Synthesis of glycidol from glycerol and dimethyl carbonate using ionic liquid as a catalyst

Article abstract of DOI:10.1016/j.catcom.2012.07.003

Transesterification of dimethyl carbonate with glycerol has been investigated using various ionic liquids as catalysts. Synthesis of glycidol with high selectivity (78%) has been achieved using tetramethylammonium hydroxide ([TMA][OH]) as a catalyst at 80°C. Effect of various reaction conditions on the activity and selectivity was investigated and catalyst concentration had a significant influence on conversion as well as selectivity to glycidol. Activity as well as selectivity of the catalyst decreased significantly with increase in moisture content. Recycle experiment indicated slight drop in glycerol conversion and selectivity to glycidol because of dilution of reaction mixture and also the presence of products from the initial experiment.

Full text of DOI:10.1016/j.catcom.2012.07.003

Catalysis Communications 27 (2012) 184–188
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Synthesis of glycidol from glycerol and dimethyl carbonate using ionic liquid
as a catalyst
⁎
Swapna M. Gade, Mudassir K. Munshi, Batul M. Chherawalla, Vilas H. Rane, Ashutosh A. Kelkar
Chemical Engineering and Process Development Division, National Chemical Laboratory, Pune 411008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Transesterification of dimethyl carbonate with glycerol has been investigated using various ionic liquids as cata-
lysts. Synthesis of glycidol with high selectivity (78%) has been achieved using tetramethylammonium hydroxide
([TMA][OH]) as a catalyst at 80 °C. Effect of various reaction conditions on the activity and selectivity was investi-
gated and catalyst concentration had a significant influence on conversion as well as selectivity to glycidol. Activity
as well as selectivity of the catalyst decreased significantly with increase in moisture content. Recycle experiment
indicated slight drop in glycerol conversion and selectivity to glycidol because of dilution of reaction mixture and
also the presence of products from the initial experiment.
Received 22 February 2012
Received in revised form 10 June 2012
Accepted 3 July 2012
Available online 14 July 2012
Keywords:
Transesterification of glycerol
Ionic liquid
© 2012 Elsevier B.V. All rights reserved.
Glycidol
Glycerol carbonate
1. Introduction
or explosion hazards associated with the reactants and are not attractive.
Similarly direct carboxylation of glycerol with CO2 is moisture sensitive
Glycerol is a non-toxic biodegradable compound, which can be
obtained from glucose fermentation, sorbitol hydrogenolysis, or in huge
amounts during the production of biodiesel from the transesterification
of plant oils and animal fats [1]. The effective utilization of the glycerol
that is formed during the production of biodiesel is a key factor to pro-
mote biodiesel commercialization and future developments. This has
led to the development in the synthesis of value added chemicals from
glycerol as can be seen from number of review articles on this subject
[1–3]. Among various products proposed, glycerol carbonate and glycidol
are important products with many applications. Glycerol carbonate has
applications in the synthesis of polymers such as polyesters, polycarbon-
ates, polyurethanes, polyamides, surfactants, and lubricating oils [3–6],
while glycidol is used as a chemical intermediate in the synthesis of
glycidyl ethers, esters, amines and as a high-value component in the pro-
duction of glycidyl carbamate resins and polyurethanes [7–9].
Several methods have been described for the synthesis of glycerol
carbonate from glycerol, including reaction of glycerol with hazardous
phosgene, or carbon monoxide and oxygen at high pressure in the pres-
ence of copper based catalyst [10], carboxylation with carbon dioxide
[11], reaction with urea [12] or transesterification with dialkyl carbonate
such as dimethyl carbonate or cyclic carbonate [13]. Routes based on
phosgene and oxidative carbonylation are hazardous because of toxicity
and is an equilibrium controlled reaction [11]. Reaction of glycerol with
urea or transesterification of dialkyl or cyclic carbonates with glycerol
are interesting and significant amount of work is being carried out on
the development of new catalysts for these reactions. Glycidol is com-
mercially produced by epoxidation of allyl alcohol using tungsten
based catalyst [14]. Drawback of this process is the number of steps in-
volved and decomposition of the catalyst. There are few patents on the
synthesis of glycidol from glycerol carbonate using basic catalysts
[15,17]. The schematic of the reactions is shown below in Scheme 1.
Bruson et al. [16] have synthesized glycidol from glycerol and cyclic
carbonates like ethylene carbonate under reduced pressure in a two
step process. The reaction is carried out under reduced pressure in a tem-
perature range of 140–240 °C to give ~63% yield of glycidol. Malkemus
and Currier [15] have disclosed a process for the preparation of glycidol
from glycerol using alkali and alkaline earth metal phosphates, chlorides,
bromides, acetates, carbonates or bicarbonates as catalyst under reduced
pressure at a temperature of 125–275 °C to obtain glycidol yield of ~72%.
Yoo et al. [17] have reported synthesis of glycidol using zeolite exchanged
with alkali or alkaline earth metals as catalyst. The reaction was carried
out under reduced pressure and temperature in a range of 170–210 °C
to obtain glycidol yield of 66–83%. Thus there are reports on the synthesis
of glycerol carbonate from glycerol and dialkyl carbonate as reactants
using basic catalysts and synthesis of glycidol from glycerol carbonate
using basic catalysts. To the best of our knowledge there are no publica-
tions on the single pot synthesis of glycidol directly from glycerol. Herein
we report our results on the synthesis of glycidol with high selectivity
under mild operating conditions using ionic liquid catalyst.
⁎
Corresponding author. Tel.: +91 20 25902544; fax: +91 20 25902621.
E-mail address: aa.kelkar@ncl.res.in (A.A. Kelkar).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.07.003

S.M. Gade et al. / Catalysis Communications 27 (2012) 184–188
185
Scheme 1. Synthesis of glycerol carbonate from glycerol and synthesis of glycidol from glycerol carbonate.
2. Experimental
thickness). Identification of products was done using gas chromatogra-
phy–mass spectrometry (GC–MS) on an Agilent 6890N gas chromato-
graph coupled to an Agilent 5973 MSD mass spectrometer using HP-5
MS capillary column of 30 m×0.32 mm×0.25 μm dimension. Activity
of catalyst was based on conversion of limiting reagent measured
under standard conditions of reaction.
2.1. Chemicals
Glycerol (GL), glycidol (GD), glycerol carbonate (GC), methyl iodide
(MeI) and the aqueous solutions of Bronsted basic ionic liquids
tetramethylammonium hydroxide (25% [TMA][OH]), tetraethylammo-
nium hydroxide (35% [TEA][OH]), tetrabutylammonium hydroxide
(40% [TBA][OH]), tetramethylammonium bromide ([TMA][Br]), and
tetrabutylammonium bromide ([TBA][Br]) were purchased from Aldrich
chemicals. 20% aqueous solution of tetrapropylammonium hydroxide
(TPAOH), dimethyl carbonate (DMC), tetramethylammonium hydroxide
(25% [TMA][OH] in methanol), and 1,4-diazabicyclo[2.2.2]octane
(DABCO) were purchased from Spectrochem. All the chemicals were
used as received from suppliers. Aqueous solutions of tetramethylam-
monium bicarbonate ([TMA][HCO3]) and tetrabutylammonium bicar-
bonate ([TBA][HCO3]) were prepared from aqueous solutions of [TMA]
[OH] and [TBA][OH] respectively according to the literature procedure
[18]. Similarly [Me-DABCO][I] [19] was prepared by literature procedure.
[Me-DABCO][OH] was prepared using an anion exchange resin in
the OH− form by halide exchange. Water was removed to obtain
[Me-DABCO][OH] as the product. Iodine present in the ionic liquid was
estimated by addition of silver nitrate to known quantity of ionic liquid.
Purity of ionic liquid prepared was 93.5% in the present case.
2.4. Catalyst characterization
All the catalysts were characterized by IR and NMR analyses. NMR
experiments were carried out on a Bruker Avance 400 wide bore spec-
trometer equipped with a superconducting magnet with a field of 9.4 T.
The operating frequency for 13C was 75.4 MHz electron microscope. IR
spectrum was recorded on Agilent Technologies, Cary 600 series FT-IR
Spectrometer.
The details of catalyst characterization for ionic liquids prepared
are as follows:
[TMA][HCO3]:
1H NMR: 3.08, 12H (s)
13C NMR: 55.17, 160.38
[TBA][HCO3]:
1H NMR: 0.89, 12H (t), 1.25–1.36, 8H (m), 1.56–1.64, 8H (m),
3.15, 8H (t)
13C NMR: 12.93, 19.1, 23.05, 57.94, 160.07
[Me-DABCO][OH]:
2.2. Experimental procedure for the synthesis of bicarbonate ionic liquid
1H NMR: 3.01, 3H 9 (s), 3.14, 6H (t), 3.35, 6H (t)
FT-IR (cm−1): 796, 1123, 2894, 3424.
Bicarbonate ionic liquids were prepared using the literature proce-
dure [18] and typical experimental procedure followed is as below.
Aqueous [TMA][OH] (25 wt.%) solution (10 ml) was taken in a 25 ml
round bottom flask. CO2 was bubbled through the solution for 2 h
under constant stirring to obtain aqueous solution of [TMA][HCO3].
[TBA][HCO3] was prepared by following the similar procedure. 13C
NMR of the solutions for both the ionic liquids showed the appearance
of a peak at δ value of 160, which is characteristic of carbonyl carbon of
the bicarbonate group [20]. This indicated the formation of bicarbonate
ionic liquids.
3. Results and discussion
Various basic ionic liquids were screened for the transesterification
of glycerol with dimethyl carbonate and the results obtained are
presented in Table 1. Halide based ionic liquids were not active for the
reaction and only trace amount of product was formed in these reactions
(Table 1, Sr. nos. 1, 2). All other ionic liquids screened were active for the
reaction. Thus moderate to high glycerol conversions (77–95%) were
obtained with all hydroxide and bicarbonate types of ionic liquids inves-
tigated with selectivity to GC in a range of 33–56% and GD selectivity in a
range of 43–67% (Table 1, Sr. nos. 3–9). The higher activity observed
with hydroxide and bicarbonate based ionic liquids could be because
of the higher basicity of hydroxide and bicarbonate counter ions com-
pared to bromide counter ions. All the hydroxide and bicarbonate
types of ionic liquids (Table 1, Sr. nos. 3–9) showed formation of GD as
a product with good selectivity. Thus, decarboxylation of GC formed as
a product leads to the formation of GD. Formation of CO2 in these exper-
iments was confirmed by passing the gas phase through saturated bari-
um hydroxide solution to obtain white precipitate of barium carbonate.
Decarboxylation of the GC to GD is well known in presence of strong
bases [15,17]. The probable reason for higher selectivity to GD could
2.3. Experimental procedure for transesterification of DMC with glycerol
The transesterification of GL was carried out in a 50 ml round bottom
flask equipped with a reflux condenser under vigorous stirring. In a typ-
ical run, 0.217 mmol of catalyst with respect to GL was charged to the
50 ml round bottom flask containing GL 2 g, (21.73 mmol) and DMC
5.87 g, (65.21 mmol). The reaction was carried out at 80 °C for the se-
lected reaction time. Standard reaction was carried out for 90 min. The
reaction mixture was cooled, a sample was taken out for analysis and it
was diluted with N,N-dimethylformamide. The products were analyzed
by gas chromatography on an Agilent 6890 gas chromatograph with
HP-Innowax capillary column (30.0 m×0.53 mm×1.00 μm film

186
S.M. Gade et al. / Catalysis Communications 27 (2012) 184–188
Table 1
Screening of ionic liquids for transesterification of glycerol.
Sr. no.
Catalyst
GL conversion
(%)
Selectivity (%)
GD
GC
1
2
3
5
5
6
8
8
9
[TMA][Br]
[TBA][Br]
[TPA][OH]
[Me-DABCO][OH]
[TMA][HCO3]
[TBA][HCO3]
[TEA][OH]
[TBA][OH]
[TMA][OH]
Very low
Very low
Trace
Trace
58
54
67
58
43
53
51
Trace
Trace
42
46
33
42
56
47
47
77
87
83
86
89
90
95
Reaction conditions: GL: 21.73 mmol, DMC: 65.21 mmol, catalyst: 0.217 mmol,
temperature: 80 °C, time; 90 min.
be higher basicity of the ionic liquids with hydroxide and bicarbonate
counter ions used in the present work. From the results it was observed
that the activity of the [TMA][OH] ionic liquid was good (95% conversion
of GL) and also the selectivity to GD was 51% after 90 min and hence it
was taken up for further investigations with the aim of improving the
selectivity to GD.
Typical concentration–time profile is presented in Fig. 1. From the C–T
profile it can be seen that at lower conversion GD selectivity is slightly
lower (till 45 min reaction time). With progress of the reaction GD selec-
tivity increases marginally from 36 to 51. At lower conversion material
balance was lower (~90%), however, GC analysis did not show any
extra peak. It is likely that the intermediate product wherein one primary
OH of GL reacts with DMC to form the aliphatic carbonate is formed as
reported by Herseczki et al. [21]. Material balance of the reaction was
>95% at higher conversions. Conversion did not increase beyond
90 min reaction time, hence further experiments were carried out for
90 min.
The effect of catalyst concentration on activity and selectivity was
investigated in a range of 0.108 to 0.868 mmol catalyst loading keeping
other parameters constant. With aqueous solution of [TMA][OH] the
quantity of water in the reaction would be high and may not give cor-
rect result. In order to avoid this, stock solution of 10 mol% [TMA][OH]
in GL was prepared from 25 wt.% [TMA][OH] solution in methanol.
Methanol from the solution was removed on rotary evaporator. The
concentration of [TMA][OH] in GL was estimated by titration with HCl.
This stock solution was used to study the catalyst loading effect
(Figs. 2 and 3). Activity of the catalyst was very high and 98% conversion
was observed in 30 min reaction time at a catalyst loading of
0.651 mmol. Hence, in order to see the effect of catalyst loading on ac-
tivity the data has been presented at 30 min reaction time in Fig. 2 for
catalyst loading in a range of 0.108 to 0.868 mmol. To see the effect of
catalyst loading on GD selectivity the data has been presented for
Fig. 2. Effect of catalyst loading on conversion and selectivity at 30 min reaction time.
90 min reaction time for catalyst loading in a range of 0.108–
1.302 mmol (Fig. 3). Conversion of glycerol increased with increase in
catalyst loading at the intermediate stage of the reaction (30 min reac-
tion time) (Fig. 2) and also selectivity to GD increased significantly from
26 to 70%. This increase in the selectivity of GD could be due to increase
in the concentration of catalyst in the reaction mixture leading to in-
crease in GC decarboxylation.
The data on the effect of catalyst loading on GL conversion and se-
lectivity at 90 min reaction time is presented in Fig. 3. Conversion of
GL was very high (>90%) at all catalyst concentration investigated
at 90 min reaction time, while GD selectivity increased significantly
with increase in catalyst concentration (Fig. 3). Thus GD selectivity
of 78% was observed at a catalyst loading of 1.302 mmol. Observed
results also suggest that GC decarboxylation increases with increase
in concentration of catalyst in the solution.
The effect of GL to DMC mole ratio on the catalyst activity was studied
by varying GL: DMC molar ratio in the range of 1:3, 1:2, 1:1, 2:1, and 3:1
respectively keeping other conditions constant and the results are
presented in Table 2. GL and DMC quantity of 21.7 mmol was used in
the experiment carried out with GL:DMC ratio of 1:1. In other experi-
ments, the quantity of one of the reactant was varied keeping the quantity
of other reactant constant at 21.7 mmol, depending on the GL:DMC ratio
investigated. From the results it was observed that conversion of GL was
very low at GL:DMC ratio of 1:1. Only 45% conversion of GL was observed
at GL:DMC ratio of 1:1. This is expected since the reaction is equilibrium
controlled and excess DMC is used to achieve high conversions [22,23].
With increase in either GL or DMC concentration, conversion increased
Fig. 1. Typical concentration–time profile for transesterification of DMC with glycerol
using [TMA][OH] as catalyst.
Fig. 3. Effect of catalyst loading on conversion and selectivity at 90 min reaction time.

S.M. Gade et al. / Catalysis Communications 27 (2012) 184–188
187
120
100
80
60
40
20
0
Conversion%
Selectivity GD%
Selectivity GC%
Table 2
Effect of GL:DMC molar ratio on activity and selectivity.
Run
GL:DMC
Conversion
(%)
Selectivity (%)
GD
GC
1
2
3
4
5
1:1a
1:2a
1:3a
2:1b
3:1b
45
74
97
66
55
51
55
52
43
45
39
40
46
30
51
Reaction conditions: [TMA][OH]: 0.217 mmol, temperature: 80 °C, time: 90 min.
a
Conversion with respect to GL.
Conversion with respect to DMC.
b
70
80
90
significantly. High conversion (97%) was observed at GL:DMC ratio of 1:3,
compared to only 55% at GL:DMC molar ratio of 3:1. GD selectivity was
not affected significantly by a change in GL:DMC ratio. Observed results
may be due to increase in viscosity of reaction mixture at high GL concen-
trations leading to mass transfer issues.
Temperature
Reaction conditions: GL: 21.73 mmol, DMC: 65.21
mmol, [TMA][OH]: 0.217 mmol, Reaction time: 90 min.
Fig. 4. Effect of temperature on activity and selectivity.
The effect of water content on the activity and selectivity of the reac-
tion was studied and the results are presented in Table 3. From the re-
sults obtained it can be clearly seen that conversion of GL as well as
selectivities to both GC and GD decreased significantly with increase in
water content. This clearly shows negative effect of water on the reac-
tion. Previously Rokicki et al. [4] have used GL with b2% water in
K2CO3 catalyzed transesterification with DMC. Similarly for reaction of
GL and urea with solid base catalysts, water has negative effect on the
reaction [24].
Effect of temperature on the conversion of glycerol was studied at
three different temperatures (70 °C, 80 °C and 90 °C) (Fig. 4) using stan-
dard reaction conditions. The conversion was found to increase signifi-
cantly with increase in temperature from 70 to 80 °C. Activity was not
affected with further increase in temperature to 90 °C. Selectivity pattern
was not significantly affected by a change in the reaction temperature.
Cho et al. [25] have observed a similar trend in the transesterification
of GL to GC using tetraalkylammonium salts immobilized on MCM-41
as the catalyst.
Finally recycle experiment was carried out to check stability of the
catalyst. Initial experiment was carried out using standard reaction con-
ditions. Sample was analyzed on GC to check conversion and selectivity.
Fresh GL (21.7 mmol) and DMC (21.7 mmol) were added to the reac-
tion mixture to maintain GL:DMC ratio of 1:3 and reaction was carried
out again. The results are presented in Table 4. Conversion of GL as
well as selectivity to GD has gone down slightly (78% conversion and
45% selectivity to GD) during recycle of the catalyst. In this experiment
significant dilution of reaction mixture is taking place and also products
of the initial experiment are present in the reaction mixture. Hence ac-
tivity and selectivity cannot be compared with the initial experiment
carried out. However, significant conversion of GL (78%) observed
shows that the catalyst is active in recycle experiment.
There is a report on the synthesis of GC by transesterification of GL
with ethylene carbonate with small amount of GD as a by-product
[12]. In the present work GD formation with very high selectivity is ob-
served at lower temperatures like 70–90 °C. From the literature it is ob-
served that syntheses of GC from GL [26] and GD from GC [15] have
been investigated separately at high temperatures and in some cases
the type of catalysts used are similar. Synthesis of GD is carried out at
higher reaction temperatures (170–200 °C) [15] and reduced pressure
to remove GD as it forms. There is a need to develop catalyst active at
lower temperatures for the synthesis of GD, since GD is reactive and
can polymerize at high temperatures [27].
Tundo et al. [28] have investigated the reaction of aliphatic alcohols
with DMC using basic catalysts at 200 °C yielding unsymmetric carbon-
ates with K2CO3. However, with basic alumina and Mg–Al hydrotalcite
(KW2000) as catalysts, decarboxylation was observed forming the
corresponding ethers in a single pot. They emphasize the significance
of both the acidic and basic properties of the catalyst for decarboxyl-
ation reaction. Kricheldorf et al. [29] also have observed decarboxyl-
ation of cyclic carbonates during polymerization with methyl triflate
(cationic initiator). They observed that the initiator alkylates the exocy-
clic oxygen forming a trioxocarbenium ion, which on rearrangement
leads to the formation of an oxonium ion. Oxonium ion is attacked by
the anion (triflate) leading to decarboxylation. Thus both cation and
anion of the catalyst are involved in the decarboxylation of carbonates.
It is quite likely that in the present work also GC formed in the first step
is decarboxylated to GD because of the presence of basic (anionic) cen-
ter and acidic (cationic) center in the ionic liquid catalyst used. Quater-
nary ammonium center can interact with oxygen of the carbonyl group
of GC making the bond weaker. Further interaction with the anion can
lead to decarboxylation and formation of GD as the product. Detailed
work on this reaction is in progress in our laboratory.
4. Conclusions
Transesterification of DMC with glycerol was studied using various
ionic liquids as catalysts. Ionic liquids containing hydroxide and bicar-
bonate counterions were active for the reaction and gave high conver-
sions of GL (77–95%) at 90 min reaction time with high selectivity to
GD (43–67%). Effect of various reaction conditions on the activity and
selectivity was investigated using [TMA][OH] as a catalyst. Highest se-
lectivity of 78% to GD was obtained using [TMA][OH] loading of
1.302 mmol at 80 °C in 90 min reaction time. Activity as well as selec-
tivity of the catalyst decreased significantly with increase in moisture
Table 3
Effect of water on activity and selectivity.
Table 4
Amount of water (g)
GL conversion
(%)
Selectivity (%)
GD
Recycle of [TMA][OH] catalyst.
GC
Sr. no.
GL conversion
(%)
Selectivity %
GD
0.059
0.118
0.177
0.238
95
66
41
35
51
47
44
41
46
40
37
34
GC
RE-0
RE-1
89
78
53
45
46
54
Reaction conditions: GL: 21.73 mmol, DMC: 65.21 mmol; [TMA][OH]: 0.217 mmol;
temperature: 80 °C, Reaction time: 90 min.
Reaction conditions: GL: 21.73 mmol, DMC: 65.21 mmol; [TMA][OH]: 0.217 mmol;
temperature: 80 °C, Reaction time: 90 min.

188
S.M. Gade et al. / Catalysis Communications 27 (2012) 184–188
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Acknowledgment
Authors would like to thank Department of Science and Technology
(DST), Government of India for the financial support to this project.
Swapna M. Gade and Mudassir K. Munshi would like to thank CSIR,
Government of India for fellowship awarded to him. The analytical
help on GC–MS by Mrs. S. K. Shingote is greatly appreciated.
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