1-Alkyl-3-methylimidazolium alkanesulfonate ionic liquids, [C nH2n+1mim][CkH 2k+1SO3]: Synthesis and physicochemical properties

Article abstract of DOI:10.1039/b910177m

A set of 1-alkyl-3-methylimidazolium alkanesulfonate ionic liquids, [C _nmim][C_kSO₃], formed by the variation of the alkyl chain lengths both in the cation and the anion (n = 1-6, 8, or 10; k = 1-4, or 6), was synthesised, with sixteen of them being novel. The ionic liquids were characterised by ¹H and ¹³C NMR spectroscopy, and mass spectrometry. Their viscosities and densities as a function of temperature, as well as melting points and decomposition temperatures, were determined. The molecular volumes, both experimental and calculated, were found to depend linearly on the sum (n + k). the Owner Societies 2009.

Full text of DOI:10.1039/b910177m

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PAPER
www.rsc.org/pccp | Physical Chemistry Chemical Physics
1
-Alkyl-3-methylimidazolium alkanesulfonate ionic liquids,
mim][C H
[
C H
SO ]: synthesis and physicochemical propertiesw
n 2n+1
k 2k+1
3
Marijana Blesic,ab Ma$gorzata Swadz
´
ba-Kwas
´
ny, Tayeb Belhocine,
a
a
H. Q. Nimal Gunaratne, Jose
´
N. Canongia Lopes, Margarida F. Costa Gomes,c
´
´ ´
Agılio A. H. Padua, Kenneth R. Seddon and Luıs Paulo N. Rebelo*
a
bd
c
ab
b
Received 22nd May 2009, Accepted 16th July 2009
First published as an Advance Article on the web 19th August 2009
DOI: 10.1039/b910177m
A set of 1-alkyl-3-methylimidazolium alkanesulfonate ionic liquids, [C mim][C SO ], formed by
n
k
3
the variation of the alkyl chain lengths both in the cation and the anion (n = 1–6, 8, or 10;
k = 1–4, or 6), was synthesised, with sixteen of them being novel. The ionic liquids were
1
13
characterised by H and C NMR spectroscopy, and mass spectrometry. Their viscosities and
densities as a function of temperature, as well as melting points and decomposition temperatures,
were determined. The molecular volumes, both experimental and calculated, were found to
depend linearly on the sum (n + k).
Introduction
Ionic liquids have recently received much attention as possible
1
alternatives to volatile organic compounds. They can replace
more conventional media to perform chemical reactions, to
support homogeneous or heterogeneous catalytic processes, or
to carry out extractions and separations. A broad range of
possible cations and anions allows us to create diverse ionic
2
liquids, tailored to various needs, but there have been few
Fig. 2 Schematic representations showing different families of ionic
studies in which both the cation and the anion have been
liquids; in (left), members of the 1-alkyl-3-methylimidazolium family
are shown with different anions, defining traditional homologous
series (different series represented by the solid lines) that can be
correlated whenever two ionic liquids have a common cation (dashed
lines); in (right), members of the [C mim][C SO ] ionic liquid family
3
systematically varied. In this work, a family of ionic liquids
,4
ꢀ
based on alkanesulfonate anions, [C
k
+
SO
3
] , and 1-alkyl-3-
methylimidazolium cations, [C
linear alkyl side chains were varied independently, was prepared
Fig. 1). A two-stage synthetic route to prepare these
n
mim] , where lengths of the
n
k
3
(
are shown. This family is characterised by a matrix-like arrangement
of its members (solid lines). The filled dots represent ionic liquids
synthesised and characterised in the present study.
5
compounds has recently been reported; however, these syntheses
were not strategically performed in a systematic manner to
obtain a matrix-like family of ionic liquids, nor was a detailed
and more complete physicochemical characterisation of the
resulting salts attempted.
counter-ion in a systematic way—i.e. by increasing the alkyl
side chain length in a homologous series, or varying the degree
of substitution. Here, the family of ionic liquids was designed
by altering the nature of both the cation and the anion in a
systematic way, and thus creating a two-dimensional matrix of
ionic liquids (see Fig. 2). This work aims to discover if there
are any correlations between the structure and properties
within this new family of ionic liquids. This is important
per se especially if one considers that the length of an alkyl
side chain appended to a cationic polar head can determine the
existence and the morphology of apolar nano-domains in neat
ionic liquids. New fundamental structural issues will naturally
emerge if one considers the present case in which alkyl side
chains of different lengths can be attached to the cation, to the
anion, or to both.
Traditionally, an ionic liquid family is established by using
one fixed anion or cation and varying the nature of the
n k 3
Fig. 1 Structure of [C mim][C SO ] ionic liquids.
a
b
The QUILL Centre, The Queen’s University of Belfast,
Stranmillis Road, Belfast, UK BT9 5AG
Instituto de Tecnologia Quı´mica e Biolo´gica, Universidade Nova de
Lisboa, Apartado 127, 2780-901, Oeiras, Portugal.
E-mail: luis.rebelo@itqb.unl.pt
Laboratoire de Thermodynamique et Interactions Mole´culaires,
Universite´ Blaise Pascal, Clermont-Ferrand/CNRS, 63177, Aubie`re,
France
Centro de Quı´mica Estrutural, Instituto Superior Te´cnico, 1049-001,
Lisboa, Portugal
c
It is also interesting to investigate how these ionic liquids
(based on alkanesulfonates) differ, in terms of their physico-
chemical properties, from the related alkanesulfate family,
d
ꢀ
1
[C SO ] , especially as the latter has been suggested as a set
k
w Electronic supplementary information (ESI) available: H NMR
and C NMR data. See DOI: 10.1039/b910177m
4
13
6,7
of particularly environmentally friendly ionic liquids and,
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more recently, as potential candidates to be used in the
8
construction of a liquid-mirror lunar telescope.
Q50 thermogravimetric analyser. The measurements were
ꢀ1
done in platinum pans, at a heating rate of 10 K min , in
A series of 1-alkyl-3-methylimidazolium alkanesulfonate
air. The onset of the weight loss in each thermogram was used
as a measure of the decomposition temperature.
ionic liquids, [C mim][C SO ] (n = 1–6, 8, or 10; k = 1–4,
n
k
3
or 6) was prepared (see Fig. 2), and their melting points,
decomposition temperatures, and density and viscosity as a
function of temperature were determined.
Density measurements. Density was measured with an
Anton Paar vibrating tube densimeter, model DMA 5000,
operating at atmospheric pressure and within the temperature
range 293 to 333 K.
Experimental
The internal calibration of the instrument was confirmed by
measuring the densities of atmospheric air and doubly distilled
water, according to the recommendations of the manufacturer.
The DMA 5000 cell was embedded in a metallic block, the
temperature of which was controlled by several Peltier units.
This arrangement allowed a temperature stability better
than ꢂ2 mK.
Instrumental procedures
NMR spectroscopy. All NMR spectra were recorded on a
Bruker Avance spectrometer DPX 300 at 27 1C, using
deuterated trichloromethane as solvent (10–20 mM solutions
1
for H NMR spectroscopy).
Mass spectrometry. All mass spectra of ionic liquids (diluted
solution in ethanenitrile) were recorded using a Waters LCT
PREMIER Electrospray mass spectrometer.
All ionic liquids used in the density determinations were
degassed under vacuum and moderate temperature conditions
for periods longer than 24 h and stored in sealed vials prior to
injection in the densimeter, using non-lubricated disposable
syringes.
Karl Fischer analysis. The water content of ionic liquids was
measured by coulometric Karl Fischer (Metrohm) titration.
Ionic liquids were tested immediately after drying under high
vacuum, and the water content was below 150 ppm for all
samples.
Viscosity measurements. The viscosity was determined using
a rheometer, Rheometrics Scientific SR200, that allows
measurements from 293 to 393 K at atmospheric pressure,
and in a wide viscosity range (1 to 3000 mPa s) depending on
the geometry used. A Couette geometry (concentric cylinders)
was chosen for this study. Temperature was maintained
constant to within 0.01 K by means of a recirculating bath
and was measured with the same accuracy using a platinum
resistance thermometer (PRT) from Hart Scientific (model
Differential scanning calorimetry (DSC). The melting points
of the synthesised ionic liquids were measured by DSC, using
a TA Instruments Modulated DSC 2920. Cooling was
accomplished by using a refrigerated cooling system capable
of controlling the temperature down to 220 K. Dry nitrogen
3
ꢀ1
gas (flow rate of ca. 20 cm min ) was purged through the
DSC cell. The heating/cooling regime was adjusted for each
sample separately.
5
612, accuracy of ꢂ0.018 1C at 0 1C), calibrated against a
secondary reference temperature standard. To decrease the
water contamination of the sample during the measurements,
the rheometer was placed inside a glove-box in an isolating
atmosphere of purified and dried air.
Typically, for solid 1-alkyl-3-methylimidazolium alkane-
ꢀ1
sulfonates, a standard heating and cooling ramp of 5 K min
was used. For liquid samples, including supercooled ionic
liquids, much lower cooling and heating rates were used
In order to improve the accuracy of the viscosity measurements,
the rheometer was calibrated, as a function of temperature,
with the standard viscosity oil N100 from Cannon Instrument
Company (280 mPa s at 293 K).
ꢀ1
(
0.2 to 1 K min ). Both the onset and the peak melting
temperatures were measured and, for each ionic liquid, the
enthalpy of fusion was determined by integration of the
experimental heat flow curves as functions of temperature.
In some cases it was impossible to detect the phase transitions
Viscosity measurements were performed in steps of approxi-
mately 10 K from 293 K up to 360 K in all the ionic
3
liquid samples in which a sufficient amount (ca. 14 cm ) was
(
crystallisation and melting) using the DSC cell. Therefore, for
[
[
C mim][C SO ], [C mim][C SO ], [C mim][C SO ], and
3
2
2
3
2
3
3
2
4
available. Similar measurements performed before in the same
9
equipment permitted a statistical analysis of the results that
C mim][C SO ], seeds were used to trigger crystallisation in
1
6
3
supercooled ionic liquid samples. This procedure could not be
implemented in the DSC cell due to the small size of the
samples used in that case. As a consequence, the samples were
heated slowly in a small glass vial, and melting points were
determined visually as the temperature of the disappearance of
the last crystal. In this case, the uncertainty of the melting
point temperatures (ꢂ3 K in most cases) is much greater than
that of measurements in the DSC cell (or even that of
commercial capillary melting point instruments). The use of
small vials instead of capillary tubes in this case is related to
the handling of the viscous ionic liquid samples.
has indicated a precision in the viscosities of 0.2% and an
overall uncertainty lower than 1%. The same precision cannot
be claimed in the present measurements due to the problems
related to the hygroscopic behaviour of ionic liquids (see two
paragraphs above). An overall uncertainty of around 10% was
estimated in this case, inferred from experiments where the
determinations were cycled over time and temperature in order
to check the reproducibility of the viscosity data.
Materials
The nineteen ionic liquids used in this study were synthesised
following the procedure described below. These include
Thermogravimetric
analysis
(TGA).
Decomposition
temperature measurements were performed in a TA Instruments
[C mim][C SO ],
1
n
=
1–6,
8 or 10; [C mim][C SO ],
n 2 3
n
3
8
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n = 2–6; [C
n = 2 or 3; and [C
-Methylimidazole (Z 99%; Aldrich) was purified by
n
mim][C
3
SO
3
], n = 2, 3, or 4; [C
n
mim][C
4
SO
3
],
Table 2 Masses of reactants (m) and reaction conditions (reaction
time, t) for the synthesis of [C mim][C SO ] ionic liquids
2
mim][C
6
SO ] (Fig. 2).
3
n
k
3
1
m/g
distillation from sodium hydroxide immediately prior to use.
Ester
SO
Yield
(%)
Dichloromethane, ethyl ethanoate, ethyl methanesulfonate
k n
C
k
3
C
n
mim
T/1C t/h
Product
(
Z98%), ethanesulfonyl chloride (Z99%), 1-propanesulfonyl
chloride (Z 98%), 1-butanesulfonyl chloride (Z 98%),
-propanol (Z 99.8%), 1-butanol (Z 99.8%), 1-hexanol
Z 99.5%), 1-octanol (Z 99%), 1-decanol (Z 99%), sodium
1
1
2
3
4
5
6
8
0
2
3
4
5
6
2
3
2
3
25.0
25.0
24.3
35.0
41.9
20.0
23.8
27.8
7.0
24.0
26.9
21.5
25.0
26.8
13.7
36.6
24.3
17.8
16.8
13.8
18.0
19.7
8.7
8.9
9.6
4.0
14.9
12.7
9.3
10.1
13.7
6.8
0
50
70
70
70
70
70
70
50
60
50
50
50
50
70
50
50
1
72
96
50
72
72
72
96
48
72
72
72
72
48
72
72
72
97
91
94
86
86
67
82
85
87
90
84
52
55
42
71
70
68
White solid
Pale yellow liquid
Pale yellow liquid
White crystals
White solid
Pale yellow liquid
Pale yellow liquid
White solid
Pale yellow liquid
Pale yellow liquid
White solid
White solid
White solid
1
(
hexanesulfonate (98%), and trimethylamine (Z 99%) were
purchased from Aldrich and used as received. Methyl methane-
sulfonate, CH
Organics.
3 3 3
SO CH (99%), was purchased from Acros
1
2
Synthetic procedures
All but three ionic liquids, 1,3-dimethylimidazolium methane-
sulfonate, 1-ethyl-3-methylimidazolium hexanesulfonate, and
3
4
Yellow liquid
White solid
Yellow liquid
Yellow liquid
1-ethyl-3-methylimidazolium methanesulfonate, were prepared
17.2
10.5
in two stages, as discussed in ref. 5 and also below in more
detail. All procedures were performed under dry nitrogen.
3
(
i) Syntheses of alkanesulfonate esters. Alkan-1-ol
dissolved in ethyl ethanoate (150 cm ). The reaction mixture
was stirred under reflux for several hours. Upon completion of
the reaction, the crude product (lower ionic liquid layer) was
(
(
C H OH; n = 2–10) (1.1 mol eq.) and triethylamine
n
3
1.1 mol eq.) were dissolved in dichloromethane (430 cm ),
2n+1
3
placed in a round-bottomed flask (fitted with a thermometer), and
stirred vigorously. The mixture was cooled in an ice-bath, and
washed six times with ethyl ethanoate (ca. 50 cm ) and the
remaining solvent removed under reduced pressure to yield the
pure product. Details of individual syntheses are given in
Table 2.
alkylsulfonyl chloride (C
3
1 mol eq.) dissolved in dichloromethane (100 cm ) was added
k 2
H2k+1SO Cl, k = 1–4, or 6)
(
dropwise to maintain a reaction temperature below 0 1C. The
reaction mixture was then stirred for several hours at room
1,3-Dimethylimidazolium
methanesulfonate.
Methyl
1
temperature (monitored by H NMR spectroscopy), until a
methanesulfonate (25 g, 1.05 mol eq) dissolved in ethyl
3
ethanoate (50 cm ) was placed in a round-bottomed flask
3
(500 cm ) and stirred vigorously. The mixture was cooled in
white solid precipitated. The solid was removed by filtration,
and dichloromethane was removed using a rotary evaporator
to yield the crude liquid product. This was purified by
fractional vacuum distillation to yield a colourless liquid.
Details of individual syntheses are given in Table 1.
an ice-bath, and 1-methylimidazole (17.8 g, 1 mol eq.)
3
dissolved in ethyl ethanoate (50 cm ) was added dropwise
using a pressure-equalising dropping funnel. Upon addition,
a strongly exothermic reaction was observed. The mixture
was stirred for 8 h; subsequently, the crude solid product
(
ii) Syntheses of 1-alkyl-3-methylimidazolium alkanesulfonate
ionic liquids. The freshly distilled alkyl alkanesulfonate ester
C H SO C H2k+1) (1.1 mol eq.) and 1-methylimidazole
was collected by filtration, washed with ethyl ethanoate
3
(
n
2n+1
3 k
(
4 ꢃ 50 cm ) in order to remove unreacted reagents, and the
(
1 mol eq.) were placed in a round-bottomed flask and
remaining solvent was removed under reduced pressure using
a rotary evaporator (60 1C, 1 h). The product was a
white solid.
Table 1 Masses of reactants (m) and reaction conditions (reaction
time, t) for the synthesis of alkanesulfonate esters, C
k
H
2k+1SO
3
C
n
H
2n+1
m/g
NEt
1-Ethyl-3-methylimidazolium
hexanesulfonate.
Sodium
hexanesulfonate (10 g, 1.0 mol eq.) and 1-ethyl-3-methyl-
imidazolium chloride (7.8 g, 1.0 mol eq.) were dissolved
k
n
C
n
H
2n+1OH
3
C
k
H
2k+1SO
2
Cl
t/h
1
3
4
5
6
8
0
2
3
4
5
6
2
3
2
3
21.5
32.0
29.2
37.4
—
33.1
29.1
17.4
20.3
26.9
23.1
19.5
46.1
49.9
42.6
42.1
—
30.0
72.6
44.7
36.1
39.3
29.2
54.2
19.9
51.1
39.3
37.3
45.2
43.5
38.1
—
21.8
60.3
45
32.8
35.7
26.5
35.1
37.3
56.5
43.4
12
12
12
48
48
48
12
12
48
12
12
12
12
12
12
3
separately in methanol (150 and 40 cm , respectively). The
3
solutions were combined in a round-bottomed flask (500 cm )
and stirred for 5 d. Then, the methanol was removed under
reduced pressure using a rotary evaporator (25 1C, 1 h).
Subsequently, propanone (100 cm ) was added to the mixture
1
3
2
in order to precipitate sodium chloride; the precipitate was
removed by filtration, and the propanone was removed under
reduced pressure to yield a yellow liquid.
Prior to use, all synthesised ionic liquid samples were
thoroughly degassed and dried to remove any small traces of
volatile compounds by applying a vacuum (ca. 0.1 Pa) at
moderate temperatures (60–80 1C) for at least 24 h.
3
4
9.27
18.3
18.3
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Results and discussion
observed for each ionic liquid in positive mode or in negative
mode, corresponding to cation or anion in each case
Synthetic procedures
(
see Table 3). Accurate mass spectrometry confirmed the
identity of each of the ions within the experimental error of
the technique.
The general procedure, used to synthesise most of the ionic liquids,
provided an efficient and chloride-ion-free synthetic route. The
yield for ionic liquids was typically better than 70%, and in one
case approached 97%. The reaction was essentially quantitative,
with purification being the yield-reducing step.
Melting point measurements
The melting points (T ) measured for the ionic liquids studied
m
In the case of 1,3-dimethylimidazolium methanesulfonate
and 1-ethyl-3-methylimidazolium methanesulfonate, the corres-
ponding esters were readily available, so step (i) was omitted.
Moreover, the reaction of the synthesis of 1,3-dimethylimid-
azolium methanesulfonate is very exothermic, hence the
procedure for step (ii) was modified and described separately.
In the case of 1-ethyl-3-methylimidazolium hexane-
sulfonate, an alternative synthetic route was used due to the
high cost of the starting material.
are reported in Table 4. A typical example of a DSC curve is
presented in Fig. 3.
The majority of the ionic liquids studied have melting
temperatures above the ambient, except in the cases of
[
C
2
mim][C
have melting points below 20 1C. Three other ionic
liquids—[C mim][C SO ], [C mim][C SO ] and [C mim][C SO ]—
3 3 2 6 3 3 2 3
SO ], [C mim][C SO ] and [C mim][C SO ] that
2
1
3
2
2
3
3
4
3
have melting points close to 30 1C and all other 1-alkyl-3-
methylimidazolium alkanesulfonate ionic liquids melt at higher
temperatures, with a maximum of 91 1C for [C mim][C SO ].
1
1
3
Nuclear magnetic resonance spectroscopy
Fig. 4 shows a dependency of the melting point upon the
cationic chain length, but there are not enough data to
determine whether there is any pattern associated with anionic
chain length. Similarly, it is difficult to perceive a pattern in the
sparse data available for the 1-ethyl-3-methylimidazolium
k 3 n
All the intermediate esters of the general formula C SO C
were prepared and purified as described above. As these were
key reagents in the syntheses of the alkylsulfonate ionic
liquids, it was important to establish that no other esters were
1
7
present. H NMR spectroscopy established the absence of any
alkylsulfates, [C mim][C SO ], where the melting point
2
k
4
7
,11
other esters or alcohols.
1
temperature seems to vary randomly.
In contrast, the
13
H and C NMR spectra of the [C mim][C SO ] ionic
n
k
3
melting point temperatures of 1-alkyl-3-methylimidazolium
1
2
13
liquids showed no major impurities in the untreated, original
samples, except for the presence of residual water (detected
independently by Karl Fischer analysis); typical spectra are
tetrafluoroborate and hexafluorophosphate ionic liquids,
although showing no monotonic behaviour, present a regular,
easy to rationalise pattern as the size of the alkyl chain in the
cation varies. The melting point temperatures of the three
1
shown in Fig. 1S of the ESI.w H NMR signals obtained for
5
the ionic liquids are also given in Table 1S of the ESI,w along
members of the family that had been previously studied,
1
3
with C NMR signals listed in Table 2S:w assignments are in
accordance with the literature, including those reported for
[C mim][C SO ], [C mim][C SO ], and [C mim][C SO ],
1
1
1
4
4
2
4
4
4
compare quite well for the two first cases, but exhibit a large
deviation in the last case (cf. Table 4).
5
,10
similar compounds.
The enthalpies of fusion are reported in Table 4. The highest
ꢀ
Mass spectrometry
1
value was found for [C10mim][C
the majority of the samples studied have enthalpies of fusion
1 3
SO ] (ca. 38 kJ mol ), while
All the ionic liquids prepared were examined by electrospray
mass spectrometry (MS), in ethanenitrile. Only one peak was
ꢀ
1
.
between 14 and 22 kJ mol
+
Table 3 Electrospray MS results obtained for [C
nominal value of the singular peak) or in negative mode (M (100) is the mass nominal value of the singular peak)
n k 3
mim][C SO ] ionic liquids obtained for each ionic liquid in positive mode (M (100) is the mass
ꢀ
+
M
a
Dm
ꢀ
a
Dm
k
n
(100)
m
calc
m
exptl
M
(100)
m
calc
m
exptl
1
1
2
3
4
5
6
8
0
2
3
4
5
6
2
3
2
3
2
97
97.0776
111.0922
125.1079
139.1235
153.1392
167.1548
181.1829
223.2174
111.0922
125.1079
139.1235
153.1392
167.1548
111.0922
125.1079
111.0922
125.1079
111.0922
97.0770
111.0922
125.1076
139.1228
153.1383
167.1499
181.1822
223.2164
111.0966
125.1073
139.1231
153.1389
167.1550
111.0924
125.1077
111.0922
125.1076
111.0921
0.0006
0
95
95
95
95
95
95
95
95
109
109
109
109
109
123
123
137
137
165
94.9803
94.9803
94.9803
94.9803
94.9803
94.9803
94.9803
94.9803
108.9959
108.9959
108.9959
108.9959
108.9959
123.0116
123.0116
137.0272
137.0272
165.0585
94.9795
94.9800
94.9801
94.9799
94.9796
94.9796
94.9799
94.9798
108.9980
108.9950
108.9953
108.9952
108.9970
123.0106
123.0112
137.0264
137.0263
165.0580
0.0008
0.0003
0.0002
0.0004
0.0007
0.0007
0.0004
0.0005
ꢀ0.0021
0.0009
0.0006
0.0007
ꢀ0.0011
0.001
111
125
139
153
167
181
223
111
125
139
153
167
111
125
111
125
111
0.0003
0.0007
0.0009
0.0049
0.0007
0.001
ꢀ0.0044
0.0006
0.0004
0.0003
ꢀ0.0002
ꢀ0.0002
0.0002
0
1
2
3
4
0.0004
0.0008
0.0009
0.0005
0.0003
0.0001
6
a
Dm = mcalc ꢀ mexptl
.
8
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Table 4 Values of the melting points, T
m
, and of the enthalpies of fusion, DHfus, for the 1-alkyl-3-methylimidazolium alkylsulfonate ionic liquids,
[
melting peak tangent-intersection procedure. Values in parentheses were reported in ref. 5
C
n
mim][C SO ], as measured by DSC or a visual method. The temperature values obtained from DSC data were calculated using the usual
k
3
k
1
2
3
4
6
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
n
T
m
/1C
DHfus/kJ mol
T
m
/1C
DHfus/kJ mol
T
m
/1C DHfus/kJ mol
T
m
/1C DHfus/kJ mol
T
m
/1C DHfus/kJ mol
1
2
3
4
5
6
8
0
91.0 (93.2) 17.5
—
—
—
14.0
—
—
—
11.3
14.1
—
—
—
—
—
—
—
20.8
—
—
—
—
—
—
19.1
—
—
—
—
—
—
12.4
—
—
—
—
—
a
a
a
30.6
39.8
16.0
15.2
26–32
19.0
57.3 (57.0) 19.6
54.4
65.7
—
37–43
32.0
53.0
—
—
—
1–7
47.2
—
—
—
73.7 (52.0) 22.0
76.7
21.9
—
33.9
38.4
16.1
16.9
—
a
44–50
38.4
57.4
—
—
1
—
—
—
—
—
a
Temperature range of the visually determined melting point temperatures.
Table 5 Decomposition temperatures, T
dynamic TGA
d
, for [C
n
k 3
mim][C SO ], by
d
T /1C
k
n
1
2
4
1
380
—
333
352
337
335
—
342
—
—
—
—
—
2
3
4
6
0
340
349
—
—
—
1
TGA scan is shown in Fig. 5. It should be noted, however, that
these data should be treated with extreme caution. Scanning
TGA significantly overestimates decomposition temperatures
Fig. 3 A typical DSC scan for [C
n
mim][C
k
SO
3
] ionic liquids; example
1
4
ꢀ
1
of [C
3
mim][C
1
SO
3
], scan speed 1 K min
.
(by up to 150 1C), but the sequence of data is reliable when
the samples are run under identical conditions.
With this caveat, the ionic liquids studied have shown good
thermal stability, with decomposition temperatures ranging
from 330 to 380 1C. In contrast, the decomposition temperature
of 1-ethyl-3-methylimidazolium ethanesulfate is significantly
lower (230 1C, determined here under identical conditions).
This confirms that, as expected, the ionic liquids based on
alkylsulfonates are significantly more stable than those based
on alkylsulfates.
Fig. 4 Dependency of the melting point upon the cationic chain
length for three series of [C mim][C SO ] ionic liquids; k = 1 (circles),
n
k
3
k = 2 (squares) or k = 3 (triangles).
Thermogravimetric analysis
Decomposition temperatures (onset of weight loss in the
thermogravimetric run) are reported in Table 5. A typical
Fig. 5 A typical TGA curve for [C mim][C SO ] ionic liquids;
n
k
3
example of [C mim][C SO ].
3
1
3
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Density
The viscosity-corrected density measurements are reported in
Table 6, along with the corresponding molar volume data,
m
V , for each studied ionic liquid. The repeatability of the
ꢀ
3
density measurements was better than 0.05 kg m
and
the expanded uncertainty was estimated as ranging from
ꢂ0.3 kg mꢀ to ꢂ2 kg m for low-viscosity and high-viscosity
3
ꢀ3
1
5
samples, respectively.
All reported density data were
corrected for the effect of viscosity on density determinations
with a vibrating tube densimeter, according to the empirical
0
.5
ꢀ4
equation, (r ꢀ rraw)/rraw = (0.5 ꢀ 0.45Z ) ꢃ 10 , where
r and rraw are the corrected and measured (raw) densities,
1
6
respectively, and Z (mPa s) is the sample viscosity. Herein,
ꢀ3
the correction can be as high as 1.7 kg m for samples with
viscosities greater than 1700 mPa s.
Fig.
6
Temperature-independent thermal expansion coefficient,
a
p
= ꢀ[q(ln r)/qT)]
p
, as a function of the total number of carbon
mim][C SO ] ionic liquids,
The temperature-dependence of the density data is fitted by
a simple linear regression, and the fitting parameters are also
shown in Table 6. The deviations between the fitted and
experimental Vm data are smaller than 0.005%—comparable
to the repeatability of the measurements—which means that a
ln(r) = f(T) function more complex than a simple straight line
is not warranted in this case (as in the case of ionic liquids in
atoms, n + k, in the alkyl side chains of [C
n
k
3
calculated from the density data obtained at atmospheric pressure.
Points are identified as (n, k). The straight line represents the linear
2
regression, R = 0.88.
The molar volume results show a consistent trend along the
series of 1-alkyl-3-methylimidazolium alkanesulfonate ionic
liquids, increasing proportionately with the number of the
1
6–18
general
). The advantage of using a linear regression to fit
, for
ln(r) values is that the thermal expansion coefficient, a
p
each ionic liquid will be a constant at a given pressure and it
will be easy to obtain from the slope of the regression line: if
methylene (–CH –) groups present in the alkyl chains of the
2
cation and/or the anion. An extra mole of methylene groups in
ln(r) = mT + b, then dln(r)/dT = ꢀa
p
= m. Fig. 6 shows the
the alkyl chains will always increase its molar volume by the
3
ꢀ1
values of a for the eight ionic liquids where density data were
p
same amount, 17.06 ꢂ 0.04 cm mol at 298.15 K, irrespective
of the ionic liquid itself; this value compares favourably with a
previous, multi-averaged determination of an increase of
measured at different temperatures.
Fig. 6 shows that, although the scatter of the a values is much
larger than that of the r data (the former quantity is a derived
property of the latter), there is a correlation between the total
p
3
ꢀ1
17,18
17.2 ꢂ 0.3 cm mol per (–CH –) at 298.15 K.
2
To the
best of our knowledge, it is shown, herein, for the first time
number of carbon atoms in the alkyl side chain and the value of a
p
.
that this change is irrespective of the (–CH –) addition taking
2
ꢀ3
Table 6 Experimental values of the density, r/g cm , and molar volume, V
m n k 3
, of [C mim][C SO ] ionic liquids, at temperatures T = 293.15 to
3
33.15 K. The dV values represent the difference between V values and molar volume data calculated using the fitting equations. In these
m
m
equations, the slope is symmetrical to the temperature-independent thermal expansion coefficient, a
p
= ꢀ[q(ln r)/qT)]
p
—see Fig. 6
k
1
2
4
ꢀ3
3
/cm mol
ꢀ1
3
/cm mol
ꢀ1
ꢀ3
3
/cm mol
ꢀ1
3
/cm mol
ꢀ1
ꢀ3
3
/cm mol
ꢀ1
3
/cm mol
ꢀ1
n
T/K
r/g cm
V
m
dV
m
r/g cm
V
m
dV
m
r/g cm
V
m
dV
m
ꢀ
3
ꢀ3
ꢀ3
2
ln(r) = 0.3754 ꢀ (0.5370 ꢃ 10 ) T
ꢀ0.005
ln(r) = 0.3439 ꢀ (0.5315 ꢃ 10 ) T
ln(r) = 0.2982 ꢀ (0.5524 ꢃ 10 ) T
2
2
3
3
93.15 1.24347 165.879
98.15 1.24020 166.317
1.20691 182.526
1.20366 183.019
1.19419 184.470
1.18149 186.453
0.002
ꢀ0.006
0.008
1.14601 216.705
1.14287 217.301
1.13343 219.110
1.12097 221.545
ꢀ0.002
0.003
0.006
0.002
0.001
13.15 1.23027 167.658
33.15 1.21706 169.478
ꢀ0.003
0.003
ꢀ0.001
ꢀ
3
ꢀ3
ꢀ3
3
ln(r) = 0.3462 ꢀ (0.5408ꢃ10 ) T
ln(r) = 0.3178 ꢀ (0.5373ꢃ10 ) T
ln(r) = 0.2779 ꢀ (0.5547ꢃ10 ) T
293.15
298.15
3
3
—
—
—
—
—
—
1.17383 199.619
1.17071 200.152
1.16128 201.778
1.14889 203.954
1.12170 221.401
ꢀ0.001
0.003
ꢀ0.003
0.001
—
1.12215 233.813
1.11912 234.446
1.10984 236.407
1.09756 239.052
ꢀ0.009
0.007
0.005
ꢀ0.003
—
13.15 1.19351 184.576
33.15 1.18067 186.583
0
0
4
6
333.15
—
—
—
—
—
ꢀ3
ln(r) = 0.2791 ꢀ (0.5613 ꢃ 10 ) T
2
2
3
3
93.15 1.12137 233.976
ꢀ0.006
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
98.15 1.11828 234.622
13.15 1.10889 236.610
33.15 1.09649 239.285
0.006
0.002
ꢀ0.002
ꢀ3
8
ln(r) = 0.2489 ꢀ (0.5707 ꢃ 10 ) T
2
2
3
3
93.15 1.08499 267.678
0.005
ꢀ0.010
0.007
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
98.15 1.08184 268.458
13.15 1.07268 270.749
33.15 1.06047 273.866
ꢀ0.002
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The idea of estimating the density along a family of ionic
liquids using the additive character of V
m
via the sum of
1
8
effective ion volumes was first proposed by Rebelo et al.
1
9–21
and further refined by other authors
who devised
empirical group contribution methods (see Table 7). The
present data confirm the general validity of those methods
and extend their scope: (i) alkanesulfonate-based ionic liquids
were added to the list of compounds whose density can be
ꢀ
estimated—at 298.15 K, the group, [C
0
SO
17,20
3
] , contributes with
3
8.9 cm mol for those methods
ꢀ1
4
(to be compared with
ꢀ
3
= 57.0 cm mol —taken as the difference between
ꢀ1
[C
0
SO
4
]
ꢀ
the molar volume of [C
0,22
methylene groups)
ꢀ
2
4
SO ]
and the volume of two
2
where the contribution of the anion
3
PF6] was postulated as 73.7 cm mol ; and (ii) most
ꢀ1
[
importantly, it was shown that these methods work not
only by regularly varying the structure of one of the ions
constituting the ionic liquid (along ‘row-like’ families of ionic
liquids) but also by simultaneously changing the structure of
the two ions (‘matrix-like’ ionic liquid families like in the
1-alkyl-3-methylimidazolium alkanesulfonate series).
Fig. 7 Experimental molar volume of 1-alkyl-3-methylimidazolium
alkylsulfonate, [C mim][C SO ], ionic liquids at 333.15 K (K) as a
function of the number of carbon atoms in the alkyl chain of the cation
x-axis), n, and the total number of carbon atoms in the alkyl chains of
n
k
3
(
both ions (secondary y-axis), (n + k). The open dots represent other
members of the 1-alkyl-3-methylimidazolium alkanesulfonate family
whose density was not measured experimentally but can be estimated
using the molar volume additive character within the family. The lines
represent series of ionic liquids with the same number of carbon atoms
The recent discovery that ionic liquids can be understood
2
3
as nano-segregated fluids, composed of a polar network
permeated by non-polar islands or domains, can help one to
understand, from a molecular point of view, the fact that an
added methylene group always contributes to an increase in
3
ꢀ1
in the anion, and have a slope of 17.45 cm mol , at 333.15 K.
3
ꢀ1
the molar volume of the ionic liquid of ca. 17 cm mol
,
place in the cation or the anion. Fig. 7 depicts such behaviour,
with the experimental molar volume points (closed circles)
superimposed in a regular grid (open circles) built taking
into account only the number of methylene groups in the
alkyl chains of the cation (x-axis) and the total number of
methylene groups of the ionic liquid (secondary y-axis). As
stated above, the nature of the family of ionic liquids studied
in this work, where the size of the alkyl chains can be varied
both in the anion and in the cation, implies that it can be
ordered not in a simple ‘row’ but in a ‘matrix’. This fact is
clearly denoted in Fig. 7 by the above-mentioned regular grid
of white points. The observation that all experimentally
determined molar volumes fit that grid, with deviations
always smaller than 0.2%, constitutes a proof of the additive
character of the molar volume within this particular family of
ionic liquids.
irrespective of the nature of the ionic liquid: such nano-
segregation implies that when a methylene group is added to
an existing alkyl side chain it will tend to be positioned near
other alkyl side chains, i.e. a molecular environment similar to
that of linear alkanes. In the series of linear alkanes (from
hexane to decane at 298 K and 1 atm), the molar volume also
increases in a monotonic and regular manner, with each extra
3
ꢀ1
–
CH – group adding 16 cm mol to the molar volume of the
2
previous member of the series (deviations from this pattern are
24
smaller than 0.2%).
Viscosity
It was observed that the ionic liquid samples were highly
hygroscopic and, even when all the appropriate precautions
were taken, water uptake by the samples could be detected.
This effect was evaluated by measuring the viscosity of the
ionic liquid samples at regular time intervals, which showed a
decrease in viscosity of less than 10% after 10 h, at 295 to
Table 7 Effective molar volumes of different constituent parts of
1-alkyl-3-methylimidazolium alkanesulfonates: extension of previously
established contribution schemes for the estimation of the molar
volume of ionic liquids. The molar volume of any ionic liquid,
3
60 K. Thus, the overall uncertainty of the present viscosity
measurements can be estimated as o5%.
[
(
(
C
n
mim][C SO ], is estimated by adding the molar volumes of (n + k)
k 3
The results obtained for the viscosity of the ionic liquid
samples are included in Table 8. The values range from 17 mPa s
for [C mim][C SO ] at 356 K to 1055 mPa s for [C mim][C SO ]
+ ꢀ
0 3
mim] and [C SO ]
–CH –) groups to the molar volumes of [C
2
values for T = 298.15 K)
0
2
2
3
2
4
3
3
/cm mol
ꢀ1
V
m
at 296 K. These values are similar to those found for alkyl-
sulfate-based ionic liquids, or for [C
in Fig. 8.
4 6
mim][PF ], as can be seen
Rebelo
et al.
Ye and
Shreeve
Jacquemin
et al.
This
work
2
2
19
20
The experimental viscosities were correlated with temperature
using both an Arrhenius-like expression, eqn (1), and a
+
a
b
a
a
[
[
–
C
C
CH
0
0
mim]
]
64.8
—
75.9
—
16.9
66.0
—
66.0
48.9
ꢀ
SO
3
2
6
2
–
17.2
17.1
17.06
Vogel–Fulcher–Tamman (VFT) equation, eqn (2):
Z = Z /RT)
exp(ꢀE
Z = AT exp(B/(T ꢀ T ))
a
ꢀ
Scheme based on the hypothesis that in [PF
ꢀ
6
] -based ionic liquids
3
to the molar volume is 73.7 cm mol
ꢀ1
ꢀ1
N
a
(1)
(2)
the contribution of [PF
b
6
]
Scheme based on a contribution of [PF ] equal to 64.4 cm mol
.
.
ꢀ
3
6
0
.5
0
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Table 8 Experimental values of the viscosity for a series of [C
n
mim][C
k
SO
3
] ionic liquids
k
1
2
4
a
b
a
b
a
b
n
T/K
Z/mPa s Dev (1) (%) Dev (2) (%) T/K
Z/mPa s Dev (1) (%) Dev (2) (%) T/K
Z/mPa s Dev (1) (%) Dev (2) (%)
2
295.06 184.73
14.30
0.50
0.03
ꢀ0.10
ꢀ0.32
1.10
0.09
ꢀ0.38
ꢀ1.61
0.16
ꢀ0.42
ꢀ0.15
0.28
1.51
2.97
—
296.11 233.61
302.61 153.51
11.09
0.86
0.05
ꢀ0.25
0.41
296.37 531.41
302.53 328.18
15.28
1.99
0.03
ꢀ0.16
0.28
ꢀ0.08
0.54
ꢀ0.48
ꢀ1.75
0.67
ꢀ3.50
2.99
5.68
5.33
4.56
3.72
—
—
—
—
—
—
—
—
3
3
3
3
3
3
02.57 113.87
12.07 68.24 ꢀ7.87
21.51 45.45 ꢀ8.71
30.97 31.53 ꢀ7.78
45.13 20.25 ꢀ0.01
312.08 91.71 ꢀ5.87
321.58 58.53 ꢀ8.45
331.02 40.36 ꢀ6.34
312.00 175.52 ꢀ7.74
ꢀ0.19
321.44 103.50 ꢀ10.99
0.35
0.39
330.93
345.05
359.25
66.57 ꢀ8.66
37.95 ꢀ0.52
345.17 25.14
357.08 17.65
295.29 566.08
302.51 329.97
1.24
9.22
13.45
1.25
59.22 14.07
12.25
10.90
ꢀ1.76
ꢀ0.11
0.34
23.88
13.98
19.52
3
4
302.55 236.95
295.92 1054.72
3
3
3
3
3
12.01 129.09 ꢀ2.05
21.52 77.49 ꢀ7.13
31.00 50.17 ꢀ7.61
45.14 29.31 ꢀ1.99
302.52 562.62 ꢀ2.10
312.00 293.88 ꢀ8.24
321.44 166.49 ꢀ10.12
312.02 179.24 ꢀ6.47
321.45 105.48 ꢀ9.65
330.89 67.01 ꢀ8.40
345.06 37.95 ꢀ0.20
0.66
ꢀ0.72
ꢀ1.70
ꢀ2.52
ꢀ4.41
0.08
330.95
345.14
359.25
—
—
—
—
—
—
—
99.94 ꢀ9.24
53.03 ꢀ0.77
15.06
59.25 18.92
9.47
—
—
—
—
—
—
—
—
—
—
—
359.22 23.48
326.32 100.89
12.70
1.67
31.72
—
—
—
—
1.05
0.01
—
—
—
—
—
—
—
—
—
—
—
—
—
335.79 64.49 ꢀ2.21
ꢀ0.49
—
—
—
—
—
—
—
345.27 44.50 ꢀ0.69
0.77
354.66 31.58
1.27
—
—
—
—
ꢀ0.26
—
—
—
—
1
0 326.17 248.52
ꢀ0.38
2.28
ꢀ2.27
ꢀ1.42
—
—
—
—
—
—
—
—
3
3
3
35.68 149.88
45.12 91.05 ꢀ3.29
54.56 62.01
2.32
—
a
exp
i
cal (eqn 1)
cal (eqn 1)
b
exp
cal (eqn 2)
cal (eqn 2)
)/Z
i
Dev(1) = (Z
ꢀ Z
i
)/Z
i
.
Dev(2) = (Z
i
ꢀ Z
i
.
which the viscosity decreases by a factor of 4 when increasing the
temperature from 326 K to 355 K.
In the family of alkylimidazolium alkanesulfonate ionic
liquids, it is observed that the viscosity of the ionic liquid
increases, as expected, when the alkyl chain increases, either in
the cation, or in the anion, or in both. This effect can be
observed in Fig. 9, where the increase in viscosity is
represented, at 323 K, as a function of the number of carbon
atoms in the alkyl chains (n or k).
An increase of the viscosity by 25 to 50 mPa s is observed
(
see Fig. 9) with the increase of one extra carbon atom in the
alkyl side chain of the 1-alkyl-3-methylimidazolium cation.
A similar trend, although smaller, has also been observed by
27
Tokuda et al. for the viscosity of 1-alkyl-3-methylimidazolium
bis{(trifluoromethyl)sulfonyl}-amide ionic liquids.
The size of the alkyl side chain in the alkanesulfonate anion
also influences the viscosity of the ionic liquids studied in
this work. The viscosity increases by (13 ꢂ 1) mPa s and by
Fig. 8 Experimental viscosities as a function of temperature: (J),
25
9
9
]; (E ),
[C
C
4
2
mim][C
mim][C
8
SO
SO
4
]; (&), [C
4
mim][PF
SO
6
]; (D), [C
]; (’), [C mim][C
2
mim][C
2
SO
].
4
[
4
3
]; (m), [C mim][C
4
2
3
2
2
SO
3
(
22 ꢂ 0.5) mPa s for each extra carbon atom in the alkyl chain
+ +
2 3
of the anion for [C mim] -based ionic liquids and [C mim] -
where Z
N
is the viscosity at infinite temperature and E
a
based ionic liquids, respectively. This behaviour confirms
that, although the high-electrostatic interactions between ions
determine the characteristic physicochemical properties of
ionic liquids, dispersive, van der Waals-type forces also play
an important role and determine the way the viscosity changes
with the size of the alkyl side chain. This suggests that the
formation of non-polar molecular domains, dominated by van
der Waals-type molecular interactions, may determine the
variation of viscosity in a family of ionic liquids. However,
their impact in equilibrium (e.g. molar volume) versus
transport (e.g. viscosity) properties is different. While (ideal)
additive behaviour is observed for the former, a more complex
response is found for the latter.
is the viscosity activation energy, two characteristic
parameters adjusted from experimental data as a function of
temperature. A, B and T0 in eqn (2) are three adjustable
parameters. Table 9 lists the parameters for the ionic liquids
studied in the present case, together with the standard relative
deviations of the fits.
The viscosity of alkanesulfonate based ionic liquids decreases
rapidly with increasing temperature. For example, for
3 4 3
[C mim][C SO ], one of the more viscous ionic liquids studied
in this work, the viscosity decreases one order of magnitude when
the temperature changes from 296 K to 330 K. This behaviour is
also found for [C10mim][C
1 3
SO ], a solid at room temperature, for
8
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a
r
Table 9 Correlation parameters of the Arrhenius-like equation, eqn (1), and of the VFT equation, eqn (2), with the deviations of the fit s
viscosity of [C mim][C SO ] as a function of temperature, determined from experimental values in the range T = 295 to T = 360 K
for the
n
k
3
Arrhenius-type equation [eqn (1)]
VFT equation [eqn (2)]
ꢀ
6
ꢀ1
ꢀ3
1/2
n
k
Z
N
/10 mPa s
ꢀE
a
/kJ mol
s
r
A/10 mPa s K
B/K
T
0
/K
s
r
2
3
1
2
4
1
2
4
2
1
97.92
62.54
9.859
25.69
8.869
2.554
50.72
6.227
35.12
37.00
43.52
40.08
43.81
48.37
39.30
0.11
0.08
0.12
0.09
0.10
0.13
0.02
0.02
19.68
11.71
11.82
6.119
7.613
8.506
7.543
9.847
555.0
711.5
728.8
837.9
849.7
812.2
843.7
844.5
207.0
195.2
203.7
193.8
193.8
204.4
198.6
209.6
0.01
0.01
0.01
0.02
0.03
0.05
0.01
0.04
4
0
1
47.44
1
0
P½
0
:5
exp
ðZ ꢀZi Þ=Z
calc
calc
i
2
ꢄ
i
a
i
@
A
Deviation defined as: sr ¼
where n is the number of experimental points and n the number of adjustable parameters.
nꢀn
were determined, and the results were compared with the
available data for other ionic liquid series (e.g. [C mim][BF
n
4
],
[C
n
mim][PF ], [C mim][NTf ] and [C mim][C SO ]). Melting
k
6
n
2
n
4
points of the alkanesulfonates showed a dependency upon
the cationic chain length, but no pattern was found for the
enthalpies of fusion. Decomposition temperatures of the
n k 3
[C mim][C SO ] series were found above 300 1C (dynamic
TGA scans). Densities of the examined ionic liquids were
correlated to the sum of the carbons in the alkyl chains, both
in the anion and in the cation (n + k); it was shown that,
irrespective of position, the additional methylene groups
increase the molar volume of the ionic liquids by the same
value. Patterns in viscosity changes observed for the
n k 3
[C mim][C SO ] series corresponded to findings for other
homologous series, e.g. hexafluorophosphates, and can be
correlated with the Vogel–Fulcher–Tamman (VFT) model.
Whereas the density and the viscosity show similar behaviour
in both families (alkanesulfonates and alkanesulfates), the
thermal stability of alkanesulfonates shows a much better
performance.
Acknowledgements
˜
This work was supported by the Fundac¸ ao para a Cieˆ ncia e
Tecnologia (FC&T), Portugal (Projects POCTI/QUI/35413/2000
and POCI/QUI/57716/2004). MB thanks FC&T for a PhD
grant (SFRH/BD/13763/2003) and Marie Curie Fellowships
for Early Stage Research Training (EST No505613). KRS
thanks the EPSRC (Portfolio Partnership Scheme, grant no.
EP/D029538/1). AAHP and MFCG are grateful to the Oeiras
Fig. 9 Variation of the viscosity at 323 K with the number of carbon
atoms in the alkyl chains in the cation, n, and in the anion, k, forming
the ionic liquid. Top: variation of viscosity with the number of carbon
atoms in the alkyl side chain of the 1-alkyl-3-methylimidazolium cation,
City Hall for the Prof. Antonio Xavier Excellence Award.
´
n. m, [C
Bottom: variation of viscosity with the number of carbon atoms in
the alkyl chain of the sulfonate anion, k. ’, [C mim][C SO ]; K,
mim][C SO ]; b, [C mim][C SO ].
n 1 3 n 2 3 n 3 3
mim][C SO ]; ., [C mim][C SO ]; E, [C mim][C SO ].
2
k
3
References
[
C
3
k
3
4
k
3
1
N. V. Plechkova and K. R. Seddon, Chem. Soc. Rev., 2008, 37,
23–150.
1
2
(a) P. Wasserscheid and T. Welton, Ionic Liquids in Synthesis,
Wiley VCH, Weinheim, 2007; (b) P. Wasserscheid and W. Keim,
Angew. Chem., Int. Ed., 2000, 39, 3772–3789.
Conclusions
A matrix of 1-alkyl-3-methylimidazolium alkanesulfonate
ionic liquids, [C mim][C SO ], formed by variations of the alkyl
3
4
(a) C. S. Santos and S. Baldelli, J. Phys. Chem. B, 2009, 113,
923–933; (b) J. S. Torrecilla, J. Palomar, J. Garcia and
n
k
3
F. Rodrı
´
M. Blesic, M. Swadz
guez, J. Chem. Eng. Data, 2009, 54, 1297–1301.
ba-Kwasny, J. D. Holbrey, J. N. Canongia
chain lengths in the cation and in the anion (n = 1–6, 8, or 10;
k = 1–4, or 6), was prepared and characterised. Viscosities,
densities, melting points and decomposition temperatures
´
´
Lopes, K. R. Seddon and L. P. N. Rebelo, Phys. Chem. Chem.
Phys., 2009, 11, 4260–4268.
This journal is ꢁc the Owner Societies 2009
Phys. Chem. Chem. Phys., 2009, 11, 8939–8948 | 8947

View Article Online
5
6
7
C. C. Cassol, G. Ebeling, B. Ferrera and J. Dupont, Adv. Synth.
Catal., 2006, 348, 243–248.
¨
P. Wasserscheid, R. van Hal and A. Bosmann, Green Chem., 2002,
4, 400–404.
J. D. Holbrey, W. M. Reichert, R. P. Swatloski, G. A. Broker,
Z. P. Visak, H. C. de Sousa, J. Szydlowski, J. N. C. Lopes and
T. C. Cordeiro, Phase behavior and thermodynamic properties of
ionic liquids, ionic liquid mixtures and ionic liquid solutions, ACS
Symposium Series 901, ed. R. D. Rogers and K. R. Seddon,
American Chemical Society, Washington, DC, 2005, pp. 270–291.
19 C. F. Ye and J. M. Shreeve, J. Phys. Chem. A, 2007, 111,
1456–1461.
W. R. Pitner, K. R. Seddon and R. D. Rogers, Green Chem., 2002,
4, 407–413.
8
9
E. F. Borra, O. Seddiki, R. Angel, D. Eisenstein, P. Hickson,
K. R. Seddon and S. P. Worden, Nature, 2007, 447, 979–981.
J. Jacquemin, P. Husson, A. A. H. Padua and V. Majer, Green
Chem., 2006, 8, 172–180.
20 J. Jacquemin, P. Ge, P. Nancarrow, D. Rooney, M. F. Costa
Gomes, A. A. H. Padua and C. Hardacre, J. Chem. Eng. Data,
2008, 53, 716–726.
21 R. L. Gardas and J. A. P. Coutinho, Fluid Phase Equilib., 2008,
263, 26–32.
22 L. P. N. Rebelo, J. N. Canongia Lopes, J. M. S. S. Esperanc¸ a,
1
0 A. G. Avent, P. A. Chaloner, M. P. Day, K. R. Seddon and
T. Welton, J. Chem. Soc., Dalton Trans., 1994, 3405–3413.
1
1
1 Merck Chemicals, Merck, http://www.merck-chemicals.com/.
2 J. D. Holbrey and K. R. Seddon, J. Chem. Soc., Dalton Trans.,
J. Lachwa, H. J. R. Guedes, V. Najdanivic-Visak and Z. Visak,
Acc. Chem. Res., 2007, 40, 1114–1121.
1
999, 2133.
23 J. N. Canongia Lopes and A. A. H. Padua, J. Phys. Chem. B, 2006,
110, 3330–3335.
1
1
1
1
1
1
3 I. Lopez-Martin, E. Burello, P. N. Davey, K. R. Seddon and
´
G. Rothenberg, ChemPhysChem, 2007, 8, 690–695.
4 T. J. Wooster, K. M. Johanson, K. J. Fraser, D. R. MacFarlane
and J. L. Scott, Green Chem., 2006, 8, 691–696.
5 J. M. S. S. Esperan c¸ a, H. J. R. Guedes, J. N. Canongia Lopes and
L. P. N. Rebelo, J. Chem. Eng. Data, 2008, 53, 867–870.
6 J. W. Magee and J. A. Widegren, J. Chem. Eng. Data, 2007, 52,
24 E. W. Lemmon, M. O. McLinden and D. G. Friend, Thermo-
physical Properties of Fluid Systems, NIST Chemistry WebBook,
NIST Standard Reference Database 69, ed. P. J. Linstrom and
W. G. Mallard, National Institute of Standards and Technology,
Gaithersburg, MD, http://webbook.nist.gov.
25 J. Jacquemin, P. Husson, V. Majer, A. A. H. Padua and
M. F. C. Gomes, Green Chem., 2008, 10, 944–950.
26 I. Gutzow and J. Schmelzer, The Vitreous State-Thermodynamics,
Structure, Rheology and Crystallization, Springer-Verlag, Berlin, 1995.
27 H. Tokuda, K. Hayamizu, I. Kunikazu, M. A. B. H. Susan and
M. Watanabe, J. Phys. Chem. B, 2005, 109, 6103–6110.
2331–2338.
7 J. M. S. S. Esperan c¸ a, H. J. R. Guedes, M. Blesic and L. P. N.
Rebelo, J. Chem. Eng. Data, 2006, 51, 237–242.
8 L. P. N. Rebelo, V. Najdanovic-Visak, R. G. de Azevedo,
J. M. S. S. Esperanca, M. N. da Ponte, H. J. R. Guedes,
8
948 | Phys. Chem. Chem. Phys., 2009, 11, 8939–8948
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