Effect of temperature on the purity of product in the preparation of 1-butyl-3-methylimidazolium-based ionic liquids

Article abstract of DOI:10.1515/znb-2004-0704

The preparation of room-temperature ionic liquids 1-butyl-3- methylimidazolium chloride, hexafluorophosphate, and dicyanamide by microwave-assisted reaction in non-solvent and solvent conditions has been studied in this contribution. A special emphasis is put on the effect of the reaction temperature on the purity of ionic liquids that was monitored by electrospray ionisation mass spectrometry and ¹H NMR. The X-ray structure of 1-butyl-3-methylimidazolium chloride is presented.

Full text of DOI:10.1515/znb-2004-0704

Effect of Temperature on the Purity of Product in the Preparation of
1-Butyl-3-methylimidazolium-Based Ionic Liquids
Johanna Ka¨rkka¨inen, Janne Asikkala, Risto S. Laitinen, and Marja K. Lajunen
Department of Chemistry, University of Oulu, P. O. Box 3000, 90014 Oulu, Finland
Reprint requests to Prof. Dr. Marja K. Lajunen. Fax: +358-8-553 1629.
E-mail: marja.lajunen@oulu.fi
Z. Naturforsch. 59b, 763 – 770 (2004); received March 16, 2004
The preparation of room-temperature ionic liquids 1-butyl-3-methylimidazolium chloride, hexa-
fluorophosphate, and dicyanamide by microwave-assisted reaction in non-solvent and solvent con-
ditions has been studied in this contribution. A special emphasis is put on the effect of the reaction
temperature on the purity of ionic liquids that was monitored by electrospray ionisation mass spec-
trometry and 1H NMR. The X-ray structure of 1-butyl-3-methylimidazolium chloride is presented.
Key words: RTIL, Purity, Side Products, Electrospray Mass Spectrum
Introduction
Ionic liquids are organic salts that are liquids at tem-
◦
peratures below 100 C. While the first room temper-
Scheme 1.
ature ionic liquid was discovered as early as 1914 [1],
early literature is sparse [2 – 4] and ionic liquids were
largely ignored until the work of Seddon [5] and
Hussey [6 – 8] in the 1980’s. Since then these species
have seen extensive research activity (for excellent re-
views on the wide variety of the use of ionic liquids,
see Refs. [9 – 16].
seems to play an important role in the purity of
some commonly used ionic liquids, 1-butyl-3-methyl-
imidazolium chloride (1), hexafluorophosphate (2),
and dicyanamide (3) (Scheme 1).
Results and Discussion
Quaternisation of appropriate amines is a general
method to prepare ionic liquids [13, 15]. This method
has been used to prepare 1-alkyl-3-methylimidazolium
salts. Halides can be made by a reaction of N-methyl-
imidazole with an appropriate haloalkane [17]. Vari-
ous anions can be introduced by anion exchange of the
halides [14, 16]. This can be done by the addition of
a metal salt or by displacement of a halide ion by a
strong acid [17 – 20].
One of the recent research interests is concerned
with the purity and quality of ionic liquids prepared by
various methods [21, 22]. A pure ionic liquid should
be colourless [23]. However, early work methods of-
ten afforded coloured products that were impure and
laborious to purify.
1-Butyl-3-methylimidazolium chloride
1-Butyl-3-methylimidazolium chloride [BMIM]Cl
(1) is a common precursor for many ionic liquids.
Its preparation by the literature method [18] produced
coloured products the purification of which was a com-
plicated and laborious process, especially when an ex-
cess butyl chloride was used. Consequently, the de-
sired product crystallized poorly. Recent studies have
reported the preparation of 1 in a microwave digester
[26, 27]. We explored further the microwave-assisted
preparation of 1 with the objective to minimize the for-
mation of coloured side products and to shorten the
reaction time. A special attention was directed to the
reaction temperature and the molar ratio of the reac-
In this paper, we explore the formation of ionic liq- tants. The reaction between N-methylimidazole and
uids by using microwave-assisted methods for which butyl chloride was performed in the molar ratio range
the information is still sparse [24– 29]. Interestingly, 1:1 – 1:1.5 in a closed microwave reactor [30] designed
we also encountered coloured products depending for synthetic◦purposes. The reaction temperature was
on the reaction conditions. In particular, temperature kept at 150 C by the automatic regulation of the ir-
c
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J. Ka¨rkka¨inen et al. · 1-Butyl-3-methylimidazolium-Based Ionic Liquids
Table 1. The effect of temperature on the preparation of Table 2. Electrospray ionization mass spectra of crude prod-
1-butyl-3-methylimidazolium chloride (1) assisted by mi- ucts of 1-butyl-3-methylimidazolium chloride (1) from sepa-
crowaves.
rate reaction temperatures.
T [◦C] Colour of Yield of 1 Purity by MS(ESI+), Colour of
T
MS (ESI+),
[◦C]
130
140
150
m/z (rel. int. %) of detected components in crude 1
83 (20) [MIM]+, 139 (100) [BMIM]+
83 (55) [MIM]+, 139 (100) [BMIM]+, 181(5) [BBIM]+
83 (70) [MIM]+, 97 (15) [MMIM]+, 139 (100) [BMIM]+,
181(55) [BBIM]+
the reaction
mixture
[%]
1H NMR m/z
the crys-
talline 1
white
80 colourless
90 colourless
100 colourless
110 colourless
120 yellowish
130 light yellow
140 light yellow
150 light yellow
7
9
–
–
–
–
white
14
29
61
77
83
84
–
–
–
–
white
white
white
milky white
[MIM]+ = methylimidazolium cation, [MMIM]+ = dimethylim-
idazolium cation, [BMIM]+ = butyl-methylimidazolium cation,
[BBIM]+ = dibutylimidazolium cation.
pure 1
pure 1
M+ 139
M+ 139
impurities M+ 139, 181 milky white
impurities M+ 139,
97, 181
160 yellowish
94
impurities –
yellowish
Reaction conditions: 3.2 mmol of 1 and butylchloride, reaction time
15 min, microwave radiation power normal.
Scheme 2.
radiation power and the reaction time varied from 5
to 10 min. The best crude yield of 1 (90%) was ob-
tained when the molar ratio was 1:1.1 and the reac-
tion time was at least 10 min. A higher molar ratio
than 1:1.1 reduced the yield. Equimolar amounts of
the reagents produced 85% of white 1-butyl-3-methyl-
imidazolium chloride (1) in 10 min. After workup the
1H NMR spectrum of 1 did not show resonances due
to starting materials. While many ionic liquids are ther-
mally stable at high temperatures [18], the preparation
of 1 at 160 ◦C resulted in partial scrambling of the side
chains in the five membered C3N2 ring, as indicated by
1H NMR spectroscopy.
ions is avoided. The ESI mass spectrum is simple and
ions can be unambiquously identified. The method is
a particularly suitable technique for the detection of
ionic liquids, because they are already in the ionic form
[31 – 34].
The peaks in ESI mass spectra of the product
mixtures at different temperatures are shown in Ta-
ble 2. The crude product derived from the reaction at
◦
140 C contained an additional peak at m/z 181 and
◦
that from the reaction at 150 C showed yet another
peak at m/z 97. The former probably arose from the
1,3-dibutylimidazolium cation [BBIM]+ and the latter
from the 1,3-dimethylimidazolium cation [MMIM]+
(see Scheme 2). The molecular peak m/z 83 [MIM]+
was obviously formed in the mass spectrometer during
ionization depending upon a used electron potential.
To study the effect of the reaction temperature on
the product formation and scrambling, we carried out
the synthesis of [BMIM]Cl at nine temperatures rang-
ing from 80 to 160 ◦C. Equimolar amounts of the start-
ing compounds were allowed to react 15 min in every
experiment.◦The reaction mixture remained colourless
below 110 C, but at higher temperatures, it became
yellowish. The highest yield of pure 1 was produced
The 1H NMR spectra also contained other reso-
nances in addition to those of 1. The scrambled prod-
◦
ucts (≥ 140 C) showed signals at 4.10 and 4.11 ppm
(the methyl groups of [MMIM]+). Small resonances
were observed near to the multiplets at 7.33 and
7.44 ppm (ring protons H-4 and H-5, respectively). The
crude product from the reaction at 150 ◦C showed three
singlets for the methine group between N atoms, in-
dicating the presence of three different imidazolium
1
at 130 ◦C (77%). According to the H NMR spectrum,
rearrangement reactions of 1-butyl-3-methylimidazo-
◦
lium chloride began to occur at 140 C. The reactions
◦
at higher temperatures than 130 C gave a better yield
of 1, but the product contained impurities (see Table 1).
The reaction mixtures formed at different tempera-
tures were analysed by 1H NMR and electrospray ion-
ization mass spectrometry MS(ESI+ and ESI−) [31].
ESI-MS is the softest available technique to transfer
1
cations. The H NMR spectra indicated that approx-
◦
imately 7% of the product had rearranged at 140 C,
20% at 150 ◦C, and 35% at 160 ◦C.
We also studied the influence of the heating on pure
positive or negative ions from solution to the gas phase, 1. A sample of 1 was heated by mi◦crowaves in ace-
from which the ions can be subjected to MS anal- tone and without the solvent at 150 C for 10 min up
1
ysis. One can define the softness of the ion-transfer to 1 h. The heated samples were analyzed by H NMR
method as the degree to which fragmentation of the and MS(ESI+). Both spectra indicated that the heating
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◦
˚
Table 3. Selected bond lengths (A) and angles ( ) of 1-butyl-
3-methylimidazolium chloride (1).
N(1)-C(2)
N(1)-C(6)
N(3)-C(10)
C(6)-C(7)
C(8)-C(9)
1.382(2) N(1)-C(5)
1.473(2) N(3)-C(2)
1.466(2) C(4)-C(5)
1.521(2) C(7)-C(8)
1.524(2)
1.473(2)
1.328(2)
1.354(2)
1.523(2)
N(1)-C(2)-N(3)
N(1)-C(6)-C(7)
C(2)-N(1)-C(5)
C(5)-N(1)-C(6)
C(2)-N(3)-C(10)
C(6)-C(7)-C(8)
108.7(1) N(1)-C(5)-C(4)
110.4(1) N(3)-C(4)-C(5)
108.7(1) C(2)-N(1)-C(6)
125.0(1) C(2)-N(3)-C(4)
124.7(1) C(4)-N(3)-C(10)
112.2(1) C(7)-C(8)-C(9)
106.9(1)
106.9(1)
125.9(1)
108.7(1)
126.5(1)
111.8(1)
C(5)-N(1)-C(2)-N(3)
C(2)-N(3)-C(4)-C(5)
C(4)-C(5)-N(1)-C(2)
−0.4(2) N(1)-C(2)-N(3)-C(4)
0.3(2)
−0.1(2) N(3)-C(4)-C(5)-N(1) −0.2(2)
Fig. 1. The crystal structure of 1-butyl-3-methylimidazolium
chloride (1) indicating the numbering of atoms. The thermal
ellipsoids have been drawn at 50% propability level. Hydro-
gen bonds involving three short H···Cl contacts connect the
cations and anions into a three-dimensional network.
0.4(2) C(4)-C(5)-N(1)-C(6) 173.3(1)
C(4)-C(5)-N(3)-C(10) −179.5(1) N(1)-C(2)-N(3)-C(10) 179.7(1)
N(3)-C(2)-N(1)-C(6) −173.2(1) C(2)-N(1)-C(6)-C(7)
82.9(2)
C(5)-N(1)-C(6)-C(7)
C(6)-C(7)-C(8)-C(9)
−88.8(2) N(1)-C(6)-C(7)-C(8) 174.2(1)
174.8(1)
does not cause rearrangement in [BMIM]Cl (1). The
formation of impurities is therefore dependent on the
temperature during the actual synthesis.
A maximum useful reaction temperature for the
microwave-assisted synthesis o◦f 1-butyl-3-methyl-
imidazolium chloride (1) is 130 C. Higher tempera-
ture leads to the formation of a product mixture. The
purification of these impurities by washing with the
solvent was not successful.
Structural information about ionic liquids is rather
sparse with few crystal structures reported for the
N,N’-dialkylimidazolium cation with different coun-
terions [35 – 44]. The X-ray structure of 1 is shown
in Figure 1 together with the numbering of the
atoms [44]. The bond lengths and angles are presented
in Table 3.
It can be seen from Table 3 that all bond lengths in
the cation of 1 are quite normal and agree with those of
other related salts [35 – 43]. There are several alterna-
tive conformations for the butyl side chain depending
on the mutual orientations of the carbon atoms in the
butyl side chain. This can be exemplified as follows:
Fig. 2. The conformation of the 1-butyl-3-methylimidazo-
lium cation in (a) the chloride salt (1), (b) the tetraphenyl-
borate salt [36, 39].
For steric reasons, the N-methylimidazole ring is
generally approximately perpendicular to the C(6)-
C(7) bond (for the numbering of the atoms, see Fig. 1).
The terminal ethyl fragment involving the carbon
atoms C(7) and C(8) has two alternative orientations X
and Y that could be energetically equally favourable.
Indeed, it can be seen from Fig. 2 that the ethyl group
in the cation of 1 adopts the X orientation and that in 1-
butyl-3-methylimidazolium tetraphenylborate [36, 39]
adopts the Y orientation. Similar alternative orienta-
tions can be conceived to exist for the methyl group
{carbon atom C(9)} at the end of the butyl chain. The
structural characterization of several 1-butyl-3-methyl-
imidazolium cations [35– 43] has demonstrated that
packing effects seem to be the determining factor in
deciding the actual conformation in the cation.
The 1-butyl-3-methylimidazolium cations and the
chloride anions are joined together by a hydrogen
bonding network, as shown in Fig. 1. The shortest
˚
H···Cl contacts of 2.485, 2.653, and 2.688 A in-
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J. Ka¨rkka¨inen et al. · 1-Butyl-3-methylimidazolium-Based Ionic Liquids
Table 4. The effect of the reaction temperature on a micro-
wave-assisted preparation of 1-butyl-3-methylimidazolium
hexafluorophosphate (2) in acetone.
volve hydrogen atoms H(2), H(6A), and H(6B), re-
spectively. These hydrogen atoms are expected to be
most acidic in the cation. The respective C-H···Cl an-
gles are 157.9, 166.0, and 145.6◦.
T
[◦C]
80
80
90
Reaction time
Colour of the
product
orange
Yield of 2
[min]
5
10
5
10
[%]
87
99
87
92
1-Butyl-3-methylimidazolium hexafluorophosphate
yellow
orange
orange
1-Butyl-3-methylimidazolium hexafluorophosphate
[BMIM]PF6 (2) was prepared from pure 1 [43]. The
starting compound was weighted in a reactor ves-
sel, and acetone was added. [BMIM]Cl does not dis-
solve noticeably in acetone at room temperature. How-
ever, the presence of some [BMIM]Cl could be in-
100
Reaction conditions: 1 mmol of [BMIM]Cl and NaPF in acetone,
6
microwave radiation power high.
terial was consumed. When the reaction time was suffi-
cient, the filtration through a sintered glass funnel was
adequate to remove completely the precipitated NaCl.
If the reaction was not complete, some [BMIM]Cl re-
mained in the solution and it could not be separated
from 2.
1
ferred from the H NMR spectrum of a pure sample
of [BMIM]Cl recorded in d6-acetone. An equimolar
amount of NaPF6 was subsequently added. The reac-
◦
tion was performed at 80 C for 5 to 15 min. After
A preparation of ionic liquids of alkylimidazolium
fluoroanions has also been performed in water [19]. We
studied the preparation of [BMIM]PF6 in water by mi-
crowave heating. The reaction was carried out in a sim-
ilar fashion as in acetone. After 5 min at 80 ◦C a cloudy,
orange reaction mixture was cooled and washed three
times with distilled water. Drying overnight in vacuum
at 90 ◦C afforded 75% of a yellow product. The crude
product was analysed by MS(ESI+) and 1H NMR. The
MS spectrum was similar to that of [BMIM]PF6 from
cooling, solid NaCl was separated by filtration through
Celite. Neutral alumina or Silica Gel could also be used
for the filtration. The yield of 2 was 95 – 99%. The
yellow/orange colour of the product was due to the
presence of traces of acetone, which can sometimes re-
sult in colouration during the quaternisation step [21].
However, the reaction without the solvent was not pos-
sible because of high melting points of [BMIM]Cl and
NaPF6.
For comparison, the above reaction was repeated
at room temperature without microwave heating. The
reagents were mixed together and allowed to react for
4.5 h. The crude product was filtered through Celite.
After removal of the solvent by evaporation and drying
in vacuum the yield of brown [BMIM]PF6 was 83%.
The 1H NMR spectrum indicated a pure product.
We also studied the effect of temperature on the
preparation of [BMIM]PF6 promoted by microwa◦ve
heating. The increase in temperature from 80 to 100 C
did not essentially improve the yield. The reaction time
needs to be long enough for a good yield (see Table 4).
The products from the separate reaction temperatures
1
the reaction in acetone. The H NMR spectrum was
also similar, but we could not observe the resonance
due to H-2.
1-Butyl-3-methylimidazolium dicyanamide
1-Butyl-3-methylimidazolium dicyanamide
[BMIM]CA (3) is a low viscosity ionic liquid which
is a suitable solvent for a wide variety of inor-
ganic and organic compounds [45 – 46]. We prepared
[BMIM]DCA by using microwave heating directly
from pure 1 and NaN(CN)2. [BMIM]Cl was weighted
in a reactor vessel, and acetone and NaN(CN)2 were
added. The solid starting compounds did not notice-
ably dissolve in acetone at room temperature. The re-
action was performed at three temperatures 80, 90 and
1
were analysed by H NMR and MS(ESI+ and ESI−).
NMR spectra were all similar. Every MS (ESI+) spec-
trum contained m/z‘s due to [BMIM]+ and [MIM]+,
and MS(ESI−) showed a peak due to [PF6]−. In addi-
tion, positive as well as negative electrospray MS spec-
trum contained double ions, which occasionally were
induced by the MS recording conditions.
◦
100 C and the reaction time was 10 min. After cool-
ing, solid NaCl was separated from the yellow prod-
uct mixture by filtration through Celite. The evapora-
tion of the solvent and the overnight drying in vacuum
◦
The best way to prepare [BMIM]PF6 (2) by a yielded 89% (reaction temperature 80 C) of crude 3
microwave-assisted reaction was to allow equimolar (see Table 5). The increase in the reaction temperature
amounts of starting compounds to react together in in fact decreased the crude yield, because the prod-
acetone for 10 min at 80 ◦C. In that time all starting ma- uct then contained unreacted [BMIM]Cl. The products
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Table 5. Preparation of 1-butyl-3-methylimidazolium di-
cyanamide (3) at separate reaction temperatures assisted by
microwave irradiation.
the microwave-assisted method compared to conven-
tional heating involve the saving of chemicals, reaction
time, and work and facilitates high yields of pure ionic
liquids.
T
Colour of the
product
yellow
Yield of
crude 3 [%]
Remarks
[◦C]
80
MS(ESI+) is a very sensitive and useful technique
for the rapid determination of the purity of ionic liq-
uids, since minor, potentionally undesirable side prod-
ucts can conveniently be detected and identified. The
presence of additional anions in the product can be de-
tected by MS(ESI−) even when their content is small.
The disadvantage in the anion mode is the variation
of the sensitivity from anion to anion. The quantitative
estimation of the content of impurities is also difficult.
The assignment of the NMR spectra is hampered
by widely varying solubilities of different ionic liquids
89
90
92
90
100
yellow
yellow
contains some [BMIM]Cl
contains some [BMIM]Cl
Reaction conditions: 1 mmol of [BMIM]Cl and NaN(CN) in ace-
2
tone, reaction time 10 min, microwave irradiation power high.
Table 6. Electrospray ionization mass spectra of the crude
products of 1-butyl-3-methylimidazolium dicyanamide (3)
from separate reaction temperatures.
T
MS (ESI+),
[◦C] m/z (rel. int. %) of detected components in crude 3
80 83 (90) [MIM]+, 139 (100) [BMIM]+
90 83 (35) [MIM]+, 139 (100) [BMIM]+, 313(15) [BMIM]2+Cl
1
that necessitates the recording of the H NMR spectra
100 83 (75) [MIM]+, 139 (100) [BMIM]+, 313(30) [BMIM]2+Cl
of each individual compound in different solvents. It is
well-known that positions of resonances in NMR spec-
tra are influenced by a solvent [47] and therefore direct
[MIM]+ = methylimidazolium cation, [MMIM]+ = butyl-methyl-
imidazolium cation.
1
comparison of H NMR spectra of different ionic liq-
from all three reaction temperatures were characterized
by 1H NMR and MS(ESI+ and ESI−). While all NMR
spectra were identical, the MS(ESI+) spectra were dif-
ferent (see Table 6). It could be inferred that the prod-
uct contained small amounts of unreact◦ed [BMIM]Cl.
The optimal reaction temperature is 80 C.
uids can be misleading. In addition, non-protonic an-
1
ions cannot be detected by H NMR. It can be con-
cluded that the reliable estimation of the side prod-
ucts and impurities during the formation of ionic liq-
uids is best carried out by combined use of ESIMS and
1H NMR spectroscopy.
Conclusions
Experimental Section
Microwave technique is a fast and simple proce-
dure to produce 1-butyl-3-methylimidazolium salts.
For the successful preparation of 1-butyl-3-methyl-
imidazolium hexafluorophosphate and dicyanamide it
is essential that the starting compound 1-butyl-3-
methylimidazolium chloride is pure. The removal of
impurities from the product by washing or by mul-
tiple recrystallisation is laborious, if not impossible.
We have shown that coloured side products can be
avoided by using a low enough reaction temperature
during the preparation of the ionic liquid. The optimum
temperatures during the preparation were 130, 80 and
80 ◦C for 1-butyl-3-methylimidazolium chloride, hex-
afluorophosphate and dicyanamide, respectively. The
higher reaction temperatures led to the formation of
product mixtures. However, pure ionic liquids do not
rearrange upon heating.
General
N-Methylimidazole and NaPF6 (Aldrich), butyl chloride
(Fluka), and NaN(CN)2 (Fluka) were used without fur-
ther purification. Ethyl acetate (Lab-Scan) was distilled over
CaH2 and acetone (J. T. Baker) stored on a Molecular Sieve
˚
(4 A).
The microwave reactor was the single mode EmrysTM
Creator (Personal Chemistry AB) [30] designed for synthetic
use and equipped with a magnetic stirrer, and a temperature
and pressure control and adjustment system. Reactor vessels
were Emrys Process VialsTM
for 0.5 – 2.0 ml. 1H NMR spectra were recorded on a
Bruker DBX 200 instrument at 200 MHz. Electrospray ion-
isation mass spectra were recorded on a Micromass, LCT
mass spectrometer.
Preparation of 3-butyl-1-methylimidazolium chloride
[BMIM]Cl (1)
Reaction time during the synthesis was also a cru-
cial factor. For a successful high-yield preparation of
ionic liquids by the microwave-assisted reaction it is
important that the reaction time is sufficiently long
N-Methylimidazole (3.2 mmol) and butylchloride
(3.5 mmol) were mixed in a sealed microwave reactor and
irradiated for 15 min at 130 ◦C. The crude product of 1 was
to allow the reaction to complete. The advantages of washed few times with dry EtOAc and dried overnight in a
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J. Ka¨rkka¨inen et al. · 1-Butyl-3-methylimidazolium-Based Ionic Liquids
vacuum at 70 ◦C. The yield of a white [BMIM]Cl was 77%.
The product was analyzed by 1H NMR and MS(ESI+).
Table 7. Details of the crystal structure determination of 1.
Empirical Formula
C8H15ClN2
174.67
150 K
1H NMR spectrum of 1 (CDCl3, 200 MHz): δ = 0.97 (t, 3H, Relative molecular mass
T [K]
J = 7.3 Hz, 9-CH3) 1.37 (m, 2H, J = 7.4 Hz, 8-CH2), 1.90
(m, 2H, J = 7.4 Hz, 7-CH2), 4.13 (s, 3H, 10-CH3), 4.33 (t,
2H, J = 7.3 Hz, 6-CH2), 7.33 (t, 1H, J = 1.8 Hz, 5-CH),
7.44 (t, 1H, J = 1.8 Hz, 4-CH), 10.9 (s, 1H, 2-CH). Lit. [23].
MS(ESI+) [m/z (rel. int.,%)]: M+. 139 (100) [BMIM]+,
83(20) [MIM]+.
Crystal system
monoclinic
P21/c
Space group
˚
a [A]
9.920(2)
11.453(2)
9.649(2)
118.81(3)
960.6(3)
4
˚
b [A]
˚
c [A]
β [◦]
3
˚
V [A ]
Z
Preparation of 3-butyl-1-methylimidazolium hexafluoro-
phosphate [BMIM]PF6 (2) in acetone
F(000)
376
1.208
0.341
0.15×0.10×0.05
4.22 – 25.99
12068
1881
1675
Dc [g cm−3
]
µ(Mo-Kα ) [mm−1
Crystal size [mm]
θ Range (deg.)
Number of reflections collected
Number of unique reflections
Number of observed reflectionsa
]
[BMIM]Cl (1) (1 mmol) was weighted into a microwave
reactor, 1 ml of acetone and NaPF6 (1 mmol) added. The
reaction mixture was heated by microwaves for 10 min at
80 ◦C. The cooled reaction mixture was filtered through
Celite to remove solid NaCl. After the evaporation of acetone
the yield of [BMIM]PF6 was 99%. The product was analyzed Number of refined parameters
103
0.0465
0.0387
0.0797
1.112
0.201, −0.255
by 1H NMR and MS(ESI+ and ESI−). 1H NMR spectrum of
RINT
R1 (all data)a
2 (MeOD, 200 MHz): δ = 0.99 (t, 3H, J = 7.3 Hz, 9-CH3)
wR2 (all data)a
1.38 (m, 2H, J = 7.4 Hz, 8-CH2), 1.86 (m, 2H, J = 7.4 Hz, 7-
GOOF
CH2), 3.92 (s, 3H, 10-CH3), 4.20 (t, 2H, J = 7.4 Hz, 6-CH2),
Max. and min. heights in final
difference Fourier synthesis (e A
−3
7.54 (t, 1H, J = 1.8 Hz, 5-CH), 7.61 (t, 1H, J = 1.8 Hz,
˚
)
4-CH), 8.85 (s, 1H, 2-CH). MS(ESI+) [m/z (rel. int.,%)]:
M+ 139 (100) [BMIM]+, 83 (45) [MIM]+. MS (ESI−) [m/z
(rel. int.,%)]: M−. 145 (100) [PF6]−.
R1 = ΣꢀFo| − |Fcꢀ/Σ|Fo|, wR2 = {[Σw(Fo − Fc2)2]
/
a
2
1
[Σw(Fo2)2]}
.
/2
89%. The product was analyzed by 1H NMR and MS(ESI+
and ESI−). 1H NMR spectrum of 3 (CDCl3, 200 MHz)
δ = 0.99 (t, 3H, J = 7.4 Hz, 9-CH3) 1.41 (m, 2H, J = 7.5 Hz,
8-CH2), 1.92 (m, 2H, J = 7.5 Hz, 7-CH2), 4.10 (s, 3H,
10-CH3), 4.30 (t, 2H, J = 7.4 Hz, 6-CH2), 7.37 (t, 1H,
J = 1.8 Hz, 5-CH), 7.43 (t, 1H, J = 1.8 Hz, 4-CH), 10.15
(s, 1H, 2-CH). MS(ESI+) [m/z (rel. int.,%)]: M+ 139 (100)
[BMIM]+, 83 (90) [MIM]+. MS(ESI−) [m/z (rel. int.,%)]:
M−. 66 (100) [N(CN)2]−, 97 (10).
Preparation of 3-butyl-1-methylimidazolium hexafluoro-
phosphate [BMIM]PF6 (2) in water
[BMIM]Cl (1) (1 mmol), NaPF6 (1 mmol) and 1 ml of
distilled water were heated in a microwave reactor for 5 min
at 80 ◦C. An orange ionic liquid settled down. After cooling
the crude product was washed three times with distilled water
and dried overnight in a vacuum. The yield of a yellow 2 was
75%. According to 1H NMR the product was pure.
X-ray crystallography
Preparation of 3-butyl-1-methylimidazolium hexafluoro-
phosphate [BMIM]PF6 (2) at room temperature
Diffraction data of 1 were collected on a Nonius Kappa
CCD diffractometer using graphite monochromated Mo-Kα
radiation (λ = 0.71073 A) by recording 360 frames via ϕ-
[BMIM]Cl (1) (2 mmol), NaPF6 (2 mmol) and 1 ml of
acetone were mixed at room temperature for 4.5 h. After fil-
tration through Celite, the solvent was evaporated and the
brown product dried in a vacuum. The yield was 83%. The
1H NMR indicated that the product was pure.
˚
rotation (δϕ = 1◦; twice 20 s per frame). Crystal data and
details of structure determination are given in Table 7.
The structure was solved by direct methods using
SHELXS-97 [48] and refined using SHELXL-97 [49]. Af-
ter the full-matrix least-squares refinement of non-hydrogen
atoms with anisotropic displacement parameters, the hydro-
gen atoms were placed in calculated positions (C-H=0.95,
Preparation of 3-butyl-1-methylimidazoliumcc dicyanamide
[BMIM]DCA (3)
˚
[BMIM]Cl (1) (1 mmol) was weighted into a microwave 0.99, and 0.98 A in the case of aromatic hydrogen atoms,
methylene hydrogen atoms, and methyl hydrogen atoms, re-
The reaction mixture was irradiated for 10 min at 80 ◦C. The spectively).
reactor, 1 ml of acetone and NaPF6 (1 mmol) were added.
product mixture was filtered through Celite to remove solid
In the final refinement the hydrogen atoms were riding
NaCl. After the evaporation of acetone the yield of 3 was with the carbon atom they were bonded to. The isotropic dis-
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placement parameters of the aromatic hydrogen atoms were Crystallographic Data Center as the supplementary publi-
fixed at 1.2 times to those of the corresponding carbon atoms, cation number CCDC 208726. Copies of the data can be
and those of the aliphatic hydrogen atoms at 1.5 times to obtained free of charge on application to CCDC, 12 Union
those of the corresponding carbon atoms. The scattering fac- Road, Cambridge CB2 1EZ, UK (fax. +44-1223-336-033; e-
tors for the neutral atoms were those incorporated with the mail: deposit@ccdc.cam.ac.uk).
programs.
Acknowledgements
We are grateful for Mrs. Pa¨ivi Joensuu and Mrs. Sari Ek
for MS analyses. Financial support from the Fortum Founda-
tion, Academy of Finland, Tauno To¨nning Foundation, and
Kemira Oyj is also gratefully acknowledged.
Supplementary material available
Crystallographic information for 1 (excluding tables of
structure factors) has been deposited with the Cambridge
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