Synthesis and properties of room-temperature choline carboxylate zwitterionic ionic liquids as potential electrolytes

Article abstract of DOI:10.1002/cplu.201200247

Choline carboxylate zwitterions were prepared by two different synthetic routes through esterification of choline salts with a range of anhydrides. Their conjugation with lithium bis(trifluoromethylsulfonyl) imide resulted in the formation of stable room-temperature ionic liquids. In view of their use as potential electrolytes the physicochemical characterization of these attractive ionic liquids was performed. These compounds presented a glass transition temperature between -43 and -34 °C, good thermal stability up to 2248C, densities above 1.44 gcm^-3 at 25°C, and viscosities between 3.56 and 12.27 Pa s at 258C. In terms of conductivity the most promising ionic liquid showed an excellent conductivity between 8.66 105 Scm^-1 at 258C and 1.8010-3 Scm^-1 at 908C. These zwitterionic ionic liquids maintained a liquid state, and no dissociation was observed even after six months of storage at room temperature.

Full text of DOI:10.1002/cplu.201200247

DOI: 10.1002/cplu.201200247
Synthesis and Properties of Room-Temperature Choline
Carboxylate Zwitterionic Ionic Liquids as Potential
Electrolytes
ffngelo Rocha,[a, b] Tânia Carvalho,[b] Pedro Vidinha,[b] and Nuno M. T. LourenÅo*[a]
Dedicated to Professor Carlos A. M. Afonso on the occasion of his 50th birthday
Choline carboxylate zwitterions were prepared by two different
synthetic routes through esterification of choline salts with
a range of anhydrides. Their conjugation with lithium bis(tri-
fluoromethylsulfonyl)imide resulted in the formation of stable
room-temperature ionic liquids. In view of their use as poten-
tial electrolytes the physicochemical characterization of these
attractive ionic liquids was performed. These compounds pre-
sented a glass transition temperature between ꢀ43 and
ꢀ348C, good thermal stability up to 2248C, densities above
1.44 gcmꢀ3 at 258C, and viscosities between 3.56 and
12.27 Pas at 258C. In terms of conductivity the most promising
ionic liquid showed an excellent conductivity between 8.66”
10ꢀ5 Scmꢀ1 at 258C and 1.80”10ꢀ3 Scmꢀ1 at 908C. These zwit-
terionic ionic liquids maintained a liquid state, and no dissocia-
tion was observed even after six months of storage at room
temperature.
Introduction
Over the last decades ionic liquids have been designed to en-
hance their already attractive physicochemical properties and
fulfill the specific needs of many applications.[1] An example of
this effort is the design of a new subclass of ionic liquids,
called zwitterionic ionic liquids (ZILs). ZILs, like other zwitter-
ionic compounds, are mainly characterized by having formal
unit electrical charges of opposite sign.[2] Among the zwitter-
ionic-type ionic liquids, imidazolium cations tethered with sul-
fonate anions are by far the most common and have been in-
tensively studied as electrolytes for lithium batteries[3] or for
fuel cells[4] (Scheme 1). These studies have shown that zwitter-
ions are excellent ion dissociators and can promote target ion
transport.[5]
liquid crystals.[9] Concerning their synthesis, these zwitterionic
carboxylates have been prepared by neutralization of the re-
spective carboxylic acid with a base and subsequent dissocia-
tion of the halide salt from the zwitterion inner salt[6,9] or by
hydrolysis of an ester derivative of the desired zwitterions
through an anion-exchange resin.[5d]
In 1953, Phillips[10] reported the synthesis of a carboxylic am-
monium salt (1) from the reaction between choline iodide (2a)
and succinic anhydride (3), two cheap, readily available, and
known low toxicity materials that caught our attention
(Scheme 2). Despite the reported synthesis of 1, to the best of
our knowledge no choline zwitterionic inner salts of this type
Other less explored zwitterionic salts based on imidazolium
cations are the compounds containing carboxylate anions.
These have been used mainly as Brønsted acidic catalysts,[6] on
desulfurization of fuels,[7] metal oxides solubilization,[8] and
Scheme 2. Synthesis of carboxylic ammonium salt from the reaction be-
tween choline iodide and succinic anhydride.[10]
[a] ff. Rocha, Dr. N. M. T. LourenÅo
IBB–Institute for Biotechnology and Bioengineering
Centre for Biological and Chemical Engineering, Instituto Superior TØcnico
Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)
Fax: (+351)218419062
E-mail: nmtl@ist.utl.pt
[b] ff. Rocha, T. Carvalho, Dr. P. Vidinha
REQUIMTE/CQFB, Departamento de Química FCT
Universidade Nova de Lisboa, 2829-516 Caparica (Portugal)
Scheme 1. Some examples of zwitterionic ionic liquids reported in the litera-
ture.[5]
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201200247.
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Ionic Liquids
have been reported until now. These zwitterionic inner salts
present some features that could be beneficial for its use as
electrolytes. Particularly, concerning their structural features,
the ester and the carboxylate group constitute added value in
terms of ion transport.[5e] Additionally, in terms of biodegrada-
bility both groups facilitate the degradation of the compound
at the end of its life cycle. Its primary degradation products are
choline and dicarboxylic acid, biomaterials that can hardly be
considered waste.[11]
peratures above the melting point of the anhydride, a liquid
homogeneous reaction mixture is achieved allowing the reac-
tion to proceed. The reaction was optimized with regard to
the temperature, choline/anhydride ratio, and reaction time.
The best experimental conditions were obtained under neat
conditions at 758C in vacuum (0.5 mbar) with 1.5 equivalents
of anhydride. Under these conditions complete esterification of
the choline acetate was achieved after 2 hours (by NMR analy-
sis; entry 1, Table 1). Over 76% of the acetic acid was removed
from the reaction mixture after 2 hours of vacuum, and less
than 5% remained after 12 hours. After the esterification reac-
However, owing to the presence of the ester moiety on
these molecules, the common alkaline and anion-exchange
methods cannot be used, because they result in the hydrolysis
of the starting material. Accordingly, mild conditions needed
to be developed to synthesize these new choline zwitterionic
inner salts.
Table 1. Synthesis of lithium bis(trifluoromethylsulfonyl)imide choline-
based zwitterionic ionic liquids.[a]
Herein, we describe two synthetic routes based on the
esterification of choline salts with anhydrides for the prepara-
tion of choline-based zwitterions, as well as the room-tempera-
ture ionic liquids obtained from their conjugation with lithium
bis(trifluoromethylsulfonyl)imide (Scheme 3).
Results and Discussion
The first synthetic route (Scheme 3, route I) arose from the re-
action of choline acetate (2c) with glutaric anhydride (4).
Under these conditions we observed the formation of the re-
spective zwitterion inner salt 8 and acetic acid instead of the
corresponding acetate salt. This interesting result can be ex-
plained by the different pKa values of the involved compounds
(pKa values of glutaric acid and acetic acid are 4.34 and 4.76,
respectively). The higher acidity of the zwitterion carboxylic
group must be decisive to protonate the acetic acid, resulting
in the formation of the zwitterion inner salt. This finding
prompted us to use choline acetate for the synthesis of this
type of zwitterions, where the acetic acid produced during re-
action could be removed from the reaction medium by contin-
uous distillation. Another important feature of this reaction is
that no solvent is required. By performing the reaction at tem-
Entry
Substrate
Anhydride
(equiv)
T
t
Conv. Product Yield
[8C] [h] [%][b]
[%]
1
2
3
4
5
6
7
2c
2d
2c
2c
2c
2e
2e
4 (1.5)
4 (1.5)
5 (2)
3 (2)
6 (2)
75
75
80
2
2
4
4
3
3
8
>98
>98
>98
90
90
>98
>98
12
12
13
11
14
12
13
73
57
74
–
–
[c]
145
80
[d]
4 (2)
5 (2.5)
75
80
67
63
[a] All reactions were performed between substrates (2c–e) and anhy-
drides (3–6) under vacuum (0.5 mbar). [b] Determined by 1H NMR spec-
troscopy for the zwitterionic compounds (7–10). [c] NMR data revealed
partial cleavage of the ester bond. [d] NMR data revealed complete cleav-
age of the ester bond.
Scheme 3. Synthetic routes for the preparation of choline-based zwitterionic liquids.
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N. M. T. LourenÅo et al.
tion the crude zwitterion inner salt 8 was dissolved in dis-
tilled water and mixed with a slight excess of LiN(Tf)2.
These two consecutive steps led to the formation of pure
glutarylmonocholine/LiN(Tf)2 salt (12; [gmch][LiN(Tf)2]) as
a colorless viscous liquid in 73% overall yield (entry 1,
Table 1).
Table 2. Data representative of the properties of new lithium bis(trifluoromethyl-
sulfonyl)imide choline-based zwitterionic ionic liquids.
Entry Product Physical Water Tg
Tdecomp Viscosity Density Direct
[d]
state[a] content [8C][b] [8C][c] [Pas][d] [gcmꢀ3
]
conductivity
[Scmꢀ1
]
[d,e]
[%w/w]
1
2
12
13
liquid
liquid
0.25
0.23
ꢀ43 224
ꢀ34 172
3.56
12.27
1.4867
1.4487
8.66”10ꢀ5
3.30”10ꢀ5
To understand the influence of the leaving group, the
reaction was performed in the presence of choline propa-
noate (2d). Under similar conditions the esterification of
choline propanoate was also complete after 2 hours but
only about 50% of the acid was removed after this time
(entry 2, Table 1).
[a] Observed visual state at room temperature. [b] Determined as the onset tem-
perature in the heating mode (108Cminꢀ1). [c] Decomposition temperature is
the temperature at which exothermic or endothermic behavior initiated after
prolonged heating. [d] At 258C. [e] Conductivity independent of frequency.
Using choline acetate as substrate, this reaction was
then extended to three other anhydrides: 3-methylgluta-
ric (5), succinic (4), and maleic anhydride (6). Under the same
tion of an ester moiety is significant to obtain low Tg values,
conditions,
3-methylglutarylmonocholine/LiN(Tf)2
(13;
and is probably due to enhancement of motional freedom, as
previously reported for the ether moiety.[5c,13] As previously re-
ported for the imidazolium cation,[5d] the addition of lithium
salt to zwitterions results only in the observation of a glass
transition temperature. No crystallization temperature or melt-
ing temperature was detected for these compounds. Evalua-
tion of the thermal stability showed that [gmch][LiN(Tf)2] and
[mgmch][LiN(Tf)2] are thermally stable up to 224 and 1728C, re-
spectively (see the Supporting Information). These decomposi-
tion temperatures are significantly lower than those observed
for similar imidazolium compounds.[5c]
[mgmch][LiN(Tf)2]) was obtained as a pale yellow viscous liquid
in 74% yield (entry 3, Table 1). The other two zwitterionic ionic
liquids (11 and 14) were found to be extremely delicate, with
ester bond cleavage occurring during the purification/drying
steps (entries 4 and 5, Table 1). Maleylmonocholine (14) with
its rigid chain and oriented carboxylate group was extensively
degraded, whereas succinylmonocholine (11) with a flexible
chain revealed less degradation. An intramolecular attack of
the carboxylate group to the ester group, and formation of
a stable five-membered ring is the most probable mechanism
for cleavage of the ester bond.[12]
The conductivity measurements, displayed in Figure 1, re-
vealed two distinct regions: the region of the electrode polari-
zation on the low frequency side, and the region where a pla-
teau is observed on the high frequency side. In the latter one,
the conductivity is independent of frequency, that is, the direct
conductivity.[14] The direct conductivity measurements at 258C
showed that [gmch][LiN(Tf)2] (12) and [mgmch][LiN(Tf)2] (13)
present an ionic conductivity of 8.66”10ꢀ5 and 3.30”
10ꢀ5 Scmꢀ1, respectively. The higher conductivity of [gmch]-
[LiN(Tf)2] should be mainly attributed to the lowest Tg between
the two compounds. The direct conductivity measurements at
different temperatures were extended for [gmch][LiN(Tf)2]
On the other hand, the ZILs [gmch][LiN(Tf)2] and [mgmch]-
[LiN(Tf)2] seem to be more stable, and no ester cleavage or
color degradation was observed even after six months of stor-
age at room temperature. In addition, during this period these
zwitterionic ionic liquids maintained a liquid state and no dis-
sociation was observed.
The second synthetic route (Scheme 3, route II) arose from
the fact that route I is dependent on the zwitterions carboxylic
acid pKa values. With this in mind, a protocol for the synthesis
of choline hydrogen carbonate (2e) from the reaction of dime-
thylaminoethanol (15) and dimethylcarbonate was developed.
Because the hydrogen carbonate anion is essentially non-nu-
cleophilic, this choline compound could also be esterified with
anhydrides to prepare halogen-free zwitterions, CO2 and water
being the only by-products. Following the previous strategy,
this reaction was performed to synthesize [gmch][LiN(Tf)2] (12)
and [mgmch][LiN(Tf)2] (13), which were obtained as viscous liq-
uids in 67% and 63% overall yields, respectively (entries 6 and
7, Table 1).
The structure of the compounds obtained by the two meth-
1
ods was confirmed by H and 13C NMR spectroscopy and ele-
mental analysis, after which they were characterized by differ-
ential scanning calorimetry (DSC), and their viscosities, densi-
ties, and conductivities measured (Table 2).
The DSC diagrams of the zwitterionic ionic liquids on their
second heating trace (108Cminꢀ1) showed that [gmch][LiN(Tf)2]
exhibits the lowest glass transition temperature (Tg) value of
the two compounds, with a Tg of ꢀ438C, whereas [mgmch]-
[LiN(Tf)2] showed a Tg value of ꢀ348C (see the Supporting In-
formation). These results seem to indicate that the introduc-
Figure 1. Ionic conductivity as a function of frequency for [gmch][LiN(Tf)2]
(12) at temperatures between 0 and 1008C (*), and for [mgmch] [LiN(Tf)2]
(13) at 258C (~).
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Ionic Liquids
(Figure 1). At 808C a conductivity of 1.45”10ꢀ3 Scmꢀ1 was ob-
tained for [gmch][LiN(Tf)2]. Pleasingly, these conductivities are
about one fold higher than the ones reported so far for ZIL
based on imidazolium salts.[5c] Furthermore, the viscosity of
[gmch][LiN(Tf)2] is three times lower than that of [mgmch]-
[LiN(Tf)2] (3.56 and 12.27 Pas, respectively).
Table 3. Parameters for the VFT equation of ionic conductivity data.
Product
s
[Scmꢀ1
]
B [K]
T0 [K]
1
12
0.268ꢁ0.048
837ꢁ45
194ꢁ3
These results seem to be in line with the study of Tokuda
et al.[15] that relates the behavior of the transport properties,
viscosity, and diffusion to a ratio of ionic conductivities, which
can be interpreted as a measure of ionic dissociation. These
authors observed that the ionic dissociation is directly related
to the diffusion coefficient, and inversely related to the viscosi-
ty, and they attribute this to a preponderance of the effect of
the Van der Waals interactions over electrostatic terms. In addi-
tion, for these compounds we have observed that the viscosity
remains constant with increasing shear rates (from 0 to
1000 s). This linear relationship between the shear stress and
the shear rate indicates that these compounds present a New-
tonian behavior (see the Supporting Information).
parameters with the ones associated with the imidazolium
ionic liquids,[15, 17] the value of s is significantly lower, mean-
1
ing that zwitterion has its lowest conductivity in the high tem-
perature limit. Regarding the B value it is possible to conclude
that the temperature dependence of zwitterion conductivity
exhibits a relatively higher curvature, meaning that its conduc-
tivity changes more with the temperature while approaching
the glass transition temperature (Tg). Concerning the value of
T0, it is possible to observe that it is in the same order of mag-
nitude.
In terms of density [gmch][LiN(Tf)2] and [mgmch][LiN(Tf)2]
showed very similar values, 1.4867 and 1.4487 gcmꢀ3 at 258C,
respectively (see the Supporting Information).
Conclusion
To conclude, two synthetic routes for the preparation of zwit-
terionic choline-based salts containing a carboxylate group
were reported. In addition, one of the synthetic routes was de-
veloped as a halogen-free strategy. The addition of lithium
salts, such as LiN(Tf)2 to the zwitterionic salts produces room-
temperature ionic liquids with low Tg values (ꢀ34 to ꢀ438C).
Besides high viscosities (3.56–12.27 Pas) the zwitterionic com-
pounds showed high ionic conductivity between 3.30”10ꢀ5
and 8.66”10ꢀ5 Scmꢀ1 at 258C and up to 1.80”10ꢀ3 Scmꢀ1 at
908C. These compounds maintained a liquid state and no dis-
sociation was observed even after six months of storage at
room temperature. These encouraging results indicate that
choline carboxylate zwitterionic ionic liquids are good candi-
dates to be applied as matrixes for electrochemical applica-
tions.
Another important aspect of the characterization of poten-
tial electrolytes is the illustration of the ionic conductivity as
a function of the inverse of temperature. Since liquid electro-
lytes do not obey Arrhenius behavior above the glass transi-
tion temperature, a similar behavior should be expected. In
fact, this behavior was observed for the tested compound,
[gmch][LiN(Tf)2] (12). One of the most common empirical
forms used to describe ion transport in these systems is ex-
pressed by the Vogel–Fulcher–Tamman (VFT) equation.[16] The
best fitting result is represented as the solid line in Figure 2,
where we can conclude that the temperature dependence of
the ionic conductivity for this compound (12) obeyed the VFT
equation quite well. These results show that the ionic conduc-
tivity increases with increasing temperature, probably owing
to the increase of the ionic dissociation and decrease of the
viscosity at higher temperatures. The fitting parameters s , B,
1
Experimental Section
and T0 for the VFT equation are described in Table 3.
Besides the zwitterionic ionic liquids reported in the litera-
ture, to the best of our knowledge, there is no published data
concerning these parameters. However, if we compare these
General methods
All reagents and solvents were obtained commercially, unless oth-
erwise noted, and appropriately purified, if necessary. The H and
1
13C NMR spectra were recorded at room temperature on a Bruker
AVANCE II 400 MHz NMR spectrometer, using [D6]DMSO as solvent
and the residual solvent peak as reference. Water content of all
ionic liquids was measured by Karl Fisher titration with a Methrom
831 KF coulometer. Elemental analyses and DSC measurements
were conducted by REQUIMTE-DQ-FCT (Portugal) and carried out
with a Thermo Finnigan Flash EA 111 and Setaram DSC 131 calo-
rimeter at a scanning rate of 108Cminꢀ1, respectively. Viscosity
measurements were performed on a Bohlin Gemini HRnano Rota-
tional reometer. Density measurements were carried out with an
Anton Paar DMA5000 density meter. The conductivity measure-
ments were performed using dielectric relaxation spectroscopy.
Two silica spacers of 0.05 mm thickness were used. The samples
were placed between two stainless-steel plated electrodes (10 mm
diameter) in a parallel plate capacitor, BDS 1200. The sample cell
was mounted on a cryostat, BDS 1100, and exposed to a heated
Figure 2. Ionic conductivity as a function of the inverse temperature for
[gmch][LiN(Tf)2] (12).
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N. M. T. LourenÅo et al.
gas stream being evaporated from liquid nitrogen in a Dewar. The
temperature control was assured by the Quatro Cryosystem and
performed within ꢁ0.5 K (all modules supplied by Novocontrol).
Measurements were carried out using an Alpha-N analyzer also
from Novocontrol GmbH, covering a frequency range from 10–
1 Hz to 1 MHz.
washed 2–3 times with distilled water (0.5 mL). Finally the ionic
liquid was dried in vacuo at RT for at least 48 h.
Succinylmonocholine lithium bis(trifluoromethylsulfonyl)imide
(11): From choline acetate 2c (0.325 g, 2 mmol) and freshly subli-
mated succinic anhydride 3 (0.400 g, 4 mmol). This mixture was
heated at 1458C in vacuo (0.5 mbar) for 4 h. Following the general
procedure, the desired product was obtained with purity never
above 90% owing to partial cleavage of the ester bond during the
purification/drying steps.
General procedure for the synthesis of choline alkanoates
2c and 2d
Glutarylmonocholine lithium bis(trifluoromethylsulfonyl)imide
(12): From choline acetate 2c (0.324 g, 2 mmol) and glutaric anhy-
dride 4 (0.346 g, 3 mmol). This mixture was heated at 758C in va-
cuo (0.5 mbar) for 2 h. Following the general procedure, the de-
sired product was obtained as a colorless viscous liquid (0.73 g,
73%; water content (% w/w): 0.43).
Choline chloride 2b (1.047 g, 7.5 mmol) dissolved in methanol
(75 mL) was slowly passed through a column filled with resin AM-
BERLITE IRA-400(OH) (12.5 g). The dripping choline hydroxide solu-
tion was collected in an Erlenmeyer flask containing a slight excess
of the desired carboxylic acid dissolved in methanol. The resulting
solution was passed through a small column filled with Celite 577,
activated basic aluminum oxide, and silica-gel, for removal of un-
reacted carboxylic acid and visible particles. After solvent removal
by evaporation under reduced pressure, the resulting product was
dried in vacuo at 508C overnight.
From choline hydrogen carbonate 2e (0.357 g, 2 mmol) and gluta-
ric anhydride 4 (0.463 g, 4 mmol). This mixture was heated at 758C
in vacuo (0.5 mbar) for 3 h. Following the general procedure, the
desired product was obtained as a colorless viscous liquid (0.68 g,
1
67%; water content (% w/w): 0.25). H NMR (400 MHz, 258C): d=
Choline acetate 2c: From acetic acid (0.430 mL, 7.5 mmol), com-
pound 2c was obtained as a white to pale yellow hygroscopic
4.44 (m, 2H), 3.75 (m, 2H), 3.11 (s, 9H), 2.38 (t, 2H), 2.26 (t, 2H),
1.76 ppm (m, 2H); 13C NMR (100 MHz, 258C): d=174.1, 172.0, 119.5
(q), 63.8, 57.8, 52.9, 32.8, 32.6, 19.8 ppm; elemental analysis calcd
(%) for C12H19F6LiN2O8S2: C 28.58, H 3.80, N 5.55; found: C 28.26,
H 3.80, N 5.38.
1
solid (1.06 g, 86%). H NMR (400 MHz, 258C): d=3.83 (m, 2H), 3.42
(m, 2H), 3.13 (s, 9H), 1.58 ppm (s, 3H); 13C NMR (100 MHz, 258C):
d=173.6, 67.3, 54.8, 53.0, 25.7 ppm.
Choline propanoate 2d: From propionic acid (0.560 mL,
7.5 mmol), compound 2d was obtained as a yellow viscous liquid
3-methyglutarylmonocholine lithium bis(trifluoromethylsulfony-
l)imide (13): From choline acetate 2c (0.326 g, 2 mmol) and 3-
methylglutaric anhydride 5 (0.513 g, 4 mmol). This mixture was
heated at 808C in vacuo (0.5 mbar) for 4 h. Following the general
procedure, the desired product was obtained as a pale yellow vis-
cous liquid (0.76 g, 74%; water content (% w/w): 0.53).
1
(1.10 g, 84%). H NMR (400 MHz, 258C): d=3.84 (m, 2H), 3.43 (m,
2H), 3.13 (s, 9H), 1.83 (q, 2H), 0.88 ppm (t, 3H); 13C NMR (100 MHz,
258C): d=176.6, 67.4, 54.9, 53.1, 31.2, 11.4 ppm.
From choline hydrogen carbonate 2e (0.358 g, 2 mmol) and 3-
methylglutaric anhydride 5 (0.646 g, 5 mmol). This mixture was
heated at 808C in vacuo (0.5 mbar) for 8 h. Following the general
procedure, the desired product was obtained as a pale yellow vis-
cous liquid (0.65 g, 63%; water content (% w/w): 0.23). 1H NMR
(400 MHz, 258C): d=4.44 (m, 2H), 3.64 (m, 2H), 3.11 (s, 9H), 2.27
(m, 5H), 0.94 ppm (d, 3H); 13C NMR (100 MHz, 258C): d=173.6,
171.4, 119.5 (q), 63.7, 57.8, 52.9, 40.4, 40.0, 26.9, 19.5 ppm; elemen-
tal analysis calcd (%) for C13H21F6LiN2O8S2: C 30.12, H 4.08, N 5.40;
found: C 30.36, H 3.90, N 5.35.
Synthesis of choline hydrogen carbonate 2e
A mixture of dimethylaminoethanol (DMAE) (8.1 mL, 80 mmol), di-
methylcarbonate (DMC) (7.4 mL, 88 mmol), and methanol (5.5 mL)
was heated at 1208C in a Teflon-coated stainless-steel reactor
(90 mL) for 6 h. The crude mixture was diluted with methanol
(15 mL), mixed with an abundant amount of activated carbon, and
left under vigorous stirring for 24 h. After filtration of solids and re-
moval of unreacted materials and solvent by evaporation under re-
duced pressure, the product was dried in vacuo at RT until a pale
yellow solid was obtained. This solid was decolorized by stirring it
in a solution of acetonitrile/tetrahydrofuran (1:2) for 48 h, with re-
newal of the solution after 24 h. After filtration, the solid was dis-
solved in a minimum amount of ethanol and two equivalents of
distilled water were added. The reaction was stirred overnight at
RT, after which the solvent was removed by evaporation under re-
duced pressure. Choline hydrogen carbonate was obtained as
Maleylmonocholine lithium bis(trifluoromethylsulfonyl)imide
(14): From choline acetate 2c (0.335 g, 2 mmol) and maleic anhy-
dride 6 (0.401 g, 4 mmol). This mixture was heated at 808C in va-
cuo (0.5 mbar) for 3 h. Following the general procedure, extensive
cleavage of the ester bond occurred, and the desired product
could not be isolated.
1
a white to pale yellow hygroscopic powder (9.08 g, 69%). H NMR
(400 MHz, 258C): d=3.83 (m, 2H), 3.42 (m, 2H), 3.11 ppm (s, 9H);
13C NMR (100 MHz, 258C): d=159.4, 67.4, 55.4, 53.5 ppm.
Acknowledgements
We thank Fundażo para a CiÞncia e Tecnologia (POCI 2010) and
FEDER (SFRH/BD/47088/2008, SFRH/BPD/41175/2007 and SFRH/
BPD/41546/2007), PTDC/CTM/100244/2008, and Banco Espirito
Santo for financial support. We thank Carla Rodrigues for DSC
measurements and GonÅalo dos Reis for viscosity measurements.
General procedure for the synthesis of choline-based zwit-
terionic ionic liquids 11–14
A mixture of choline compound 2c–e (2 mmol) and anhydride 3–6
(from 3–5 mmol) was heated (from 75–1458C) in vacuo (0.5 mbar)
for 2–8 h. After cooling at RT, the crude product was dissolved in
distilled water (2 mL), mixed with lithium bis(trifluoromethylsulfo-
nyl)imide (2.2 mmol), and vigorously stirred at RT for at least 14 h.
Then the aqueous phase was removed and the ionic liquid phase
Keywords: anhydrides · choline · conductivity · ionic liquids ·
zwitterions
1110
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Ionic Liquids
[1] a) J. P. Hallett, T. Welton, Chem. Rev. 2011, 111, 3508; b) C. Austen Angell,
Y. Ansari, Z. F. Zhao, Faraday Discuss. 2012, 154, 9.
[2] IUPAC Compendium of Chemical Terminology, 2nd ed. (Eds.: A. D.
McNaught, A. Wilkinson), Blackwell Scientific Publications, Oxford, 1997.
[3] E. Quartarone, P. Mustarelli, Chem. Soc. Rev. 2011, 40, 2525.
[4] R. Devanathan, Energy Environ. Sci. 2008, 1, 101.
[13] M. Yoshizawa, H. Ohno, Chem. Lett. 2004, 33, 1594.
[14] A. Schçnhals, F. Kremer in Analysis of Dielectric Spectra, Broadband Die-
lectric Spectroscopy (Eds.: F. Kremer, A. Schçnhals), Springer-Verlag,
Berlin, 2003, Chapter 3.
[15] H. Tokuda, K. Hayamizu, K. Ishii, M. Susan, M. Watanabe, J. Phys. Chem. B
2005, 109, 6103.
[5] a) M. Yoshizawa, M. Hirao, K. Ito-Akita, H. Ohno, J. Mater. Chem. 2001,
11, 1057; b) M. Yoshizawa, H. Ohno, Chem. Commun. 2004, 1828; c) M.
Yoshizawa-Fujita, T. Tamura, Y. Takeoka, M. Rikukawa, Chem. Commun.
2011, 47, 2345; d) M. Yoshizawa, A. Narita, H. Ohno, Aust. J. Chem. 2004,
57, 139; e) D. Q. Nguyen, J. Hwang, J. S. Lee, H. Kim, H. Lee, M. Cheong,
B. Lee, H. S. Kim, Electrochem. Commun. 2007, 9, 109.
[6] Z. F. Fei, D. B. Zhao, T. J. Geldbach, R. Scopelliti, P. J. Dyson, Chem. Eur. J.
2004, 10, 4886.
[7] E. Lissner, W. F. de Souza, B. Ferrera, J. Dupont, ChemSusChem 2009, 2,
962.
[8] P. Nockemann, B. Thijs, S. Pittois, J. Thoen, C. Glorieux, K. Van Hecke, L.
Van Meervelt, B. Kirchner, K. Binnemans, J. Phys. Chem. B 2006, 110,
20978–20992.
[9] J. C. Y. Lin, C.-J. Huang, Y.-T. Lee, K.-M. Lee, I. J. B. Lin, J. Mater. Chem.
2011, 21, 8110.
[16] a) H. Vogel, Phys. Z. 1921, 22, 645; b) G. S. Fulcher, J. Am. Ceram. Soc.
1925, 8, 339; c) G. Tammann, W. Hesse, Z. Anorg. Allg. Chem. 1926, 156,
245.
[17] a) T. Carvalho, V. Augusto, A. R. Bras, N. M. T. Lourenco, C. A. M. Afonso,
S. Barreiros, N. T. Correia, P. Vidinha, E. J. Cabrita, C. J. Dias, M. Dionisio,
B. Roling, J. Phys. Chem. B 2012, 116, 2664; b) C. Krause, J. R. Sangoro, C.
Iacob, F. Kremer, J. Phys. Chem. B 2010, 114, 382; c) H. Tokuda, K. Haya-
mizu, K. Ishii, M. Susan, M. Watanabe, J. Phys. Chem. B 2004, 108, 16593;
d) H. Tokuda, K. Ishii, M. Susan, S. Tsuzuki, K. Hayamizu, M. Watanabe, J.
Phys. Chem. B 2006, 110, 2833; e) J. Leys, M. Wübbenhorst, C. P. Menon,
R. Rajesh, J. Thoen, C. Glorieux, P. Nockemann, B. Thijs, K. Binnemans, S.
Longuemart, J. Chem. Phys. 2008, 128, 064509.
[18] By following the general procedure, extensive cleavage of the ester
bond occurred and the desired product could not be isolated.
[10] A. P. Phillips, J. Am. Chem. Soc. 1953, 75, 4725.
Received: September 19, 2012
[11] Y. Fukaya, Y. Iizuka, K. Sekikawa, H. Ohno, Green Chem. 2007, 9, 1155.
[12] F. C. Lightstone, T. C. Bruice, J. Am. Chem. Soc. 1996, 118, 2595.
Published online on November 19, 2012
ChemPlusChem 2012, 77, 1106 – 1111
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