Redox Reaction: A New Route for the Synthesis of Water-Miscible Imidazolium Ionic Liquids

Article abstract of DOI:10.1055/s-0036-1589402

A novel chemical redox route was developed for the preparation of water-miscible imidazolium ionic liquids (ILs). In this method, the reaction between 1-alkyl-3-methylimidazolium bromides or 3-butyl-1-phenylimidazolium bromide and the appropriate acid reactant was promoted by the redox reaction between the bromide ion and aqueous hydrogen peroxide, with hex-1-ene as both solvent and bromine scavenger. The residual bromide ion and water contents of the prepared ILs were determined by ion chromatography and the Karl-Fischer test, respectively. This method not only produces water-miscible ILs in high purity and high yield, but also simplifies the reaction conditions in comparison with previous routes.

Full text of DOI:10.1055/s-0036-1589402

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2016, 48, A–H
paper
A
W. Li et al.
Paper
Synthesis
Redox Reaction: A New Route for the Synthesis of Water-Miscible
Imidazolium Ionic Liquids
Wenxiu Li
R1
R2
R1
R2
N
N
N
N
Shangwu Dai
Dong Li
Br
A
Qinqin Zhang
Hongtao Fan
Tao Zhang
H2O2
HA
hex-1-ene
R1 = Et, Bu, Bz, CO2Me
R2 = Me, Ph
A = BF4, MsO, CF3CO2,
HSO4, NO3, TsO, PF6
Zhigang Zhang*
redox reaction
25 °C, 3 –6 h
Shenyang University of Chemical Technology, Shenyang,
110142, P. R. of China
Ionic liquids, 20 examples
yields up to 97%
halide content up to 0.0031%
zhzhgang@syuct.edu.cn
Received: 23.09.2016
Accepted after revision: 29.09.2016
Published online: 16.11.2016
and can result in products with unacceptably high levels of
impurities, and, consequently, considerable efforts have
been devoted to the synthesis of water-miscible ILs.
Water-miscible imidazolium ILs can be prepared by di-
rect alkylation, without byproducts or halide ions (Scheme
1, path 1). However, only a limited range of ILs can be ob-
tained by this route, because the anion scope is restricted
by the choice of alkylating reagents, such as inorganic or or-
ganic esters.10 Furthermore, some of these alkylating re-
agents are unstable, toxic, or expensive.
DOI: 10.1055/s-0036-1589402; Art ID: ss-2016-h0009-op
Abstract A novel chemical redox route was developed for the prepara-
tion of water-miscible imidazolium ionic liquids (ILs). In this method,
the reaction between 1-alkyl-3-methylimidazolium bromides or 3-bu-
tyl-1-phenylimidazolium bromide and the appropriate acid reactant
was promoted by the redox reaction between the bromide ion and
aqueous hydrogen peroxide, with hex-1-ene as both solvent and bro-
mine scavenger. The residual bromide ion and water contents of the
prepared ILs were determined by ion chromatography and the Karl–
Fischer test, respectively. This method not only produces water-misci-
ble ILs in high purity and high yield, but also simplifies the reaction con-
ditions in comparison with previous routes.
R32CO3, R32SO4, R3N(Tf)2, R33OPF6 etc.
R2
R3
R2
(1)
Key words ionic liquids, redox reaction, protic acids, imidazolium
salts
N
N
OR3
OR3
N
N
A
+ HA
OR3
R1
In recent years, considerable attention has been paid to
ionic liquids (ILs) for their unique physicochemical proper-
ties, such as their good thermal and chemical stabilities,
high conductivity, strong solvent power, and negligible va-
por pressure.1 Imidazolium-based ILs are the most fre-
quently studied,2 and show excellent performance in a vari-
ety of fields, such as separation engineering,3 catalysis,4
electrochemistry,5 organic synthesis,6 and energy-storage
technology.7 Previously, applications of ILs have focused
A = PF6, NTf2 etc.
R3
R2
R3X
R2
R3
R2
YA
– YX
(2)
N
N
N
N
N
N
A
X
X = Cl, Br, I
Y = Ag, Li, Na
A = PF6, NTf2 etc.
Scheme 1 Previous methods for preparing ionic liquids
–
mainly on ILs with water-immiscible anions, such as BF4 ,
Another typical method for preparing water-miscible
imidazolium ILs is by salt metathesis (two-step method;
Scheme 1, path 2).11 A dialkylimidazolium halide is synthe-
sized and the halide ion is subsequently exchanged with a
sodium, lithium, or silver salt containing the desired anion.
Unfortunately, this method is restricted by the high cost of
silver salts and it suffers from high levels of residual halide
impurities that affect the performance of catalysts when
they are used in the new media.12 It is clear that the above-
mentioned methods have their own virtues and disadvan-
–
PF6 , or Tf2N–. However, these hydrophobic ILs contain fluo-
rinated anions that can decompose to form HF gas in aque-
ous environments, resulting in an environmental hazard.8
Water-miscible ILs eliminate these problems and interact
more easily with the natural environment. In addition, wa-
ter-miscible ILs have been successfully applied in aqueous
biphasic liquid–liquid separations.9 However, considerable
problems occur in the purification of water-miscible ILs
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–H

B
W. Li et al.
Paper
Synthesis
tages. To the best of our knowledge, the conventional two-
step method is still the main method used for the synthesis
of ILs. In this method, halide ions retain their original va-
lence (–1) throughout the reaction process, which leads to
residues of halides in the water-miscible IL products, and
obviously affects their purity. To reduce the shortage of
high-purity water-miscible ILs, we attempted to develop a
method in which the byproduct composition is changed.
An electrolytic method has been reported13 for the
preparation of ILs with low levels of residual halides. Al-
though the operations are complex, this method estab-
lished a compelling rationale for the synthesis of water-
miscible ILs. Here, we report a novel chemical redox route
to water-miscible ILs that not only produces water-miscible
ILs in high purities and yields, but also simplifies the reac-
tion conditions.
the same conditions as described above. After addition of
H2O2 to the mixtures, the desired products were successful-
ly obtained in excellent yields in six hours or less at room
temperature (entries 2–6).
Table 1 Redox Reaction To Give [RMIM][A]a
R1
R2
R1
R2
H2O2 + HA
N
N
N
N
hex-1-ene
A
Br
Entry Substrate
1
Product
Time (h) Yieldb(%)
[EMim]MeSO3
[EMim]BF4
[EMim]CF3CO2
[EMim]TsO
[EMim]HSO4
[EMim]NO3
4
4
5
5
3
4
93
93
94
90
95
90
2
3
4
5
6
Et
N
N
Br
As shown in Scheme 2, the desired water-miscible ILs
are prepared by oxidation of 1-alkyl-3-methyl imidazolium
bromides ([RMim]Br) at room temperature. Hydrogen per-
oxide was chosen as the oxidant, because it has strongly ac-
tive chemical properties and forms water on reaction,
which is environmentally friendly. In this process, hydrogen
peroxide reacts with bromide ions derived from [RMim]Br
and hydrogen ions derived from protic acids containing the
desired anions;14 the bromine byproduct is absorbed by
hex-1-ene, which is converted into 1,2-dibromohexane in
situ.15 When we attempted to use cheaper solvents such as
CCl4, CH2Cl2, or hexane as reaction media, a quantity of Br–
remained in the resulting liquid, resulting in a low purity of
the desired product. The 1,2-dibromohexane can be readily
removed from the resulting liquid, and the water produced
as a byproduct of the reaction can be removed by azeo-
tropic distillation with cyclohexane.
7
8
9
10
11
12
[BMim]CF3CO2
[BMim]TsO
[BMim]BF4
[BMim]MeSO3
[BMim]HSO4
[BMim]NO3
3
3
3
4
3
4
96
96
93
86
97
97
Bu
N
N
Br
13
14
15
16
17
18
[BzMim]MeSO3
[BzMim]TsO
[BzMim]CF3CO2
[BzMim]HSO4
[BzMim]NO3
[BzMim]PF6
6
4
6
3
3
3
53
90
85
93
94
96
N
N
Br
O
HO
c
19
20
21
[CMI]HSO4
3
3
3
87
N
N
N
Br
Br
N
N
d
e
[AEIm]MeSO3
–
R1
R2
R1
R2
H2O2 + HA
N
N
N
N
hex-1-ene
A
f
[BPim]HSO4
90
Br
Bu
N
Scheme 2 Preparation of water-miscible ionic liquids by a redox reac-
tion
Br
a All reactions were performed at r.t.
b Isolated yield of IL in water phase after purification and drying.
c CMI = 1-carboxymethyl-3-methylimidazolium.
d AEIm = 1-allyl-3-methylimidazolium.
Initially,
1-ethyl-3-methylimidazolium
bromide
e Mixture of products.
([EMim]Br) was synthesized as previously described.16
[EMim]Br was treated with an equimolar amount of meth-
anesulfonic acid as a protic acid in the presence of 0.5
equivalents of hydrogen peroxide at room temperature
(25 °C) for four hours in hex-1-ene as solvent. The product,
f BPim = 3-butyl-1-phenylimidazolium.
The structure of [EMim]MeSO3 was confirmed by NMR
spectroscopy. It has been reported that the existence of
chlorine ion can change the chemical shift of ILs in 1H NMR
due to the formation of a hydrogen bond between the chlo-
ride ion and the C2 proton of the 1,3-dialkylimidazolium
salt, resulting in a downfield shift in comparison the re-
ported value for the shift of the C2 proton.17 As can be seen
in Figure 1, [EMim]MeSO3 produced by our method (Figure
1, A) showed an upfield shift of the C2 proton (δ = 8.72
ppm; D2O) in the 1H NMR spectrum, whereas [EMim]MeSO3
1-ethyl-3-methylimidazolium
methanesulfonate
([EMim]MeSO3), was obtained in high yield after removal of
the solvent and byproducts (Table 1, entry 1). To extend the
scope of this method, five other acids (tetrafluoroboric acid,
trifluoroacetic acid, 4-toluenesulfonic acid, sulfuric acid,
and nitric acid) were examined as sources of the corre-
sponding anions for the synthesis of ILs. The acids were
mixed with [EMim]Br, in the presence of hex-1-ene, under
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–H

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W. Li et al.
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Synthesis
containing large amounts of residual Br– (Figure 1, B)
showed a downfield shift (δ = 9.81 ppm; D2O), possibly due
to the stronger hydrogen bond formed between the Br– ion
and the C2–H bond, compared with that between the meth-
anesulfonate anion and the C2–H bond.18
Figure 2 IR spectrum of [AEIm]MeSO3
a different post-processing treatment, involving only distil-
lation and drying of the oil phase.
Figure 1 1H NMR spectra: (A) our product [EMim]MeSO3; (B)
[EMim]MeSO3 containing >20% [EMim]Br.
High levels of residual halides are often detected in ILs
prepared by conventional two-step methods, because these
halides can dissolve in the resulting ILs during the ion-ex-
change process. To test the purity of the products produced
by our method, we used ion chromatography (IC) to deter-
mine the concentration of residual Br– (Table 2).26 Although
some products showed a slightly higher content of Br– than
those synthesized by direct alkylation (which gives almost
no residual halide impurities), ILs such as [EMim]NO3,
[BMim]HSO4, [BMim]CF3CO2 and [BzMim]TsO contained
low levels of Br–. These results were consistent with the re-
sults of 1H NMR studies. Although all the ILs were dried un-
der vacuum for 12 hours, small amount of water remained
in the hydrophilic ILs. We are currently working to optimize
this process to reduce the water content.
Inspired by the achievements described above, we
switched our focus to other cations by loading typical or-
ganic substituents onto the 1-methylimidazole. Five new
ILs, 1-butyl-3-methylimidazolium bromide ([BMim]Br),19
1-benzyl-3-methylimidazolium bromide ([BzMim]Br),20 1-
carboxymethyl-3-methylimidazolium bromide21 ([CMI]Br),
1-allyl-3-methylimidazolium bromide22 ([AEIm]Br), and 3-
butyl-1-phenylimidazolium bromide23 ([BPim]Br) were
prepared. By following the method described above,
[BMim]A (A = anion), [BzMim]A, [CMI]HSO4, and [AEIm]Me-
SO4 were synthesized (Table 1, entries 7–20). The [BMim]A
ILs, [CMI]HSO4,24 and [BPim]HSO4 were obtained in good
yields (entries 7–12, 19, and 21). For [BzMim]A, protic acids
such as H2SO4, HNO3, TsOH, and CF3CO2H (entries 14–17)
worked well, whereas MeSO3H (entry 13) as the acid re-
source gave a low yield of the corresponding IL. Because
[BzMim]MeSO3 IL has a low solubility in water, some of this
product remained in the organic phase, resulting in the low
yield.
Next, we discuss the reasonability of our experiment re-
sults on the basis of the electrochemical principle, the
Nernst equation27 (Equation 1).
RT
nF
[R]
[O]
E = Eθ –
lg
Equation 1
The infrared spectrum of [AEIm]MeSO3 (Table 1, entry
20) showed a characteristic peak for a C–Br bond at 623 cm–1
(Figure 2) . This product cannot therefore be produced in a
pure form, because during the process, the bromine mole-
cules formed in the reaction add to the C=C double bond in
the side chain of the product.25 Consequently, ILs with side
chains containing unsaturated C–C bonds are not well toler-
where E is the electric potential (V), Εθ is the standard
electric potential of given oxidation–reduction process (V),
R is the universal gas constant (8.314 J/mol/K), T is the ab-
solute temperature (K) (298.15 K), F is the Faraday constant
(96500 C/mol), n is the number of electrons transferred
during the reaction (2), [O] is the activity of the oxidant,
and [R] is the activity of the reductant. The electrode reac-
tions are as given in Equation 2.
–
ated, because during the reaction the tribromide ion (Br3 )
can form an onium salt with the side chain.
The less water-soluble ionic liquid [BzMim]PF610f (entry
18) was readily produced in high yield by our method with
The extremity of the redox reaction can be calculated
approximately by means of Equation 3 and Equation 4.
When the reaction time is infinite, the reaction approaches
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–H

D
W. Li et al.
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Synthesis
2 Br– – 2 e–
Br2
E = Eθ (H2O2|H2O)-Eθ (Br2|Br–)
–1.087 V anodic reaction
1.770 V cathodic reaction
Equation 4
H2O2 + 2 H+ + 2 e–
Equation 2
2 H2O
Compared with the reported methods, the route devel-
oped in this work not only serves as an alternative strategy
for the preparation of water-miscible ILs, but also has addi-
tional advantages. The reaction process shown in Scheme 2
is time-saving, as the time needed for the reaction is six
hours or less, whereas the conventional two-step method
takes 12 hours or more. Furthermore, even after 24 hours,
0.3–4 mass% of residual halide remains in the products ob-
tained by the conventional two-step method.11 Additional-
ly, the temperature required for the redox process is below
room temperature (25 °C), which means a lower energy
consumption, whereas the temperature required for the
conventional methods is 70 °C or more.10,11 Another advan-
tage is that the post-treatment, which includes extraction
and azeotropic distillation, is easy to carry out. Our method
can therefore be used to produce water-miscible ILs at low
cost with common equipment and it has the potential to be
applied in the manufacture of ILs. Another advantage is that
the range of desired ILs is enlarged compared with that of
the direct alkylation reaction method, as various cations
can be obtained by the alkylation of 1-methylimidazole,
and a range of anions can be derived from various protonic
acids.
Table 2 Residual Bromide and Water Contents of the Products
Entry
Product
Br contenta (%)
Water contentb (%)
1
2
[EMim]MeSO3
[EMim]BF4
0.5447
0.4597
0.6115
0.1852
0.3601
0.0454
0.0460
0.0917
0.7437
0.1199
0.0635
0.3599
0.0971
0.0631
0.0562
0.1961
0.1097
0.0978
0.0476
0.0526
0.0139
0.0155
0.0074
0.0278
0.0733
0.0145
0.1046
0.0284
0.0119
3
[EMim]CF3CO2
[EMim]TsO
4
5
[EMim]HSO4
[EMim]NO3
6
7
[BMim]MeSO3
[BMim]BF4
8
9
[BMim]CF3CO2
[BMim]TsO
c
10
11
12
13
14
15
16
17
18
19
20
–
[BMim]HSO4
[BMim]NO3
[BzMim]MeSO3
[BzMim]CF3CO2
[BzMim]TsO
[BzMim]HSO4
[BzMim]NO3
[BzMim]PF6
[CMI]HSO4
0.0044
0.2809
0.0359
0.0050
c
–
Finally, we compared the residual halide content of
commercial [BMim]HSO4 (≥99%) (B) with that of the prod-
uct obtained by our strategy (A). Our product had a much
lower halide content (0.064 mass% versus 1.56 mass%) (Fig-
ure 3). In addition, the anion-mode mass spectrum29 of the
commercial sample showed a residual chloride peak at
m/z = 507.1456, whereas our sample showed almost no
such peak (Figure 3 and Figure 4).
0.1353
0.0031
c
–
0.0112
0.0012
[BPim]HSO4
a By ion chromatography.
b By Karl Fischer analysis.
c Solid product.
equilibrium. The ultimate concentration of Br– can be cal-
culated, and the value is less than 6.5 × 10–6 mol/L (0.052
mg/L),28 which is very low. Although our method does not
reach this extreme concentration, the results of analyses of
some of the products showed very low contents of Br–, es-
pecially those shown in Table 2, entries 6, 7, 8, 14, and 15. It
can also be seen from Equation 3 that the method does not
work in the case of weak acids such as AcOH or H3PO4. With
weak acids such as these, the value of E approaches 0 or
even a negative value, and the original force driving the re-
action is lost because these weak acids cannot ionize a suf-
ficient number of hydrogen ions.
Figure 3 Ion chromatography of [BMim]HSO4
In summary, we have developed a novel redox method
for the synthesis of water-miscible imidazolium ionic liq-
uids under mild reaction conditions (room temperature)
and with a shorter reaction time. [RMim]Br and protic acids
react with H2O2 to give ILs with high yields and high purity.
The products synthesized by our method contained low
levels of residual Br-. The halide content of [BMim]HSO4 ob-
tained from our laboratory determined by IC was 24 times
[H2O]2[Br2]
E = Eθ –0.026 lg
[H2O2][H+]2[Br–]2
Equation 3
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–H

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1H NMR (500 MHz, D2O): δ = 8.72 (s, 1 H), 7.51 (s, 1 H), 7.45 (s, 1 H),
4.25 (q, J = 7.5 Hz, 2 H), 3.91 (s, 3 H), 2.82 (s, 3 H), 1.52 (t, J = 7.5 Hz, 3
H).
13C NMR (126 MHz, D2O): δ = 135.01, 122.97, 121.36, 44.23, 38.04,
35.12, 13.98.
1-Ethyl-3-methylimidazolium Tetrafluoroborate ([EMim]BF4; Ta-
ble 1, Entry 2)31
Colorless liquid; yield: 36.7908 g (93%).
1H NMR (500 MHz, D2O): δ = 8.60 (s, 1 H), 7.40 (s, 1 H), 7.34 (s, 1 H),
4.15 (q, J = 7.5 Hz, 2 H), 3.81 (s, 3 H), 1.42 (t, J = 7.5 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 134.77, 122.65, 120.96, 43.93, 34.63,
13.46.
19F NMR (377 MHz, D2O): δ = 150.52.
1-Ethyl-3-methylimidazolium Trifluoroacetate ([EMim]F3CCO2;
Table 1, Entry 3)32
Colorless liquid; yield: 42.112 g (94%).
1H NMR (500 MHz, D2O): δ = 8.81 (s, 1 H), 7.58 (s, 1 H), 7.51 (s, 1 H),
4.31 (q, J = 7.5 Hz, 2 H), 3.98 (s, 3 H), 1.58 (t, J = 7.5 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 161.46, 135.18, 123.17, 121.55, 117.32,
44.43, 35.36, 14.19.
19F NMR (377 MHz, D2O): δ = –75.47.
Figure 4 High-resolution mass spectra of [BMim]HSO4
1-Ethyl-3-methylimidazolium Tosylate ([EMim]TsO; Table 1, Entry
4)32
lower than that of the commercial product. Further investi-
gations on the purification of the ILs produced by our meth-
od are ongoing.
Colorless liquid; yield: 50.760 g (90%).
1H NMR (500 MHz, D2O): δ = 8.59 (s, 1 H), 7.70 (d, J = 8.1 Hz, 2 H), 7.37
(d, J = 30.9 Hz, 4 H), 4.16 (qd, J = 7.3, 4.2 Hz, 2 H), 3.83 (s, 3 H), 2.38 (s,
3 H), 1.47 (t, J = 8.5 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 141.66, 139.31, 134.70, 128.84, 124.81,
122.87, 121.24, 44.19, 35.03, 19.97, 13.86.
NMR spectra were recorded in deuterated solvents (CDCl3, D2O, or
DMSO-d6) on a Bruker Avance 500 MHz spectrometer. IR spectra were
recorded on a Nexus 470. The water content was determined by Karl–
Fischer titration. The halide content was detected by ion chromatog-
raphy (Wayee IC-6200). Mass spectra (ESI) were recorded in positive-
and negative-ion modes on a hybrid quadrupole time-of-flight mass
spectrometer (Bruker micrOTOF-QII) at the Institute of Process Engi-
neering, Chinese Academy of Sciences. The ionic liquid used for com-
parison was 1-butyl-3-methylimidazolium hydrogen sulfate
([BMim]HSO4) (>98%, Yulu Fine Chemicals Co., Ltd)
1-Ethyl-3-methylimidazolium Hydrogen Sulfate ([EMim]HSO4; Ta-
ble 1, Entry 5)33
Colorless liquid; yield: 39.520 g (95%).
1H NMR (500 MHz, D2O): δ = 8.31 (s, 1 H), 7.11 (s, 1 H), 7.05 (s, 1 H),
3.86 (q, J = 7.5 Hz, 2 H), 3.52 (s, 3 H), 1.13 (t, J = 7.5 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 134.74, 122.75, 121.12, 44.02, 34.86,
13.75.
Ionic liquids (Table 1, Entries 1–19, 21); General Procedure
1-Ethyl-3-methylimidazolium Nitrate ([EMim]NO3; Table 1, Entry
6)34
A mixture of the appropriate imidazolium bromide (0.2 mol) and
hex-1-ene (30 mL) was stirred in a flask, and a mixture of the appro-
priate protonic acid (0.2 mol) and H2O2 (0.1 mol) was added dropwise
at room temperature (25 °C). After the appropriate time (Table 1), the
liquid was placed in a separatory funnel and the oil phase was re-
moved. The aqueous phase was washed with portions of CH2Cl2 (50
mL) until it was colorless. Residual H2O in the product was removed
by azeotropic distillation with cyclohexane. For [BzMim]PF6 (Table 1,
entry 18), which has low water solubility, post-processing required
only distillation and desiccation of the oil phase.
Colorless liquid; yield: 31.140 g (90%).
1H NMR (500 MHz, D2O): δ = 8.61 (s, 1 H), 7.40 (s, 1 H), 7.34 (s, 1 H),
4.14 (q, J = 7.5 Hz, 2 H), 3.81 (s, 3 H), 1.41 (t, J = 7.5 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 135.56, 123.45, 121.83, 44.79, 35.56,
14.40.
1-Butyl-3-methylimidazolium Tetrafluoroborate ([BMim]BF4; Ta-
ble 1, Entry 9)10f
Colorless liquid; yield: 41.9988 g (93%).
1-Ethyl-3-methylimidazolium Mesylate ([EMim]MeSO3; Table 1,
Entry 1)30
1H NMR (500 MHz, D2O): δ = 8.35 (s, 1 H), 7.17 (s, 1 H), 7.13 (s, 1 H),
3.91 (t, J = 7.0 Hz, 2 H), 3.61 (s, 3 H), 1.57 (quin, J = 7.1 Hz, 2 H), 1.04
(m, 2 H), 0.65 (t, J = 7.3 Hz, 3 H).
Colorless liquid; yield: 38.316 g (93%).
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13C NMR (126 MHz, D2O): δ = 135.60, 123.31, 122.02, 49.11, 35.42,
1H NMR (500 MHz, DMSO-d6): δ = 9.04 (s, 1 H), 7.51 (d, J = 12.3 Hz, 2
31.07, 18.57, 12.42.
H), 7.33 (m, 5 H), 5.34 (s, 2 H), 3.81 (s, 3 H).
19F NMR (377 MHz, DMSO-d6): δ = –146.13, –148.09.
13C NMR (126 MHz, DMSO-d6): δ = 136.08, 134.30, 128.92, 128.88,
128.75, 128.39, 123.80, 123.77, 123.73, 121.97, 51.85, 36.02, 35.96.
19F NMR (377 MHz, DMSO-d6): δ = –74.02.
1-Butyl-3-methylimidazolium Tosylate ([BMim]TsO; Table 1, En-
try 8)10f
White solid; yield: 59.520 g (96%); mp 70 °C.
1-Benzyl-3-methylimidazolium Tosylate ([BzMim]TsO; Table 1,
Entry 14)37
1H NMR (500 MHz, D2O): δ = 8.53 (s, 1 H), 7.66 (d, J = 8.1 Hz, 2 H), 7.29
(m, 4 H), 4.02 (t, J = 2.5 Hz, 2 H), 3.78 (s, 3 H), 2.32 (s, 3 H), 1.71 (m, 2
H), 1.22 (m, 2 H), 0.87 (t, J = 2.5 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 141.22, 139.68, 134.84, 128.68, 124.79,
122.85, 121.49, 48.57, 35.02, 30.60, 19.96, 18.21, 12.17.
White solid; yield: 62.100 g (90%); mp 40 °C.
1H NMR (500 MHz, DMSO-d6): δ = 9.26 (s, 1 H), 7.79 (s, 1 H), 7.71 (s, 1
H), 7.53 (d, J = 8.1 Hz, 2 H), 7.42 (m, 5 H), 7.14 (d, J = 7.9 Hz, 2 H), 5.42
(s, 2 H), 3.85 (s, 3 H), 2.30 (s, 3 H).
13C NMR (126 MHz, DMSO-d6): δ = 145.25, 137.95, 136.67, 134.82,
128.94, 128.70, 128.31, 128.15, 125.47, 123.96, 122.28, 51.83, 35.80,
20.74.
1-Butyl-3-methylimidazolium Mesylate ([BMim]MeSO3; Table 1,
Entry 10)35
Colorless liquid; yield: 40.248 g (86%).
1H NMR (500 MHz, D2O): δ = 8.48 (s, 1 H), 7.26 (s, 1 H), 7.21 (s, 1 H),
3.96 (t, J = 7.5 Hz, 2 H), 3.67 (s, 3 H), 2.55 (s, 3 H), 1.61 (quin, J = 7.3 Hz,
2 H), 1.08 (m, 2 H), 0.68 (t, J = 7.4 Hz, 3 H).
1-Benzyl-3-methylimidazolium Hydrogen Sulfate ([BzMim]HSO4;
Table 1, Entry 16)38
Colorless liquid; yield: 50.406 g (93%).
13C NMR (126 MHz, D2O): δ = 135.23, 122.97, 121.68, 48.68, 38.06,
1H NMR (500 MHz, D2O): δ = 8.45 (s, 1 H), 7.19 (m, 7 H), 5.11 (s, 2 H),
35.11, 30.68, 18.19, 12.14.
3.62 (s, 3 H).
13C NMR: δ = 136.33, 134.51, 128.96, 128.77, 128.38, 123.85, 122.03,
51.82, 35.68.
1-Butyl-3-methylimidazolium Trifluoroacetate ([BMim]F3CCO2;
Table 1, Entry 7)32
Colorless liquid; yield: 48.384 g (96%).
1-Benzyl-3-methylimidazolium Nitrate ([BzMim]NO3; Table 1, En-
try 17)39
1H NMR (500 MHz, D2O): δ = 8.67 (s, 1 H), 7.43 (s, 1 H), 7.39 (s, 1 H),
4.14 (t, J = 7.5 Hz, 2 H), 3.85 (s, 3 H), 1.79 (m, 2 H), 1.26 (m, 2 H), 0.86
(t, J = 7.5 Hz, 3 H).
Colorless liquid; yield: 44.368 g (94%).
1H NMR (500 MHz, D2O): δ = 9.28 (s, 1 H), 7.78 (s, 1 H), 7.71 (s, 1 H),
7.40 (m, 5 H), 5.43 (s, 2 H), 3.86 (s, 3 H).
13C NMR (126 MHz, CDCl3): δ = 160.66, 136.56, 123.63, 122.16,
114.92, 49.59, 35.96, 31.75, 19.10, 12.95.
19F NMR (377 MHz, DMSO-d6): δ = –74.87, –76.05.
13C NMR (126 MHz, D2O): δ = 137.17, 135.27, 129.45, 129.20, 128.77,
124.46, 122.75, 52.36, 36.25.
1-Butyl-3-methylimidazolium Hydrogen Sulfate ([BMim]HSO4; Ta-
ble 1, Entry 11)36
1-Benzyl-3-methylimidazolium Mesylate ([BzMim]MeSO3; Table 1,
Entry 13)40
Colorless liquid; yield: 45.784 g (97%).
Colorless liquid; yield: 28.514 g (53%).
1H NMR (500 MHz, D2O): δ = 8.26 (s, 1 H), 7.06 (s, 1 H), 7.02 (s, 1 H),
3.78 (t, J = 7.5 Hz, 2 H), 3.48 (s, 3 H), 1.43 (m, 2 H), 0.89 (m, 2 H), 0.50
(t, J = 7.5 Hz, 3 H).
1H NMR (500 MHz, D2O): δ = 8.70 (s, 1 H), 7.40 (ddd, J = 12.6, 10.2, 6.9
Hz, 7 H), 5.31 (s, 2 H), 3.83 (s, 3 H), 2.76 (s, 3 H).
13C NMR (126 MHz, DMSO-d6): δ = 136.53, 136.50, 134.68, 128.94,
128.72, 128.35, 123.91, 122.15, 51.80, 39.53, 39.50, 35.76.
13C NMR (126 MHz, D2O): δ = 134.97, 122.73, 121.44, 48.48, 34.87,
30.43, 17.94, 11.87.
1-Benzyl-3-methylimidazolium Hexafluorophosphate
([BzMim]PF6; Table 1, Entry 18)10f
MS (ESI, +ve): m/z = 140.1229 ([BMim]).
MS (ESI, −ve): m/z = 96.9603 (HSO4).
White solid; yield: 62.148 g (96%); mp 130 °C.
1H NMR (500 MHz, D2O): δ = 9.18 (s, 1 H), 7.76 (s, 1 H), 7.69 (s, 1 H),
7.40 (m, 5 H), 5.41 (s, 2 H), 3.85 (s, 3 H).
1-Butyl-3-methylimidazolium Nitrate ([BMim]NO3; Table 1, Entry
12)10f
Colorless liquid; yield: 38.994 g (97%).
13C NMR (126 MHz, DMSO-d6): δ = 137.14, 135.29, 129.47, 129.22,
128.73, 124.47, 122.82, 52.37, 36.32.
19F NMR (377 MHz, DMSO-d6): δ = –69.21, –71.10.
1H NMR (500 MHz, D2O): δ = 8.41 (s, 1 H), 7.19 (s, 1 H), 7.14 (s, 1 H),
3.88 (t, J = 7.5 Hz, 2 H), 3.60 (s, 3 H), 1.52 (m, 2 H), 0.99 (m, 2 H), 0.59
(t, J = 7.5 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 135.65, 123.31, 122.01, 49.11, 35.43,
31.15, 18.65, 12.43.
1-Carboxymethyl-3-methylimidazol-3-ium Hydrogen Sulfate
([CMI]HSO4; Table 1, Entry 19)24
Colorless liquid; yield: 41.586 g (87%).
1H NMR (500 MHz, D2O): δ = 8.68 (s, 1 H), 7.39 (s, 1 H), 7.37 (s, 1 H),
4.99 (s, 2 H), 3.82 (s, 3 H).
1-Benzyl-3-methylimidazolium Trifluoroacetate ([BzMim]F3CCO2;
Table 1, Entry 15)37
Colorless liquid; yield: 48.790 g (85%).
13C NMR (126 MHz, D2O): δ = 170.11, 137.32, 123.48, 50.04, 35.95.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–H

G
W. Li et al.
Paper
Synthesis
3-Butyl-1-phenylimidazolium Hydrogen Sulfate ([BPim]HSO4; Ta-
ble 1, Entry 21)
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Wasserscheid, P. Green Chem. 2006, 8, 887. (b) Kuhlmann, E.;
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Colorless liquid; yield: 53.640 g (90%).
IR (KBr): 3136, 2960, 2928, 2871, 2600, 2849, 1737, 1635, 1549, 1493,
1460, 1300, 1003, 879, 850, 762 cm–1
.
1H NMR (500 MHz, D2O): δ = 8.65 (s, 1 H), 7.31 (s, 1 H), 7.16 (s, 1 H),
7.05 (d, J = 9.2 Hz, 5 H), 3.78 (t, J = 7.1 Hz, 2 H), 1.40 (quin, J = 7.1 Hz, 2
H), 0.86 (q, J = 7.4 Hz, 2 H), 0.43 (t, J = 7.3 Hz, 3 H).
13C NMR (126 MHz, D2O): δ = 134.20, 133.54, 129.87, 129.59, 122.76,
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Acknowledgment
This work was financially supported by the National Science Founda-
tion of China (Project No. 21576166), and Liaoning Province Science
Foundation of China (Project No. 2014020140). We thank the Insti-
tute of Process Engineering, Chinese Academy of Sciences for per-
forming the high-resolution mass spectrometry.
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–H