Synthesis of Ditetrahydrofurfuryl Carbonate as a Fuel Additive Catalyzed by Aminopolycarboxylate Ionic Liquids

Article abstract of DOI:10.1007/s10562-017-2043-3

Abstract: A new series of aminopolycarboxylate ionic liquids were designed, synthesized, and applied for efficient and selective synthesis of ditetrahydrofurfuryl carbonate (DTC). Tetraethylammonium nitrilotriacetate ([N₂₂₂₂]₃[NTA]) was demonstrated to show the best catalytic performance, in which DTC could be obtained at a yield of 80% under optimum conditions. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-017-2043-3

Catal Lett
DOI 10.1007/s10562-017-2043-3
Synthesis of Ditetrahydrofurfuryl Carbonate as a Fuel Additive
Catalyzed by Aminopolycarboxylate Ionic Liquids
Wei Huang1 · Duan‑Jian Tao1 · Feng‑Feng Chen1 · Wei Hui1 · Jia Zhu1 · Yan Zhou1
Received: 12 December 2016 / Accepted: 27 March 2017
© Springer Science+Business Media New York 2017
Abstract A new series of aminopolycarboxylate ionic
liquids were designed, synthesized, and applied for effi-
cient and selective synthesis of ditetrahydrofurfuryl car-
bonate (DTC). Tetraethylammonium nitrilotriacetate
([N2222]3[NTA]) was demonstrated to show the best cata-
lytic performance, in which DTC could be obtained at a
yield of 80% under optimum conditions.
Graphical Abstract
Keywords Fuel additive · Dimethyl carbonate ·
Transesterification · Ionic liquids
1 Introduction
Organic carbonates (OCs), such as dimethyl carbonate
(DMC) and diethyl carbonate (DEC), have numerous appli-
cations in lubricating oils, fuel additives, solvents, reaction
intermediates, and polymeric materials [1–4]. Particularly,
in the field of fuel additives, OCs are expected to improve
energy efficiency and reduce particulate matter emissions
for decreasing energy consumption and protecting our envi-
ronment [5, 6]. As a potential oxygenated fuel additive,
ditetrahydrofurfuryl carbonate (DTC) is considered to be a
better substitute for DMC and DEC, owing to its distinct
properties such as high oxygen contents (35 wt%), high
boiling point, and good mutual solubility with diesel fuel
(Table S1, Electronic supplementary material). In terms
of these advantages, the demand of DTC will be growing
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-017-2043-3) contains supplementary
material, which is available to authorized users.
* Duan-Jian Tao
djtao@jxnu.edu.cn
1
College of Chemistry and Chemical Engineering, Jiangxi
Inorganic Membrane Materials Engineering Research
Centre, Jiangxi Normal University, Nanchang 330022,
People’s Republic of China
Vol.:(0123456789)
1 3

W. Huang et al.
fast accompany with the development of facile synthesis of
DTC.
resonance (NMR) spectra investigations and density
functional theory (DFT) calculations were further per-
formed to clarify the catalysis of APC-ILs. Moreover,
the reaction parameters such as reaction time, tempera-
ture, catalyst loading, and molar ratio of reactants were
explored in detail to obtain the optimum conditions. The
reusability of APC-ILs and the transesterification of
DMC with other alcohols were also studied.
Traditionally, the efficient catalytic synthesis of OCs
such as DEC and DTC requires highly toxic phosgene as a
raw material [7]. Despite the excellent performance of such
phosgene technology, the phosgene-free synthesis of OCs
with a more environmentally friendly process continues to
be appealing. Recently, the transesterification of DMC with
alkyl alcohols has attracted much attention as the alterna-
tive route for the synthesis of OCs, with the advantages of
low pollution, green raw material, and mild reaction con-
ditions [8–11]. Till now, various heterogeneous catalysts
such as K2CO3/AC (AC, active carbon),[12] CaO,[13]
KF/Al2O3,[14] NaOH/γ-Al2O3,[15] K2CO3/ZrO2,[16] and
TiO2@SiO2,[17] had been reported for efficient synthesis
of OCs. For example, Fan and Zhang had found that the
supported K2CO3/AC catalyst showed higher activity for
the transesterification reaction of DMC with propyl alcohol
[12]. Bai et al. had studied the synthesis of glycerol car-
bonate from DMC and glycerol using NaOH/γ-Al2O3 as
catalyst [15]. Tang et al. reported that the transesterification
of DMC with phenol in the presence of core–shell TiO2@
SiO2 could obtain diphenyl carbonate with a yield of 24%
at 9 h [17].
2 Experimental Section
2.1 Materials
Tetraethylammonium hydroxide (25 wt% aqueous solu-
tion) was purchased from Sigma-Aldrich. THFA (purity
≥99%), cyclopentanol (purity ≥99%), pipecolinic acid
(purity ≥99%), iminodiacetic acid (purity ≥99%), nitrilo-
triacetic acid (purity ≥99%) were purchased from Alad-
din Chemical Reagent Co. Ltd. (Shanghai, China). Other
reagents such as DMC, alcohol, triethyl amine, sodium
carbonate, and sodium hydroxide were of analytical grade
and used without any further purification.
However, to our best knowledge, there is no mention of
efficient synthesis of DTC from the transesterification of
DMC with tetrahydrofurfuryl alcohol (THFA) in any stud-
ies. Moreover, those solid basic catalysts usually suffer
from many inherent drawbacks such as complex prepara-
tion, high mass transfer resistance, easy deactivation, and
harsh reaction conditions. There remains a strong need to
develop novel catalyst materials with high efficiency and
selectivity for facile synthesis of OCs, especially for DTC.
Recently, ionic liquids (ILs) have been received more
attention and successfully applied for many catalytic
reactions owing to their favorable properties such as
environmentally friendly, high thermal stability, non-
volatility, and structural variety [18–20]. Thus, basic ILs
possessing certain basicities could present a broad appli-
cation prospect in the catalytic synthesis of OCs through
the transesterification reaction. Herein, we designed and
prepared a new series of aminopolycarboxylate ionic liq-
uids (APC-ILs), and they were introduced for the first
time into the transesterification of DMC with THFA to
obtain high-yielding DTC (Scheme 1). Nuclear magnetic
2.2 Preparation and Characterization of APC‑ILs
The preparation method of three APC-ILs was similar
to the procedure described in our previous works [21],
as follows. A stoichiometric ratio of [N2222]OH aqueous
solution was neutralized with pipecolinic acid, iminodi-
acetic acid, and nitrilotriacetic acid by stirring at room
temperature for 6 h, respectively. After neutralization,
water was evaporated under reduced pressure at 60 °C.
Then these three APC-ILs were heated to 90 °C in a vac-
uum oven containing P2O5 for 48 h to remove the residual
COO
H
COO
N
OOC
N
H
COO
OOC
N
N
COO
N2222
Pipe
NTA
IDA
Scheme 2 Structures of three APC-ILs
Scheme 1 Two-step process for
the synthesis of DTC
1 3

Synthesis of Ditetrahydrofurfuryl Carbonate as a Fuel Additive Catalyzed by…
Table 1 The transesterification of DMC with THFA using various
water prior to use. The structures of APC-ILs (Scheme 2)
were confirmed by NMR, FTIR spectra, CHN elements
and thermal analysis. All the detailed characterization
results were given in the Supporting Information.
catalysts
Entry Catalyst
Conversion of Yield of
Yield
DMC (%)
DTC (%) of MTC
(%)
2.3 Typical Procedures for the DTC Synthesis
1
2
3
4
5
6
7
8
[N2222]3[NTA]
97
96
95
94
93
65
75
41
11
80
71
65
58
55
18
13
Trace
7
17
25
30
36
38
47
62
41
4
[N2222]2[IDA]
[N2222][Pipe]
NaOH
Na2CO3
Et3N
DBU
Na3(NTA)
l-Proline
Amberlite-IRA400 47
K2CO3/ZrO2
The transesterification reaction was carried out in a 50 mL
round-bottomed flask, equipped with a condenser, thermostat
and magnetic stirring. A calculated amount of DMC, THFA,
and APC-ILs were added to the reactor, and the reaction mix-
ture was stirred and allowed to proceed for 0.5–2.5 h with the
heating at the designed temperature (e.g., 130°C). After the
reaction was completed, qualitative analyses of products were
examined by a Thermo Trace 1300 GC-ISQ, and quantita-
tive analyses were carried out by a GC-FID (Agilent 7890B)
equipped with a capillary column HP-5 (methyl polysiloxane,
30 m×0.32 mm×1 μm). The detailed analysis conditions
were described as follows: The temperatures of injector and
detector were 280 and 250°C, respectively. The column tem-
perature was increased stepwise to 200°C, holding at 80°C
for 2 min, increasing to 200°C at 40°C min−1, holding at
240°C for 3 min. Then the conversion of DMC and yield of
DTC were calculated according to the area of chromatograph
peaks using 1,3,5-trimethylbenzene as an internal standard.
After the completion of reaction, the reaction system was
cooled down to room temperature and extracted with deion-
ized water, and the system thus forms a liquid–liquid biphase,
and the aqueous phase containing APC-ILs could be easily
separated by simple decantation. After that, the catalyst APC-
ILs were further heated in a vacuum oven at 90°C for 6 h to
remove water and the residual reactants. The water content
of recycled APC-ILs was measured prior to the next run and
checked to be less than 0.15 wt% by the Karl Fisher titration.
9
10
11a
12b
29
5
55
18
66
34
71
89
[N2222]3[NTA]
Reaction conditions: catalyst loading (0.5 wt%), molar ratio of THFA
to DMC (4:1), reaction time (2 h), reaction temperature (130°C)
aThe catalyst was prepared according to the reference [16]
b2 wt% water was added into the reaction mixture
in Table 1. It is found that three APC-ILs show different
catalytic activities and the sequence of catalytic perfor-
mance is [N2222]3[NTA]>[N2222]2[IDA]>[N2222][Pipe]
(entries 1–3). That is to say, the more carboxylate groups
the APC-ILs possess, the higher the yield of DTC. Among
these APC-ILs, [N2222]3[NTA] possessing three carboxy-
late groups catalyzed the reaction to have the highest
conversion of DMC (97%) and yield of DTC (80%). This
implies that the carboxylate group of APC-ILs is favorable
to the synthesis of DTC. Subsequently, several other typical
basic catalysts were studied for comparison (entries 4–10).
The results showed that four typical inorganic and organic
base catalysts had high conversions of DMC but low yields
of DTC (entries 4–7). Solid bases Na3(NTA), l-proline,
Amberlite-IRA400 resin, and K2CO3/ZrO2 also showed
poor catalytic activity (entries 8–11). This demonstrates
that the first step of the transesterification of DMC with
THFA to form MTC is easily proceed but the second step
of the formation of DTC is hard to perform in the presence
of those conventional base catalysts [23]. In addition, the
pH values of those three APC-ILs aqueous solution were
further explored. As can be seen in Table S2, it is indicated
that [N2222]3[NTA] has a relatively low basicity but shows
an excellent catalytic performance. This demonstrates that
the basic sites of the APC-IL are not the key active sites
in the transesterification of DMC with THFA. In order to
clarify the catalysis behavior of APC-ILs, we performed
1H NMR spectroscopy of THFA and the reaction mixture
of THFA and APC-ILs to understand the catalytic mecha-
nism in principle. It can be seen from Fig. 1 that all the OH
2.4 Quantum Computation
Theoretical calculations were performed at the DFT level
using the B3LYP hybrid functional, as implemented in the
Gaussian 09 software package [22]. And the 6-31G(d,p)
basis set was adopted for all the structural optimizations
and natural bond orbital (NBO) charge analysis of each
APC-ILs. Frequency calculations were performed to con-
firm geometries were true minimum and to obtain thermo-
dynamic data.
3 Results and Discussion
3.1 Catalytic Performance of APC‑ILs
Our work started with the screening of APC-ILs for cata-
lytic synthesis of DTC. The results obtained are presented
1 3

W. Huang et al.
Fig. 1 1H NMR spectra of
(a) THFA, (b) the mixture
of THFA and [N2222][Pipe],
(c) the mixture of THFA and
[N2222]2[IDA], (d) the mixture
of THFA and [N2222]3[NTA]
signals of THFA became broad and were shifted downfield
after adding APC-ILs, revealing that there exists hydrogen
bonding interactions between THFA and APC-ILs [24, 25].
For example, the peak of hydroxyl group was observed at
4.42 ppm in the free THFA, while the OH signal in the
mixture of THFA and [N2222]3[NTA] were shifted down-
field to 5.21 ppm. This shows that among these three APC-
ILs, the hydrogen bonding interaction between THFA and
[N2222]3[NTA] are strongest. [N2222]3[NTA] can activate
THFA well through the hydrogen bond, and thus catalyze
the transesterification to have the highest yield of DTC.
Furthermore, the effect of water on the catalytic perfor-
mance of [N2222]3[NTA] was also studied (entry 12). It is
found that the conversion of DMC and the yield of DTC
were obviously reduced to 89 and 55%, respectively, when
2 wt% water was added into the reaction system. This dem-
onstrates that water has a significant effect on the catalytic
activity of [N2222]3[NTA] and it may remarkably break the
intermolecular hydrogen bonding interaction of THFA with
[N2222]3[NTA], resulting in the decrease in DTC yield.
Table 2 The binding energy of THFA interaction with APC-ILs
Complex
THFA-[Pipe]
−65.88
THFA-[IDA]
−92.30
THFA-[NTA]
−127.96
ΔE (KJ/mol)
ΔE=Ecomplex −ETHFA −EAPC-IL
hydrogen bonding lengths between THFA and APC-ILs
are shown in Fig. 2. It can be seen that the binding ener-
gies between THFA and APC-ILs are calculated to be
more than −60 kJ/mol, and all the O–H bond lengths in
the complexes of THFA and APC-ILs are predicted to
be stretched and are longer than that in the free THFA.
This indicates that the intermolecular hydrogen bond-
ing interactions between THFA and APC-ILs are strong,
and result in an increase in the O–H bond length.
[N2222]3[NTA] enables THFA to have the longest O–H
bond length compared with the other two APC-ILs,
owing to its larger binding energies. Moreover, Fig. 3
shows the natural bond orbital (NBO) charges of carbon,
hydrogen, and oxygen atoms in the free THFA and the
complexes of THFA with APC-ILs. It is obvious that
compared with the free THFA counterpart, the NBO
negative charge of the oxygen atom O (1) increases from
0.452 to 0.629 in the presence of [N2222]3[NTA]. This
means that the nucleophilicity of THFA could improve
effectively by interacting with [N2222]3[NTA], and then it
is favorable to make a nucleophilic attack to DMC. As
a result, a high DTC yield can be obtained catalyzed by
[N2222]3[NTA].
3.2 DFT Study
To get more insight into the catalysis of the carboxy-
late group of APC-ILs, we further calculated the geom-
etry optimization for the free THFA and the complexes
of THFA with APC-ILs, respectively. Then the binding
energies of THFA with APC-ILs are given in Table 2,
and the corresponding O–H bond lengths of THFA and
1 3

Synthesis of Ditetrahydrofurfuryl Carbonate as a Fuel Additive Catalyzed by…
Fig. 2 Optimized structures of
a free THFA and the complexes
of b THFA-[Pipe], c THFA-
[IDA], and d THFA-[NTA]
(blue N, red O, white H, the
bond length is in Å)
Fig. 3 NBO charge analysis of
a free THFA and the complexes
of b THFA-[Pipe]; c THFA-
[IDA]; and d THFA-[NTA]
(blue N, red O, white H)
3.3 Optimization of Reaction Conditions
and reversible. High reaction temperature would decrease
the equilibrium constant and is favorable to the reverse of
transesterification reaction, resulting in a decrease in the
selectivity of DTC [20]. These indicating that the excessive
high reaction temperature was not beneficial to the selec-
tivity of DTC. Thus, an optimized reaction temperature
would choose at 130°C. Figure 5 shows the effect of reac-
tion time on the reaction. It is found that the yield of DTC
increases notably to 80% in the first 2 h but remains almost
unchanged as reaction proceeds. Hence further increase in
the reaction time is not very necessary. As a result, 2 h is
identified as the optimal reaction time.
In order to obtain the optimum conditions, reaction param-
eters such as reaction time, temperature, catalyst amount,
and initial molar ratio of reactants were studied in detail
in the system of [N2222]3[NTA]. Figure 4 shows the effect
of reaction temperature on the synthesis of DTC at dif-
ferent temperatures ranging from 100 to 150°C. It can be
seen that the conversion of DMC and selectivity of DTC
remarkably increase with the elevated temperature from
110 to 130°C. However, when the temperature further
increased to 150°C, a slight drop in the selectivity of DTC
was observed and the corresponding yield of DTC was
reduced to 74%. It could be reasoned that the transesterifi-
cation reaction of DMC with THFA is slightly exothermic
The effect of catalyst loading on the reaction was
evaluated, and the results are shown in Fig. 6. The yield
of DTC increases rapidly by increasing the amount of
1 3

W. Huang et al.
Fig. 6 Effect of catalyst loading on the reaction. Reaction condi-
tions: reaction temperature (130°C), reaction time (2 h), molar ratio
of THFA to DMC (4:1)
Fig. 4 Effect of reaction temperature on the reaction. Reaction condi-
tions: reaction time (2 h), molar ratio of THFA to DMC (4:1), catalyst
(0.5 wt%)
Fig. 5 Effect of reaction time on the reaction. Reaction conditions:
reaction temperature (130°C), molar ratio of THFA to DMC (4:1),
catalyst (0.5 wt%)
Fig. 7 Effect of molar ratio on the reaction. Reaction conditions:
reaction temperature (130°C), reaction time (2 h), catalyst (0.5 wt%)
catalyst. The yields increased from 19 to 80% with the
rise of catalyst loadings from 0.1 to 0.5 wt%. This shows
that with an increase in the dosage of ILs, the total num-
ber of catalytic sites available for the reaction increases
and thus the rate of transesterification is enhanced,
resulting in a higher yield of DTC. However, as the cat-
alyst loading further increases from 0.5 to 0.9 wt%, the
conversion of DMC and yield of DTC remain almost
unchanged. This means that too large catalyst loading is
not favorable to this reaction, and 0.5 wt% is regarded as
the optimal catalyst loading. Figure 7 shows the effect of
the THFA/DMC molar ratio from 1:1 to 5:1 on the reac-
tion. The yield of DTC was obviously increased from 33
to 80% in 2 h, while the initial THFA/DMC molar ratio
increased from 1:1 to 4:1. The reason for this phenome-
non is that excess amount of THFA can shift the reaction
equilibrium towards products. Nevertheless, the reaction
rates in the initial molar ratio of 5:1 was just comparable
to the case of 4:1, indicating that a further increase in the
amount of THFA can not continue to improve the yield.
Thus, the optimal THFA/DMC molar ratio for the pro-
duction of DTC is 4:1.
1 3

Synthesis of Ditetrahydrofurfuryl Carbonate as a Fuel Additive Catalyzed by…
[N2222]3[NTA] into active carbon and employed to test its
reaction performance and recyclability. The results listed in
Table S3 indicated that even though [N2222]3[NTA]/AC cat-
alyst can be separated from the reaction system effortlessly
by filtration, the catalytic activity of [N2222]3[NTA]/AC cat-
alyst decreased obviously from 60 to 42% DTC yield after
three recycle times. This implies that [N2222]3[NTA] may
be lost during the reaction process because of active carbon
loaded with [N2222]3[NTA] using physical impregnation.
Therefore, we believe that the homogeneous catalysis of
APC-ILs is still a good strategy for highly efficient synthe-
sis of DTC, although its separation and recycle is tedious.
Fig. 8 Recycle test of [N2222]3[NTA] catalyst
3.5 Reaction of DMC with Other Alcohols
To obtain more information about other dialkyl carbonate,
the transesterification reaction of DMC with other alcohols
such as ethanol, propanol, pentanol, cyclopentanol, benzyl
alcohol and phenol was studied and the results are listed
in Table 3. It is indicated that both DMC conversion and
dialkyl carbonate yield improve with the increase of car-
bon chain length of fatty alcohol (entries 1–4). This 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 [26, 27].
Moreover, a low yield was obtained and resulted from the
steric effect of cyclopentanol. Diphenyl carbonate was also
not detected in the transesterification of DMC with phenol
because of its very high reaction activation energy. Thus,
the catalyst [N2222]3[NTA] was demonstrated to display
considerable catalytic performance for the transesterifica-
tion of DMC with many alkyl alcohols, implying the wide
applicability of APC-ILs in the production of various OCs.
Fig. 9 FTIR spectra of (a) fresh [N2222]3[NTA] catalyst, and (b) used
[N2222]3[NTA] catalyst after five times run
3.4 Catalyst Recycles
The reusability of catalysts is very important for their
industrial applications. Thus, the catalyst [N2222]3[NTA]
was recycled for five times in order to test its activity as
well as stability. The results obtained in five consecutive
runs are shown in Fig. 8. It is indicated that no obvious
drop in both the conversion of DMC and selectivity of DTC
was observed during these five successive recycles, which
shows that the catalyst [N2222]3[NTA] is stable enough. The
slight decrease in the activity may be ascribed to the slight
loss of the catalyst [N2222]3[NTA] due to the transferring of
samples during the regeneration. Moreover, compared with
the fresh [N2222]3[NTA] catalyst, these above characteris-
tic bands also appeared in the reused [N2222]3[NTA] cata-
lyst (Fig. 9). This further showed that [N2222]3[NTA] could
be very stable in the synthesis of DTC for several runs. In
addition, supported ionic liquid catalyst [N2222]3[NTA]/AC
(AC, active carbon) was prepared by impregnating 20 wt%
4 Conclusions
In summary, a new methodology based on using APC-ILs
as catalysts for high-yielding synthesis of DTC was devel-
oped in this work. It is found the catalytic performance
of APC-ILs can be related to their carboxylate groups in
anions, and the more carboxylate groups the APC-ILs pos-
sess, the higher the catalytic activity. The best APC-IL
[N2222]3[NTA] displays excellent activity in the catalytic
synthesis of DTC, with the conversion of DMC of 97% and
yield of DTC of 80%, being superior to traditional base cat-
alysts. [N2222]3[NTA] is also featured with fairly good reus-
ability and wide applicability in the synthesis of other OCs.
The strategy introduced herein opens up a new opportunity
to improve the efficiency of current industrial process for
the production of OCs.
1 3

W. Huang et al.
9. Ono Y (1997) Catal Today 35:15
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10. Ono Y (1997) Appl Catal A 155:133
Conversion of
DMC (%)
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Entry
Alcohols
Product
Yield (%)
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O
OH
1
95
54
O
O
O
O
O
OH
2
3
4
5
96
99
97
86
59
66
61
47
14. Murugan C, Bajaj HC (2011) Fuel Process Technol 92:77
15. Bai R, Wang Y, Wang S, Mei F, Li T, Li G (2013) Fuel Process
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O
O
O
O
O
O
OH
16. Zhang B, Ding GQ, Zheng HY, Zhu YL (2014) Appl Catal B
152:226
3
3
17. Tang RZ, Chen T, Chen Y, Zhang YZ, Wang, GY (2014) Chin J
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OH
18. Tike MA, Mahajani VV (2007) Ind Eng Chem Res 46:3275
19. Zhou Y, Ouyang F, Song ZB, Yang Z, Tao DJ (2015) Catal Com-
mun 66:25
OH
O
O
O
20. Ouyang F, Wang ZZ, Zhou Y, Cheng Z, Lu ZH, Yang Z, Tao DJ
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OH
21. Chen FF, Huang K, Zhou Y, Tian ZQ, Zhu X, Tao DJ, Jiang D,
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O
6
trace
trace
O
O
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GA, Nakatsuji H, Caricato M, Li FX, Hratchian HP, Izmaylov
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Reaction conditions: reaction temperature (130°C), reaction time
(2 h), molar ratio of alcohol to DMC (4:1), catalyst (0.5 wt%)
Acknowledgements This work was supported by the National
Natural Science Foundations of China (Nos. 21566011, 31570560),
the Natural Science Foundations of Jiangxi Province (No.
20151BAB213016), and the Jiangxi Province Sponsored Program for
Distinguished Young Scholars (20162BCB23026).
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