CaO-catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate: Isolation and characterization of an active Ca species

Article abstract of DOI:10.1016/j.apcata.2011.05.024

The transesterification of dimethyl carbonate (DMC) with glycerol to produce glycerol carbonate was investigated in the presence of CaO under various reaction conditions. CaO was completely dissolved in the reaction mixture of glycerol and DMC in 5 min at 75 °C and at the molar ratio of glycerol/DMC/CaO of 1/2/0.01. The isolation and the characterization of the dissolved Ca species by means of TOF-SIMS, elemental analysis, and FT-IR revealed that an active species, Ca(C₃H₇O ₃)(OCO₂CH₃) is generated from the interaction of CaO with glycerol and DMC. The mechanistic pathways to the formations of Ca(C₃H₇O₃)(OCO₂CH₃) and glycerol carbonate are discussed on the basis of experimental and spectroscopic results.

Full text of DOI:10.1016/j.apcata.2011.05.024

Applied Catalysis A: General 401 (2011) 220–225
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
CaO-catalyzed synthesis of glycerol carbonate from glycerol and dimethyl
carbonate: Isolation and characterization of an active Ca species
Fidelis Stefanus Hubertson Simanjuntaka,b, Tae Kyung Kima, Sang Deuk Leea, Byoung Sung Ahna,
Hoon Sik Kimc,∗∗, Hyunjoo Leea,b,∗
a Clean Energy Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Sungbuk-gu, Seoul 136-791, Republic of Korea
b Green Process and System Engineering, University of Science and Technology, Daejeon 305-355, Republic of Korea
c Department of Chemistry and Research Institute of Basic Sciences, Kyung Hee University, 1 Hoegi-dong, Dondaemun-gu, Seoul 130-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The transesterification of dimethyl carbonate (DMC) with glycerol to produce glycerol carbonate was
investigated in the presence of CaO under various reaction conditions. CaO was completely dissolved in
the reaction mixture of glycerol and DMC in 5 min at 75 ◦C and at the molar ratio of glycerol/DMC/CaO of
1/2/0.01.
The isolation and the characterization of the dissolved Ca species by means of TOF-SIMS, elemental anal-
ysis, and FT-IR revealed that an active species, Ca(C3H7O3)(OCO2CH3) is generated from the interaction
of CaO with glycerol and DMC.
Received 12 February 2011
Received in revised form 8 May 2011
Accepted 17 May 2011
Available online 26 May 2011
Keywords:
Glycerol
Glycerol carbonate
Dimethyl carbonate
CaO
The mechanistic pathways to the formations of Ca(C3H7O3)(OCO2CH3) and glycerol carbonate are
discussed on the basis of experimental and spectroscopic results.
© 2011 Elsevier B.V. All rights reserved.
Homogeneous catalyst
1. Introduction
membrane component for gas separation, as a component of coat-
ings and detergents, and as a monomer of polycarbonate and
The interest in renewable feedstocks is increasing rapidly
because of their low CO2 emission potential as fuels and poten-
tial uses as substitutes for petroleum-based materials. European
Union Directive announced that transportation fuels should con-
tain at least 5.75% of renewable bio-components by the end of 2010.
U.S. government also plans to replace 2% of on-road diesel by a
biodiesel by 2012 [1].
polyurethane [2–6].
A number of synthetic processes are known for the preparation
of glycerol carbonate from glycerol. Aresta et al. reported that glyc-
erol carbonate could be produced from the reaction of glycerol with
CO2 in the presence of a catalyst at elevated temperature and pres-
sure, but the yield of glycerol carbonate is too low to be used for
practical purposes [7].
Of the various types of renewable feedstocks, triglycerides are
regarded as good prospective raw materials for biodiesel pro-
duction, due to their easy availability from vegetable oils and
animal fats. In the preparation of biodiesel from triglycerides, how-
ever, 10 wt% of glycerol is always co-produced, which inevitably
reduces the economics of the process. In this context, transfor-
mation of glycerol into high value added chemicals is highly
necessary.
A direct reaction of glycerol with urea in the presence of a cata-
lyst is another method for preparing glycerol carbonate [8–11]. The
process, however, has some disadvantages such as the need for the
use of vacuum to remove evolved ammonia to accelerate the reac-
tion and to reduce the formation of undesirable side products such
as isocyanic acid and biuret [8].
Dimethyl carbonate (DMC) has also been employed as a car-
boxylating agent as a green alternative to urea and CO2 as depicted
in Scheme 1 because carboxylation with DMC can be operated at
much milder conditions without the production of problematic side
products.
Glycerol carbonate is a valuable glycerol derivative, which is
being widely used as a solvent in the cosmetics industry, as a
Transesterification of an ester with an alcohol is often conducted
in the presence of a base catalyst such as an alkali metal hydrox-
ide or alkaline earth metal oxide [12–14]. However, for the facile
recovery and reuse of catalysts, heterogeneous catalysts are clearly
more desirable [15]. The transesterification between glycerol and
DMC using CaO as the catalyst has been extensively investigated by
∗
Corresponding author at: Korea Institute of Science and Technology.
Tel.: +82 2 9585868; fax: +82 2 958 5809.
∗∗
Corresponding author at: Kyung Hee University. Tel.: +82 2 9610432;
fax: +82 2 9596443.
E-mail addresses: khs2004@khu.ac.kr (H.S. Kim), hjlee@kist.re.kr (H. Lee).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.05.024

F.S.H. Simanjuntak et al. / Applied Catalysis A: General 401 (2011) 220–225
221
O
O
HO
OH
+
+
2CH3OH
O
O
H3C
CH3
OH
O
O
OH
Glycerol Carbonate
Glycerol
Dimethyl Carbonate
(DMC)
Scheme 1. Synthesis of glycerol carbonate from glycerol and DMC.
many researchers. Recently Ochoa-Gomez et al. reported that CaO
is highly active for transesterification and the activity is strongly
influenced by the pretreatment temperature [16]. Later, Li et al.
explained that the reason for the high activity of CaO could be
the formation of active homogeneous species through the interac-
tion with glycerol and DMC, but the characterization of the species
was not successful [17]. A similar phenomenon was also observed
when CaO was used as a catalyst for the reaction of triglyceride
with methanol to produce biodiesel (FAME) and glycerol. In this
reaction, calcium diglyceroxide (Ca(C3H7O3)2) was suggested as an
active species [18,19].
To have a deeper insight into the nature of the active species
for the CaO-catalyzed transesterification of glycerol with DMC, we
have conducted the characterization of the isolated Ca species dis-
solved in the reaction mixture by means of elemental analysis,
TOF-SIMS and FT-IR.
washed with CH3CN, dried under vacuum, and stored inside the
glove box. The weight of isolated powder was 3.15 g (yield: 86%).
Elemental analysis calcd for CaC5H10O6 (%): Ca, 19.4; C, 29.1: H, 4,9.
Found: Ca (ICP-Mass), 18.8; C, 28.4; H, 4.6.
2.3. Instrumentation
Sample preparations for TOF-SIMS and IR experiments were
conducted in a glove box filled with Ar. TOF-SIMS analysis was per-
formed with an IONTOF, TOF-SIMS5 equipped with a pulsed Bi+
ion gun operated at 25 kV. Sample surfaces were biased at +3 or
−3 kV with respect to the grounded extraction electrode for posi-
tive and negative mode SIMS, respectively. The dc ion beam current
(∼14 nA) was pulsed at 10 kHz and the area analyzed was approx-
imately 100 ␮m × 100 ␮m. The vacuum of the system was held
below 1 × 10−6 Torr throughout the TOF-SIMS measurements. To
clean the surface, the analysis regions were sputtered for 1 scan
using a 100 ␮m × 100 ␮m dc rastering bismuth ion gun prior to
the SIMS measurements. The pre-analysis cleaning was carried out
largely to remove surface contaminants from the polishing process.
FT-IR spectra of catalyst samples were recorded on a Nicolet
FT-IR spectrometer (iS10, USA) equipped with a SMART MIRACLE
accessory.
Herein, we report that
a
highly active species,
[Ca(C3H7O3)(OCO2CH3)] is generated from the interaction of
CaO with glycerol and DMC. The mechanistic pathways to the
formation of Ca(C3H7O3)(OCO2CH3) and glycerol carbonate are
also discussed on the basis of experimental and spectroscopic
results.
2. Experimental
3. Results and discussion
Glycerol, DMC, and CaO were purchased from Aldrich Chem-
ical Co. Glycerol carbonate and CH3CN were obtained from the
TCI (Japan) and JT Baker, respectively. All reagents were used as
received without further purifications. CaO was calcined at 900 ◦C
for 3 h and stored in a glove box filled with Ar.
3.1. Transesterification of DMC with glycerol
Transesterification of DMC with glycerol was investigated
at 75 ◦C using various basic metal oxides. The molar ratio of
glycerol/DMC/catalyst was maintained at 1/2/0.03 for all the trans-
esterification reactions. Among the catalysts tested, as listed in
Table 1, Na2O showed the highest activity, producing glycerol car-
bonate at a yield of 92.6%. By contrast, the activities of MgO and
ZnO were extremely low, producing glycerol carbonate in yields of
10.2% and 0.5%, respectively. However, interestingly, CaO exhibited
2.1. Transesterification reaction
Glycerol (1.84 g, 20 mmol), DMC (3.6 g, 40 mmol) and CaO
(0.011 g, 0.2 mmol) were loaded into a 100 mL round-bottom flask
having condenser and reacted at 75 ◦C for 15 min with a vigorous
stirring. The reactions conducted at temperatures higher than 75 ◦C
were carried using a 170 mL high pressure glass vessel (Andrewss
Glass Co., USA). After the completion of the reaction, t-butanol was
added to the reaction mixture as an external standard. The amount
of glycerol carbonate produced and unreacted glycerol were ana-
lyzed using a HPLC (Waters) equipped with an Aminex HPX-87H
column (Biorad) and a RI detector (Waters 410). The mobile phase
used was a 5 mM H2SO4 aqueous solution and the flow rate was set
at 0.6 mL/min.
Table 1
Effect of metal oxide for the transesterification of dimethyl carbonate with glycerol.a
Entry
Catalyst
Convertion of
glycerol (%)
Yield of
glycerol
carbonate (%)
Selectivity to
glycerol
carbonate (%)
1
2
3
4
5
6
7
Na2O
95.5
91.2
94.3
91.7
46.2 (2.3)
20.5
0.5
92.6
90.2
94.0
91.4
41.8(2.5)
10.2
0.5
96.9
98.9
99.7
99.7
90.4 (92.0)
49.9
100.0
CaO
CaOb
Calcium complexc
Calcium complexd
MgOe
2.2. Isolation of an active species; Ca(C3H7O3)(OCO2CH3)
All the reactions related to the isolation of the calcium com-
plex were conducted using a Shlenk line technique. Glycerol
(310.0 mmol, 28.56 g), DMC (618.5 mmol, 55.72 g), and CaO cal-
cined at 900 ◦C for 3 h (17.8 mmol, 1.00 g) was loaded into a
250 mL round-bottom flask and stirred at 75 ◦C for 30 min. After
the reaction was completed, anhydrous CH3CN was added slowly
to the transparent reaction mixture to precipitate the dissolved cal-
cium complex. The white precipitates recovered by filtration were
ZnO
a
Glycerol (20 mmol), DMC (40 mmol), catalyst (0.6 mmol), T = 75 ◦C, t = 30 min.
Calcined at 900 ◦C for 3 h.
Calcium complex isolated from the reaction of glycerol, DMC and CaO;
b
c
Ca(C3H7O3)(OCO2CH3).
d
After 1 h exposure of Ca(C3H7O3)(OCO2CH3) to air. The numbers in paren-
theses are conversion, yield, and selectivity obtained with the air-exposed
Ca(C3H7O3)(OCO2CH3) for 3 h.
Calcined at 900 ◦C for 3 h t = 180 min.
e

222
F.S.H. Simanjuntak et al. / Applied Catalysis A: General 401 (2011) 220–225
100
100
80
60
40
20
80
60
DMC/glycerol = 2:1
DMC/glycerol = 4:1
DMC/glycerol = 6:1
Yield (%)
Conversion (%)
Selectivity (%)
40
20
0
0.5
1.0
1.5
2.0
2.5
3.0
0
10
20
30
40
50
60
70
80
90
catalyst/glycerol (mol%)
reaction time (min)
Fig. 1. Effect of the amount of CaO on the transesterification of dimethyl carbon-
ate with glycerol. Reaction condition: Glycerol (20 mmol), DMC (40 mmol), 75 ◦C,
30 min.
Fig. 2. Effect of the reaction time (CaO uncalcined) on the yield of glycerol carbonate.
Reaction condition: catalyst/glycerol = 1 mol%, T = 75 ◦C.
became slightly turbid, but, at the catalyst concentrations lower
than 1 mol%, the solution was completely transparent.
considerably high activity almost comparable to Na2O although the
basicity of CaO is much weaker than that of Na2O. When reagent
grade CaO was used as a catalyst, glycerol carbonate was produced
in 90.2% yield and 98.9% selectivity. The yield of glycerol carbonate
increased further to 94.0% when CaO was used after calcination at
900 ◦C for 3 h. One interesting point observed with the use of cal-
cined CaO is that the dissolution of CaO is completed in 5 min (see
Supporting information, Fig. S1). In contrast, the reaction mixture
with uncalcined CaO showed a little turbidity even after the com-
pletion of the reaction. The reason for this turbidity is not clear at
the moment, but it seems that H2O and or CO2 adsorbed on the
surface of the uncalcined CaO retards the dissolution. The possible
effect of water on the dissolution of CaO is somewhat supported by
the turbidity of the solution after the exposure of the calcined CaO
in air for 3 h. As a whole, the activity of a metal oxide catalyst is
greatly affected by the dissolution time and the degree of dissolu-
tion: the more soluble the catalyst, the higher the catalytic activity,
suggesting that the transesterification proceeds mostly in a homo-
geneous way. Therefore, the significantly lower activity of MgO and
ZnO can be ascribed in part to their extremely poor solubilities in
the reaction mixtures. In the metal oxide-catalyzed transesterifi-
cation between glycerol and DMC, it is easily conceivable that the
first step for the generation of an active species is the acid-base
interaction between a hydroxyl group of glycerol and metal oxide.
In this context, the generation of the active species from the less
basic MgO would be much more difficult than that from the more
basic CaO. In other word, the basicity of MgO is not sufficiently
high enough to generate the similar homogeneous active species
to that observed in the CaO-catalyzed transesterification [20,21].
Considering the extremely low activity and solubility of MgO, the
transesterification in the presence of MgO seems to proceed in a
heterogeneous way.
The effect of reaction time was also investigated at 75 ◦C at
varying molar ratio of DMC/glycerol. The catalyst loading was main-
tained at 1 mol% with respect to glycerol. Fig. 2 reveals that, at the
early stages of the reaction up to 2–3 min, the formation of glycerol
carbonate was negligible. However, the yield of glycerol carbonate
started to increase rapidly thereafter, implying that there exists an
induction period for the formation of an active calcium species from
CaO. It is interesting to notice that the reaction time to reach equi-
librium increases with the increasing molar ratio of DMC/glycerol
from 2 to 6. This result may imply that, above the molar ratio of
2, heterogeneous catalysis is also functioning in the CaO-catalyzed
transesterification (vide infra).
The effect of molar ratio of DMC to glycerol was also investigated
at 75 ◦C for 15 min. As shown in Fig. 3, the yield of glycerol carbon-
ate reaches a maximum of 85.4 at the molar ratio of 2 and then
decreases steadily with the increase of the molar ratio up to 10,
again suggesting that, above the molar ratio of 2, heterogeneous
catalysis is also functioning in the CaO-catalyzed transesterifica-
tion. In fact, the turbidity of the reaction mixture increased with
the increase of DMC concentration. It is likely that the increased
concentration of DMC in the reaction solution limits the interaction
of CaO with glycerol, thereby preventing the formation of soluble
Ca species.
To see the correlation between the amount of dissolved Ca
species and the catalytic activity, the amount of dissolved Ca
species was analyzed (Fig. 3). When the molar ratio of DMC/glycerol
increased from 1 to 2, the dissolved Ca content decreased from 15.6
to 11.5 mg. Considering that the initial Ca content in CaO was 17 mg,
approximately 91.8% and 67.6% of CaO transformed into soluble
species at the DMC/glycerol molar ratios of 1 and 2, respectively.
It is worth to note that, in spite of decrease in the amount of dis-
solved Ca species as going from 15.6 to 11.5 mg, the yield of glycerol
carbonate increased from 68.0 to 85.3%. On further increase of the
molar ratio to 4, the dissolved Ca content drastically dropped down
to 0.3 mg, which is only 2.6% of that measured at the molar ratio
of 2. On the contrary, the reduction of glycerol carbonate yield was
much smaller from 85.3 to 63.9% as the molar ratio was decreased
from 2 to 4. It is surprising to observe that the transesterification
proceeds smoothly even in the presence of such a low dissolved Ca
content in the solution. These results may suggest that DMC plays a
pivotal role to shift the transesterification toward the formation of
glycerol carbonate is strongly affected by the concentration of DMC.
The effect of catalyst loading on the yield of glycerol carbonate
also supports the idea that CaO-catalyzed transesterification take
places in a homogeneous way. As illustrated in Fig. 1, the yield and
the selectivity of the glycerol carbonate did not vary much when the
catalyst loading was decreased from 3 to 0.5 mol% with respect to
glycerol. Likewise, the yield of glycerol carbonate remained almost
constant with the decrease of catalyst loading from 1 to 0.5 mol%.
However, the yield of glycerol carbonate was reduced to 62.9%
when the catalyst loading was further decreased to 0.25 mol%. The
turbidity of the reaction mixture was affected by the catalyst con-
centration. When 1 mol% CaO (uncalcined) was used, the solution

F.S.H. Simanjuntak et al. / Applied Catalysis A: General 401 (2011) 220–225
223
18
15
12
9
100
80
60
40
20
0
Yield (%)
Conversion (%)
Selectivity (%)
Ca amount (mg)
6
3
0
0
2
4
6
8
10
DMC/Glycerol (molar ratio)
Fig. 3. Effect of DMC/glycerol molar ratio. Reaction condition: Glycerol (20 mmol), CaO (0.2 mmol), 75 ◦C, 15 min.
Or, there is a considerable contribution of heterogeneous catalyst to
the transesterification, especially at the molar ratio of DMC/glycerol
higher than 2.
The effect of temperature on the transesterification was inves-
tigated in the temperature range of 35–125 ◦C at the catalyst
concentration of 0.5 mol% with respect to glycerol. As shown in
Fig. 4, the yield of glycerol carbonate increased with the temper-
ature rise up to 100 ◦C, and then remained constant on further
increase of the temperature to 125 ◦C. The formation of side prod-
ucts was not observed in the temperature range tested.
ionization process. Above the mass range of 100 m/z, the strongest
peak was observed at 112.99 m/z, which could be assigned as a
dehydrated calcium monoglycerol species. Interestingly, except
112.99 m/z, major peaks detected seem to be related to the
calcium species with both the glycerol and methyl carbonate moi-
eties, including Ca(C3H7O3)(OCO2CH3), Ca(C3H7O3)(OCO2CH3)2,
[Ca(C3H7O3)(OCO2CH3)][Ca(C3H7O3)], and [Ca(C3H7O3)(OCO2
CH3)]2. Among these, Ca(C3H7O3)(OCO2CH3) seems to be the most
probable structure of the active species on the basis of elemental
analysis. Other species are believed to be formed instantly during
the ionization condition. In fact, the presence of an intensive peak
at 112.99 m/z could imply the existence of other calcium glycerol
compounds such as calcium monoglyceroxide (Ca(C3H6O3)), cal-
cium diglyceroxide (Ca(C3H7O3)2), and tricalcium octaglyceroxide
(Ca3(C3H7O3)6(C3H7O3)2). Fuji et al. reported that Ca–glycerol
complexes such as calcium diglyceroxide (Ca(C3H7O3)2) could be
produced by the interaction of CaO with glycerol [22]. The forma-
tion of calcium diglyceroxide as an active species was confirmed by
Kouzu et al. in the CaO-catalyzed transesterification of triglyceride
with methanol [18]. Calcium diglyceroxide was also expected to
form in the transesterification of DMC by glycerol through the
direct interaction of CaO with glycerol. However, TOF-SIMS, FT-IR
and X-ray diffraction results clearly reveal that calcium diglycerox-
ide is not generated in this transesterification reaction, implying
that the presence of DMC prohibits the formation of calcium
diglyceroxide (see Figs. S3 and S4 in Supporting information).
The presence of a carboxylate group in the isolated calcium
species is evident from a series of FT-IR spectra shown in Fig. 5.
3.2. Characterization of active Ca species
To identify the active species generated in situ from the CaO-
catalyzed transesterfication of DMC with glycerol, the dissolved
Ca species was isolated and characterized by means of TOF-SIMS
analysis. As summarized in Table 2 and Fig. S2 in Supporting infor-
mation many kinds of calcium-containing cations were detected
at the positive ion target. Below the mass range of 100, Ca species
like Ca, CaH, CaO, and CaOH were also detected with high inten-
sities, most of which seemed to be instantly formed from the
100
80
60
Table 2
Relative intensities of detected positive ion at the TOF-SIMS and their estimated
structures.
40
Yield (%)
Conversion (%)
Selectivity (%)
Detected
positive ion
mass
Relative
intensity
Estimated positive ion structure (mass)
20
112.99
168.98
208.03
225.03
281.05
319.00
337.01
393.00
50765
13124
1948
7131
2184
526
Ca(C3H7O3) − H2O
Ca(C3H7O3) (OCO2CH3) − 2H2O − H
0
Ca(C3H7O3) (OCO2CH3) + 2H
Ca(C3H7O3) (OCO2CH3) H2O + H
Ca(C3H7O3)(OCO2CH3)2
[Ca(C3H7O3) (OCO2CH3)][Ca(C3H7O3)] − H2O
[Ca(C3H7O3) (OCO2CH3)][(C3H7O3)Ca]
2[Ca(C3H7O3) (OCO2CH3)] − H2O − H
20
40
60
80
100
120
140
Temperature (ºC)
1912
588
Fig. 4. Effect of reaction temperature. Reaction condition: Glycerol (50 mmol), DMC
(100 mmol), CaO (0.25 mmol), 75 ◦C, 15 min.

224
F.S.H. Simanjuntak et al. / Applied Catalysis A: General 401 (2011) 220–225
CaO + glycerol
OH
HO
O Ca OH
DMC
glycerol
carbonate
I
MeOH
O
O
O
O
OH
OH
HO
O Ca
O
O
OH
HO
O Ca
OH
III
II
MeOH
glycerol
Scheme 2. A plausible reaction mechanism for the CaO-catalyzed transesterification of dimethyl carbonate with glycerol.
The strong peak observed at 1058 cm−1 corresponds to the C–O
stretching frequency of glycerol group in the complex [23]. Upon
the interaction of CaO with glycerol and DMC, two strong peaks
appeared at 1640 and 1324 cm−1, which can be associated with the
carbonyl (C O) stretching frequency and C–O–C vibrational band
of the CH3–O–CO2–Ca, respectively [24–26].
The catalytic activity of the isolated Ca(C3H7O3)(OCO2CH3) was
also evaluated for the reaction of glycerol and glycerol carbonate.
As expected, Ca(C3H7O3)(OCO2CH3) exhibited the similar activity
to CaO. However, the catalytic activity of Ca(C3H7O3)(OCO2CH3)
decreased after exposure to air. As listed in Table 1, the yield
of glycerol carbonate was reduced by more than 50% when
Ca(C3H7O3)(OCO2CH3) was exposed to air for 1 h (entry 5). The
catalytic activity of Ca(C3H7O3)(OCO2CH3) was negligible after the
exposure to air for 3, strongly indicating that the calcium species is
transformed into an inactive form, most possibly due to the interac-
tion with atmospheric CO2. This is supported by a FT-IR experiment.
When Ca(C3H7O3)(OCO2CH3) was exposed to air for 1 h, a strong
peak centered at 1392 cm−1 appeared, whereas the intensities of
the peaks related to glyceroxyl and methoxycarboxylate groups
(1324, 1640, and 1058 cm−1) were reduced significantly (Fig. 5(c)).
The peak at 1392 cm−1 became more pronounced after 3 h of expo-
sure to air (Fig. 5(d)). The appearance of the peak at 1392 cm−1
and the extinction of the peaks at 1324, 1640, and 1058 cm−1
clearly suggest that, on exposure to air, Ca(C3H7O3)(OCO2CH3)
transformed into CaCO3 or a species similar to CaCO3 due to CO2
present in air, and the glyceroxyl and methoxy carboxylate groups
were completely dissociated from the Ca center.
The activation energy for the transesterification between glyc-
erol and DMC was also measured using the Ca(C3H7O3)(OCO2CH3)
as the catalyst. The molar ratio of glycerol/catalyst was fixed at
0.1 mol%. As depicted in Fig. S5 in Supporting information, the
activation energy was calculated as 9.67 kJ/mol, indicating that
the transesterification is a feasible reaction in the presence of
Ca(C3H7O3)(OCO2CH3) (see Supporting information). TOF (h−1
,
turnover frequency) values of 766, 991, and 1087 at 25, 75 and
85 ◦C, respectively also demonstrate that Ca(C3H7O3)(OCO2CH3) is
a highly active catalyst for the transesterification reaction.
3.3. Reaction mechanism
A plausible mechanism for the CaO-catalyzed transesterification
between glycerol and DMC is depicted in Scheme 2. The calcium
species, I bearing a glyceroxyl and a hydroxyl groups is likely
to form first from the interaction of CaO with glycerol, which in
turn reacts with DMC to generate species, II with the concomi-
tant loss of CH3OH. The subsequent attack of a glycerol molecule
on the carbonyl carbon of II and the simultaneous loss of CH3OH
would produce an active species III. The intramolecular attack of
the hydroxyl oxygen atom on the carbonyl carbon of II would
Fig. 5. IR of glycerol carbonate (a), glycerol (b), Ca complex (c), Ca complex exposed
to air for 1 h (d) and for 3 h (e), and CaCO3 (f).

F.S.H. Simanjuntak et al. / Applied Catalysis A: General 401 (2011) 220–225
225
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