol) in a round
bottom flask, and then 30 mL of THF was added to the mixture. After
stirred at 80 °C for 24 h with protection of nitrogen current, the reaction
mixture was cooled to room temperature and the yellow viscous liquid
was obtained by removing the solvent phase. The yellow viscous liquid
was further washed with anhydrous diethyl ether three times
20 mL × 3) to remove any impurities and then mixed with 50 mL of
hydrobromic acid (0.03 mol/L). After stirred at room temperature for
.5 h, the yellow liquid, carboxypropyl-tripentylammonium bromide
[CPTPA]Br) was obtained by removing the solvent. Finally, the
CPTPA]OH was obtained by the reaction of [CPTPA]Br with KOH.
(
0
(
[
2.5. Product analysis
The sample was taken from the cooled reaction mixture and diluted
with a certain amount of DMF, and then analyzed by the gas chroma-
tography (Fuli 9790-II) equipped with a flame ionization detector (FID)
and a capillary column DM-FFAP (30 m long, 0.25 mm i.d). As an in-
ternal standard, n-Butanol was used to determine GD, methanol, and
DMC while tetraethylene glycol was used to determine GL and GLC.
Nitrogen (99.999% pure) was used as the carrier gas with a flow rate of
30 mL/min at 0.3 MPa. The injector and detector temperatures were
250 °C and 270 °C, respectively. The temperature of the column was
programmed as follows: 2 min initial hold at 70 °C, 15 °C/min ramp
from 70 °C to 250 °C, and then 15 min hold at 250 °C A good peak se-
paration was achieved for all components in the sample at these con-
ditions.
2
.3. FQAILs characterization
All the FQAILs catalysts were characterized by the nuclear magnetic
1
resonance (NMR). The H NMR spectra were measured on a Bruker
Advance 400 MHz spectrometer. The results are listed as following:
1
[
HPTPA]OH: yellow liquid, H NMR (400 MHz, CD
3
CN, 25 °C,
TMS): δ = 3.66 – 3.16 (m, 8 H), 2.95 – 2.30 (m, 7H), 2.10 (t, J = 6.2
HZ, 1H), 1.10–1.60 (m, 7H), 1.50 – 1.40 (m, 10H), 1.02 – 1.00 ppm (m,
8
H).
[
CPTPA]OH: yellow liquid, 1H NMR (400 MHz, CD
CN, 25 °C,
3
TMS): δ = 3.20 – 2.30 (m, 5H), 2.44 – 2.41 (m, 15 H), 1.80 – 1.64 (m,
6
H), 1.42 – 1.31 (m, 8H), 1.00 – 0.93 ppm (m, 7H).
APTPA]OH: yellow viscous liquid, 1H NMR (400 MHz, CD
5 °C, TMS): δ = 2.43 – 2.40 (m, 7 H), 1.50 – 1.40 (m, 7 H), 1.34 – 1.26
[
3
CN,
The conversion of GL, XGL, the yield of GLC, YGLC, and the yield of
GD, YGD, were calculated by using Eqs. (1)–(3), respectively, while the
selectivity of GLC, SGLC, was calculated by Eq. (4):
2
(
m, 11 H), 0.92 – 0.90 (m, 13 H).
MPTPA]OH: yellow viscous liquid, 1H NMR (400 MHz, CD
5 °C, TMS): δ = 3.42 - 3.33 (m, 2 H), 2.50 – 2.30 (m, 7 H). 1.74 – 1.70
[
3
CN,
in
out
GL
n
− n
GL
2
X
GL
=
=
× 100%
in
n
(1)
(2)
(3)
(4)
(
1
m, 1 H) 1.50 – 1.40 (m, 6 H), 1.34 – 1.24 (m, 13 H), 0.91 – 0.84 (m,
2 H).
TPA]OH: colorless liquid, H NMR (400 MHz, CD
δ = 2.41 – 2.30 (m, 5 H), 2.20 – 2.02 (m, 1 H), 1.50 – 1.40 (m, 6 H),
.30 – 1.24 (m, 9 H), 1.05 – 0.84 (m, 11 H).
PTPA]OH: colorless liquid, 1H NMR (400 MHz, CD
TMS): δ = 2.70 – 2.32 (m, 7 H), 1.60 – 1.50 (m, 6 H), 1.40–1.60 (m,
4 H), 0.91 – 0.90 (m, 12).
HPTPA]Cl: yellow liquid, H NMR (400 MHz, CD
δ = 3.83 – 3.40 (m, 5 H), 3.21 – 3.20 (m, 8 H), 2.60 – 2.40 (m, 1 H),
.02 – 1.60 (m, 7 H), 1.40 – 1.13 (m, 8 H), 1.00 – 0.80 (m, 7 H).
HPTPA]Br: yellow liquid, 1H NMR (400 MHz, CD Cl , 25 °C, TMS):
δ = 3.84 – 3.51 (m, 4 H), 3.30 – 2.30 (m, 9 H), 2.12 – 1.60 (m, 8 H),
.40 – 1.11 (m, 10 H), 1.10 – 0.92 (m, 9 H).
GL
out
1
n
GLC
in
[
3
CN, 25 °C, TMS):
YGLC
× 100%
n
GL
1
out
n
n
GD
in
[
3
CN, 25 °C,
YGD =
× 100%
GL
1
out
n
GLC
1
SGLC =
× 100%
[
3
CN, 25 °C, TMS):
in
out
n
− n
GL
in
GL
out
out
2
where, nGL is the initial mole number (mol) of GL while nGL ,
n
GLC, and
out
[
3
3
nGD are the mole numbers (mol) of GL, GLC, and GD in the residual
reaction mixture after the reaction, respectively.
1
1
[
HPTPA]I: yellow viscous liquid, H NMR (400 MHz, CD
3
CN, 25 °C,
3. Results and discussion
TMS): δ = 3.82 – 3.20 (m, 13 H), 2.40 – 2.36 (m, 1 H), 2.02 – 1.55 (m,
8
H), 1.40 – 1.20 (m, 8 H), 1.00 – 0.91 (m, 8 H).
3.1. Catalytic performance of various catalysts
A Bruker VERTEX 70 FT-IR spectrometer was used to obtain the FT-
−
1
IR spectra of samples with 2 cm
resolution over the wavenumber
Table 1 shows the catalytic performance of various FQAILs catalysts
with hydroxyl, carboxyl, amino, and ether group (entry 1 ˜ 4), TPA
entry 5), and the traditional quaternary ammonium salts ILs without
−1
range 4000-400 cm
.4. Reaction procedure
The synthesis of GLC from the reaction of GL with DMC by using
FQAILs as catalysts was carried out in a 50 mL round bottom 3-neck
glass flask as a batch reactor equipped with a magnetic stirrer, a ther-
mometer, and a reflux condenser. The energy was applied to the glass
flask with a constant temperature oil bath. The accuracy of the tem-
perature measurements was ± 0.5 °C. The reflux condenser, which was
a straight condenser tube with the tap water as the cooling medium, can
cool all the volatiles and return them into the glass flask to keep the
material balance of the reaction. In a typical run, 21.70 mmol of GL
.
(
2
any functional group, such as [TPA]OH and [PTPA]OH (entry 6, 7), for
the synthesis of GLC from GL and DMC. It is found that the organic base
TPA catalyst has a lower catalytic activity whereas the FQAILs catalysts
display higher catalytic activities than TPA (entry 1 ˜ 4, 5). Meanwhile,
traditional quaternary ammonium salts ILs without any functional
group, such as [TPA]OH and [PTPA]OH, also exhibit lower catalytic
activities than FQAILs (entry 1 ˜ 4, 6, 7). The results indicate that the
functional groups play an important role in the acceleration of the re-
action of GL with DMC. It is also discovered that the activity order of
FQAILs is [HPTPA]OH > [CPTPA]OH > [APTPA]OH > [MPTPA]OH,
which means that the activities of the four functional groups are in-
(
2.0 g) and 43.40 mmol of DMC (3.91 g) were mixed in the flask, and
2
creased based on the following order: −OH > −COOH > -NH > -O-.
then 0.20 mmol [HPTPA]OH was loaded into the mixture, which was
quickly heated to 80 °C and kept for 90 min with a stirring speed of
Recently, it was reported that hydroxyl-functionalized quaternary am-
monium hydroxide ILs displayed a good catalytic activity for synthesis
21

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Table 1
a
Catalytic performance of various catalysts .
Entry
Cat.
XGL(%)
Y
GLC(%)
SGLC(%)
YGD(%)
1
2
3
4
5
6
7
8
9
[HPTPA]OH
[CPTPA]OH
[APTPA]OH
[MPTPA]OH
TPA
91.3
87.7
86.9
44.5
13.9
39.3
54.0
89.5
24.7
31.6
12.6
82.7
59.7
49.1
39.4
11.1
37.9
44.2
49.5
21.2
20.7
11.0
90.6
68.1
56.5
88.6
80.4
96.5
81.8
55.3
85.6
65.4
87.8
8.6
28.0
37.8
5.1
2.7
1.4
9.8
40.1
3.6
10.9
1.5
[TPA]OH
[PTPA]OH
[HPMIM]OH
[HPTPA]Cl
[HPTPA]Br
[HPTPA]I
1
1
0
1
a
Reaction conditions: GL: 2.0 g; reaction time: 90 min; reaction temperature:
80 °C; Cat./GL molar ratio: 0.009; DMC/GL molar ratio: 2.
Fig. 1. The effect of reaction temperature on the synthesis of GLC from GL and
DMC (Reaction conditions: GL: 2.0 g; reaction time: 90 min; [HPTPA]OH/GL
molar ratio: 0.009; DMC/GL molar ratio: 3).
of DMC from methanol and carbon dioxide due to the generation of
hydrogen bond between hydroxyl oxygen atom and the hydrogen atom
of methanol molecule and between hydroxyl hydrogen atom and
oxygen atom of carbon dioxide molecule [41,42]. The result suggests
that during the reaction of GL with DMC over [HPTPA]OH, the hy-
drogen bond is generated between hydroxyl oxygen atom and the hy-
drogen atom of GL molecule and between hydroxyl hydrogen atom and
carboxyl oxygen atom of DMC molecule, which is beneficial for the
activation of GL molecule and DMC molecular. In addition, the reason
of [HPTPA]OH possesses the highest catalytic activity between the four
FQAILs (entry 1 ˜ 4) may be due to the strength of hydrogen bonding
between hydroxyl of [HPTPA]OH and DMC.
GLC from GL and DMC by using [HPTPA]OH as a catalyst. When the
reaction temperature increases from 60 °C to 80 °C, the GL conversion
and GLC yield increase rapidly from 41.5% and 39.8% to 96.0% and
8
6.6% at 75 °C and then at 80 °C slightly increase to 96.2% and 87.6%,
respectively. Meanwhile, the GD yield increases from 1.7% at 60 °C to
5.8% at 70 °C and then decreases to 8.5% at 80 °C. Because the
1
transesterification of GL with DMC is an exothermic reaction [44], the
high reaction temperature can shift the reaction equilibrium towards
product side. Hence, the temperature of 80 °C is suitable for the reaction
of GL with DMC to produce GLC.
The traditional quaternary ammonium salts ILs, such as [TPA]OH
and [PTPA]OH, exhibit higher catalytic activity than TPA, indicting the
−
positive role of the basic anion OH in this reaction. In order to de-
termine the anion effects, the hydroxyl-functionalized quaternary am-
3
.2.2. Effect of DMC/GL molar ratio
The effect of DMC/GL molar ratio on the transesterification of GL
−
−
−
−
monium salt ILs with different anions, such as OH , Cl , Br , and I
were prepared and used to catalyze the reaction of GL with DMC (entry
, 9˜11). It is observed that for the four FQAILs with different anions,
,
with DMC to produce GLC in the presence of [HPTPA]OH as a catalyst
was investigated and the result is listed in Fig. 2. The results demon-
strate that when the DMC/GL molar ratio is increased from 1 to 2, the
GL conversion and GLC yield increase remarkably from 52.0% and
1
−
−
−
−
the GLC yield increase in the following order: OH > Cl > Br > I
,
which is consistent with the order of the basic strength of anion. During
−
the reaction of GL with DMC, the OH as a strong Brønsted base has the
1
9.7% to 91.3% and 82.7%, respectively. With the further increase of
strongest proton accepting ability and the GL is easily activated to form
the glyceroxide. In addition, it also can be found that the [PTPA]OH
DMC/GL molar ratio to 5, the GL conversion is increased to 94.9%
while the GLC yield decreases from 94.8% at DMC/GL molar ratio of 4
to 90.1%. In addition, with the increase of DMC/GL molar ratio from 1
to 5, the GD yield gradually decreases from 32.4% to 4.8%. Due to the
short reaction time of 90 min, except GD, any other byproduct is not
detected in the reaction mixture. These results indicate that the higher
DMC/GL molar ratio rather than stoichiometric ratio is required to
without hydroxyl has a lower catalytic activity than [HPTPA]OH, while
−
[
HPTPA]Cl, [HPTPA]Br, or [HPTPA]I without anion OH also displays
a lower catalytic activity than [HPTPA]OH. This result suggests that
there may be a synergic effect between cation with hydroxyl and anion
−
OH , which results in a good catalytic activity of [HPTPA]OH for the
reaction of GL with DMC [43].
In addition, the hydroxyl functionalized imidazolium salt ILs
[
HPMIM]OH was also prepared and used to catalyze the reaction of GL
with DMC. The result indicates that the GL conversion and GLC yield
are 89.5% and 49.5%, respectively, for [HPMIM]OH (entry 8), which
are less than that for [HPTPA]OH. Furthermore, the GLC selectivities
for [HPMIM]OH and other FQAILs, such as [CPTPA]OH, [APTPA]OH,
and [HPTPA]Br are also less than that for [HPTPA]OH. For all the
catalysts, the by-product is GD, which is produced by the decarbox-
ylation of GLC. The above results indicate that among these catalysts,
the highest GL conversion and GLC yield and higher GLC selectivity are
obtained over [HPTPA]OH. Accordingly, in this study, the [HPTPA]OH
is used as a catalyst to investigate the effects of other reaction para-
meters, such as reaction temperature, DMC/GL molar ratio, reaction
time, and catalyst amount.
3
3
.2. Optimization of reaction conditions
Fig. 2. The effect of DMC/GL molar ratio on the synthesis of GLC from GL and
DMC (Reaction conditions: GL: 2.0 g; reaction time: 90 min; reaction tempera-
ture: 80 °C; [HPTPA]OH/GL molar ratio: 0.009).
.2.1. Effect of reaction temperature
Fig. 1 shows the effect of reaction temperature on the synthesis of
22

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Fig. 3. The effect of reaction time on the synthesis of GLC from GL and DMC
(
Reaction conditions: GL: 2.0 g; reaction temperature: 80 ᵒC; DMC/GL molar
ratio: 3; [HPTPA]OH/GL molar ratio: 0.009).
Fig. 5. the gas chromatogram of the reaction mixture ((1) methanol, (2) DMC,
(
3) n-butanol, (4) DMF, (5) GD, (6) GL, (7) Tetraethylene, (8) GLC).
optimize the GLC synthesis since the reaction of GL with DMC is a re-
versible one. Hence, the DMC/GL molar ratio of 3 or 4 can be suitable
for the reaction of GL with DMC.
the components. In addition, the carbon balance of the reaction process
is 97.4% indicating the reliability of the results.
3.2.3. Effect of reaction time
The effect of reaction time on the synthesis of GLC from GL and
3.2.4. Effect of catalyst amount
DMC was also scrutinized. As shown in Fig. 3, at the initial 20 min, the
reaction of GL with DMC proceeds very quickly and gives the GL con-
version of 74.0% and GLC yield of 64.2%. As the reaction time increases
to 40 min, the reaction rate decreases slightly and the GL conversion
and GLC yield increase to 93.5% and 77.2%, respectively. Further in-
crease in the reaction time to 180 min increases the ratio of conversion
of GL (96.2%) and yield of GLC (87.6%) at 90 min, and then the GL
conversion and GLC yield remain constant with the reaction time.
Meanwhile, the GD yield increases to 16.2% at 40 min and then slowly
decreases to 11.3% at 180 min. Therefore, the reaction time of 60 ˜
The effect of the catalyst amount on the synthesis of GLC from GL
and DMC with [HPTPA]OH as a catalyst is presented in Fig. 6. It can be
observed that with the increase of catalyst amount from 0.3 mol% to
1
.5 mol% (based on GL), the GL conversion and GLC yield further in-
crease from 92.2% and 81.8% to 96.2% and 87.6%, respectively, at
catalyst amount of 0.9 mol%, and then, they almost keep constants with
catalyst amount. Meanwhile, the GD yield decreases slowly from 10.4%
to 7.0% with increase of catalyst amount. Considering that the less
amount of catalyst is better for the industrial production of GLC, hence,
the catalyst amount of 0.9 mol% is suitable for the synthesis of GLC
from GL and DMC.
90 min is suitable for the synthesis of GLC from GL and DMC.
The Fig. 4 illustrates the change of concentrations of each compo-
nent in the reaction mixture with the reaction time. It can be observed
that during the reaction process, the reactants, GL and DMC are con-
sumed gradually while the product, GLC is generated continually with
the time. Moreover, the methanol is also produced during the reaction,
as a by-product. The Fig. 5 is the gas chromatogram of the reaction
mixture. It can be seen that a good peak separation is achieved for all
3
.2.5. Effect of agitation speed
In the previous studies [33,36], it was found that when the tradi-
2 3
tional catalysts, such as K CO and lipases, were used for the reaction,
there are two liquid phases in the reaction mixture at the initial reaction
stage due to the limited miscibility of GL with DMC and lower GL
conversion [11]. Therefore, the solvents, such as THF, are often added
in the reaction system to overcome the resistance of mass transfer,
Fig. 4. The change of the concentrations of each component in the reaction
mixture with the reaction time in the synthesis of GLC from GL and DMC
Fig. 6. The effect of catalyst amount on the synthesis of GLC from GL and DMC
(Reaction conditions: GL: 2.0 g; reaction temperature: 80 °C; reaction time:
90 min; DMC/GL molar ratio: 3).
(Reaction conditions: GL: 2.0 g; reaction temperature: 80 ᵒC; DMC/GL molar
ratio: 3; [HPTPA]OH/GL molar ratio: 0.009).
23

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Fig. 7. The effect of agitation speed on the synthesis of GLC from GL and DMC
Fig. 8. The stability of catalyst on the synthesis of GLC from GL and DMC
(Reaction conditions: GL: 2.0 g; reaction temperature: 80 ᵒC; DMC/GL molar
(Reaction conditions: GL: 2.0 g; reaction temperature: 80 °C; reaction time:
ratio: 3; [HPTPA]OH/GL molar ratio: 0.009; Reaction time: 90 min).
90 min; DMC/GL molar ratio: 3; [HPTPA]OH/GL molar ratio: 0.009).
which further increases the difficulty of purifying the product. How-
ever, when the [HPTPA]OH is used as a catalyst for the reaction of GL
with DMC, the miscibility of GL with DMC will be improved because the
GL can be completely dissolved in [HPTPA]OH IL while the DMC can be
partially dissolved in IL. It means that at the initial reaction stage, the
resistance of mass transfer in the reaction mixture for [HPTPA]OH is
less than that for traditional catalyst because [HPTPA]OH not only has
higher catalytic activity, but also has stronger solubility for GL and
DMC. Though the limited miscibility of GL with DMC is not beneficial
for the reaction, the mass transfer may have no larger negative effect on
the catalytic performance of [HPTPA]OH. Compared with other cata-
lysts that need an additional solvent to overcome the resistance of mass
transfer, the [HPTPA]OH presents a remarkable advantage owing to its
strong solubility.
indicates when the anhydrous diethyl ether was added into the product
phase, only a very little of catalyst were separated from the product
phase, reflecting that the amount of [HPTPA]OH remained in product
phase is very small and most of the IL catalysts can be recovered by
adding the anhydrous diethyl ether into the reaction mixture.
The fresh [HPTPA]OH, the recovered [HPTPA]OH after the first
recycle, and the recovered [HPTPA]OH after the third recycle are
characterized by FTIR and the results are shown in Fig. 9. In these
−1
spectra in the Fig. 9, the wide band at about 3388 cm are assigned to
−1
the −OH stretching vibration while the band at 1063 cm
are at-
tributed to the C–N stretching vibration. In addition, the peaks at
−1
−1
−1
2
940 cm , 2869 cm , and 1664 cm
suggest the presence of am-
monium salt. After the third recycle, it can be observed that these
characteristic band are also strong almost without any significant shift
of the absorption frequency (Fig. 8(c)), indicating the [HPTPA]OH has
strong structure stability during the reaction process. According to
these results, it can be inferred that the important reason for the de-
activation of [HPTPA]OH is the loss of the catalyst during the experi-
ment process because the amount of the recovered catalyst is decreased
after every recycle experiment, especially after the fifth recycle.
The resistance of mass transfer can be further decreased by in-
creasing the agitation speed. The effect of agitation speed on the re-
action performance has been studied and the results are given in Fig. 7.
It can be found that when the agitation speed increases from zero to
3
7
00 rpm, the GL conversion and GLC yield increase from 82.5% and
0.8% to 96.2% and 87.6%, respectively. These results indicate that a
high agitation speed can improve the diffusion of reactant molecules
resulting in an increase of reaction rate and GL conversion. With further
increase of agitation speed to 500 rpm, the GL conversion and GLC yield
almost keep constant. Hence, the agitation speed of 300 rpm is suitable
for the reaction of GL with DMC.
3.2.6. Stability of catalyst
In order to investigate the stability of [HPTPA]OH catalyst, re-
cycling experiments were also carried out. Firstly, the catalyst was se-
parated by extraction method with anhydrous diethyl ether. Then, after
dried in a vacuum dryer, the recovered catalyst was reused for the next
run under the same conditions. As shown in Fig. 8, at the third recycle,
the GL conversion and the GLC yield still can reach 92.6% and 80.9%,
respectively, over the recovered catalyst. However, at the forth recycle,
the GL conversion and GLC yield decrease to 63.0% and 57.8%, re-
spectively, for recovered [HPTPA]OH catalyst. This result indicates that
the [HPTPA]OH can be reused efficiently at least for three times.
In the above recycling experiments, the catalyst was recovered by
adding anhydrous diethyl ether into the reaction mixture to make two
phases: product phase and catalyst phase. The catalyst [HPTPA]OH is
concentrated in the catalyst phase while the product phase consists of
unreacted GL, excess DMC, GLC, GD and methanol. In order to de-
termine whether any catalyst still remain in the product phase and are
not recovered completely, another 15.0 mL of anhydrous diethyl ether
was again added into the product phase. If there are some catalysts in
the product phase, it will be separated out. However, the result
Fig. 9. The FT-IR spectra of the fresh [HPTPA]OH and recovered [HPTPA]OH:
(a) the fresh [HPTPA]OH; (b) the recovered [HPTPA]OH after the first recycle;
(c) the recovered [HPTPA]OH after the third recycle (Reaction conditions: GL:
2
3
.0 g; reaction temperature: 80 °C; reaction time: 90 min; DMC/GL molar ratio:
; [HPTPA]OH/GL molar ratio: 0.009).
24

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Table 2
a
Comparison of catalytic activity of [HPTPA]OH with other catalysts for GLC synthesis from reaction of GL with different organic carbonates .
TOF (h 1)b
−
Ref.
Catalyst
T (◦C)
Time (h)
n(carbonate/GL)
Cat (mol%)
XGL (%)
Y
GLC (%)
[
[
[
HPTPA]OH
HPTPA]OH
HPTPA]OH
90
90
120
50
35
2
3(DEC/GL)
3(PC/GL)
3(EC/GL)
2(EC/GL)
2(EC/GL)
5(DEC/GL)
1(PC/GL)
0.9
0.9
0.9
7 w%
0.5 w%
0.5
91.5
85.4
97.9
86.0
92.0
–
79.4
75.5
73.7
78.0
83.0
99.1
84.0
44.5
52.6
47.9
0.3
31.3
100
1.80
this work
this work
this work
[28]
[28]
[45]
1.5
1.5
5
1
2
MgO
CaO
1
,3-Dichlorodistannoxanes
100
160
(Ca-HT)
5
0.1
84.0
[46]
a
T: reaction temperature; Time: reaction time; n(carbonate/GL): carbonate/GL molar ratio; Cat: Cat amount (based on GL amount).
TOF = mol of product per mol of catalyst per hour.
b
3.3. Synthesis of GLC from GL and other organic carbonates over [HPTPA]
OH
The above results indicate that the [HPTPA]OH is an effective cat-
alyst for the synthesis of GLC from GL and DMC. In order to investigate
the applicability of [HPTPA]OH to other organic carbonates, the
transesterification of GL with other organic carbonates, such as DEC,
PC, and EC to produce GLC was also examined and the results are listed
in Table 2 (in row 1 ˜ 3). It can be found that the [HPTPA]OH also
exhibits considerable activity for these carbonates. The highest GL
conversion (97.9%) was obtained for EC as the substrate while the
highest GLC yield of 79.4% was obtained for DEC. When PC was used as
reactant, the GL conversion and GLC yield can reach 85.4% and 75.5%,
respectively, in the presence of [HPTPA]OH. The catalytic activities of
the other molecular catalysts for GLC synthesis from GL and these
different organic carbonates are also showed in Table 2 (in row 4 ˜7). It
can be found that the [HPTPA]OH has a slightly lower GLC yield than
MgO, CaO, 1,3-Dichlorodistannoxanes, and Ca-HT catalysts. However,
compared with these catalysts, the [HPTPA]OH possesses a higher
turnover frequencies (TOFs) (except 1,3-Dichlorodistannoxanes). These
results indicate that the highly efficient of [HPTPA]OH can be extended
to a variety of organic carbonates to produce to GLC.
Fig. 10. The FTIR spectra of the mixture of DMC and ILs with different contact
times: (a) pure DMC; (b) DMC+[HPTPA]OH, 10 min; (c) DMC+[HPTPA]OH,
30 min; (d) DMC+[HPTPA]OH, 60 min; (e) DMC+[HPTPA]OH, 90 min; (f)
DMC+[PTPA]OH, 60 min; (g) pure [HPTPA]OH. The molar ratio of DMC to ILs
was set at 0.01 and the temperature is 90 °C.
3.4. Proposed reaction mechanism
There are few reports on the role of both cation and anion of the ILs
for activation of the substrates in the GLC synthesis process. In order to
clearly understand the reaction mechanism of GL with DMC in the
presence of [HPTPA]OH, the FTIR spectra are used to characterize the
interaction between [HPTPA]OH and DMC and between [HPTPA]OH
and GL. The results are illustrated in Figs. 10 and 11. In Fig. 10(a), the
−
1
peak at 1762 cm is attributed to the vibration of C]O of DMC, which
−1
shifts to the lower frequency of 1753 cm
when DMC is mixed with
[
HPTPA]OH (Fig. 10(b–d)). Furthermore, the strength of peak of C]O
decreases with the increase of contact time (except Fig. 10 (e)). It in-
dicates that there is a interaction between C]O of DMC and [HPTPA]
OH. However, as the DMC is mixed with [PTPA]OH, the peak of C]O
do not shift to the low frequency, meaning there is no interaction be-
tween C]O and [PTPA]OH. Therefore, the results indicate that the C]
O of DMC prefer to interacting with hydroxyl group of cation rather
than with anion OH-. Based on the report in literature [38–40], we
believe that the interaction of C]O of DMC with hydroxyl group of
cation is due to the formation of hydrogen bond between the oxygen
atom of C]O and the hydrogen atom of hydroxyl, which will result in
the activation of DMC molecular. By the same token, in Fig. 11(a), the
Fig. 11. The FTIR spectra of the mixture of GL and ILs with different contact
times: (a) pure GL; (b) GL+[HPTPA]OH, 10 min; (c) GL+[HPTPA]OH, 30 min;
(d) GL+[HPTPA]OH, 60 min; (e) GL+[HPTPA]OH, 90 min; (f) GL+[PTPA]
OH, 60 min; (g) pure [HPTPA]OH. The molar ratio of GL to ILs was set at 0.01
and the temperature is 90 °C.
[
PTPA]OH. These results suggest that the interaction of hydroxyl group
−1
absorption band centered at 3462 cm corresponding to the hydroxyl
of GL with [HPTPA]OH is produced between hydroxyl group of GL and
anion OH- of [HPTPA]OH with the formation of hydrogen bond be-
tween the hydrogen atom of hydroxyl group of GL and oxygen atom of
anion OH- [38,39]. The above FTIR spectra results clearly indicate that
during the reaction of GL with DMC in the presence of [HPTPA]OH, the
two kinds of hydrogen bonds are formed between hydrogen atom of
−
1
group of GL shifts to the lower frequency of 3367 cm
when GL is
contacted with [HPTPA]OH (Fig. 11(b–d)), indicating that there is a
interaction between hydroxyl group of GL and [HPTPA]OH. Mean-
while, the shifting of peak of hydroxyl group of GL to low frequency
also occurs in the mixture of GL and [PTPA]OH (Fig. 11 (e)), meaning
that there also is a interaction between hydroxyl group of GL and
25

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Scheme 2. The proposed reaction mechanism for the synthesis of GLC from the reaction of GL with DMC by using [HPTPA]OH as a catalyst.
hydroxyl group of GL and anion OH- of [HPTPA]OH and between
carbonyl oxygen atom of DMC and hydroxyl hydrogen atom of cation,
resulting in the activation of GL and DMC to initiate the reaction. These
results further prove there is a synergic effect between anion and cation
of [HPTPA]OH for the synthesis of GLC.
larger DMC/GL molar ratio, or at larger catalyst amount than [HPTPA]
OH. In addition, the TOFs of these catalysts also are listed in Table 3 (in
eighth column). It is also noticed that the TOF of [HPTPA]OH is higher
than of Dicyanamide, Triethylamine, TBAB, DABCO-DMC, [Bmin]Im,
2
and BMIM-2−CO . Furthermore, the catalytic activities of other non-
Based on the results of experiments and characterization of
ILs catalysts for GLC synthesis from GL and DMC are also showed in
[
HPTPA]OH, a possible reaction mechanism for the GLC synthesis from
Table 3 (in row 15 ˜ 31). It is found that the TOF of [HPTPA]OH is also
GL and DMC is proposed as shown in Scheme 2. During the reaction,
3
higher than that of these non-ILs catalysts (except CaCO ). Compared
firstly, the C]O bond of DMC and the primary OeH bond of GL can be
activated by the hydroxyl of cation and the OH anion of [HPTPA]OH,
with these catalysts, the [HPTPA]OH can give higher GLC yield of
87.6% under milder conditions: reaction temperature of 80 °C, 1.5 h,
DMC/GL molar ratio of 3, and catalyst amount of 0.9 mol% (based on
GL). Furthermore, as a FQAIL, [HPTPA]OH has simpler prepared pro-
cess, cheaper cost, less toxicity as well as higher activity and thereby, it
may be as a alternative active component of industrial catalyst for GLC
synthesis.
−
respectively, resulting in a active state of DMC and GL with the for-
mation of (OeH…O) hydrogen bond and (HO⋯H) hydrogen bond.
Afterwards, activated GL makes nucleophilic attack to the carbonyl-
carbon atom of DMC to form a methyl glyceryl carbonate intermediate
with elimination of methoxy group in the form of methanol. Subse−-
quently, the secondary OeH bond of GL is also activated by the OH
anion of the [HPTPA]OH with the formation of the (HO⋯H) hydrogen
bond and then its oxygen atom makes an intramolecular nucleophilic
attack on carbonyl carbon atom to give GLC with a loss of another
molecule of methanol.
4. Conclusion
Several FQAILs show excellent catalytic activities for GLC synthesis
from GL and DMC. The activity of functional groups in this study in-
crease in the following order: −OH > −COOH > -NH > -O-, which
may be relative with the strength of their hydrogen bonds with DMC,
while the anions show the following activity order:
2
3.5. Comparison of the catalytic activity between different catalysts
−
−
−
−
The comparison of the catalytic activity of [HPTPA]OH with other
OH > Cl > Br > I , which is consistent with their basic strength.
−
ILs catalysts for GLC synthesis is listed in Table 3 (in row 1 ˜ 14). Al-
though the different reaction conditions were used for these catalysts,
these reaction conditions should be the optimized one for each catalyst.
So the catalytic activities of these catalysts can be compared by using
the GLC yields at these optimal conditions. It is found that the catalytic
activity of [HPTPA]OH is slightly higher than that of TBA-MCM41,
DABCO-DMC, [TMG]TFE, [TMA]OH, [TEA]OH, and [TBA]OH. Mean-
while, it is also discovered that though the catalysts, such as Emim[Ac],
Dicyanamide, Triethylamine, TBAB, DBU, [Bmin]Im, and BMIM-
Among these catalysts, the [HPTPA]OH with hydroxyl and anion OH
gives the highest catalytic activity. FTIR characterization clearly shows
there are the strong interactions between hydroxyl and dimethyl car-
bonate molecular and between anion OH- and glycerol molecular.
Under the mild reaction conditions of reaction temperature of 80 °C,
90 min, DMC/GL molar ratio of 3, and catalyst amount of 0.9 mol%
(based on GL), the GL conversion and GLC yield can respectively reach
96.2% and 87.6% over [HPTPA]OH catalyst. The high efficiency of
[HPTPA]OH can be extended to other organic carbonates for the
synthesis of GLC. This catalyst can be easily recovered and reused and
may be used as an alternative active component for industrial process.
2
−CO
2
, gave higher GLC yields than [HPTPA]OH, these catalysts were
used at higher reaction temperature, or at longer reaction time, or at
26

E. Elhaj, et al.
Molecular Catalysis 468 (2019) 19–28
Table 3
a
Comparison of catalytic activity of [HPTPA]OH with other catalysts for GLC synthesis .
TOF(h 1)b
−
Ref.
catalyst
T(◦C)
Time (h)
n(DMC /GL)
Cat.(mol%)
X
GL.(%)
Y
GLC (%)
ILs type
[
HPTPA]OH
80
80
1.5
1.5
2
13
2.5
6
0.25
0.5
7.5
1.5
1.5
1.5
1.5
1.3
3
0.9
0.3
0.5
2.5
10
1
0.1
6
0.01
10
1
96.2
94.0
93.5
100.0
99.0
92.0
91.8
97.0
98.0
98.4
95.0
89
87.6
78.8
88.7
95.0
98.0
92.0
87.7
80.5
94.1
98.4
44.7
49.8
42.3
100
64.4
175.0
88.7
0.43
3.9
15.3
1753.2
26.8
1254.7
6.6
this work
[47]
[40]
[48]
[49]
[50]
[37]
[51]
[52]
[38]
[53]
[53]
[53]
[54]
TBA-MCM41
Emim[Ac]
Dicyanamide
Triethylamine
TBAB
2(EC/GL)
2(DEC/GL)
3
4
2
2
3
3
2.5
3
3
3
3
120
120
68-88
120
80
100
100
70
80
80
80
74
[TMG]TFE
c
DABCO-DMC
DBU
[
[
[
[
Bmin]Im
TMA][OH]
TEA][OH]
TBA][OH]
29.8
33.3
28.2
76.9
1
1
1
90
99
BMIM-2-CO
non-ILs type
CO
KOH
NaOH
CaCO
Na PO
2
K
2
3
73-75
75
75
75
70
78
170
60
80-92
85
70
95
95
90
80
75
75
1
3
5
5
5
2
2
3
2
2
3
3
4
4
5
2.5
2
2
3
10
10
–
97.0
100
10.8
6.7
6.5
[55]
[30]
[30]
[53]
[56]
[57]
[58]
[59]
[59]
[60]
[61]
[62]
[63]
[64]
[33]
[65]
[65]
1.5
1.5
1.5
1
100
98.9
91.5
99.5
97.9
84.7
94.7
45.2
94.4
99.0
96.7
97.4
95.0
99
98.5
90.6
99.0
96.9
71.4
87.8
40.7
86.4
94.6
94.3
95.8
74.0
99
3
0.1
1.7
6.9
15w%
3.7
0.8
0.9
1.5
18.8
6
604
58.2
14.0
1.2
15.8
33.9
32.0
42.0
20.2
3.8
3
3
NaOH/ᵞ-Al
CHT-HMS
NaAlO
La
Li-La
NaOH-LF
Na SiO
Li/ZnO
Ca/La
K
2
O
3
1
2.5
1.5
1.5
3
1.5
0.25
4
1.5
2
0.5
0.5
2
O
2 3
2
O
3
2
3
18.8 w%
1w%
3
5.8
2
CO
3
/MgO
14.4
61.5
61.7
CaO
NaO
91.2
95.5
90.2
92.6
3
a
T: reaction temperature; Time: reaction time; n(DMC/GL): DMC/GL molar ratio; Cat.: Cat amount (based on GL amount).
TOF = mol of product per mol of catalyst per hour.
it is the yield of GD.
b
c
A possible reaction mechanism for GLC synthesis from GL and DMC is
also proposed.
527–549.
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[
[
[
11] H. Wang, P. Lu, J. Chem. Eng. Data 57 (2012) 582–589.
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[
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We acknowledge the financial support by the National Natural
Science Foundation of China (NSFC) (21106050), the Specialized
Research Fund for the Doctoral Program of Higher Education (SRFDP)
[
[
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