Preparation of 1-butyl-3-methylimidazolium salts and study of their phase behavior and intramolecular intractions

Article abstract of DOI:10.1134/S1070363209080246

Seven organic salts of 1-butyl-3-methylimidazolium with anions Br ^-, BF₄^-, NO₃^-, SO ₄^2-, HSO₄^-, SCN^-, PO ₄^3- were prepared. Structure of these compounds is elucidated and purity is confirmed. The products are characterized by melting point, thin layer chromatography, data of elemental analysis, cromatomass-, NMR and IR spectroscopy. All these compounds are ionic liquids, five are low temperature ones. Principal thermal characteristics are found that allow accounting for the phase behavior of the prepared compounds at their application. Existence of intramolecular and intermolecular interactions between the heterocyclic anion and inorganic cation in by means of the formation of hydrogen bond is established.

Full text of DOI:10.1134/S1070363209080246

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 8, pp. 1720–1727. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © M.S. Gruzdev, L.M. Ramenskaya, U.V. Chervonova, R.S. Kumeev, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79,
No. 8, pp. 1360–1368.
Preparation of 1-Butyl-3-methylimidazolium Salts
and Study of Their Phase Behavior
and Intramolecular Intractions
M. S. Gruzdev, L. M. Ramenskaya, U. V. Chervonova, and R. S. Kumeev
Institute of the Chemistry of Solutions, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153045 Russia
e-mail: gms@isc-ras.ru
Received February 5, 2009
Abstract—Seven organic salts of 1-butyl-3-methylimidazolium with anions Br–, BF4–, NO3–, SO42–, HSO4–, SCN–,
PO43– were prepared. Structure of these compounds is elucidated and purity is confirmed. The products are
characterized by melting point, thin layer chromatography, data of elemental analysis, cromatomass-, NMR and
IR spectroscopy. All these compounds are ionic liquids, five are low temperature ones. Principal thermal
characteristics are found that allow accounting for the phase behavior of the prepared compounds at their
application. Existence of intramolecular and intermolecular interactions between the heterocyclic anion and
inorganic cation in by means of the formation of hydrogen bond is established.
DOI: 10.1134/S1070363209080246
Among the priority directions of the modern “green
chemistry” an important one is application of ionic
liquids [1], the salts of heterocyclic bases with acid
anions, as the most promising medium for some
reactions. It is expected that application of ionic
liquids can lead to change in rate, conversion, yield
and selectivity, of catalitic processes in particular [2].
The ionic liquids are also used in biocatalysis, for
producing membranes with improved transfer of
substrate, as electrolyte in electrochemistry and
stationary phase in chromatography, in certain modes
of mass-spectrometry, for determination of vapors of
volatile substances by gravimetric method [3–6]. Now
the methods of treatment of plant biomass [7] and new
methods for utilization of nuclear wastes are in
development. In this connection, preparation of ionic
liquids with predefined properties, optimization of
current methods for the preparation of the known ionic
liquids, and the study of their properties is urgent.
There are different opinions now on the problem of
intramoleclar interaction, in particular, of hydrogen
bonding of counter ions in ionic liquids [7,8], and this
is a theme of active investigations because it is closely
connected with some physical properties of ionic
liquids such as viscosity, conductivity, density and
crystalline structure.
The aim of this work is preparation and study of
phase behavior of ionic liquids, the salts of 1-butyl-3-
methylimidazolium with different anions, and
elucidation of hydrogen bonding of the heterocyclic
cation with various ionorganic anions.
Br−
H3C
H3C
70oC
4 h
N
N
N+
N
+ Br
CH3
CH3
I
Br−
N+
H3C
H3C
AgBF4
CH3
CH3
− + AgBr.
N
N
N+
BF4
II
1720

PREPARATION OF 1-BUTYL-3-METHYLIMIDAZOLIUM SALTS
1721
Br−
H3C
H3C
AgNO3
N
N+
N
N+
III
CH3
CH3
NO3−+ AgBr
Br−
N+
H3C
H3C
(NH4)2SO4
N+
IV
CH3
CH3
N
N
SO42−
2
2
−2NH4Br
H3C
C4H9
H3C
H3C
N+
N
N+
2
Br− + Ag2SO4 + H2SO4
HSO4−
N
+ 2 AgBr
2
C4H9
V
Br−
N+
H3C
C4H9
NH4CNS; H2O
−NH4Br
N+
CNS−
N
N
CH3
VI
C4H9
Br−
N+
H3C
H3C
Ag3PO4
PO34−
N
N+
3
N
+ 3 AgBr
CH3
3
VII
Phase behavior of the synthesized compounds. The
values of thermodynamic parameters obtained by the
investigations with differential scanning calorimetry
(DSC) and thermogravimetry (TG) in the cycles of
heating of the prepared compounds are listed in Table 1.
Further we use formula [BuMeIm] to denote 1-butyl-3-
methylimidazolium cation.
Bis-1-butyl-3-methylimidazolium sulfate [BuMeIm]2·
SO4 can be classed with high-temperature ionic liquids
(mp = 158.71°С). At first and second heating of
[BuMeIm]2SO4 occurs two crystal–crystal phase
transitions (107.9°C and 136.3°C) followed by
complete melting at 158.7°C. These phase transitions
most probable occur by the disruption of the cation–
Table 1. Thermodynamic parameters of synthesized compounds
Crystallization,
Glass transition
Melting,
Decomposition
endothermic effect
exothermic effect
Composition
Тg, °C
ΔCp, J g–1 K–1
Tc, °C
ΔН, J g–1
mp, °C
ΔН, J g–1
Тdec, °C
Δm, wt %
BMImBr
–58.2
0.4
30.4
69.2
2.85
76.4
–66.30
6.15
66.2
0.16
0.36
9.51
0.67
0.456
26.47
1.67
0.69
36.70
1.41
287
296
–2.74
–7.58
[BMIm]BF4
–91.99
[BMIm]NO3
[BMIm]2SO4
–20.28
44.36
2.06
113.52
229.92
–1.65
–4.43
107.9
136.31
158.71
4.3
[BMIm]HSO4
–65.5
0.035
291
–2.05
24.8
31.52
–28.63
BMImSCN
–58.83
–71.3
0.032
0.610
–
–
–
–
[BMIm]3PO4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 8 2009

1722
GRUZDEV et al.
inorganic anion. This interaction is registered clearly
mp 31.5°C
first heating
mp 24.8°C
mp 4.3°C
Тg –65.5°C
by means of IR spectroscopy as will be shown below.
At further heating the substance suffers two phase
crystal–crystal transitions, finally with melting at 31.5°C.
At the second cooling the substance transfers from the
melt to glassy state directly at –62.5°C, and then
undergoes crystallization at 9.8°C and complete
melting at 28.6°C. Noteworthy that at the second
cooling of [BuMeIm]HSO4 only the transition to
glassy state was registered at –67.7°C.
first cooling
mp 28.6°C
Tc –43.5°C
second heating
Тc 9.8°C
Тg –62.8°C
second cooling
Тg –67.1°C
–80 –60 –40 –20
T, °C
Fig. 1. DSC curves of 1-butyl-3-methylimidazolium
0
20 40 60
Among the prepared compounds, 1-butyl-3-
methylimidazolium tetrafluoroborate and nitrate also
belong to the group of low-temperature ionic liquids.
Due to their low crystallization temperature (–91.99
and –20.28°С, respectively), they even at room
temperature are in the state of stable melt. Noteworthy
that we failed to register crystallization and melting
hydrosulfate in the cycles of heating and cooling.
anion interaction by hydrogen bonding. In the cycle of
cooling, the crystallization occurs only at 86.3°C. This
substance has also high enough decomposition
temperature (Tdecomp. = 229.92°С) and can be used as a
medium for carrying out high temperature syntheses in
the range 160–220°С.
points
for
tris-1-butyl-3-methylimidazolium
orthophosphate that has vertification temperature in
–71.32°С, below that of bromide (–58.2°С) and
hydrophophosphate (–65.5°C). By the data of DSC,
tris-1-butyl-3-methylimidazolium
orthophosphate
1-Butyl-3-methylimidazolium bromide being low-
temperature ionic liquid (mp = 76.4°С) can be used at
the temperature up to 240°С (Tdecomp. = 241°С). This
compound is a solid glassy substance at room
temperature. At heating the crystallization of the
sample occurs at the temperature ~30°С. The melting
point characterizing the salt transition into a stable
melt is ~76°С [11]. Noteworthy that at cooling the
melt its transition into the crystalline state does not
occur but proceeds direct transition to the glassy state.
Just due to such phase behavior 1-butyl-3-methyl-
imidazolium bromide synthesized by us is a thermally
stable substance. Even more, the substance in glassy
state is less hygroscopic as compared with the same
substance in crystalline phase.
exists at low temperature (below zero) in glassy state
while at room temperature in isotropic state (melt),
therewith the processes of crystallization–melting have
not been registered. Such existence of a compound in
liquid state is ideal for its practical application.
The cation–anion interaction. One target at the
study of physicochemical properties of the prepared
compounds is to confirm the structure of these
compounds by the methods of IR and NMR
spectroscopy. Below is shown general structural
formula of the studied compounds:
6
X−
2
H3C
10
N+
8
N
7
9
CH3
4
5
1-Butyl-3-methylimidazolium hydrosulfate resembles
bromide by its thermal behavior. A difference in their
phase behavior is that at the first cooling of the
hydrosulfate from room temperature to the temperature
below zero occurs its crystallization at –43.6°C
followed by transition to glassy state (Fig. 1). Such
behavior is specific for [BuMeIm]HSO4, while at the
first cooling of other ionic liquids from room
temperature to low temperatures the crystallization
does not occur but there is only the phase transition to
glassy state. This feature can be ascribed to the
existence of strong hydrogen bonds inside the
molecules due to interaction of organic cation with
X = Br–, BF–4, NO–3, SO42–, HSO–4, SCN–, PO43–.
For each salt we obtained characteristic IR
absorption bands of respective anion, but this does not
allow elucidation of its location relative to the
heterocycle. Nevertheless, we succeeded in registering
a strong interaction between the organic cation and
inorgatic anion. In the IR spectrum of 1-butyl-3-
methylimidazolium tetrafluoroborate the bands of
vibration of aromatic system 3217–3064 cm–1 and
aliphatic groups 3021–2801 cm–1 [12] (Fig. 2) are
strictly separated. The water absorption band 3435 cm–1
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 8 2009

PREPARATION OF 1-BUTYL-3-METHYLIMIDAZOLIUM SALTS
1723
in the spectrum of BuMeImBr is shifted to the value
1
BF4–
3449 cm–1 and is not of clear character that is
understandable because of the low content of water in
the sample (0.24 wt %, Table 2). The shift of aromatic
С–Н vibration bands for Н2, Н4, Н5 of imidazolium
cation in the region of 3100–3200 cm–1 (Table 2)
reflects the existence of С–Н···F hydrogen bonds.
Something similar occurred in the IR spectrum of 1-
butyl-3-methylimidazolium tetrafluoroborate synthesized
by another procedure [12]. Dupont assumed the
interaction of anion and cation through B–F···H–C
hydrogen bond that has been latter confirmed by the
3640
3562
hydrogen
bond
2
HSO4–
2497
hydrogen bond
H2O
4000 3500 3000 2500 2000 1500 1000 500
ν, cm–1
1
data of two-dimensional Н NMR spectroscopy. In
[12] was also shown appearance of strong bands at
3640 and 3562 cm–1. Unfortunately, Dupont restricted
himself to the statement of a fact of cation–anion
interaction on account of formation of intramolecular
bonds explaining the mechanism of its formation by
analogy with [13, 14] and leaving without answer the
appearance of the obvious bands of the formed dimers
and trimers via intermolecular hydrogen bond [15–17].
The band at 3640 cm–1 supposedly points to formation
of inter-molecular hydrogen bond between fluorine
atom and hydrogen atoms Н4, Н5 of imidazole ring.
Another new band of lower intensity at 3562 cm–1
indicates the presence of hydrogen bond between
anion and the imidazole ring hydrogen atom Н2. The
possibility of appearance of cross-linked structures due
to binding of cations and anions through hydrogen
bonds is shown also in [18], by the examples of 1-
butyl-3-methyl-imidazolium tetrafluoroborate and hexa-
fluorophosphate.
Fig. 2. IR spectra of 1-butyl-3-methylimidazolium tetra-
fluoroborate and hydrosulfate.
To confirm the conclusions about the hydrogen
bonding of the organic cation with anion we carried
out NMR investigation of all seven prepared
compounds. From the data of 13С NMR spectra
collected in Table 3 it is not possible to the interaction
of cation and anion on the intermolecular level.
However, it can be concluded unambiguously that the
structure of the spectrum of carbon skeleton remains
unchanged with different anions. This evidences
indirectly that in the interaction are involved the
hydrogen atoms of imidazole ring rather than of
1
aliphatic groups of the cation. From the analysis of Н
NMR spectrum of the studied compounds follows that
the interaction of anion with cation results in the shifts
of the signals of the imidazole ring protons and in
variations of spin–spin coupling constant J of the
protons Н4 and Н5 (Table 4). The interactions like that
were also detected in 1-butyl-3-methylimidazolium
hexafluorophosphate [18, 22]. Note that rather strong
Introduction of less polar groups such as the anion
(HSO4–) on the contrary leads to appearance of a broad
but weak band (2497 cm–1) in the IR spectrum of 1-
butyl-3-methylimidazolium hydrosulfate (Fig. 1). This
is due to the formation of a dimer of two HSO4– ions
(H–O–S–O···H–O–S–O···), like that found for KHSO4
Table 2. Vibration bands of π-system of the obtained
compounds
–
[18, 20]. The HSO4 dimer in its turn interacts with the
imidazole protons with the formation of a hydrogen
bond. Similar picture was observed for dimethyl-
imidazolium hydrosulfate [21] and was understood as
Vibration
band
Vibration
band
Vibration
band
Compound
Ph1, ν, cm–1
Ph2, ν, cm–1
H2O, ν, cm–1
–
H···O hydrogen bonding of imidazole ring and HSO4
BMImBr
3065.66
3124.39
3100.25
3032.13
3109.34
3070.95
3115.63
3139.74
3158.79
3148.24
3138.24
3152.69
3150.92
3157.96
3435.98
3449.51
3490.41
3371.35
3449.51
3453.53
3391.35
ions. This conclusion confirms hydrophilic character
of the compound and explains its phase transitions in
the first cycle of heating and cooling. Similar picture is
observed in the IR spectra of 1-butyl-3-methylimida-
zolium nitrate. In the region of 2386 cm–1 appears a
sharp strong band that supposedly reflects H···O
interaction of imidazole ring and NO3– ions (Fig. 3).
BMImBF4
BMImNO3
[BMIm]2SO4
BMImНSO4
BMImSCN
[BMIm]3PO4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 8 2009

1724
GRUZDEV et al.
Table 3. 13С NMR chemical shifts of the synthesized compounds
Compound
C10
C9
C8
C6
C7
C5
C4
C2
[BMIm]Br
[BMIm]BF4
13.43
13.27
13.23
13.46
13.31
13.49
13.32
19.49
19.42
19.38
19.46
19.46
19.57
19.38
32.01
31.95
31.90
31.96
31.56
32.06
31.84
36.48
36.23
36.18
36.52
36.36
35.5
50.02
49.92
49.88
49.96
49.93
50.07
49.90
122.96
122.86
122.80
122.93
122.88
122.95
122.84
124.20
124.15
124.06
124.17
124.16
124.2
136.55
136.49
136.43
136.47
136.52
136.53
136.26
[BMIm]NO3
[BMIm]2SO4
[BMIm]HSO4
[BMIm]SCNа
[BMIm]3PO4
a For SCN 17.63.
36.32
124.13
1
Table 4. H NMR signals of imidazole ring protons of the
EXPERIMENTAL
prepared liquids
The IR spectra of compounds were registered on an
Avatar 360 FT–IR ESP instrument in the region of
350–4500 cm–1 from KBr pellets and between KRC
Compound
[BMIm]Br
С2(Н)
С4(Н)–С5(Н)
J(H4H5)
8.72
8.71
8.58
8.78
8.53
8.73
8.41
7.44
7.53
7.35
7.48
7.34
7.47
7.14
10.99
7.32
1
[BMIm]BF4
[BMIm]NO3
[BMIm]2SO4
[BMIm]HSO4
[BMIm]SCN
[BMIm]3PO4
plates. The NMR spectra on the nuclei Н (200.13
MHz) and 13С (50.32 MHz) were registered on a
Bruker АС-200 spectrometer, with deuterated water as
a solvent, external reference cyclohexanol. The
elemental analysis of crystalline compounds was
carried out on a FlashEA 1112 analyzer, that allows
determination of carbon, hydrogen, sulfur and nitrogen
in the samples by oxidation. The chromatograms and
mass-spectra were registered on a Saturn 2000R
chromato-mass spectrometer, carrier gas helium.
Content of water was measured by amperometric
titration by Fisher method. The thermogravimetric
analysis (TG) was carried out on a NETZCH TG 209
F1 analyzer in the argon flow 20 ml min–1, the heating
rate 10 deg min–1. The differential scanning calori-
metry (DSC) was carried out on a NETZCH DSC 204
F1 instrument, the capsule material Al, sample weight
~20 mg, heating under N2 atmosphere from –110 to
100°С, heating rate 10 deg/min. The capsule was
prepared along the standard procedure just prior to
each measurement. Thin layer chromatography was
performed on Silufol UV 254 plates, Czech Republic.
The plates were developed in a chamber filled with
iodine vapor or under a UV lamp (λ = 254 nm).
9.77
10.98
9.77
10.99
8.55
spin-spin interaction of the protons in the organic
cation (Н4, Н5) occurs for the salts that at room
temperature are in melted state (liquid). On this basis
we assume that the glassy state dominating in most of
the prepared compounds is defined by the interaction
of organic cation with inorganic anion with
involvement of the hydrogen bond between these
cation and anion. The strength of such interaction is
defined by the nature of the acid anion.
NO3–
2386
hydrogen
bond
1-Butyl-3-methylimidazolium bromide (I). Two
basic methods of synthesis of 1-butyl-3-methyl-
imidazolium bromide as a source reagent for the
following preparation of representatives of ionic
liquids have been published. The first is to carry out
the quarternization reaction at elevated temperature
(110–130°C) for 3–4 hours, sometimes with the use of
solvent [9]. As a result, the target product yield reaches
95–98%. The main disadvantage of this approach is
4000 3500 3000 2500 2000 1500 1000 500
ν, cm–1
Fig. 3. IR spectrum of 1-butyl-3-methylimidazolium nitrate.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 8 2009

PREPARATION OF 1-BUTYL-3-METHYLIMIDAZOLIUM SALTS
1725
formation of a number of impurities that affect the
physical and chemical properties and application of the
product. The second way is based on the prolonged (72 h)
stirring at low temperature (50°C) in an inert medium
in a solvent, which leads to an increase in the synthesis
duration and thus increases the costs of its production.
The yield of the product reaches 80–90% [10]. We
developed a modified method for the synthesis of 1-
butyl-3-methylimidazolium bromide, which is featured
by controlled temperature (not above 75°C) and
controlled feeding of the second reagent, butyl
bromide. This approach allows to prepare the product
in a relatively short time interval and does not increase
the cost of subsequent stages of purification. The main
advantage of our approach is to reduce the moisture
content in the final product, which makes it convenient
for further application and for the use in physical and
chemical research without prior drying.
amount of 1-butyl-3-methylimidazolium bromide (48 g)
in water (30 ml), with thorough stirring was added
dropwise the AgBF4 solution. The reaction mixture
was vigorously stirred in the dark for 2 h. Then the
resulting AgBr precipitate was filtered off and washed
with water. The filtrate was concentrated on a rotory
evaporator. The resulting mass of amber color was
chromatographed on a column (silica gel, eluent
chloroform-acetonitrile, 1:2). The product is a light-
yellow liquid. Yield 43.2 g (87%). IR spectrum
(BMImBF4), ν, cm–1: 3162, 3122 s (aromatic C–H
vibrations), 2964, 2877 s [(CH2)n–CH3 vibrations],
1467 s (symmetric aromatic ring vibrations ), 1171 s
(symmetric vibrations of aromatic ring), 1054 br.s
1
(BF4 vibrations), 624 m [amide (III) band]. H NMR
spectrum (D2O), δ, ppm: 0.97 t (3H, CH3), 1.39 sextet
(2H, CH3–CH2–(CH2)N); 1.91 q (2H, N–CH2–CH2),
3.83 s (3H, N–CH3), 4.24 t (2H, N–CH2), 7.53 d (2H,
N–CH–CH–N); 8.71 s (1H, N–C(H)–N). 13C NMR
spectrum (D2O), δC, ppm, reference cyclohexanol:
13.27, 19.42, 31.95, 36.23, 49.92, 122.86, 124.15,
136.49. Water content 0.24 wt %.
For this purpose, according to the developed
scheme, to 33.75 g of 1-methylimidazole at 70°C with
stirring was added butyl bromide (60.96 g), so that the
temperature did not rise above 70°C. After adding the
entire butyl bromide, the mixture was maintained at
stirring for 4 h at a temperature of about 70°C. The
product (BMImBr) is a light-yellow liquid that
crystallizes into a white solid mass. Yield 90 g
(98.5%). IR spectrum of BMImBr, ν, cm–1 : 3100–
3000 s (aromatic C–H vibrations), 2970–2760 (CH2
aliphatic); 1600–1480 (C–N); 1070–1000 (1,3-
substituted system), 622 [amide (III) band). Mass
spectrum, m/e: calculated M 219, found 219 [M]+, 125
[M – Me]+, 97 [M – CH2–CH2–Me]+, 82 [M – C(H)NC(H)–
1-Butyl-3-methylimidazolium
nitrate
(III).
Weighted amount (16.31 g) of 1-butyl-3-methylimida-
zolium bromide was dissolved in 30 ml of water, and a
solution of 12.65 g of silver nitrate in 20 ml of water
was added dropwise. Stirring was continued for 2 h in
the dark. The AgBr precipitate was filtered off, the
resulting filtrate was evaporated on a rotary evaporator
and then subjected to azeotropic distillation with ethyl
alcohol. Then a few portions of dry acetone were
added to remove unreacted AgNO3. The product,
dissolved in ethanol, was applied to the chromato-
graphic column filled with activated carbon. The
solvent was removed on a rotory vacuum evaporator.
The product is a light-yellow viscous liquid. Yield
12.28 g (83%). IR spec-trum (BMImNO3), ν, cm–1:
3147, 3101 s (aromatic C–H vibrations), 2962, 2875 s
[(CH2)n–CH3 vibrations), 1465 s (symmetric vibrations
of aromatic ring), 1169 s (symmetric vibrations of
aromatic ring), 1344 br.s (NO3 vibrations), 624 m
1
CH2–CH2–CH2–Me]+. H NMR spectrum (D2O), δ,
ppm: 0.8 t (3H, CH3), 1.21 m (2H, CH3–CH2–(CH2)2–
N); 1.73 m (2H, N–CH2–CH2); 3.81 s (2H, N–CH2),
4.07 t (3H, N–CH3); 7.43 d (2H, N–CH–CH–N); 8.72 s
(1H, N–C(N)–N). 13C NMR spectrum (D2O), δC, ppm,
reference cyclohexanol: 13.43, 19.49, 32.01, 36.48,
50.02, 122.96, 124.20, 136.55. Water content 0.64 wt
%. Found, %: C 42.16, H 7.50; N 13.38; Br 37.96.
C8H15BrN2. Calculated, %: C 43.58, H 7.47; N 12.70;
Br 36.24.
1
[amide (III) band]. H NMR spectrum (D2O), δ, ppm:
0.78 t (3H, CH3), 1.20 sextet (2H, CH3–CH2–(CH2)N);
1.74 q (2H, N–CH2–CH2); 3.82 s (3H, N–CH3), 4.09 t
(2H, N–CH2), 7.35 d (2H, N–CH–CH–N); 8.58 s (1H,
N–C(H)–N). 13C NMR spectrum (D2O), δC, ppm,
reference cyclohexanol: 13.23, 19.38, 31.9, 36.18,
49.88, 122.80, 124.06, 136.46. Water content 8 wt %.
1-Butyl-3-methylimidazolium tetrafluoroborate
(II). 29.1 g of fresh silver(I) oxide was stirred with
100 ml of water in a Teflon beaker to formation of a
homogeneous mass. Then from a plastic burette was
added within 30 minutes 32.8 ml of tetrafluoroboric
acid (Aldrich, 48%). Stir ring was continued for 2 h,
and then the colorless clear solution of salt AgBF4 was
filtered from unreacted silver oxide. To a weighted
Bis-1-butyl-3-methylimidazolium sulfate (IV).
To a solution of 1-butyl-3-methylimidazolium bromide
(4.19 g) in water (30 ml), with careful stirring was
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 8 2009

1726
GRUZDEV et al.
added a solution of (NH4)2SO4 (2.51 g). The reaction
mixture was stirred at room temperature for 7 days.
Water was removed on a vacuum rotory evaporator.
The product was washed with a mixture of acetone
(100 ml) and ethanol (50 ml). The reaction mixture
was several times dissolved in ethanol and subjected to
azeotropic distillation on a rotory evaporator. The
product obtained is a viscous yellow liquid. After
adding dichloromethane, white crystals precipitated
that were filtered off on a glass filter and washed with
cold CH2Cl2. Yield 0.82 g (16.42%). IR spectrum
([BMIm]2SO4), ν, cm–1: 3147, 3032 s (aromatic C–H
vibrations), 2971, 2889, s [(CH2)n–CH3 vibrations),
2798 w [(CH2)n–CH3 vibrations], 1398 s (symmetric
vibrations of aromatic ring), 1170 s (symmetric
vibrations of aromatic ring), 1009. br.s (SO4
vibrations), 607 w [amide (III) band]. Mass spectrum,
m/e: calculated M 348.54, found [M+ + Na+] 371, [M+ +
7.3 d (2H, N–CH–CH–N); 8.53 s [1H, N–C(H)–N].
13C NMR spectrum (D2O), δC, ppm, reference
cyclohexanol: 13.31, 19.46, 31.96, 36.3, 49.93, 122.88,
124.16, 136.52. Water content 1.5 wt %. Found, %: C
39.31; H 7.43; N 11.86; S 13.16; O 28.23 C8H16N2O4S.
Calculated, %: C 40.43; H 7.39; N 11.79; S 13.47; O
26.92.
1-Butyl-3-methylimidazolium tiocyanate (VI).
To a solution of NH4CNS (5.79 g) in 10 ml of H2O in
small portions was added a solution of 1-butyl-3-
methylimidazolium bromide (16.65 g) in 20 ml of
H2O. The mixture was stirred for 7 days at room
temperature. Then water was distilled off on a rotory
evaporator. Ethyl alcohol was added several times in
small portions, and azeotropic distillation followed.
Then to the flask was added 50 ml of chloroform, and
white crystalline precipitate formed was filtered off.
The resulting product is a dark red solution. By TLC
data, the product consists of two compounds: 1-butyl-
3-methylimidazolium bromide and thiocyanate. The
existence of thiocyanate ions was also confirmed by
infrared spectroscopy. Isolation of 1-butyl-3-methyl-
imidazolium tiocyanate was performed by column
chromatography on aluminum oxide, eluent aceto-
nitrile–carbon tetrachloride in the ratio 2:1. The target
product contained in the second fraction. Yield about
1.3 g (51%). IR spectrum (BMImSCN), ν, cm–1: 3145,
3105 s (aromatic C-H vibrations), 2962, 2873 s [(CH2)n–
CH3 vibrations], 2932 w [(CH2)n–CH3 vibrations),
2055 br.s (SCN vibrations) 1464 s (symmetric
vibrations of aromatic ring), 1167 s (symmetric
vibrations of aromatic ring), 621 [m, amide (III) band].
Mass spectrum m/e: calculated M 197.33, found 207
1
Ca2+] 390. H NMR spectrum (D2O), δ, ppm: 0.93 t
(6H, CH3), 1.4 sextet (4H, CH3–CH2–(CH2)N); 1.92 q
(4H, N–CH2–CH2); 3.98 s (6H, N–CH3), 4.28 t (4H,
N–CH2), 7.48 d (4H, N–CH–CH–N); 8.78 s (2H, N–C
(H)–N). 13C NMR spectrum (D2O), δC, ppm, reference
cyclohexanol: 13.46, 19.46, 31.96, 36.52, 49.96,
122.93, 124.17, 136.47. Water content 3 wt %. Found,
%: C 55.01, H 9.45; N 8.43; O 17.94. C16H30N4O4S.
Calculated, %: C 55.05; H 9.49; N 8.02; S 9.17; O
18.32.
1-Butyl-3-methylimidazolium hydrosulfate (V).
To a solution of silver sulfate (4.08 g) in 40% H2SO4
(20 ml) was added 1-butyl-3-methylimidazolium
bromide (4.05 g) dissolved in ethyl alcohol. The
mixture was stirred for 2 h at 50°C. The precipitate
was filtered off. To the filtrate was added acetonitrile,
the mixture was filtered again, and acetonitrile was
distilled off. The procedure was repeated several times.
The product is a liquid of amber color, which
crystallized at storage. The product was recrystallized
from a mixture of acetonitrile and ethyl acetate, 1:5.
Yield is about 7.75 g (75%). IR spectrum of
(BMImNSO4), ν, cm–1: 3150, 3108 s (aromatic C–H
vibrations), 2962, 2875 with [(CH2)n–CH3 vibrations],
2936 with [(CH2)n–CH3 vibrations], 1466 s (symmetric
vibrations of aromatic ring), 1171 s (symmetric
vibrations of aromatic ring), 1046 br.s (NSO4
vibrations), 624 m [amide (III)]. Mass spectrum, m/e:
1
[M+ + Na+ + K+]. H NMR spectrum (D2O), δ, ppm:
0.85 t (3H, CH3), 1.21 sextet (2H, CH3–CH2–(CH2)N);
1.80 quintet (2H, N–CH2–CH2) 3.85 s (2H, N–CH2),
4.6 t (2H, N–CH3), 7.47 d (2H, N–CH–CH–N); 8.74 s
(1H, N–C(H)–N). 13C NMR spectrum (D2O), δC, ppm,
reference cyclohexanol: 13.49, 17.63, 19.57, 32.06,
35.5, 50.07, 122.95, 124.2, 136.53. The appearance of
a new signal (17.63 ppm) corresponds to the carbon
nucleus in the SCN– anion. Water content 1.5 wt %.
Found, % C 53.18; H 6.744 N 20.17; S 11.34.
C9H15N3S. Calculated, %: C 54.79; H 7.66; N 21.29; S
16.25.
Tris-1-butyl-3-methylimidazoly orthophosphate
(VII). A weighted amount of Ag3PO4 (8.16 g) was
dissolved in 60 ml of H3PO4 and a solution of 1-butyl-
3-methylimidazolium bromide (12.81 g) in water
(30 ml) was added dropwise at permanent vigorous
1
calculated M 237, found 235 [M]+. H NMR spectrum
(D2O), δ, ppm: 0.75 t (3H, CH3), 1.66 sextet [2H,
CH3–CH2–(CH2)N]; 1.68 q (2H, N–CH2–CH2], 3.73 s
(3H, N–CH3), 3.99 s (1H, NSO4), 4.06 t ( 2H, N–CH2),
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 8 2009

PREPARATION OF 1-BUTYL-3-METHYLIMIDAZOLIUM SALTS
1727
6. Liang, C., Yuan, C.-Y., and Warmack, R.J., Anal.
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8. Aslanova, L.A. and Zakharov, M.A., Abramycheva N.L.,
Ionnye zhidkosti v ryadu rastvoritelei (Ion Liquids as
Solvents), Moscow: Mosk. Gos. Univ., 2005.
stirring. The reaction was carried out in the dark for
4 h. The reaction mixture was filtered, water was
distilled off from the filtrate on a vacuum rotory
evaporator. As a result we obtained a viscous yellow
liquid with pH 2–3. For the neutralization of H3PO4 the
crude product was dissolved in ethanol and neutralized
with a solution of KOH in alcohol. The reaction
mixture was then filtered through a fine-porous glass
filter. Alcoholic filtrate was applied to a chromato-
graphic column filled with activated carbon. Solvent
was then distilled off on a vacuum rotory evaporator.
The product is a viscous yellow liquid. Yield about
8.73 g (87.3%). IR spectrum ([BMIm]3PO4), ν, cm–1:
3154, m 3148 (conjugated vibrations of heterocyclic
ring), 2964, 2876 s [(CH2)n–CH3 vibrations], 1465 s
(symmetric vibrations of aromatic ring), 1172 s
(symmetric vibrations of aromatic ring), 937, 879
(vibrations of PO4 surrounded by three heterocyclic
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2001, vol. 38, p. 265.
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1
rings), 624 [amide (III) band]. H NMR spectrum
(D2O), δ, ppm: 0.95 t (9H, CH3), 1.36 sextet [6H,
CH3–CH2–(CH2)N]; 2.01 q (6H, N–CH2–CH2) 3.98 s
(9H, N–CH3), 4.27 t (6H, N–CH2), 7.14 d (6H, N–CH–
CH–N); 8.41 s [3H, N–C(H)–N]. 13C NMR spectrum
(D2O), δC, ppm, reference cyclohexanol: 13.32, 19.38,
31.84, 36.32, 49.9, 122.84, 124.13, 136.26. Water
content 0.5 wt %.
16. Pentin, Yu.A. and Kuramshina, G.M., Osnovy
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