Pyrrolidine-based dicationic acidic ionic liquids: Efficient and recyclable catalysts for esterifications

Article abstract of DOI:10.1002/cjoc.201090334

A highly efficient and eco-friendly esterification was achieved by a series of novel dicationic acidic ionic liquids (DAILs) containing double -SO₃H cations. High yields of the product esters were obtained by using 2 mol% of the DAILs as catalysts and DAIL I could be reused at least ten times without appreciable loss of its efficicency.

Full text of DOI:10.1002/cjoc.201090334

FULL PAPER
Pyrrolidine-based Dicationic Acidic Ionic Liquids: Efficient and
Recyclable Catalysts for Esterifications
Liu, Xiaofeia,b(刘晓飞)
Zhao, Yingweia,b(赵应伟)
Li, Zhena(李臻)
Chen, Jing*,a(陈静)
Xia, Chungu*,a(夏春谷)
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences, Lanzhou, Gansu 730000, China
b Graduate University of Chinese Academy of Sciences, Beijing 100039, China
A highly efficient and eco-friendly esterification was achieved by a series of novel dicationic acidic ionic liq-
uids (DAILs) containing double — SO3H cations. High yields of the product esters were obtained by using 2 mol%
of the DAILs as catalysts and DAIL I could be reused at least ten times without appreciable loss of its efficicency.
Keywords esterification, dicationic acidic ionic liquids, pyrrolidine, reuse
Introduction
of pyrrolidine-based dicationic acidic ILs (DAILs) with
double — SO3H moieties in their cations were synthe-
sized for the first time (Scheme 1). Measurement results
of acidity and solubility reveal that these
SO3H-functionalized DAILs demonstrate quite strong
acidities and visible hydrophilic properties, which are
key factors for an efficient catalyst in esterification.
These novel DAILs show good tolerance toward both
aromatic- and aliphatic-acid with excellent yields of the
desired esters at only 2 mol% catalyst loading. Fur-
thermore, the separation of the product and DAILs can
be facilely achieved by decantion. For comparison, the
performances of monocationic acidic ILs (Figure 1, ILs
V— VIII) were also tested.
Esterification is one of the most significant reactions
in industrial processes because of enormous practical
importance and widely applications of organic esters.1
Inorganic acid such as sulfuric acid, hydrochloric acid
and orthophoric acid are traditional catalysts in the es-
ters manufacturing industries. However, such acid cata-
lytic system suffers from the problems of corrosion of
equipments, contamination of water, producing large
volumes of acidic wastes, and also facing the difficulty
of recycling acid catalysts.2 With the increasing eco-
logical and economic concerns on the esterification
process, great efforts have been made to replace the tra-
ditional inorganic acid and develop clean catalyst such
as zeolite,3,4 heteropoly acid,5 solid superacid,6
ion-exchange resin,7 organic or inorganic salt for the
production of esters.8 Although previous-mentioned
problems of corrosion and pollution have been partially
solved, recycling of catalysts still remains unsatisfac-
tory.
Ionic liquids (ILs) have attracted enough interest as
catalysts and alternative solvents in green chemistry.9,10
Since Forbes and co-workers firstly reported a new ap-
proach for esterification using Brønsted acidic ILs as
both solvents and catalysts, many Brønsted acidic ILs,11
including SO3H-functionalized ILs,12-17 ILs with acidic
counteranion18 and protonated acidic ILs19,20 have been
used in esterification reactions with satisfactory cata-
lytic performances and stable catalyst recycling. How-
ever, most of these reports used large amounts of ILs to
maintain their high catalytic efficiencies. With our con-
tinuous interest in development of novel and efficient
acidic ILs for the esterification,21 in this report, a series
Scheme 1 Synthesis of pyrrolidine-based dicationic acidic ILs
O
O
O
acetonitrile
80 °C
CH2
S
nN
2
+
N
+
+
N
CF3SO3H, toluene or
p-CH3C6H4SO3H, EtOH
N
n
-
-
O3S
SO3
+
+
N
N
I. n = 6, A = OTf
n
II. n = 10, A = OTf
III. n = 6, A = TsO
IV. n = 10, A = TsO
2A-
HO3S
SO3H
*
E-mail: chenj@licp.cas.cn (Chen, Jing); cgxia@licp.cas.cn (Xia, Chungu); Tel.: 0086-931-4968089; Fax: 0086-931-4968129
Received March 9, 2010; revised May 26, 2010; accepted June 7, 2010.
Project supported by the National Science Fund for Distinguished Young Scholars of China (No. 20625308).
Chin. J. Chem. 2010, 28, 2003— 2008
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2003

Liu et al.
FULL PAPER
The phase behaviors and thermal stabilities of ILs
I—VIII were investigated by DSC and thermogravim-
etric analysis, and the glass transition temperature (Tg)
and the thermal decomposition temperatures (Td) are
shown in Table 1. ILs I—VIII have no freezing points
and melting points but possess lower glass transition
temperatures (－58.6—－43.0 ℃). The thermal de-
composition temperatures (with mass loss of 10%) of
the ILs employed in this work are ranged 239.5—329.6
℃ (Table 1). In comparison with monocationic ILs
V—VIII, DAILs I—IV have some decrease in thermal
stabilities [see e.g., IL I (279.2 ℃), vs. IL VI (325.6
℃)], and the ILs containing OTf－ anion have higher
thermal stabilities than the ILs containing TsO− anion.
Table 1 also gives the ionic conductivities of ILs I—
VIII, and the data indicate that ILs I—VIII exhibit
R
+ N
SO3H
A-
V. R = CH3, A = OTf
VI. R = (CH2)5CH3, A = OTf
VII. R = (CH2)9CH3, A = OTf
VIII. R = (CH2)9CH3, A = TsO
Figure 1 Structures of pyrrolidine-based monocationic acidic
ILs.
Results and discussion
Pyrrolidine-baesd acidic ionic liquids
The ILs used in this article are viscous liquids at
room temperature, and some usual physicochemical
properties were measured and listed in Table 1. It can be
seen that both cations and anions have significant ef-
fects on their physicochemical properties. DAILs I—IV
possess higher densities and viscosities than monoca-
tionic ILs V—VIII, and the viscosities of DAILs I—IV
even could not be determined by the viscometer at 40
℃ because of their high viscosities. As for the same
－
－
2
2
good ionic conductivities (1.23×10 —5.09×10
S/m) at 25 ℃. The ionic conductivities of DAILs are
smaller than those of monocationic ILs, and slight de-
crease in ionic conductivity was also observed when
OTf－ anion of the IL was replaced by TsO－ anion.
This might be attributed to higher viscosity and larger
ion size, which may reduce the rate of ion mobility.
Acidity and solubility are of great importance for
acidic ILs, especially when they are used as catalysts in
catalytic reactions. Table 2 shows the acidities and
solubilities of ILs I—VIII. The Brønsted acidities of
cation, the ILs containing TsO－ (p - CH3C6H4SO3 )
－
anion have higher densities and viscosities than the ILs
containing OTf－ (CF SO3 ) anion. The increase of
－
3
size or symmetry of the cation and anoin may lead to
the interaction modification between the cation and the
anion.
Table 1 Density, viscosity, glass transition temperature, thermal decomposition temperature and ionic conductivity of ILs I—VIII
Density/(g•mL－
)
Visicosity/(mPa•s)
1
Ionic conductivitya/(S•m－
)
1
IL
Tg/℃
Td/℃
40 ℃
100 ℃
1.3311
1.3248
1.3374
1.3330
1.2737
1.2335
1.1865
1.2007
40 ℃
100 ℃
550.8
611.2
642.5
719.8
43.15
138.3
251.2
313.1
I
II
—
—
－56.4
－57.2
－52.2
－52.8
－43.0
－58.4
－58.6
－52.5
279.2
294.7
239.5
258.1
329.6
325.6
324.8
265.7
2.99×10－
2
1.68×10－
2
—
—
2.10×10－
2
III
IV
V
—
—
2
—
—
1.23×10－
2
1.3129
1.2737
—
576.8
2988
—
5.09×10－
VI
VII
VIII
4.28×10－
2
3.41×10－
2
2
—
—
1.88×10－
a Measured at 25 ℃.
Table 2 Acidities and solubilities of ILs I—VIII (25 ℃)
Miscibility withb
a
Entry
IL
H0
Water
Methanol
Ethyl acetate
Chloroform
Toluene
—
Diethyl
—
1
2
3
4
5
6
7
8
I
II
－0.727
－0.202
0.607
＋＋＋
＋＋＋
＋＋＋
＋＋＋
＋＋＋
＋＋＋
＋＋＋
＋＋＋
＋＋
—
—
—
—
＋
—
—
＋
＋
＋＋
—
—
—
III
IV
V
＋＋
—
—
—
0.838
＋＋＋
＋＋＋
＋＋＋
＋＋＋
＋＋＋
—
＋
＋
0.412
—
＋
−
VI
VII
VIII
0.434
＋
＋
＋
0.531
＋＋
＋＋
＋
1.273
＋＋
＋＋
＋＋
a Hamette acidity function of the ILs. b ＋＋＋＝easily miscible,＋＋＝miscible,＋＝slight miscible, —＝immiscible.
2004
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 2003— 2008

Pyrrolidine-based Dicationic Acidic Ionic Liquids
these ILs were determined by Hammett method with
UV-vis spectroscopy as reported.22 The indicators used
in the measurements were 2-nitro-aniline (pKa＝－0.2)
length between the two pyrrolidine moities or N-alkyl
chain length of monocations almost did not influence
the catalytic activities (Entries 1, 2, Entries 5—7). Sig-
nificantly different catalytic activities were observed on
variation of the counterions. Methyl benzoate with yield
of 94% was obtained when I was used as catalyst, and
that was 79% for III, which suggests that the anion
plays a significant role in catalytic activity of esterifica-
tion.
Upon completion of this reaction, the reaction sys-
tems were biphasic. The upper layer is the produced
esters, and the lower layer is the IL phase that contains
the unreacted materials, produced water and a portion of
the produced esters. For comparing the separating effi-
ciencies of ILs I—VIII from the produced ester, yields
of methyl benzoate were got respectively from the upper
and lower layers as shown in Table 3. The produced
esters in the upper phase were isolated by decantation,
and the esters dissolved in the lower phase were ex-
tracted with ethyl acetate. As seen in Table 3, the dis-
tributions of the ester between the two phases varied for
different ILs. Because of their immiscibility with the
ester, DAILs I—IV presented better biphasic behavior
than monocationic ILs V—VIII, especially for I, in
which, only less than 0.1% of methyl benzoate was dis-
solved (Table 3, Entry 1) and could be neglected.
Therefore, in the following reactions, when I was used
as catalyst, the yields of product esters were obtained
directly from the upper phase, and the separation pro-
cedure was simplified in this way.
and 4-nitro-aniline (pKa＝0.99) respectively for the ILs
with anions of O T f －
(CF SO3 ) and TsO－
－
3
－
(p - CH3C6H4SO3 ) . The obtained H0 values of the ILs
are shown in Table 2. The Brønsted acidity order of the
ILs can be infered from their H0 values as follows: I＞
II＞VI＞VI＞VII＞III＞IV＞VIII.
From Table 2, it can be seen that ILs I—VIII are all
water-soluble. Due to double —SO3H groups contained
in their cations, DAILs I—IV display poorer solubilities
in organic solvents than monocationic ILs V—VIII.
DAILs I—IV are almost immiscible with common or-
ganic solvents (ethyl acetate, chloroform, toluene and
diethyl) except for methanol.
Esterification catalyzed by pyrrolidine-based dica-
tionic acidic ILs
Initially, the esterfication of methanol with benzoic
acid was chosen as model reaction, and the effects of
different acidic ILs on the reaction were investigated.
Since there were two SO3H groups in DAILs I—IV
compared to one SO3H group in ILs V—VIII, 2 mol%
of ILs with respect to benzoic acid were used in the case
of I—IV and 4 mol% in the case of V—VIII to allow
for the comparison of their catalytic activities. The reac-
tions were carried out at 80 ℃ for 8 h with the
acid/alcohol/IL molar ratio of 1∶1.5∶0.02, and the
results were presented in Table 3. Good yields were
obtained in all cases. The yield of methyl benzoate in-
creased slightly when the monocationic acidic ILs were
replaced by DAILs [see e.g., Entry 5 (92%), vs. Entry 1
(94%)]. While the differences in the alkanediyl chain
To optimize the reaction conditions, DAIL I was se-
lected as the catalyst to investigate the effects of reac-
tion time, temperature, catalyst dosage and alcohol/acid
ratio on the esterification of methanol by benzoic acid,
and the results are summarized in Table 4. The results
demonstrate that chemical equilibrium can be reached in
6 h at 80 ℃ (Table 4, Entries 1—3). Therefore, other
esterification reactions were conducted for 6 h. The ef-
Table 3 Results of esterification of methanol and benzoic acid
catalyzed by different ILsa
COOH
COOCH3
acidic IL
CH3OH
+
+
H2O
Table 4 Results of esterication of methanol and benzoic acid
under different conditions
Fraction of methyl benzoate
Upper phase/% Lower phasec/%
Methanol/acid Amount of
Total yield of
esterd/%
Entrya
T/℃ Time/h Yieldb/%
Entry IL
molar ratio
1.5∶1
1.5∶1
1.5∶1
1.5∶1
1.5∶1
1.5∶1
1.5∶1
1.5∶1
2∶1
IL/mol%
1
2
2
2
80
80
80
80
80
80
40
100
80
80
3
6
8
6
6
6
6
6
6
6
79
94
94
55
83
94
65
93
96
86
1
2
I
＞99.9
99.7
98.2
96.9
92.1
83.3
74.5
47.5
＜0.1
94
94
79
78
92
92
93
76
II
0.3
3
2
3
III
IV
V
1.8
4
0.5
1
4
3.1
5b
6b
7.9
5
6
3
VI
16.7
25.5
52.5
7b VII
8b VIII
7
2
8
2
a
9
2
Reaction conditions: 80 ℃, 8 h. Acid/alcohol/IL molar ratio of
1∶1.5∶0.02. b Acid/alcohol/IL molar ratio of 1∶1.5∶0.04. c IL
phase. d Yield of ester is based on crude isolated product. Purity
of ester was tested by GC and the content of ester was no less
than 95% (GC).
10
1∶1
2
a Reaction conditions: ionic liquid＝IL I, benzoic acid (0.10 mol),
b
methanol (0.15 mol). Yield of ester is based on isolated crude
product.
Chin. J. Chem. 2010, 28, 2003— 2008
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2005

Liu et al.
FULL PAPER
fect of temperature on ester yield was examined in the
temperature range 40—100 ℃ (Table 4, Entries 2, 7, 8)
and the best reaction temperature was ca. 80 ℃ as
shown in Table 4 (Entry 2). Increasing of the catalyst
dosage had a propitious influence on the yield of methyl
benzoate (Table 4, Entries 2, 4—6). When the amount
of I increased from 0.5 mol% to 1 mol% (Table 4, En-
tries 4, 5), the yield of methyl benzoate increased rap-
idly from 55% to 83%, and a further increase to 2 mol%
resulted in a 94% yield (Table 4, Entry 2). The data in
Entries 2, 9, 10 (Table 4) indicated that the yield was
enhanced while increasing the amount of methanol be-
cause the excess of one of the reactants makes the equi-
librium shifting towards the products side. However,
further increase of the alcohol/acid ratio to 2∶1 (Entry
9) resulted in complication of separating the produced
ester from ILs phase because overmuch methanol mixed
with I and formed one phase at the end of the reaction.
Thus, the best fit alcohol/acid ratio herein was 1.5∶1
for the reaction (Entry 2).
detected. And all of the esters produced could be easily
separated due to their immiscibility with the IL.
Table 5 Results of esterification for various acid and alcohol
catalyzed by IL I
Entrya
Acid
Alcohol T/℃ Time/h Yieldb/%
1
2
3
4
5
6
Benzoic acid
Lauryl acid
Stearic acid
Acetic acid
Ethanol
80
6
10
10
6
91
98
Methanol 80
Methanol 80
94
Ethanol
80
93
n-Butyric acid Methanol 80
Acetic acid n-Octanol 80
3
＞99
96
6
a
Reaction conditions: acid (0.10 mol), methanol (0.15 mol),
b
n(acid)∶n(methanol)∶n(IL)＝1∶1.5∶0.02. GC yield. No
by-products were found.
Conclusion
The recycling performance of DAIL I in esterifica-
tion of methanol with benzoic acid was investigated. As
the foregoing results shown (Table 3), most of the
methyl benzoate formed the upper layer, and only less
than 0.1% of the ester was dissolved in DAIL I phase
after the reaction. Thereupon, leaving out extraction
procedure, I could be easily separated by decantation
and regenerated by removing water in a vacuum at 110
℃ for 1 h for the next reuse. This procedure was re-
peated for 10 cycles (See Figure 2), and even in the 10th
recycle, over 88% product yield was still obtained. This
indicates that I was stable enough to be recycled as the
catalyst for the reaction.
We have prepared a series of novel dicationic acidic
ionic liquids (DAILs) with strong acidities and visible
hydrophilic properties, and established the potential ap-
plication of these DAILs as efficient and reusable cata-
lysts in esterification. Satisfactory yields of esters were
obtained in the presence of 2 mol% of DAILs as cata-
lysts for esterifications of methanol with aromatic or
aliphatic acid, and the DAILs could be more easily
separated from the produced esters than monocationic
acidic ILs due to their immiscibility with organic sol-
vents and DAIL I could be recycled and reused at least
10 times in esterification of methanol with benzoic acid.
ILs with triflate anion showed better catalytic activities
than those with p-toluene-sulfonic acid anion.
Experimental
General remarks
Toluene was distilled over Na. MeCN was distilled
over CaH2. All other chemicals (A.R. grade) were
commercially available and used without further purifi-
cation. 1H and 13C NMR spectra: Varian INOVA 400 M
spectrometer; chemical shifts (δ) were relative to Me4Si
as an internal standard. ESI-MS: Waters ZQ 4000; in
m/z (rel. %). The density and viscosity were measured
by Anton Paar SVM 3000 Stabinger Viscometer at 40
and 100 ℃. Thermal analysis and temperature-depend-
ent phase behavior were examined in the circular range
of －100 to 110 ℃ by using a NETZSCH DSC 200F3
Differential Scanning Calorimeter with scan rate of 10
℃/min under N2 atmosphere. The samples for DSC
measurements were tightly sealed in Al pans. The glass
transition temperature (Tg) was recorded as the midpoint
of the glass transition. The decomposition temperature
(Td) was recorded with 10% of mass loss by using a
Pyris Diamond Perkin-Elmer TG/DTA with scan rate of
20 ℃/min under N2 atmosphere. The samples for
TG/DTA measurements were sealed tightly in Al2O3
Figure 2 Catalyst recycling of esterification of methanol with
benzoic acid using IL I. Reaction conditions: benzoic acid (0.10
mol), methanol (0.15 mol), IL (2 mmol), 80 ℃, 6 h.
Finally, the generality and scope of the esterification
reaction of various acids with methanol or ethanol over
DAIL I was investigated, and the results are summa-
rized in Table 5. It was found that I was of very high
activity for esterification. Both aliphatic acids and aro-
matic acids were smoothly transformed to esters in high
yields. No by-products, such as olefins or ethers, were
2006
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 2003— 2008

Pyrrolidine-based Dicationic Acidic Ionic Liquids
pans. The ion conductivity was measured by using a
Mettler-FE30 digital conductivity-meter at 25 ℃.
Brønsted acidity: measurement of the H0 values with an
Agilent 8453 UV-vis spectrophotometer and a basic
indicator.
39.43, H 6.38, N 3.28; found C 39.35, H 6.52, N 3.21.
1,1'-(Hexane-1,6-diyl)bis[N-(4-sulfobutyl)pyrrol-
idine]-p-toluenesulfonate (1∶ 2) (III) 1H NMR (D2O,
400 MHz) δ: 7.52 (d, J＝8.4 Hz, 4H), 7.20 (d, J＝8.0
Hz, 4H), 3.35 (t, J＝6.8 Hz, 8H), 3.18 (t, J＝6.8 Hz,
4H), 2.86 (t, J＝6.0 Hz, 4H), 2.80 (t, J＝7.2 Hz, 4H),
2.22 (s, 6H), 2.03 (t, J＝6.8 Hz, 8H), 1.77 (t, J＝8.0 Hz,
4H), 1.63 (t, J＝8.0 Hz, 4H); 13C NMR (D2O, 100 MHz)
δ: 142.37, 139.39, 129.38, 125.26, 64.23, 64.21, 63.38,
57.34, 49.91, 47.90, 47.86, 21.91, 21.15, 20.39, 16.71.
ESI-MS: m/z (＋) 497.8, m/z (－) 171.2. Anal. calcd for
C36H60N2O12S4 (841.13): C 51.41, H 7.19, N 3.33;
found C 51.25, H 7.27, N 3.26.
1,1'-(Decane-1,10-diyl)bis[N-(4-sulfobutyl)pyrrol-
idine]-p-toluenesulfonate (1∶ 2) (IV) 1H NMR (D2O,
400 MHz) δ: 7.50 (d, J＝8.4 Hz, 2H), 7.19 (d, J＝8.0
Hz, 2H), 3.31 (t, J＝6.8 Hz, 8H), 3.07 (t, J＝8.0 Hz,
4H), 2.78 (t, J＝8.0 Hz, 4H), 2.22 (s, 6H), 1.97 (t, J＝
6.8 Hz, 8H), 1.72 (t, J＝8.0 Hz, 4H), 1.69 (t, J＝8.0 Hz,
4H), 1.58 (t, J＝6.8 Hz, 4H), 1.16—1.22 (m, 12H); 13C
NMR (D2O, 100 MHz) δ: 141.69, 140.22, 129.21,
125.36, 59.99, 59.00, 57.83, 57.32, 49.94, 31.77, 29.24,
29.17, 28.74, 25.84, 22.43, 21.23, 20.87, 20.79, 19.19,
16.70. ESI-MS: m/z (＋) 553.8, m/z (－) 171.2. Anal.
calcd for C40H68N2O12S4 (897.23): C 53.55, H 7.64, N
3.12; found C 53.47, H 7.69, N 3.08.
Preparation of SO3H-functionalized ionic liquids
Starting materials (α,ω-dipyrrolidino-alkanes and
N-alkylpyrrolidine) were synthesized according to a
similar approach as reported previously.23-25
Ionic liquids used in this article (Scheme 1 and Fig-
ure 1) were synthesized according to similar previous
literatures.11-13 1,6-Dipyrrolidino-hexane (or 1,10-dipyr-
rolidino-decane) and 1,4-butane sultone were mixed and
refluxed with a molar ratio of 1∶2 in anhydrous ace-
tonitrile for 48 h to give a white solid zwitterion salt.
After washing the salt repeatedly with acetonitrile and
ether to remove any unreacted starting material, the
solid was dried in vacuo. Then, a twofold stoichiometric
amount of CF3SO3H was added dropwise and the mix-
ture stirred in anhydrous toluene at 80 ℃ for 24 h, re-
sulting in the formation of dicationic acidic IL I or II.
The IL phase was washed with toluene and ether to re-
move the non-ion residue and dried in vacuo. ILs III
and IV could be synthesized when the zwitterion salts
and p-CH3C6H4SO3H•H2O were mixed with a molar
ratio of 1∶2 in anhydrous ethanol and refluxed for 8 h.
Yields of ILs I—IV: 91%—93%.
N-Methyl-[N-(4-sulfonbutyl)pyrrolidine]trifluoro-
methanesulfonate (V) 1H NMR (D2O, 400 MHz) δ:
3.33 (t, J＝4.8 Hz, 4H), 3.20 (t, J＝7.6 Hz, 2H), 2.86 (s,
3H), 2.80 (t, J＝7.2 Hz, 2H), 2.03 (t, J＝4.8 Hz, 4H),
1.78 (t, J＝7.6 Hz, 2H), 1.63 (t, J＝7.6 Hz, 2H); 13C
NMR (D2O, 100 MHz) δ: 119.71 (q, JC-F＝315.2 Hz,
CF3), 64.41, 63.54, 57.51, 50.06, 48.06, 22.06, 21.30,
16.86. ESI-MS: m/z (＋) 222.3, m/z (－) 149.0. Anal.
calcd for C10H20F3NO6S2 (371.39): C 32.34, H 5.43, N
3.77; found C 32.37, H 5.59, N 3.80.
N-Alkylpyrrolidine reacted with 1,4-butane sultone
in a molar ratio of 1∶1 to form the white solid zwit-
terion. And conversion to the monocationic acidic ILs
(V—VIII) was accomplished by combining equimolar
quantities of the zwitterion and acid (CF3SO3H or
p-CH3C6H4SO3H•H2O). Yields: 94%—96%.
All the above ILs are viscous liquids, and their spec-
tral data are shown as follows.
1,1'-(Hexane-1,6-diyl)bis[N-(4-sulfobutyl)pyrrol-
idine]trifluoromethanesulfonate (1∶ 2) (I) 1H NMR
(D2O, 400 MHz) δ: 3.36 (t, J＝6.8 Hz, 8H), 3.16 (t, J＝
8.0 Hz, 4H), 3.10 (t, J＝8.0 Hz, 4H ), 2.81 (t, J＝7.2 Hz,
4H), 2.24 (t, J＝6.8 Hz, 8H), 1.75 (t, J＝8.0 Hz, 4H),
1.71 (t, J＝8.0 Hz, 4H), 1.65 (t, J＝6.8 Hz, 4H), 1.26 (t,
J＝6.8 Hz, 4H); 13C NMR (D2O, 100 MHz) δ: 119.71 (q,
JC-F＝315.2 Hz, CF3), 64.24, 64.21, 63.73, 49.89, 47.91,
21.90, 21.13. ESI-MS: m/z (＋) 497.8, m/z (－) 149.0.
Anal. calcd for C24H46F6N2O12S4 (796.88): C 36.17, H
5.82, N 3.52; found C 36.05, H 5.91, N 3.50.
1,1'-(Decane-1,10-diyl)bis[N-(4-sulfobutyl)pyrrol-
idine]trifluoromethanesulfonate (1∶ 2) (II) 1H NMR
(D2O, 400 MHz) δ: 3.33 (t, J＝6.8 Hz, 8H), 3.14 (t, J＝
8.0 Hz, 4H), 3.07 (t, J＝8.0 Hz, 4H), 2.79 (t, J＝7.2 Hz,
4H), 1.98 (t, J＝6.8 Hz, 8H), 1.79 (t, J＝8.0 Hz, 4H),
1.68 (t, J＝8.0 Hz, 4H), 1.58 (t, J＝6.8 Hz, 4H), 1.14—
1.18 (m, 12H); 13C NMR (D2O, 100 MHz) δ: 119.71 (q,
JC-F＝315.2 Hz, CF3), 62.80, 59.63, 58.75, 57.34, 49.95,
28.18, 27.97, 25.42, 22.71, 22.48, 22.35, 22.19, 21.48,
21.38, 21.14, 16.69. ESI-MS: m/z (＋) 553.8, m/z (－)
149.0. Anal. calcd for C28H54F6N2O12S4 (852.98): C
N-Hexyl-[N-(4-sulfonbutyl)pyrrolidine]trifluoro-
methanesulfonate (IL VI) 1H NMR (D2O, 400 MHz)
δ: 3.35 (t, J＝4.8 Hz, 4H), 3.12 (t, J＝7.6 Hz, 2H), 3.08
(t, J＝7.6 Hz, 2H), 2.80 (t, J＝7.2 Hz, 2H), 2.00 (t, J＝
4.8 Hz, 4H), 1.76 (t, J＝7.6 Hz, 2H), 1.62 (t, J＝7.6 Hz,
2H), 1.55 (t, J＝4.8 Hz, 4H), 1.12—1.21 (m, 6H), 0.55
(t, J＝6.4 Hz, 3H); 13C NMR (D2O, 100 MHz) δ: 119.71
(q, JC-F＝315.2 Hz, CF3), 62.79, 59.67, 58.78, 57.34,
49.93, 49.76, 30.35, 25.29, 22.99, 22.37, 21.66, 21.48,
21.39, 21.14, 16.70, 13.12. ESI-MS: m/z (＋) 292.4, m/z
(－) 149.0. Anal. calcd for C15H30F3NO6S2 (441.53): C
40.80, H 6.85, N 3.17; found C 40.87, H 6.99, N 3.14.
N-Decyl-[N-(4-sulfonbutyl)pyrrolidine]trifluoro-
methanesulfonate (IL VII) 1H NMR (D2O, 400 MHz)
δ: 3.33 (t, J＝4.8 Hz, 4H), 3.12 (t, J＝7.6 Hz, 2H), 3.07
(t, J＝7.6 Hz, 2H), 2.78 (t, J＝7.2 Hz, 2H), 1.99 (t, J＝
4.8 Hz, 4H), 1.71 (t, J＝7.6 Hz, 2H), 1.63 (t, J＝7.6 Hz,
2H), 1.55 (t, J＝4.8 Hz, 4H), 1.10—1.12 (m, 12H), 1.00
(t, J＝6.8), 0.69 (t, J＝6.4, 3H); 13C NMR (D2O, 100
MHz) δ: 119.71 (q, JC-F＝315.2 Hz, CF3), 62.99, 59.89,
59.34, 57.57, 50.26, 31.94, 29.54, 29.40, 29.04, 26.27,
23.06, 22.66, 21.84, 21.58, 16.94, 13.88. ESI-MS: m/z
Chin. J. Chem. 2010, 28, 2003— 2008
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2007

Liu et al.
FULL PAPER
(＋) 348.5, m/z (－) 149.0. Anal. calcd for C19H38F3-
NO6S2 (497.63): C 45.86, H 7.70, N 2.81; found C
45.87, H 7.87, N 2.83.
3
4
5
6
7
8
9
Jermy, B. R.; Pandurangan, A. Appl. Catal. A: Gen. 2005,
288, 25.
Adoor, S. G.; Manjeshwar, L. S.; Bhat, S. D.; Aminabhavi,
T. M. J. Membr. Sci. 2008, 318, 233.
Abd El-Wahab, M. M. M.; Said, A. A. J. Mol. Catal. A:
Chem. 2005, 240, 109.
Furuta, S.; Matsuhashi, H.; Arata, K. Appl. Catal. A: Gen.
2004, 269, 187.
Toukoniitty, B.; Mikkola, J. P.; Eränen, K.; Salmi, T.;
Murzin, D. Y. Catal. Today 2005, 100, 431.
Nakamura, R.; Komura, K.; Sugi, Y. Catal. Commun. 2008,
9, 511.
(a) Wasserscheid, P. J.; Keim, W. Angew. Chem., Int. Ed.
2000, 39, 3772.
N-Decyl-[N-(4-sulfonbutyl)pyrrolidine]-p-toluene-
sulfonate (IL VIII) 1H NMR (D2O, 400 MHz) δ: 7.51
(d, J＝8.4 Hz, 2H), 7.18 (d, J＝8.0 Hz, 2H), 3.84 (t, J＝
4.8 Hz, 4H), 3.31 (t, J＝7.6 Hz, 2H), 3.24 (t, J＝7.6 Hz,
2H), 2.79 (t, J＝7.2 Hz, 2H), 2.21 (s, 3H), 1.97 (t, J＝
4.8 Hz), 1.65 (t, J＝7.6 Hz, 2H), 1.63 (t, J＝7.6 Hz, 2H),
1.51 (t, J＝4.8 Hz, 4H), 1.10—1.12 (m, 14H), 0.69 (t,
J＝6.8 Hz, 3H); 13C NMR (D2O, 100 MHz) δ: 142.62,
139.71, 129.62, 125.54, 62.97, 59.68, 58.87, 57.51,
50.17, 31.88, 29.43, 29.38, 29.30, 28.89, 26.08, 22.88,
22.64, 21.73, 21.65, 21.45, 20.68, 16.96, 13.95. ESI-MS:
m/z ( ＋) 348.5, m/z ( －) 171.2. Anal. calcd for
C25H45NO6S2 (519.76): C 57.77, H 8.73, N 2.69; found
C 57.65, H 8.81, N 2.67.
(b) Brown, R. A.; Pollet, P.; Mckoon, E.; Eckert, C. A.; Li-
otta, C. L.; Jessop, P. G. J. Am. Chem. Soc. 2001, 123, 1254.
10 Pârvulescu, V. I.; Hardacre, C. Chem. Rev. 2007, 107, 2615.
11 Cole, A. C.; Jensen, J. L.; Ntai, I.; Tran, K. L. T.; Weave, K.
J.; Forbes, D. C.; Davis, J. H. J. Am. Chem. Soc. 2002, 124,
5962.
Typical esterification procedure
Weighed amounts of acid, alcohol, and IL were
charged into a 25 mL flask equipped with a water cool
condenser, then the reaction was allowed to proceed at
the desired temperature for 3—10 h with vigorous stir-
ring. Upon completion, the system became biphasic.
The upper phase that contains the produced ester was
isolated by decantation. The lower phase, the IL phase
that contains the unreacted materials, water and a por-
tion of the produced ester, was extracted with ethyl ace-
tate (5 mL×3). The combined washing layers were
washed twice with 5 wt% NaHCO3 solution, then with
H2O, dried over MgSO4 and filtered, the filtrate was
concentrated firstly by rotary evaporation then distilled
under reduced pressure to get the crude product. Then
the ILs could be regenerated by removing water under
vacuum (1.33 Pa) at 110 ℃ for 1 h. The qualitative
analyses were conducted with HP 6890/5793 GC-MS
and the compositions of the products were analyzed by
GC Agilent 6820 GC system equipped with FID detec-
tor.
12 Gui, J. Z.; Cong, X. H.; Liu, D.; Zhang, X. T.; Hu, Z. D.;
Sun, Z. L. Catal. Commun. 2004, 5, 473.
13 Gu, Y. L.; Shi, F.; Deng, Y. Q. J. Mol. Catal. A: Chem.
2004, 212, 71.
14 Joseph, T.; Sahoo, S.; Halligudi, S. B. J. Mol. Catal. A:
Chem. 2005, 234, 107.
15 Xing, H. B.; Wang, T.; Zhou, Z. H.; Dai, Y. Y. Ind. Eng.
Chem. Res. 2005, 44, 4147.
16 Fang, D.; Zhou, X. L.; Ye, Z. W.; Liu, Z. L. Ind. Eng. Chem.
Res. 2006, 45, 7982.
17 Li, X. Z.; Eli, W. J. Mol. Catal. A: Chem. 2008, 279, 159.
18 Fraga-Dubreuil, J.; Bourahla, K.; Rahmouni, M.; Bazureau,
J. P.; Hamelin, J. Catal. Commun. 2002, 3, 185.
19 Zhu, H. P.; Yang, F.; Tang, J.; He, M. Y. Green Chem. 2003,
5, 39.
20 Zhang, H. B.; Xu, F.; Zhou, X. H.; Zhang, G. Y.; Wang, C.
X. Green Chem. 2007, 9, 1208.
21 Zhao, Y. W.; Long, J. X.; Deng, F. G.; Liu, X. F.; Li, Z.;
Xia, C. G.; Peng, J. J. Catal. Commun. 2009, 10, 732.
22 Thomazeau, C.; Olivier-Bourbigou, H.; Magna, L.; Luts, S.;
Gilbert, B. J. Am. Chem. Soc. 2003, 125, 5264.
23 Phillips, A. P. J. Am. Chem. Soc. 1955, 77, 1693.
24 Liu, T.; Li, Q. Fine Specialty Chem. 2004, 12, 24 (in Chi-
nese).
References
1
Ogliaruso, M. A.; Wolfe, J. F. Synthesis of Carboxylic Acids,
Esters and Their Derivatives, Wiley, New York, 1991, pp.
3— 5.
25 Yu, J. G.; Song, X. F.; Liu, G. S.; Zhang, S. S.; Xie, K. M.;
Shan, Z. K. CN 1312247A, 2001.
2
Inui, K.; Kurabayashi, T.; Sato, S. Appl. Catal. A: Gen.
2002, 237, 53.
(E1003091 Pan, B.)
2008
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 2003— 2008