Water effect on physicochemical properties of 1-butyl-3-methylimidazolium based ionic liquids with inorganic anions

Article abstract of DOI:10.1016/j.molliq.2012.10.023

Room temperature ionic liquids of 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF₄], nitrate, [NO₃] ^-, phosphate, [PO₄]^{3 -}, and hydrogen sulfate, [HSO₄]^-, have been synthesized and characterized by ¹H-NMR, ¹³C-NMR, mass spectrometry and IR spectroscopy methods. The effect of nature of inorganic anion on hygroscopic property has been studied. Physicochemical properties such as density, viscosity, melting point, freezing point, glass transition, thermal decomposition temperature and specific electrical conductivity have been determined. The influence of temperature and water concentration on density, viscosity and specific electrical conductivity values has been investigated. The dependence of physicochemical properties against anion nature and water content has been explained according to cation-anion interactions. The anomalous behaviors of density or conductivity values for equimolecular aqueous solutions of 1-butyl-3-methylimidazolium hydrogen sulfate or tetrafluoroborate ionic liquids have been found and associated with significant restructuring. The formation of crystalline hydrates of the composition of [bmim][BF₄]x0.5H ₂O was observed.

Full text of DOI:10.1016/j.molliq.2012.10.023

Journal of Molecular Liquids 177 (2013) 267–272
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Water effect on physicochemical properties of 1-butyl-3-methylimidazolium based
ionic liquids with inorganic anions
⁎
E.P. Grishina, L.M. Ramenskaya , M.S. Gruzdev, O.V. Kraeva
G.A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences (ISC RAS), Akademicheskaya St., 1, Ivanovo 153045, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2012
Received in revised form 5 October 2012
Accepted 16 October 2012
Available online 31 October 2012
Room temperature ionic liquids of 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF4], nitrate,
[NO3]−, phosphate, [PO4]3−, and hydrogen sulfate, [HSO4]−, have been synthesized and characterized by
1H-NMR, 13C-NMR, mass spectrometry and IR spectroscopy methods. The effect of nature of inorganic
anion on hygroscopic property has been studied. Physicochemical properties such as density, viscosity,
melting point, freezing point, glass transition, thermal decomposition temperature and specific electrical
conductivity have been determined. The influence of temperature and water concentration on density, vis-
cosity and specific electrical conductivity values has been investigated. The dependence of physicochemical
properties against anion nature and water content has been explained according to cation–anion interac-
tions. The anomalous behaviors of density or conductivity values for equimolecular aqueous solutions of
1-butyl-3-methylimidazolium hydrogen sulfate or tetrafluoroborate ionic liquids have been found and as-
sociated with significant restructuring. The formation of crystalline hydrates of the composition of [bmim]
[BF4]x0.5H2O was observed.
Keywords:
1-Butyl-3-methylimidazolium based ionic
liquids
Physicochemical properties
Hydrogen interactions
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
stronger effect on physical properties especially hydrophilic ILs [5].
The water occurrence causes on reduction for instance a viscosity
In the middle of the 1990s first reports on syntheses and applications
in organic catalysis of the air stable room temperature ionic liquids
(RTILs) corresponded salts of 1-butyl-3-methylimidazolium cation and
some inorganical anions were reported [1–3]. 1,3-Dialkylimidazolium
salts are one of the most popular classes of ionic liquids (ILs). Associated
with halide ([Cl]−, [Br]−, [I]−), tetrafluoroborate ([BF4]−), hexafluoro-
phosphate ([PF6]−), bis(trifluoromethylsulfonyl)imide ([Tf2N]−) and
other anions these ILs are compounds with unique properties such as
large temperature range of liquid state, high thermal stability and density,
relatively low viscosity and volatility, and large electrical conductivity.
Therefore, imidazolium based ionic liquids are applied as alternative sol-
vents or mediums for organic synthesis, low temperature extractions,
electrochemical processes and devices.
One impediment to the use of ILs is the shortage of reliable phys-
ical property data for these interesting materials differing signifi-
cantly from usual molecular organic or inorganic solvents. The
physicochemical properties of 1,3-dialkylimidazolium based ionic
liquids depend on nature of anion, alkyl substitutes of cation and
water content. The anion identity was shown to be of foremost im-
portance for the key properties of hygroscopicity, density, viscosity,
surface tension, melting point and thermal stability of some hydro-
philic and hydrophobic 1-alkyl-3-methylimidazolium ILs [4]. At the
same time the water being omnipresent of ionic liquids has a much
[6]. The similar water implication was expected to exist for some
other physical properties such as the electrolytic conductivity [7].
Cammarata et al. [8] showed that in the range of 0.2–1.0 mol⋅dm−3
water molecules are present mostly in the ‘free’ state and bound via
H-bonding with the anion of ionic liquid, including those with [BF4]−
and [PF6]− anions. In ILs with anions of stronger basicity such as
[NO3]− anion, water molecules can also form self-associated structures.
When these ILs are exposed to air, water concentrations exceed
1.0 mol·dm−3. It was found also that as in hydrophilic and in hydro-
phobic 1-alkyl-3-methylimidazolium ILs, water molecules tend to be
isolated from each other or exist in small independent clusters in mix-
tures with less ions than water molecules. When the molar proportion
of water molecules reaches 75%, a continuous network of water is
found as a predominated water structure which changes the mixture
and its properties dramatically [9]. It was found [10] that the phase
state of [bmim][Br] depend on the water content: if c(H2O)/wt.%=
0.64, it was only as a solid salt; if 1bc(H2O)/wt.% b6.5, it could exist
both in solid and in liquid state like subcooled melt; if c(H2O)/wt.%=
7, it was divided in two phases, notably transparent crystals of [bmim]
[Br]×0.5H2O composition and a [bmim][Br] fluid; if c(H2O)/wt.%>7–8
it corresponded only to homogeneous liquid.
We have been focused mainly on hydrophilic 1-butyl-3-
methylimidazolium ([bmim]+) based ionic liquids with tetrafluoroborate
[BF4]−, nitrate [NO3]−, phosphate [PO4]3− and hydrogen sulfate [HSO4]−
anions here. The data of investigated previously [bmim][Br] IL [10] has
been used for comparison. About physicochemical properties of [bmim]
⁎
Corresponding author. Tel.: +7 4932 336259; fax: +7 4932 336237.
E-mail address: lmr@isc-ras.ru (L.M. Ramenskaya).
0167-7322/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molliq.2012.10.023

268
E.P. Grishina et al. / Journal of Molecular Liquids 177 (2013) 267–272
[BF4], [PO4]3− and [NO3]− ILs were reported early [11–21]. However,
some of these are not quite complete, especially for [bmim][NO3],
[PO4]3− and [HSO4]− ionic liquids.
remaining extremely viscous oil was recrystallized from acetonitrile/
diethyl ether (1:5) to yield colorless crystals. Yield 7.75 g, 75%. Found,
%: С 39.31; H 7.43; N 11.86; S 13.16; O 28.23 С8Н16N2O4S. Calc. for %:
In this work [bmim][X] (X=[BF4]−, [NO3]−, [PO4]3− and [HSO4]−
)
С :
40.43; H 7.39; N 11.79; S 13.47; O 26.92. vmax(film)/cm−1
salts have been prepared and defined by NMR, chromatography-mass
spectrometry and IR spectroscopy methods. The ability of these ILs to
water absorption has been estimated. Physical–chemical characteristics
such as density (ρ), dynamic viscosity (η), melting point (Tm), freezing
point (Tc), glass transition (Tg), thermal decomposition temperature
(Td) and specific electrical conductivity (κ) have been determined.
Water and temperature influences on ρ and κ values have been studied.
3150–3108 (s., aromatic С-Н stretch); 2962–2875 (m., С-Н aliphatic
stretch); 1600–1480 (CN); 1466 (s., sym. ring stretch), 1171 (s., sym.
ring stretch), 1046 (s., NO3 stretch), 583 (s., SO4 stretch), 624 (amid
(III)). δН(250 MHz; D2O; Me4Si): 0.75 (3H, triplet, J 7.4, -CH3); 1.66
(2H, sextet,
J 7.3, CH3-СН2-(СН2)N); 1.68 (2H, quintet, J 7.4,
N-СН2-СН2); 3.73 (3H, singlet, N-СН3); 3.99 (1H, singlet, HSO4); 4.06
(2H, triplet, J 7.3, N-СН2-); 7.3 (2H, doublet, J 5.2, N-СН-СН-N); 8.53
(1H, singlet, N-С(Н)-N). δC(50.32 MHz; D2O; cyclohexanol): 13.31;
19.46; 31.96; 36.3; 49.93; 122.88; 124.16; 136.52. m/z: Calc. for М
2. Experimental
237; found 235 [М]+
.
2.1. The synthesis of ionic liquids
2.1.4. Tris-1-Butyl-3-methylimidazolium phosphate
2.1.1. 1-Butyl-3-methylimidazolium tetrafluoroborate
To solution of Ag3PO4 (8.16 g, 0.019 mol) in 85% H3PO4 solution in
water (60 cm3) was added dropwise to a cooled, rapidly stirring solu-
tion of 1-butyl-3-methylimidazolium bromide (12.81 g, 0.019 mol)
in water (30 cm3). The reaction mixture was stirred at room temper-
ature for 4 h. The resulting yellow precipitate of silver bromide was
removed by filtration. Water was removed under reduced pressure
at 110 °C. For neutralization of free H3PO4 product was dissolved in
ethanol and was titrated by KOH in ethanol. White precipitate was
removed by filtration on glass filter and solvent under reduced
pressure. The product was chromatographed on activated charcoal
column with dry ethanol. The solvent was removed by rotary evapo-
rator to give the phosphate salt as pale yellow extremely viscous oil.
Yield 8.73 g, 87%. vmax(film)/cm−1: 3154–3148 (s., aromatic С-Н
stretch); 2964–2876 (m., С-Н aliphatic stretch); 1600–1480 (CN);
1465 (s., sym. ring stretch), 1172 (s., sym. ring stretch), 937, 879 (s.,
PO4 stretch), 624 (amid (III)). δН(250 MHz; D2O; Me4Si): 0.95 (9H,
triplet, J 7.1, -CH3); 1.36 (6H, sextet, J 7.4, CH3-СН2-(СН2)N); 2.01
(6H, quintet, J 7.4, N-СН2-СН2); 3.98 (9H, singlet, N-СН3); 4.27 (6H,
triplet, J 7.3, N-СН2-); 7.14 (6H, doublet, J 7.2, N-СН-СН-N); 8.41
(1H, singlet, N-С(Н)-N). δC(50.32 MHz; D2O; cyclohexanol): 13.32;
19.38; 31.84; 36.32; 49.9; 122.84; 124.13; 136.26.
Tetrafluoroboric acid (32.8 cm3, 0.232 mol, 48% solution in water)
was added slowly to a rapidly stirred slurry of silver (I) oxide (29.1 g,
0.106 mol) in water (50 cm3) over 15 min. The reaction mixture was
stirred for further hour until all the silver (I) oxide had completely
reacted to give
a colourless solution. A solution of 1-butyl-3-
methylimidazolium bromide (48 g, 0.219 mol) in water (30 cm3)
was added to the reaction mixture and stirred at room temperature
for 2 h. The resulting yellow precipitate of silver bromide was
removed by filtration and the solvent removed by rotary evaporator.
After ionic liquid was passed through a short SiO2 column with
acetonitrile: chloroform, the solvents were removed by rotary evapo-
rator to give the tetrafluoroborate salt as pale yellow liquid, which
was dried in vacuo for ca. 24 h. Yield 43.2 g, 87%. vmax(film)/cm−1
:
3162–3122 (s., aromatic С-Н stretch); 2964–2877 (m., С-Н aliphatic
stretch); 1600–1480 (CN); 1467 (s., sym. ring stretch), 1171 (s.,
sym. ring stretch), 1054 (br s., BF4 stretch), 624 (amid (III)).
δН(250 MHz; D2O; Me4Si): 0.97 (3H, triplet, J 7.4, -CH3); 1.39 (2H,
sextet, J 7.4, CH3-СН2-(СН2)N); 1.91 (2H, quintet, J 7.4, N-СН2-СН2);
3.83 (3H, singlet, N-СН3); 4.24 (2H, triplet, J 7.3, N-СН2-); 7.53 (2H,
doublet, J 1.8, N-СН-СН-N); 8.71 (1H, singlet, N-С(Н)-N). δC(50.32 MHz;
D2O; cyclohexanol): 13.27; 19.42; 31.95; 36.23; 49.92; 122.86; 124.15;
136.49.
The ionic liquids were kept in to the glove box and dried before
use in vacuo of 133 Pa and the temperature of 70 °C for ca. 24 h.
2.1.2. 1-Butyl-3-methylimidazolium nitrate
2.2. Methods and apparatus
To solution of 1-butyl-3-methylimidazolium bromide (16.31 g,
0.074 mol) in water (30 cm3) was added dropwise, rapidly stirring so-
lution of AgNO3 (12.65 g, 0.074 mol) in water (20 cm3) over 20 min
and stirred at room temperature for 2 h. The resulting yellow precipi-
tate of silver bromide was removed by filtration and the solvent re-
moved by rotary evaporator. The product was chromatographed on
activated charcoal column with dry ethanol. The solvent was removed
by rotary evaporator to give the nitrate salt as pale yellow liquid. Yield
12.28 g, 83%. vmax(film)/cm−1: 3147–3101 (s., aromatic С-Н stretch);
2962–2875 (m., С-Н aliphatic stretch); 1600–1480 (CN); 1465 (s.,
sym. ring stretch), 1169 (s., sym. ring stretch), 1344 (br s., NO3 stretch),
624 (amid (III)). δН(250 MHz; D2O; Me4Si): 0.78 (3H, triplet, J 7.3,
-CH3); 1.20 (2H, sextet, J 7.3, CH3-СН2-(СН2)N); 1.74 (2H, quintet, J
7.4, N-СН2-СН2); 3.82 (3H, singlet, N-СН3); 4.09 (2H, triplet, J 7.3,
N-СН2-); 7.35 (2H, doublet, J 5.09, N-СН-СН-N); 8.58 (1H, singlet,
N-С(Н)-N). δC(50.32 MHz; D2O; cyclohexanol): 13.23; 19.38; 31.9;
36.18; 49.88; 122.80; 124.06; 136.46.
The chromatograms and mass spectra were obtained on Saturn
2000R chromato-mass spectrometer, carrier gas helium. 1H and 13C
NMR spectra in D2O solution at 200.13 and 50.32 MHz respectively
were recorded on Bruker AC-200 NMR spectrometer. The sample was
placed in 5 mm NMR tube, degassed by three freeze–pump–thaw
cycles and sealed under vacuum. Cyclohexanol was used as external
reference. IR transmission spectra in the frequency range of 350–
4500 cm−1 were recorded on Avatar 360 FT-IR ESP spectrometer. Sam-
ples of RTIL as a KBr disk or a thin film placed between two KRS-5 ma-
terial plates were used.
The model LT-VO/20 vacuum oven of the attainable vacuum of
133 Pa was applied for drying of ionic liquids. The water content of
each of RTIL was determined by Karl–Fischer titrations conducted
with M906 micro ammeter. Each sample was at least 50 mg and du-
plicated measurements were performed on each sample with results
agreeing to within 5%. The quality of water absorbed from air by the IL
sample of mass near 65 mg was determined by gravimetrically accu-
rate to 0.01 mg.
2.1.3. 1-Butyl-3-methylimidazolium hydrogen sulfate
To solution of AgSO4 (4.08 g, 0.013 mol) in 40% H2SO4 solution in
water (20 cm3) was added dropwise to a cooled, rapidly stirring solu-
tion of 1-butyl-3-methylimidazolium bromide (4.05 g, 0.018 mol) in
ethanol (50 cm3). The reaction mixture was stirred at 50 °C for 2 h.
The resulting yellow precipitate of silver bromide was removed by fil-
tration and the solvents were removed by rotary evaporator. The
Thermal properties were analyzed by thermogravimetric (TG) and
differential scanning calorimetric (DSC) methods. The decomposition
temperature was obtained on a NETZCH TG 209 F1 analyzer as onset
gravimetric reduction point of TG curve. The sample inserted in a
platinum tingle was heated in argon flow with rate of 10 °C min−1
to terminal temperature of 1000 °C. The melting point, crystallization

E.P. Grishina et al. / Journal of Molecular Liquids 177 (2013) 267–272
269
0,20
point and glass transition temperature were decided on NETZCH DSC
401 F1calorimeter. Each sample approximately 10 mg in hermetically
sealed aluminum pan was cooled by liquid nitrogen to −110 °C and
heated then up to 100 °C with rate of 10 °C min−1. These measure-
ments were carried out under nitrogen atmosphere.
The density of as solid as liquid ILs was determined by gravimetric
analysis at 20, 40, 60 and 80 °C. The ethyl acetate was used as medium
for determination of density of solid samples by volumetric method.
Pycnometer volumes of 1, 2 and 5 cm3 were calibrated by distilled
water. The dynamic viscosity of some ILs was determined on a
BROOKFIELD DVII+Pro viscometer over the range of angular rotation
rates from 0.3 to 100 rpm. A special small-volume cell with a plate radi-
us and a gap between plates of 7.5 mm and 1 mm respectively was
used. All measurements were taken at (20 0.1 °C).
0,16
0,12
0,08
0,04
0,00
0
2
4
6
8
Exposition /days
The conductivity of ionic liquids melts was determined using an E7-20
immittance measuring instrument in hermetically closed temperature
controlled conductometric cell with smooth platinum electrodes. Mea-
surements were performed over the alternating current frequency
range f/kHz 1–20 using the procedure described in reference [22]. The
conductivity G was extrapolated to an infinite frequency in G–1/f coordi-
nates. The constant of the conductometric cell was determined using a
0.01 mol⋅dm−3 solution of KCl, whose electrical conductivity was com-
parable with that of the ionic liquid studied [23]. The temperature range
of measurements was varied from 20 to 80 °С. The accuracy of tempera-
ture remained as 0.1 °С.
Fig. 1. Amounts of the absorbed water per unit weight of ionic liquids, [bmim][X], ex-
posed to air at relative humidity 65%; [X]: [BF4]− (■), [HSO4]− (○), [PO4]3− (▼),
[NO3]− (▲) and [Br]− (●) [10].
that the water content in [bmim]+ ionic liquids (Fig. 1) also correlates
with the strength of those H-bonding interactions and follows the general
trend [PO4]3−b[HSO4]−≤[BF4]−b[Br]−≤[NO3]−
.
3.2. The density of ‘dried’ and watered ILs
Density values (ρ) of ‘dried’ [bmim][BF4], [HSO4]−, [PO4]3−, and
[NO3]− ILs have been determined at several temperatures, presented
in Table 1 and compared to literature data in Fig. 2. Density values
obtained in this paper are in a good agreement with literature data.
Some differences are explained generally by water as well as chloride
impurities. The residual water and chloride contents of referred ILs on
Fig. 2 were c(H2O)/ppm (c[Cl-]/ppm): 4530 [4], 336 (421) [17] and
1900 [20] for [bmim][BF4] and unreported for [PO4]3− and [NO3]− ILs.
Table 1 shows that ρ values of [bmim]+ ionic liquids with similar
water amount increased in the order [PO4]3−≈[HSO4]− >>[BF4]−
>[NO3]−. It means that the parking of [bmim]+ based ionic liquids
with [PO4]3− and [HSO4]− anions are more compact as compared with
[BF4]− and [NO3]− anions. It appears that a multiple charged [PO4]3−
anion provides a higher density due to strong Coulombic forces, although
the hydrogen bonding was shown to be the dominating force which de-
termines a packing of ions in crystal lattices of these ILs [24]. The hydro-
gen bonding between [bmim]+ cation with single charged [HSO4]−
anion is more preferred than with [BF4]− anion. The strongly directional
rather than purely electrostatic interaction of [HSO4]− anion with
1-butyl-2, 3-dimethylimidazolium cation was found [24]. Therefore, ap-
parently the strength of those H-bonding interaction was also increased
as [BF4]−b[HSO4]−. The [bmim][NO3] ionic liquid exhibits the lowest
density obviously since it contains the bond water as liquid-like associat-
ed aggregates in contrast to ‘free’ (not self-aggregated) water molecules
bonded via H-bonding with anions of another ILs [8].
3. Results and discussions
The series of hydrophilic 1-butyl-3-methylimidazolium [BF4]−
,
[NO3]−, [PO4]3− and [HSO4]− salts were prepared and dried under
the vacuum and their physical properties were determined. All of
ILs studied are completely water soluble at experiment conditions
(T>20 °C and the atmospheric pressure), and even after the drying
procedure still contained some water. The physicochemical proper-
ties and moisture contents (c) of ‘dried’ bmimX are presented in
Table 1. All of these ILs are liquids which did not crystallize on stand-
ing in a freezer (−15 °C), except [bmim][HSO4] IL. The [bmim][HSO4]
was crystallized rapidly after synthesis.
3.1. The water absorption
All of investigated ionic liquids absorbed the air moisture. The frac-
tional increase of water content in [bmim][BF4], [HSO4]−, [PO4]3− and
[NO3]− as well as [Br]− [10] ILs exposed to air at relative humidity 65%
are shown in Fig. 1. The maximum quantity of water absorbed by ionic
liquids was achieved after 24 h exposure to the atmosphere. The water
content of [bmim][BF4] IL at these conditions was about 68000 ppm as
compared with 19500 ppm obtained at relative humidity 59% by Tomida
et al. [17] (Karl-Fisher titration). Fig. 1 exhibited also that bmim+ ionic
liquids show a more pronounced uptake of water for [NO3]− anion. As
was demonstrated [21], under the same atmospheric conditions the
[bmim][NO3] IL is able to absorb about 10 mol% of the water during the
first 3 min. It was found [8] that the ability of water absorption from the
air by 1-alkyl-3-methylimidazolium ionic liquids arises from the water in-
teractions with anions by H-bonding increasing in the order [PF6]−
b[SbF6]−b[BF4]−b[ClO4]−b[CF3SO3]−b[NO3]−b[CF3CO2]−. It appears
The introduction of water molecules occurs with a disruption of the
hydrogen bond network of 1,3-dialkylimidazolium salts [25]. Density
values determined experimentally for aqueous solutions of [bmim]
[BF4], [HSO4]− and [Br]− [10] ILs in the range of 20–80 °C are presented
in Table 2 and Fig. 3. It appears that density values decrease as the tem-
perature and the water concentration increase. About c(H2O)/mol%=
45–50, the density of [bmim][HSO4] ionic liquid was decreased
Table 1
Physico-chemical properties of ‘drying’ 1-butyl-3-methylimidazolium ionic liquids, [bmim][X].
[X]
c(H2O)/wt.%
Tg/°C
Tc/°C
Tm/°C
Td/°C
ρ20/g cm−3
ηT/cP
κ20/mS sm-1
[BF4]−
0.21
0.83
0.24
0.33
−92.0
−96.8
−65.5
−71.3
–
–
430
285
330
140
1.19
1.12
1.32
1.33
13021
0.374
0.255
0.014
0.0055
[NO3]−[a]
[HSO4]−
[PO4]3−
−20.3
9.9
2.1
28.7
–
7322
157223.8
1146225.0
–
[a] η indicated at c(H2O)=1.75 wt.%.

270
E.P. Grishina et al. / Journal of Molecular Liquids 177 (2013) 267–272
1,5
1,4
1,3
1,2
1,1
1,0
10
20
30
40
50
60
70
80
Temperature /°C
Fig. 2. Densities of ‘dried’ [bmim][X] as a function of temperature and comparison with
literature values.4,17–20 [BF4]−: (■) this work, (+) [4], ( ) [17], (□) [20]; [NO3]−: (▲)
this work, (△)[18]; [PO4]3−: (▼) this work, (∇) [19] and [HSO4]−: (○) this work.
Fig. 3. Density (close symbol) and viscosity (open symbol) of aqueous solution of
[bmim][X] versus molar concentration of water at the temperature of 20 °C; X:
[HSO4]− (circles), [BF4]− (triangles), [NO3]− (rhombic) and [Br]− (squares).
considerably (Fig. 3). Apparently the structure of [bmim][HSO4] IL is
changed owing to formation of continuous water network found for
the same anion of 1,3-dialkylimidazolium ILs at high water concentra-
tion by molecular dynamic simulations [9].
[bmim][HSO4] and [bmim][Br] decrease dramatically as water con-
tent increase. After c(H2O)/mol%~50, the influence of the water on
viscosity begin more less. This phenomenon correlates with depen-
dence of ρ vs. mol % of [bmim][HSO4] (Fig. 3) and caused by reduction
of cation–anion interactions under the action of water molecules. The
viscosity of ionic liquids such as [bmim][BF4] and [bmim][NO3] as
compared with [bmim][HSO4] and [Br]− ILs decries negligible.
The η values of watered 1-butyl-3-methylimidazolium based ionic
liquids have been investigated in detail for [bmim][Br] in our research
[10]. At c(H2O)/wt.%>3.0, the [bmim][Br] IL appeared to exist as a
Newtonian liquid [26], for which the dynamic viscosity is indepen-
dent from the shear rate, but at c(H2O)/wt.% b1.8 it was like
superstructured fluids [26], for which the dynamic viscosity increases
with rate of shear. This indicate that the crystal-like structure exists
as in solid state as in subcooled melt of [bmim]+ based ionic liquids
by means of intramolecular and intermolecular cation–anion hydro-
gen bonds.
3.3. The dynamic viscosity
Dynamic viscosity values (η) of ‘dried’ ILs at ambient tempera-
tures are determined and presented in Table 1. As can see from
Table 1, the η magnitude of [bmim][NO3] is the lowest. This value is
in agreement with η45 =67 cP [6] determined by Seddon et al., but
different from η20 ~260 cP (taken from [17(a)]) indicated in the fol-
lowing publication by the same authors (water content is not
reported). The viscosity of [bmim][BF4] (Table 1) is in agreement
with magnitude of ηT/cP (c(H2O)/ppm) of 15420 (b200) [6], 13220
(336) [17(a)], but different from 21925 (4530) [4], 18025 (b50) [11],
104.920 (1.8–3.7 ppm) [17(b)], 153.780425 [17(c)] and 23320 [13].
The viscosities of [bmim][SO4] and [PO4]3− ILs (Table 1) are the
highest as compared with η values of another studied ionic liquids
with imidazolium cation, for instance, ηT/cP (c(H2O)/ppm): 111025
(1870) [4] for [bmim][I], 38220 (130) [17(a)] for [PF6]− and 6925
(474) [4] for [Tf2N]− ILs.
3.4. The thermodynamic parameters
The thermal parameters of ‘dried’ [bmim][X] obtained on heating
from TG – and DSC – traces are listed in Table 1. DSC curves on second
heating (solid line) and cooling (dash line) cycles are shown in Fig. 4.
All of investigated ILs displayed the glass transition temperature (Tg) in
the range −60 to −97 °C. On heating, two ionic liquids, [bmim][BF4]
and [bmim]3[PO4], displayed only glass formation events, and no other
phase transitions were observed as on heating as on cooling ways. There-
fore, these salts remain generally in liquid sate up to −70 °C, but become
increasingly viscous and turn finally into glasses. The DSC thermograms
for [bmim][NO3] and [HSO4]− ILs similar to [bmim][Br] IL [10] showed
also the broad first order peaks of crystallization (Tc), followed by a melt-
ing transition (Tm) on heating, but on cooling no any crystallization
events were observed. This is a kinetic phenomenon and promotes the
subcooled prior to crystallization. A subcooled state and a glasses forma-
tion were noted to be general characteristics of the ambient temperature
dialkylimidazolium ILs [4,12]. The [bmim][NO3] IL show Tm/°C 2.1 and
Tc/°C −20.3 and exist only as a fluid at ambient temperature.
Fig. 5 exhibits thermogravimetric analysis traces of [bmim][BF4],
[HSO4]−, [NO3]− and [PO4]3− ionic liquids. All of these ones show a
gradual some weight loss between 50 and 240–360 °C associated
with slow thermal degradation of the anion, followed by the main
catastrophic weight loss event associated with degradation of the cat-
ion [27]. The thermal decomposition temperatures of ILs (Td) are
presented in Table 1 as the onset of the main weight loss, determined
from step tangent as demonstrated [20].
From the above data, the viscosity of ionic liquids strongly depend
on water content. The effect of water on the dynamic viscosity of ILs is
shown in Fig. 3. The viscosities of more viscous ionic liquids such as
Table 2
Densities, ρ of aqueous solutions of [bmim][BF4] and [bmim][HSO4] ionic liquids, c is a
total water content.
c(H2O)/wt.%
ρ/g⋅cm−3
20 °C
40 °C
60 °C
80 °C
[bmim][BF4]
0.80
1.80
2.17
3.13
4.15
5.45
6.42
7.30
1.183
1.178
1.177
1.175
1.173
1.172
1.169
1.167
1.163
1.160
1.170
1.166
1.165
1.161
1.158
1.151
1.146
1.143
1.138
1.135
1.158
1.157
1.155
1.149
1.147
1.135
1.130
1.126
1.122
1.119
1.149
1.147
1.144
1.139
1.137
1.119
1.115
1.112
1.108
1.105
9.10
10.15
[bmim][HSO4]
2.41
4.56
6.03
7.72
1.318
1.316
1.313
1.300
1.237
1.226
1.316
1.314
1.312
1.295
1.230
1.220
1.314
1.313
1.310
1.289
1.222
1.213
1.312
1.311
1.308
1.278
1.219
1.203
8.52
11.02
As appeared, in the temperature region between 50 °C and Td
(Fig. 5), there was a weight loss about 8 wt.% for [bmim][BF4] and

E.P. Grishina et al. / Journal of Molecular Liquids 177 (2013) 267–272
271
[BF4]− >[HSO4]− >[NO3]−, generally according to tendency of the
water absorption.
3.5. The conductivity of watered ionic liquids
The conductivity is an important property of liquid-phase mate-
rials and depends on associate and dissociate reactions that occurred
in these systems. In the review [30], the dependence of specific
conductivity against concentration for aqueous solutions of some N,
N′-dialkylimidazolium based ionic liquids with [Cl]−, [Br]− and
[BF4]− anions was shown. Dependences of (κ – c) have the curve
form like for solutions of salts, and the maximum of the electrical
conductivity was observed at 0.1–0.25 mol fraction of IL. At higher
IL contents, the conductivity of IL – H2O systems increases as the
water content increase.
The water of the binary [bmim][Br] – H2O system is an active com-
ponent and interacts with salt. Near to c(H2O)/mol% 50 as demon-
strated [31], there were maximums on (κ – cH2O) or (κ η – cH2O)
curves apparently because of the following change of the structure:
ð½bmimꢀ½Brꢀ; cðH2OÞ=mol% < 50Þmelt↔ð½bmimꢀ½Brꢀ; cðH2OÞ=mol% > 50Þsolution
:
At same time we observed the formation of large, cubic and trans-
parent crystals of [bmim][Br]×0.5H2O composition. This composition
has been determined by Fisher method and conformed also by litera-
ture data [9], about that the single water molecule can interact with
only two halide anions.
Specific conductivity isotherms of aqueous solution of [bmim]
[HSO4] and [bmim][BF4] ILs are shown on Figs. 6 and 7. At all concen-
tration range of the first of them (Fig. 6), the κ value increases
exponentially as the water content increases similar to some of
dialkylimidazolium salts [30]. Whereas, of the second (Fig. 7), there
are maximums near to c(H2O)/mol 0.5 similar to [bmim][Br] – H2O
system. It is clear, that unlike to [bmim][HSO4], the watered [bmim]
[BF4] IL can form crystalline hydrates of composition of [bmim]
[BF4]×0.5H2O. The photo of this crystal (x100 multiplications) is
shown in Fig. 8.
The temperature influence on specific conductivities of ILs is shown
by Fig. 9. The [bmim][BF4] and [NO3]− ILs with low viscosity (1 and 2
curves) exhibit the linear behavior of lgκ against the reverse tempera-
ture (T−1), whereas [bmim][HSO4] and [PO4]3− ILs with higher viscos-
ity (3 and 4 curves) exhibit the deviation from linearity.
Fig. 4. DSC curves on second heating (solid line) and cooling (dash line) cycles for
‘dried’ [bmim][X].
[NO3]− ILs on account of decomposition of unstable anions. This behav-
ior is typical of ionic liquids with fluorinated anions [28] such as [BF4]−
,
which undergo hydrolysis reactions [29]. The start of weight loss of
[bmim]3[PO4] occurred well before the onset of the main weight loss.
Therefore, we indicated the Td value as 140 °C (Table 1) as compared
with 107 °C determined by Bagienski and Wishart [19]. Before the Td
value, the [bmim][HSO4] salt displays mass loss about 1.5 wt.% and cor-
responds to more stable ILs for series of investigated [bmim]+ based ILs.
Fig. 5 shows that only [bmim][BF4] IL combusted as scale-free. The de-
composition products of [bmim][NO3], [PO4]3− and [HSO4]− ILs obvi-
ously reacted with aluminum pan resulted with scale residues about
40 wt.% at 800 °C.
4. Conclusion
As follows from Table 1, the thermal stability order of [bmim]+
contained salts with singly charged anions can be summarized as
1-Butyl-3-methylimidazolium based ionic liquids with [BF4]−, [NO3]−
,
[PO4]3− and [HSO4]− anions have been synthesized and their physico-
chemical properties have been determined at several temperatures and
100
80
60
40
20
0
0
200
400
600
800
Temperature /°C
Fig. 5. Thermogravimetric traces for [bmim][X]; [X]: [HSO4]− (○), [NO3]− (■), [BF4]−
(▲) and [PO4]3− (▼).
Fig. 6. Specific conductivity isotherms of the [bmim][HSO4]–H2O binary system as
function of temperature and water content. T/°C: 20 (■), 40 (●), 60 (▲), 80 (▼).

272
E.P. Grishina et al. / Journal of Molecular Liquids 177 (2013) 267–272
Fig. 9. Specific conductivity values of watered [bmim][X] ionic liquids with c(H2O)/mol% in
Arrhenius plot. [X]: [BF4]− (■), [NO3]− (▲), [HSO4]− (●) and [PO4]3− (▼).
Fig. 7. Specific conductivity isotherms of the [bmim][BF4]–H2O binary system as func-
tion of temperature and water content. T/°C: 20 (■), 40 (●), 60 (▲), 80 (▼).
References
[1] Y. Chauvin, L. Mussmann, H. Oliver, Angewandte Chemie (International Ed. in En-
glish) 34 (1996) 2698–2700.
[2] P. Bonhŏte, A.P. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Grätzel, Inorganic
water contents. Some of these properties were determined for the
first time. The comparison of parameters such as hygroscopicity,
density, viscosity, thermostability and conductivity has shown that
the anion nature has an effect on their properties and correlated
with ability to form H-bonds. Ionic liquids are considerably struc-
tured owing to extensive system of hydrogen bonds. The water
molecules compete with anions to contact with hydrogen atoms of
imidazolium cation, resulting in the disruption of the structure of
ionic liquids. In aqueous solutions of ionic liquids, when concentra-
tion of the water is close to 50 mol%, the density of [bmim][HSO4]
IL decreases considerably from 1.313 to 1.237 g⋅cm−3, and the con-
ductivity of [bmim][BF4] IL exhibits the local maximum. In equimolar
water solution, the crystalline hydrates of composition of [bmim]
[BF4]×0.5H2O can be observed.
Chemistry 35 (1996) 1168–1178.
[3] P.A.Z. Suarez, J.E.L. Dullius, S. Einloft, R.F. deSouza, J. Dupont, Polyhedron 15
(1996) 1217–1219.
[4] J.G. Huddleston, A.E. Visser, W.M. Reichert, H.D. Willauer, G.A. Broker, R.D. Rogers,
Green Chemistry 3 (2001) 156–164.
[5] P. Wasserheid, T. Welton, Ionic liquids in synthesis, Wiley-VCH Verlag, Weinheim,
2003.
[6] K.R. Seddon, A. Stark, M.-J. Torres, Pure and Applied Chemistry 72 (2000) 2275–2287.
[7] J.A. Widegren, A. Laesecke, J.W. Magee, Chemical Communications (2005) 1610–1612.
[8] L. Cammarata, S.G. Kazarin, P.A. Salter, T. Welton, Physical Chemistry Chemical
Physics 3 (2001) 5192–5200.
[9] C.G. Hanke, R.M. Lynden-Bell, The Journal of Physical Chemistry. B 107 (2003)
10873–10878.
[10] L.M. Ramenskaya, E.P. Grishina, A.M. Pimenova, M.S. Gruzdev, Russian Journal of
Physical Chemistry A 82 (2008) 1098–1103.
[11] T. Nishida, Y. Tashiro, M. Yamamoto, Journal of Fluorine Chemistry 120 (2003) 135–141.
[12] J.D. Holbrey, K.R. Seddon, Journal of the Chemical Society Dalton Transactions
(1999) 2133–2139.
[13] S. Carda-Broch, A. Berthod, D.W. Armstrong, Analytical and Bioanalytical Chemis-
try 375 (2003) 191–199.
[14] H. Olivier-Bourbigou, L. Magna, Journal of Molecular Catalysis A: Chemical
182–183 (2002) 419–437.
Acknowledgements
[15] P.A.Z. Suarez, V.M. Selbach, J.E.L. Dullius, S. Einloft, C.M.S. Piatnicki, D.S. Azambuja,
R.F. de Souza, J. Dupont, Electrochimica Acta 42 (1997) 2533–2535.
[16] R. Hagiwara, Y.J. Ito, Journal of Fluorine Chemistry 105 (2000) 221–227.
[17] (a) D. Tomida, A. Kumagai, K. Qiao, C. Yokoyama, International Journal of
Thermophysics 27 (2006) 39–47;
This work was supported by Russian Academy of Sciences. We
thank Dr. N.G. Manin, Dr. V.P. Barannikov and Dr. C.C Guseinov for
DSC and TG measurements.
(b) Luís C. Branco, Joăo N. Rosa, Joaquim J. Moura Ramos, Carlos A.M. Afonso,
Chemistry A European Journal 16 (2002) 3671–3677;
(c) W. Liu, T. Zhao, Y. Zhang, H. Wang, M. Yu, Journal of Solution Chemistry 35 (2006)
1337–1346.
[18] M.D. Bermejo, M. Montero, E. Saez, L.J. Florusse, A.J. Kotlewska, M.J. Cocero, F. van
Rantwijk, C.J. Peters, The Journal of Physical Chemistry. B 112 (2008) 13532–13541.
[19] http://www.scied.science.doe.gov/scied/Abstracts2008/chem.htm.
[20] C.P. Fredlake, J.M. Crosthwaite, D.G. Hert, N.V.K. Aki, J.F. Brennecke, Journal of
Chemical & Engineering Data 49 (2004) 954–964.
[21] A.A. Strechan, A.G. Kabo, Y.U. Paulechka, A.V. Blokhin, G.J. Kabo, A.S. Shaplov, E.I.
Lozinskaya, Thermochimica Acta 474 (2008) 25–31.
[22] B.A. Lopatin, Teoreticheskie osnovy elektrokhimicheskikh metodov analiza,
Vysshaya shkola, Moskva, 1975.
[23] K.W. Pratt, W.F. Koch, Y.C. Wu, P.A. Berezansky, Pure and Applied Chemistry 73
(2001) 1783–1793.
[24] P. Kölle, R. Dronskowski, Inorganic Chemistry 43 (2004) 2803–2809.
[25] J. Dupont, Journal of the Brazilian Chemical Society 15 (2004) 341–350.
[26] T.G. Mezger, Rheology handbook: for users of rotational and oscillatory rheome-
ters, second ed. Vincenttz Network, Hannover, 2006.
[27] J.D. Holbrey, W.M. Reichert, R.P. Swatllski, G.A. Broker, W.R. Pitner, K.R. Seddon,
R.D. Rogers, Green Chemistry 4 (2002) 407–413.
[28] K. Goossens, K. Lava, P. Nockemann, K. Van Hecke, L. Van Meervelt, K. Driesen, C.
Görller-Walrand, K. Binnemans, T. Cardinaels, Chemistry A European Journal 15
(2009) 656–674.
[29] R.P. Swatloski, J.D. Holbrey, R.D. Rogers, Green Chemistry 5 (2003) 361–363.
[30] O. Cabeza, S. García-Garabal, L. Segade, M. Domínguez-Pérez, E. Rilo, in: A.
Kokorin (Ed.), Ionic Liquids: Theory, Properties, New Approaches, INTECH,
Zagreb, 2011, pp. 111–136.
[31] E.P. Grishina, A.M. Pimenova, L.M. Ramenskaya, O.V. Kraeva, Russian Journal of
Electrochemistry 44 (2008) 1257–1262.
Fig. 8. Photo (X100) of the crystal of [bmim][BF4]×0.5H2O.