Highly efficient and selective synthesis of dibutyl carbonate via the synergistic dual activation catalysis of tetraethylammonium prolinate ionic liquids

Article abstract of DOI:10.1016/j.apcata.2014.12.037

A facile, highly efficient and phosgene-free synthesis process of dimethyl carbonate (DMC) with nbutanol (BuOH) to dibutyl carbonate (DBC) by transesterification reaction has been studied in detail using tetraethylammonium-based amino acid ionic liquids ([N₂₂₂₂][AA]) as homogeneous catalysts. The results indicated that tetraethylammonium prolinate ([N₂₂₂₂][Pro]) exhibited the best catalytic activity in compared to other four [N₂₂₂₂][AA], and DBC could be obtained at a yield of 72% under optimum conditions. Furthermore, quantum-mechanical calculations manifested that such high DBC yield originated from the synergistic dual activation catalysis of [N₂₂₂₂][Pro]. [N₂₂₂₂][Pro] could activate BuOH and DMC well at the same time, which enhances the electrophilicity of BuOH and the nucleophilicity of DMC respectively, leading to the excellence catalytic performance.

Full text of DOI:10.1016/j.apcata.2014.12.037

Applied Catalysis A: General 492 (2015) 177–183
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Highly efficient and selective synthesis of dibutyl carbonate via the
synergistic dual activation catalysis of tetraethylammonium prolinate
ionic liquids
Fan Ouyang, Zhen-Zhen Wang, Yan Zhou, Zheng Cheng, Zhang-Hui Lu,
Zhen Yang, Duan-Jian Tao∗
College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A facile, highly efficient and phosgene-free synthesis process of dimethyl carbonate (DMC) with n-
butanol (BuOH) to dibutyl carbonate (DBC) by transesterification reaction has been studied in detail
using tetraethylammonium-based amino acid ionic liquids ([N2222][AA]) as homogeneous catalysts. The
results indicated that tetraethylammonium prolinate ([N2222][Pro]) exhibited the best catalytic activity
in compared to other four [N2222][AA], and DBC could be obtained at a yield of 72% under optimum
conditions. Furthermore, quantum-mechanical calculations manifested that such high DBC yield origi-
nated from the synergistic dual activation catalysis of [N2222][Pro]. [N2222][Pro] could activate BuOH and
DMC well at the same time, which enhances the electrophilicity of BuOH and the nucleophilicity of DMC
respectively, leading to the excellence catalytic performance.
Received 24 October 2014
Received in revised form
18 December 2014
Accepted 20 December 2014
Available online 30 December 2014
Keywords:
Dibutyl carbonate
Dimethyl carbonate
Ionic liquid
© 2014 Elsevier B.V. All rights reserved.
Transesterification
1. Introduction
green raw material, and mild reaction conditions [8,9]. Generally,
this transesterification route can be described as a two-step pro-
Dibutyl carbonate (DBC) is an important long-chain alkyl car-
bonate in petrochemical industry, and it is extensively used for the
production of various organic and polymeric materials, particularly
for the synthesis of polycarbonate [1–5]. DBC is also considered to
be an excellent environmental protection lubricant base material
because of its good lubricity and wearability, corrosion resistance,
high thermal oxidative stability, and outstanding solubility [1–4].
The synthesis of DBC therefore has been growing fast in the past
years due to a continual demand.
Traditionally, DBC has been produced by the reaction of
phosgene with n-butanol (BuOH). However, this phosgenation
technology has several serious inherent drawbacks, including the
use of highly toxic phosgene, the corrosion of metal equipment,
and a large mount of by-product hydrogen chloride. Consequently,
the phosgene-free synthesis of DBC with a more environmen-
tally friendly process continues to be appealing [6,7]. Recently, the
transesterification of dimethyl carbonate (DMC) with BuOH has
attracted much attention as the alternative route for the produc-
tion of DBC, with the advantages of low pollution and corrosion,
cess, which involves the first step of the transesterification of DMC
with BuOH to form methyl butyl carbonate (MBC) (Eq. (1)) and the
second step of the transesterification of MBC with BuOH to produce
DBC (Eq. (2)).
DMC + BuOH ꢀ MBC + MeOH
MBC + BuOH ꢀ DBC + MeOH
(1)
(2)
At present, there are already several literatures on the synthesis
of long-chain alkyl carbonate (such as diethyl carbonate, dipropyl
carbonate, dibutyl carbonate, dipentyl carbonate, and diphenyl
carbonate) through transesterification reaction. For example,
Murugan and Bajaj [10] studied the synthesis of diethyl carbon-
ate using KF/Al2O3 as catalyst and the yield of diethyl carbonate
could reach 61.6%. Ma and co-worker [11] reported the synthesis
of dipropyl carbonate with a yield of 70% using Mg–Al compos-
ite oxide containing La as efficient and reusable catalyst. Shaikh
and Sivaram [12] reported that the transesterification of DMC with
BuOH could obtain the DBC yield of 72% at 12 h in the presence
of n-Bu2SnO as catalyst. Tang et al. [13] had further investigated
the transesterification of DMC with phenol catalyzed by core–shell
TiO2@SiO2 the yield of diphenyl carbonate was only 24.1% at 9 h.
Although these investigations have made strides, these results are
not entirely satisfactory because of low reaction selectivity and
∗
Corresponding author. Tel.: +86 79188121974.
E-mail address: djtao@jxnu.edu.cn (D.-J. Tao).
http://dx.doi.org/10.1016/j.apcata.2014.12.037
0926-860X/© 2014 Elsevier B.V. All rights reserved.

178
F. Ouyang et al. / Applied Catalysis A: General 492 (2015) 177–183
ILs thus obtained were dried in high vacuum for 12 h at 90 ◦C. The
structures of these [N2222][AA] ILs were confirmed by 1H NMR, ele-
mental analysis and FT-IR spectroscopy, and no impurities were
found by 1H NMR. All the detailed characterization results were
given in supplementary data.
2.2. Reaction procedures
In a typical procedure, [N2222][Pro] (0.5 wt%, based on the total
weight of DMC and BuOH), DMC (20 mmol) and BuOH (80 mmol)
were added into a round-bottomed flask (50 mL) fitted with a
magnetic stirrer and condenser. Then, the reaction mixture was vig-
orously stirred and allowed to proceed for 1–6 h with the heating at
the designed temperature (e.g., 110 ◦C). After the reaction was com-
pleted, the reactor was cooled down. About 0.2 mL of liquid sample
was taken from the reactor and detected by gas chromatography
(GC). Subsequently, the reaction mixture was extracted with deion-
ized water (10 mL × 3), and the system thus forms a liquid–liquid
biphase, and the aqueous phase containing ILs could be easily sepa-
rated by simple decantation. After that, the catalyst ILs were further
in a vacuum oven at 80 ◦C for 12 h to remove water and the resid-
ual reactants prior to reuse in the next run. Qualitative analyses
of products were examined by a Thermo Trace 1300 GC-ISQ, and
quantitative analyses were carried out by a GC-FID (Agilent 7890B).
The detailed analysis conditions were described as follows: the
injector and detector temperatures were 250 and 250 ◦C, respec-
tively; the column temperature was increased stepwise to 200 ◦C,
Scheme 1. Structures of five [N2222][AA] ILs.
product yield, harsh reaction conditions, high mass transfer resis-
tance, and easy deactivation of catalysts. There remains a strong
need to develop novel catalyst materials with high efficiency and
selectivity for the synthesis of long-chain alkyl carbonate, espe-
cially for DBC.
In recent years, ionic liquids (ILs), as new type of green solvent
and efficient catalyst, have been received much attention in indus-
trial and academic area. They present a broad application prospect
and have been successfully introduced into the field of cataly-
sis owing to their unique chemical properties such as negligible
vapor pressure, structural variety, excellent thermal stability, and
remarkable solubility [14–17]. To date, ILs have been extensively
used in alkylation, esterification, tansesterification, acetalization,
and so on [18–22], which obviously exhibits high catalytic activ-
ity and selectivity. However, to the best of our knowledge, there
has been no mention of using ILs as catalysts for the synthesis of
DBC. Moreover, most studies have only focused on the catalytic per-
formance of various ILs. The key investigation on the relationship
between the structural geometry of ILs and their catalytic perfor-
mance to study the intrinsic reaction mechanism is still scarce in
the literatures. Hence, we believe that there is a need to investigate
the activation mechanism of ILs for the highly efficient synthesis of
DBC, and these results will be applicable to explore the possibility
of IL-based industrial processes and to provide optimal parameters.
Therefore, a series of tetraethylammonium-based amino acid
ionic liquid ([N2222][AA]) had been prepared and their catalytic
activities for the synthesis of DBC were investigated in this work.
The reaction parameters such as reaction time, temperature, cat-
alyst loading, and molar ratio of reactants were explored in detail
to obtain the optimum conditions. Furthermore, the effect of struc-
tural geometry of ILs on their catalytic activity was studied and a
plausible reaction mechanism involved the synergistic dual activa-
tion catalysis of [N2222][AA] was then proposed.
holding at 80 ◦C for 2 min, increasing to 200 ◦C at 40 ◦C min−1
,
holding at 200 ◦C for 5 min. Then the conversion and selectivity
were calculated according to the area of chromatograph peak using
biphenyl as an internal standard.
2.3. Definition of DMC conversion, DBC selectivity and DBC yield
Qualitative analysis of GC–MS confirmed that DMC reacted to
give DBC and MBC as the unique products and no other prod-
ucts were detected in the reaction. Thus the conversion of DMC
is defined as the ratio of the number of moles of DBC and MBC pro-
duction in the reaction to the total number of moles of DMC initially
added. The selectivity for DBC is defined as the ratio of the number
of moles of DBC to the number of moles of DBC and MBC. The date
of DMC conversion multiply by DBC selectivity was the DBC yield.
moles of (DBC + MBC) produced
DMC conversion =
moles of DMC initially added
mol (DBC)
DBC selectivity =
mol (DBC) + mol (MBC)
2. Experimental
2.4. Computational methods
2.1. Chemicals and catalyst preparations
Density functional theory (DFT) was employed to perform the
geometry optimizations and natural bond orbital (NBO) charge
analysis at the B3LYP/6-31++G(d,p) level using the Gaussian 09 pro-
gram package [23] Each final optimized structure of [N2222][AA],
DMC, BuOH and their complexes was checked to be a true minimum
through frequency calculation at the corresponding levels.
Tetramethylammonium hydroxide pentahydrate (purity ≥99%),
and tetraethylammonium hydroxide (25 wt% aqueous solution)
were purchased from Aldrich Chemical Reagent Co. Ltd. Other
reagents such as DMC, amino acid, alcohol, triethyl amine, potas-
sium carbonate, and sodium hydroxide were of analytical grade and
used without any further purification.
Five [N2222][AA] ILs (as shown in Scheme 1) were synthesized
via the simple neutralization reactions as follows. Slightly excess
amount of amino acid (glycine, valine, alanine, serine and proline)
was added to [N2222]OH aqueous solution. The mixture was then
stirred at room temperature for 2 h. Subsequently, water was dis-
tilled off at 60 ◦C under reduced pressure. The reaction mixture was
added into ethanol, and filtrated to remove excess amino acid. Fil-
trate was evaporated to remove solvents. The product [N2222][AA]
3. Results and discussion
3.1. Catalytic activities of different catalysts
Five [N2222][AA] ILs were employed as catalysts to test
their catalytic activities in the transesterification reac-
tion of DMC with BuOH, and the results are summarized

F. Ouyang et al. / Applied Catalysis A: General 492 (2015) 177–183
179
Fig. 1. The O H bond length of BuOH in the free BuOH and the complexes of BuOH with [N2222][AA].
in Table 1. It is obvious that these five [N2222][AA] cata-
lysts show different catalytic activities, and the sequence is
[N2222][Pro] > [N2222][Gly] > [N2222][Ala] ≈ [N2222][Val] > [N2222][Ser]
(entries 1–5). Among [N2222][AA] ILs, [N2222][Pro] catalyzed the
reaction to have the highest conversion of DMC (96%) and selectiv-
ity of DBC (75%). In order to illustrate the underlying mechanism,
we calculated the geometry optimization for the free BuOH, the
complex of BuOH with [N2222][AA], and the complex of DMC with
[N2222][AA] at the B3LYP/6-31++G(d,p) level of theory. Then the
binding energies of BuOH-[N2222][AA] and DMC-[N2222][AA] are
given in Table 2, and the corresponding O H bond lengths of
BuOH are shown in Fig. 1. It can be seen that the binding energy
of BuOH-[N2222][AA] is calculated to be more than −50 kJ/mol,
and all the O H bond lengths in the BuOH-[N2222][AA] complexes
are predicted to be stretched and are longer than that in the free
BuOH. This indicates that the intermolecular interactions between
BuOH and [N2222][AA] are strong, and result in an increase in
the O H bond length. Moreover, it is found that [N2222][Pro]
enables BuOH to have the longest O H bond length compared
with other ILs, owing to its larger binding energies. The binding
energy of DMC-[N2222][Pro] is also greater than those of other
ILs. This demonstrates that [N2222][Pro] can activate BuOH and
DMC well at the same time, and thus synergistically catalyze the
transesterification to have the highest yield of DBC.
Subsequently, we investigated the catalytic activities of
other basic carboxylate and prolinate ILs such as [N2222][Ace],
[P4444][Ace], [P4444][Pro] and [N1111][Pro] for the synthesis of DBC
(entries 6–9). The results showed that all of these ILs performed
good DMC conversion but low DBC selectivity compared with
[N2222][Pro] under the same conditions. Moreover, several typical
industrial basic catalysts such as K2CO3, NaOH, triethylamine, and
Amberlite-IRA400 resin were employed for comparison. It is also
found that these four conventional basic catalysts induced high
conversions of DMC but their selectivities of DBC were relatively
too low (entries 10–13). This implies that the second step of the
Table 1
Results of transesterification of DMC with BuOH in the presence of different
catalysts.a
Entry
Catalyst
DMC conversion (%)
DBC selectivity (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
[N2222][Pro]
[N2222][Gly]
[N2222][Ala]
[N2222][Val]
[N2222][Ser]
[N2222][Ace]
[P4444][Pro]
[P4444][Ace]
[N1111][Pro]
NaOH
96
94
92
89
37
93
95
88
90
94
94
95
92
46
75
31
24
22
7
42
65
36
45
30
37
42
35
9
Table 2
The binding energy of [N2222][AA] interaction with DMC and BuOH.
Entry
IL
E (kJ/mol)
DMC
BuOH
Et3N
K2CO3
Amberlite-IRA400
Proline
1
2
3
4
5
[N2222][Pro]
[N2222][Gly]
[N2222][Ala]
[N2222][Val]
[N2222][Ser]
−36.87
−31.95
−30.85
−27.59
−23.66
−77.04
−59.42
−56.03
−56.60
−55.05
a
Reaction conditions: DMC (20 mmol), BuOH (80 mmol), catalyst (0.5 wt%), reac-
tion temperature (110 ◦C), reaction time (4 h).

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F. Ouyang et al. / Applied Catalysis A: General 492 (2015) 177–183
Fig. 3. Effect of catalyst amount on the reaction. Reaction conditions: DMC
Fig. 2. Effect of reaction temperature on the reaction. Reaction conditions: DMC
(20 mmol), BuOH (80 mmol), catalyst (0.5 wt%), reaction time (4 h).
(20 mmol), BuOH (80 mmol), reaction temperature (110 ◦C), reaction time (4 h).
the selectivity of DBC increased obviously from 35% to 72% with the
increase in the dosage of [N2222][Pro] from 0.1 wt% to 0.5 wt%. How-
ever, when the catalyst amount was further added to 0.75 wt% and
1 wt%, respectively, a decrease in the selectivity of DBC was exam-
ined while the conversion of DMC did not change significantly. This
shows that too much catalyst amount has less impact on the con-
version of DMC and is not favorable to the selectivity of DBC. As
a consequence, considering the reaction rate and the cost of cata-
lysts, 0.5 wt% is taken as the optimum catalyst loading and used in
most of the experiments.
transesterification of MBC with BuOH to form DBC is hard to per-
form in the presence of these catalysts. In addition, the raw material
proline was found to have less catalytic effect to the transesterifi-
cation reaction, and low DMC conversion and low DBC selectivity
were then detected (entry 14). This is because that proline is dif-
ficult to soluble in this reactive system and thus hard to contact
with the reactants. Thus, it is validated from the comparison of cat-
alytic performance that [N2222][Pro] is considered to be a promising
catalyst with high activity and selectivity for the synthesis of DBC.
[N2222][Pro] was then chosen as the catalyst for further studies.
The effect of reaction time on the conversion of DMC and the
selectivity of DBC was also evaluated, and the results are given in
Fig. 4. The experiments are performed at 110 ◦C, catalyst amount of
0.5 wt%, and the molar ratio of BuOH/DMC of 4. It is indicated that
reaction time has an obvious influence on the reaction, the DMC
conversion and DBC selectivity increased in the initial stage and
remained almost unchanged between 4 h and 5 h. Nevertheless, the
DMC conversion and DBC selectivity began to decrease when the
reaction time was further prolonged to 6 h. This may be reasoned
that the produced overmuch methanol could promote the reverse
reaction with enough time and thus decrease the DMC conver-
sion and DBC selectivity. Thus, it suggests that too long time is not
3.2. Effects of various reaction conditions on the reaction
In order to obtain the optimum conditions, reaction parameters
such as reaction time, temperature, catalyst amount, and initial
molar ratio of reactants were studied in detail. Fig. 2 illustrates
the catalytic performance of [N2222][Pro] at different temperatures
ranging from 90 ◦C to 130 ◦C, while reaction was carried out using
molar ratio of BuOH to DMC of 4:1 in the presence of 0.5 wt%
[N2222][Pro] as catalyst for 4 h. These results suggest that increasing
the reaction temperature has a pronounced effect on the activity of
the catalyst, as reaction temperature increased from 90 ◦C to 110 ◦C,
the conversion of DMC and selectivity of DBC also increased. For
example, the conversion of DMC increased obviously from 42% to
95% and the selectivity of DBC increased from 4% to 75%, while
the temperature increased from 90 ◦C to 110 ◦C. However, when
the temperature further increased to 120 ◦C and 130 ◦C, a sharp
decrease in the selectivity of DBC was observed, and the corre-
sponding yields of DBC were reduced to 65% and 60%, respectively.
It could be explained that the transesterification reaction of DMC
with BuOH is slightly exothermic and the equilibrium constant
would decrease with the increase of reaction temperature. High
reaction temperature is beneficial to the reverse of transesterifi-
cation reaction, resulting in a decrease in the yield of DBC. This
demonstrates that the overhigh reaction temperature is negative
to the yield of DBC, and an optimized temperature for [N2222][Pro]
would choose at 110 ◦C for the efficient synthesis of DBC.
Subsequently, the influence of catalyst amount on the transes-
terification reaction of DMC with BuOH were investigated at 110 ◦C,
with the reaction time of 4 h and the molar ratio (BuOH/DMC) of
4, and the results are shown in Fig. 3. It is demonstrated that with
an increase in the amount of ILs, the total number of base sites
available for the reaction increases and thus the rate of transesteri-
fication is enhanced, resulting in a higher yield of DBC. For example,
Fig. 4. Effect of reaction time on the reaction. Reaction conditions: DMC (20 mmol),
BuOH (80 mmol), catalyst (0.5 wt%), reaction temperature (110 ◦C).

F. Ouyang et al. / Applied Catalysis A: General 492 (2015) 177–183
181
Fig. 5. Effect of molar ratio of BuOH to DMC on the reaction. Reaction conditions:
DMC (20 mmol), catalyst (0.5 wt%), reaction temperature (110 ◦C), reaction time
(4 h).
favorable to the forward reaction, and an appropriate reaction time
should be chosen at 4 h for the synthesis of DBC. In addition, Fig. 5
represents the effect of molar ratio of BuOH to DMC on the reac-
tion at 110 ◦C, with the reaction time of 4 h and the catalyst dosage
of 0.5 wt%. It is illustrated that as the amount of BuOH increased
varying from 2:1 to 4:1, the conversion of DMC and the selectivity
of DBC were rapidly improved. However, the molar ratio of BuOH
to DMC was greater than 4:1, the yield of DBC did not substan-
tially increase, thereby, the optimal molar ratio of BuOH to DMC is
preferred to be 4:1.
Fig. 6. Optimized structures and NBO charge analysis of (a) free BuOH and the com-
plexes of BuOH with [N2222][Pro] and (b) free DMC and the complexes of DMC with
[N2222][Pro].
3.4. Reaction mechanism study
On the basis of the above-mentioned results and the previous
literatures [24–26], a plausible mechanistic pathway for the for-
mation of DBC is proposed and then shown in Fig. 7. Firstly, the
3.3. NBO analysis
C
O bond of DMC and the O H bond of BuOH can be activated
In order to clarify the synergistic catalysis of [N2222][Pro] in the
synthesis of DBC, we further calculated the natural bond orbital
(NBO) atomic charges of carbon, hydrogen, and oxygen atoms in the
free BuOH and DMC, the complexes of BuOH with [N2222][Pro], and
the complexes of DMC with [N2222][Pro] at the B3LYP/6-31++G(d,p)
level of theory, respectively (Fig. 6). The electrostatic potential
maps of [N2222][Pro] and these complexes are also listed in sup-
plementary data. As can be seen in Fig. 6a, compared with the free
BuOH counterpart, the NBO atomic charge of the oxygen atom O (1)
in the complexes of BuOH with [N2222][Pro] increased from −0.542
to −0.603 because of the electron-donating effect of the carbox-
ylate group in the [Pro] anion. On the other hand, the hydroxyl
group in BuOH shares the negative charge of the oxygen atom
in the [Pro] anion and thus the O H bond lengths is stretched,
leading to an increase in the electrophilicity of BuOH. Moreover,
Fig. 6b shows NBO atomic charges of C (1), O (2), and O (3) atoms
in the free DMC and the complex of DMC with [N2222][Pro]. It is
obvious that both the NBO positive charge of the carbon atom C
(1) and the NBO negative charge of the oxygen atoms O (2) and
O (3) increase. This means that the electrophilicity of DMC could
improve after the interaction of the free DMC with the secondary
amine group of [N2222][Pro], which is in favor of the nucleophilic
attack by the activated BuOH. As a result, a high DBC yield can be
obtained in the presence of [N2222][Pro]. Therefore, [N2222][Pro]
is proved to have a dual activation catalysis for BuOH and DMC.
The catalytic performance results in Table 1, together with the
binding energy in Table 2, provide strong evidence for this hypoth-
esis.
by secondary amine group and carboxylate group in [N2222][Pro],
respectively, resulting in an active state of DMC and BuOH
with the formation of (N H· · ·O) hydrogen bond and (O H· · ·O)
hydrogen bond. Subsequently, activated BuOH makes nucleophilic
attack to the carbonyl-carbon atom of DMC to form MBC and
methanol. After that, MBC continues to interact with [N2222][Pro]
and reacts with nucleophilic butoxyanion to give DBC. Therefore,
it is obviously demonstrated that the synergistic dual activation
catalysis of [N2222][Pro] are highly favorable for transesterifica-
tion reaction and thus catalyze this reaction to have good yields of
DBC.
Fig. 7. The plausible reaction mechanism for [N2222][Pro] promoted transesterifica-
tion.

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F. Ouyang et al. / Applied Catalysis A: General 492 (2015) 177–183
4. Conclusions
In summary, five [N2222][AA] ILs had been synthesized and
applied in the synthesis of DBC via the transesterification reac-
tion of DMC with BuOH. Among five ILs, [N2222][Pro] was found
to play the best catalytic performance with 96% conversion to DMC
and 75% selectivity to DBC, and the optimal condition was set as
follows: temperature of 110 ◦C, reaction time of 4 h, initial molar
ratio of 4:1, and catalyst dosage of 0.5 wt%. Quantum-mechanical
calculations further manifested that such high DBC yield origi-
nated from the synergistic dual activation catalysis of [N2222][Pro].
It was demonstrated that the O H bond length of BuOH could be
stretched and the NBO atomic charge of the carbon atom in DMC
was increased by [N2222][Pro], which enhances the electrophilicity
of BuOH and the nucleophilicity of DMC respectively, resulting in
the excellence yield of DBC. In addition, [N2222][Pro] could be read-
ily recovered and reused up to five times without significant losses
in catalytic activity and quantity. Therefore, [N2222][Pro] is consid-
ered to be an effective recyclable homogeneous catalyst for the
phosgene-free synthesis of DBC and shows potential application
in industry.
Fig. 8. The recycle test of [N2222][Pro] catalyst.
3.5. Evaluation of catalyst stability
Acknowledgements
Under the optimum reaction condition, we conducted recycling
experiments to examine the recyclability of [N2222][Pro] on the
transesterification reaction of DMC with BuOH. As shown in Fig. 8,
no significant drop in both the conversion of DMC and the selec-
tivity of DBC is detected after five successive recycles. Also, there
is no obvious change in the IR spectra of the fresh catalyst and
the recovered catalyst (Fig. S4 in supplementary data). This find-
ing shows that the catalyst [N2222][Pro] for the transesterification
is stable enough to be recycled. In addition, the weight recovery
results (Table S1 in supplementary data) indicate that after five
runs about 7% of [N2222][Pro] catalyst is lost due to the transferring
of samples during the regeneration, and this loss is considered to
be the main cause for the slight decrease in DMC conversion and
DBC selectivity.
We thank the financial support by the National Natural Sci-
ence Foundation of China (Nos. 21206063 and 21206031), the
Department of Education and the Department of Science and
Technology of Jiangxi Province (Nos. GJJ14239, 20123BBE50081
and 20132BDH80003), and the Sponsored Program for Cultivating
Youths of Outstanding Ability in Jiangxi Normal University.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
2014.12.037.
References
[1] A.G. Shaikh, S. Sivaram, Chem. Rev. 96 (1996) 951–976.
[2] S.M. Gross, W.C. Bunyard, K. Erford, G.W. Roberts, D.J. Kiserow, J.M. Desimone,
J. Polym. Sci. A 40 (2002) 171–178.
3.6. Transesterification reaction of DMC with other alcohols
[3] S. Fukuoka, M. Kawamura, K. Komiya, M. Tojo, H. Hachiya, K. Hasegawa, M.
Aminaka, H. Okamoto, I. Fukawa, S. Konno, Green Chem. 5 (2003) 497–507.
[4] B. Veldurthy, J.M. Clacens, F. Figueras, Eur. J. Org. Chem. (2005) 1972–1976.
[5] S. Gryglewicz, F.A. Oko, G. Gryglewicz, Ind. Eng. Chem. Res. 42 (2003)
5007–5010.
[6] T. Sakakura, K. Kohno, Chem. Commun. (2009) 1312–1330.
[7] Y. Ono, Catal. Today 35 (1997) 15–25.
[8] X.G. Zhang, X.B. Ke, Z.F. Zheng, H.E. Liu, H.Y. Zhu, Appl. Catal. B 150/151 (2014)
330–337.
[9] B. Zhang, G.Q. Ding, H.Y. Zheng, Y.L. Zhu, Appl. Catal. B 152/153 (2014) 226–232.
[10] C. Murugan, H.C. Bajaj, Fuel Process. Technol. 92 (2011) 77–82.
[11] Q.X. Ma, T.S. Zhao, D. Wang, W.Q. Niu, P. Lv, N. Tsubaki, Appl. Catal. A 464/465
(2013) 142–148.
[12] A.-A.G. Shaikh, S. Sivaram, Ind. Eng. Chem. Res. 31 (1992) 1167–1170.
[13] R.Z. Tang, T. Chen, Y. Chen, Y.Z. Zhang, G.Y. Wang, Chin. J. Catal. 35 (2014)
457–461.
To obtain more information about other dialkyl carbonates,
the transestfication reaction of DMC with other alcohols such
as ethanol, propanol, pentanol and phenol in the presence of
[N2222][Pro] was also studied, and then the results are listed in
Table 3. It is indicated that both DMC conversion and dialkyl carbon-
ate selectivity improve with the increase of carbon chain length of
fatty alcohol (entries 1–3). This finding shows that long chain fatty
alcohol has the better nucleophilicity to form corresponding dialkyl
carbonate, and the reverse reaction of higher dialkyl carbonate is
suppressed. In addition, no products were detected in the transes-
terification of DMC with phenol (entry 4). It should be ascribed to
a very small reaction equilibrium constant (KP = 3 × 10−4 at 453 K),
resulting in too low DPC yield [27].
[14] T. Welton, Chem. Rev. 99 (1999) 2071–2083.
[15] P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 39 (2000) 3772–3789.
[16] R.A. Brown, P. Pollet, E. Mckoon, C.A. Eckert, C.L. Liotta, P.G. Jessop, J. Am. Chem.
Soc. 123 (2001) 1254–1255.
[17] W. Leitner, Nature 423 (2003) 930–931.
[18] K. Titze-Frech, N. Ignatiev, M. Uerdingen, P.S. Schulz, P. Wasserscheid, Eur. J.
Org. Chem. (2013) 6961–6966.
Table 3
Results of transesterification of DMC with other alcohols.a
[19] H.B. Xing, T. Wang, Z.H. Zhou, Y.Y. Dai, Ind. Eng. Chem. Res. 44 (2005)
4147–4150.
[20] S. Han, M. Luo, X.L. Zhou, Z. He, L.P. Xiong, Ind. Eng. Chem. Res. 51 (2012)
5433–5437.
[21] D.M. Li, F. Shi, J.J. Peng, S. Guo, Y.Q. Deng, J. Org. Chem. 69 (2004) 3582–3585.
[22] D.J. Tao, Z.M. Li, Z. Cheng, N. Hu, X.S. Chen, Ind. Eng. Chem. Res. 51 (2012)
16263–16269.
[23] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
Entry
Alcohols
DMC conversion (%)
Dialkyl carbonate selectivity (%)
1
2
3
4
Ethanol
89
94
97
–
44
63
81
–
n-Propanol
n-Pentanol
Phenol
a
Reaction conditions: DMC (20 mmol), alcohol (80 mmol), catalyst (0.5 wt%),
reaction temperature (110 ◦C), reaction time (4 h).

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183
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J.A.E. Montgomery Jr., J. Peralta, F. Ogliaro, M.
Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09 (Revision C.01), Gaussian, Inc.,
Wallingford, CT, 2009.
[24] S. Kumar, S.L. Jain, New J. Chem. 37 (2013) 2935–2938.
[25] B. List, Chem. Commun. (2006) 819–824.
[26] P.N.K. Babu, B.R. Devi, P.K. Dubey, Chem. Sin. 4 (2013) 107–113.
[27] P. Tundo, F. Trotta, G. Molaglio, F. Ligorati, Ind. Eng. Chem. Res. 27 (1988)
1565–1571.