Conductometric study of ionic liquids in the presence of N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base in acetonitrile solutions at 298.15 K

Article abstract of DOI:10.1016/j.electacta.2014.09.101

In recent years, Schiff bases and their metal complexes in the presence of ionic liquids (ILs) have been used in synthesis of various chemical compounds. To better understanding of ionic liquid influence on these processes, it is required to obtain information about the ion association behavior of the ionic liquids. Therefore, in this work, the molar conductivities of the ILs [RMIm]X (R= propyl, pentyl, and hexyl; X= Br^- and Cl^-) in different concentrations of N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base + acetonitrile solutions were determined at 298.15 K. The obtained conductivity data were analyzed by low concentration Chemical Model (lcCM) conductivity equation to calculate the limiting molar conductivities (Λ₀) and ion association constants (K_A). The results show that BPIE, alkyl chain length of cation, and anion type have effect on the ionic association process of the ILs. The Λ₀ and K_A values decrease as the Schiff base concentration, alkyl chain length of cation, and anion size increase in the solution. The association constants were also used to calculate the standard Gibbs energy (ΔG⁰_A) of ion-pairing association. The resulted ΔG⁰_A values are negative and become more negative as the alkyl chain length of the cation and the size of anion increase. The large negative values of the standard Gibbs energy obtained for [HMIm]Br indicates the more spontaneity and the more feasibility of the association process for this ionic liquid.

Full text of DOI:10.1016/j.electacta.2014.09.101

Accepted Manuscript
Title: Conductometric study of ionic liquids in the presence of
N,N’-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE)
Schiff base in acetonitrile solutions at 298.15 K
Author: Hemayat Shekaari Amir Kazempour Maryam
Khoshalhan
PII:
S0013-4686(14)01932-X
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.electacta.2014.09.101
EA 23453
To appear in:
Electrochimica Acta
Received date:
Revised date:
Accepted date:
17-7-2014
12-9-2014
21-9-2014
Please cite this article as: Hemayat Shekaari, Amir Kazempour, Maryam
Khoshalhan, Conductometric study of ionic liquids in the presence of N,N’-bis(2-
pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base in acetonitrile solutions at
2
98.15K, Electrochimica Acta http://dx.doi.org/10.1016/j.electacta.2014.09.101
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Conductometric study of ionic liquids in the presence of N,N'-bis(2-
pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base in
acetonitrile solutions at 298.15 K
*
a
a,b
c
Hemayat Shekaari , Amir Kazempour , Maryam Khoshalhan
a
Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
Department of Chemistry, Faculty of Sciences, Islamic Azad University of Tabriz, Tabriz, Iran
Department of Chemistry, Faculty of Sciences, University of Guilan, Guilan, Iran
b
c
Abstract
In recent years, Schiff bases and their metal complexes in the presence of ionic liquids
(ILs) have been used in synthesis of various chemical compounds. To better
understanding of ionic liquid influence on these processes, it is required to obtain
information about the ion association behavior of the ionic liquids. Therefore, in this
work, the molar conductivities of the ILs [RMIm]X (R= propyl, pentyl, and hexyl; X=
-
-
Br and Cl ) in different concentrations of
N,N'-bis(2-pyridylmethylidene)-1,2-
diiminoethane (BPIE) Schiff base + acetonitrile solutions were determined at 298.15 K.
The obtained conductivity data were analyzed by low concentration Chemical Model
(
lcCM) conductivity equation to calculate the limiting molar conductivities (Λ ) and ion
0
association constants ( K ). The results show that BPIE, alkyl chain length of cation, and
A
anion type have effect on the ionic association process of the ILs. The Λ and KA values
0
*
Corresponding author, Tel: +98-41-33393139; Fax: +98-41-33340191.
E-mail addresses: hemayatt@yahoo.com; hemayatt@tabrizu.ac.ir (H. Shekaari).

decrease as the Schiff base concentration, alkyl chain length of cation, and anion size
increase in the solution. The association constants were also used to calculate the
0
A
0
A
standard Gibbs energy (∆G ) of ion-pairing association. The resulted ∆G values are
negative and become more negative as the alkyl chain length of the cation and the size of
anion increase. The large negative values of the standard Gibbs energy obtained for
[HMIm]Br indicates the more spontaneity and the more feasibility of the association
process for this ionic liquid.
Keywords: Ionic liquids; BPIE Schiff base; Molar conductivity; Low concentration
Chemical Model (lcCM).
1
. Introduction
The oxidation of alcohols to the corresponding aldehydes, ketones, and carboxylic
acids is one of the most important reactions in organic chemistry, especially in industrial
synthetic chemistry [1]. From the past, this transformation is performed with toxic,
expensive inorganic oxidizing agents in organic solvents. The selective oxidation of
alkenes is another important process to reach fine chemicals [2]. Enantiomerically pure
epoxides obtained from the oxidation of alkenes have shown a good potential as key
molecules, useful intermediates, and building blocks in the synthesis of optically active
compounds. The industrial importance of these processes and environmental concerns
made chemists develop effective, greener catalytic systems that use inexpensive oxidants.
Schiff bases and their transition metal complexes are attractive oxidation catalysts
because of their cheap, ease of preparation, and chemical and thermal stability [3-7].
They are considered as an appropriate catalyst to oxidize alcohols and alkenes to the
relative products [8-10]. However, the practical use of selective catalytic system faces the

fundamental problem of the separation of products from the reaction mixture, and the
recovery of catalysts often becomes difficulty. The fascinating possibilities of two-phase
catalysis motivated large research efforts devoted to the use of ionic liquids as solvents
for the transition-metal catalysts. These systems are able to separate the reaction products
from the catalytic solution by simple decantation of the insoluble liquid phases. It has
also been reported that ionic liquids enhances the activity of catalyst in the mixture. The
IL/Schiff base systems, therefore, provide a means to develop reusable catalysts with
high activity. Moreover, the addition of co-solvents has been found to strongly affect
various physico-chemical properties of ionic liquids. The mixed organic solvents and
ionic liquids can be used advantageously to achieve homogeneous systems in which the
reactants and catalysts have the best solubility. The efficiency of these systems is strongly
dependent on the various molecular interactions between ionic liquid and mixed solvent.
Thermodynamic properties of ionic liquids in Schiff base solutions are very useful tools
to discuss different interactions of the system. One natural difference between ionic
liquids and conventional molecular solvents is that ionic liquids exhibit high electrolytic
conductivity and wide electro-chemical window, which is a measure for their
electrochemical stability against oxidation and reduction processes. When selecting an
ionic liquid for electrochemical usages, electrical conductivity is of great importance.
Since ILs are entirely composed of ions, the formation of ion pairs is expected to be one
essential feature for describing both solvation in ILs and solvation of ILs in other media.
The phenomenon of ion-pair formation is by itself of fundamental importance to the
chemical field, as it influences reaction rates or may be exploited in numerous chemical
applications. Conductometry is an electrochemical technique, which provides most

precise data and valuable information regarding ion association and ion solvation
behavior and character of the ion pair in electrolyte solutions. Most of the papers
presenting conductometric studies of the ILs analyze the conductance data using different
conductivity equations in terms of the ionic association constant and the limiting molar
conductivity. It is shown that the alkyl chain length of the cations and type of anion affect
the ionic association constants and limiting molar conductivities of the ILs. A large
portion of the conductivity data reported in literatures are related to pure ionic liquids or
their binary mixtures in water or in molecular solvent for both dilute region and the
whole composition range of ionic liquids solutions [11-20]. However, the number of
works performed for ternary solutions of ionic liquids is very limited. Hence, in this
communication, the conductivities of a number of imidazolium based ionic liquids
[PMIm]Br, [PnMIm]Br, [HMIm]Br, and [HMIm]Cl in BPIE + MeCN solutions were
measured at 298.15 K. The obtained data were analyzed using low concentration
Chemical Model (lcCM) conductivity equation, and the values of limiting molar
conductivity ( Λ ) and ion association constant ( K ) were calculated. The K values
0
A
A
0
A
were used to estimate the standard Gibbs energy ( ∆G ) of ion association process. All
the parameters were discussed based on the ion-solvent interactions that occur in the
system. It was also attempted to study the effects of the alkyl chain length of the cations
and the type of anion on the solvation behavior of the ILs.
2
. Experimental
2
.1. Chemicals
The chemicals used to synthesize the ionic liquids were N-methylimidazole
>99%), 1-bromopropane (>99%), 1-bromopentan (>99%), 1-bromohexane (>99%), 1-
(

chlorohexane (>99%), and ethyl acetate (GR, >99.8%) that were bought from Merck
company. Pyridine-2-aldehyde (>99.8%), ethylenediamine (>99.9%), and acetonitrile
(
>99.9%) were also purchased from Merck. All the materials were used without any
further purification.
.2. Synthesis of the ionic liquids
-Alkyl-3-methylimidazolium halide (C
2
1
n 6
MImBr, n = 3, 5, 6 and C MImCl) was
synthesized according to the procedure described in literatures [21-23] by direct
alkylation of N-methylimidazole with an excess amount of 1-haloalkane in a round
bottom flask mixed by a magnetic stirrer under a nitrogen atmosphere. The mixing of the
chemicals was done at first under ice-cooling, but after the temperature was risen to room
temperature. The temperature was then gradually increased over a period of several hours
0
to a final reaction temperature of about 50 C and kept constant until the end of the
reaction. The reaction mixture was stirred for one week. Finally, the crude product was
separated from reagents and then washed three times with fresh ethylacetate. The
removal of residual volatile compounds from the ionic liquid was done in high vacuum at
0
6
0 C using a rotary evaporator for at least 4 hours at reduced pressure. The obtained
1
ionic liquid has purity about 98% verified by H NMR spectroscopy
.
The ionic liquid was
used after vacuum desiccated for at least 48 hours to remove trace amount of moisture.
Water content found by Karl Fischer method in the ionic liquid was less than 0.2%.
2
.3. Synthesis of the Schiff base
N,N'-Bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) was synthesized
according to literature method [24]. The pyridine-2-aldehyde (0.6 mol) was added slowly
to the ethylenediamine (0.3 mol) in ethanol solution. After stirring the mixture gently for

1
hour and the removal of the ethanol by rotary evaporation, an orange-yellow residual
liquid product was obtained. The product was extracted with hot hexane in several times.
After cooling, a solid orange product was obtained and recrystallized from diethyl ether.
1
Yield, 36%. H NMR (CDCl
3
versus TMS): δ = 4.06 (s, 4H, =NCH
2
CH
2
N=), 7.30 (m,
2
H, –N=CH-py), 7.73 (m, 2H, py), 7.98 (m, 2H, py), 8.42 (m, 2H, py), 8.63 (m, 2H, py).
Fig. 1 shows the structure of N,N'-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE)
Schiff base.
2
2
.4. Apparatus and procedure
.4.1. Density and viscosity measurements
The sample densities were measured with a vibrating tube densimeter (Anton
Paar, DMA 4500M, Austria), which was calibrated with doubly distilled water at
atmospheric pressure. Density is extremely sensitive to temperature, so it was kept
−
3
constant within ±1.0 × 10 K using the Peltier technique built in densimeter. The
−
5
uncertainty of density measurements for BPIE + DMF was better than ±4.0 × 10
g
−
3
cm . The analytical balance was Sartrious (AG TE214S, Switzerland) with an
−
4
uncertainty ±1 × 10 g.
The viscosities were measured using an Ubbelohde-type viscometer, which was
calibrated with doubly distilled water. Viscosity of solution (
following equation
η
) is obtained by the
η
K
t
=
Lt −
(1)
, and K are the viscometer
d
where
d
is the density,
t
is the flow time of the solution,
L
constants. A digital stopwatch with a resolution 0.01 s has been used for the measurement

of flow time. The estimated uncertainly of the experimental viscosity was
s.
± 0.002 mPa
2
.4.2. The measurement of specific conductivity
Specific conductivities were measured using a conductivity meter (Metrohm
model 712, Switzerland) with accuracy ±0.5%. The cell constant was calculated by
−
1
repeated measurements of KCl solution in 0.01 mol kg . About 50 ml of solvent was
filled into the conductivity cell and the cell was closed. Weighting was performed by an
−
4
analytical balance (Sartrious, AG TE214S) with precision ±1×10 g. After the
measurement of the solvent conductivity, a weighed amount of pure ionic liquid was
added with a syringe to the cell containing solvent and the measurement was repeated. To
minimize the risk of the presence of concentration gradients in the cell, the solution was
continuously stirred with a magnetic stirrer. The water from a thermostatically regulated
bath was circled around the cell with double wall to maintain the temperature with an
uncertainty ±0.02 K.
3
. Model detail
The values of molar conductivity (Λ) obtained for the ionic liquids in
investigated solutions (BPIE + MeCN) have been calculated by the relation
Λ =1000 / c , where is the specific conductivity of the ionic liquid solutions. The
κ
κ
obtained values of molar conductivity are given in Table 1. The conductivity data were
analyzed with low concentration Chemical Model (lcCM) conductivity equation using the
following set of equations [25] which is the Fuoss-Onsager type equation.
(2)
1
)
/ 2
3/ 2
)
Λ =
α
[
Λ − S
(cα
+ Ec
α
ln
(c
α
)
+ J1cα
+ J2
(cα
]
0

1−α
(3)
K =
A
2
2
α
cγ
±
κ
q
lnγ± = −
(4)
1
+
κ
R
2
2
α
1
6000N z e
c
2
A
(5)
κ
=
ε0εkBT
2
2
z e
πε0εkBT
q =
8
(6)
In above equations,
dilution, (1-α) is the fraction of oppositely charged ions acting as ion pairs, γ
corresponding mean activity coefficient of the free ions, is the Debye parameter, e is
the electronic charge, z is the ionic charge, ε0 is the permittivity of vacuum,
is the
dielectric constant of the solvent, and the other symbols have their usual meanings. The
coefficients E, J , and J required for calculations were taken from Ref. [25]. The
Λ
and Λ are molar conductivities at molarity c and at infinite
0
±
is the
κ
ε
1
2
parameter R represents the center-to-center distance between the ions in the ion pairs.
Due to the lack of association constant for the studied solutions, the KA was first
estimated from the Arrhenius-Ostwald relation [26] and then the other parameters were
determined using Eq. 2.
Three-parameter fits were used to obtain the limiting molar conductivity (Λ ),
0
association constant ( K ), and distance parameter (R) by non-linear least squares
A
iterations. The calculation is made by finding the values Λ , K , and R that minimized
0
A

the standard deviation
σ (Λ) . The standard deviation of the measured molar
conductivities (Λ ) and the calculated one ( Λ ) was computed as follows
exp
cal
1
2
2


∑(Λexp
− Λ ) 
(7)
cal
σ
(Λ) =

n − p




where n and p show the number of experimental data and parameters, respectively. The
values of K , Λ , and R obtained by this procedure are given in Table 2.
A
0
4
. Results and discussion
4
.1. Limiting molar conductivities
It is shown that the molar conductivity (
Λ
) decreases with increasing the ionic
liquids concentration due to ionic atmosphere effects, and in more concentrated solutions,
ion paring is responsible for the observed reduction in molar conductivities. Moreover,
the molar conductivity (
Λ ) values of ionic liquids decrease at higher concentrations of
BPIE solution. Increasing Schiff base concentration causes stronger interaction between
the alkyl chain of ionic liquid and the pyridinyl group of Schiff base, which leads to a
reduction in the molar conductivity of ILs. The effect of Schiff base concentration on the
Λ
values of [PnMIm]Br is depicted by Fig. 2.
Table 2 shows that the limiting molar conductivities of the studied ionic liquids in
pure acetonitrile are greater than those in BPIE + MeCN solutions. It is also clear that the
Λ values for each ionic liquid decrease with increasing the concentration of BPIE in the
0
solutions (see Fig. 4). This reduction is due to the fact that the viscosity of medium
increases as BPIE is added to the solution. Moreover, the solvated radii of the ions get
larger due to the interactions with the Schiff base. Both of theses reasons make the ionic

mobility decrease, and consequently the molar conductivity of the ILs reduces. To
eliminate the effect of viscosity on the ionic mobility, Walden products ( Λ0
) were
η
calculated and given in Table 2. Walden product is a useful tool to discuss ion-solvent
interactions. The conductivity of an ion at infinite dilution depends only on its speed.
Therefore, it is expected that the product of ion conductivity by the viscosity of the
medium is independent of the solvent nature. A constant Walden product for solutions
with different concentrations indicates that the radius of the ions remains unchanged.
Table 2 shows that the Λ0η
values of all the ionic liquids change with the concentration
of BPIE. This suggests that the ions do not have the same effective radius in different
solvent compositions and provides evidence for the solvation of ions in the solutions.
It is also obvious from Figs. 3 and 4 that the ionic liquid with a longer alkyl chain
has larger Λ values in both pure solvent and solution. Accordingly, the limiting molar
0
conductivities of the ionic liquids increase with the alkyl chain length of the cation in the
order propyl < pentyl < hexyl. The reason of the observed trend could be related to the
solute–solvent interactions between the ionic liquid and MeCN. Acetonitrile is a
relatively polar solvent and its interaction with ionic liquids must decrease as the non-
polarity of ILs enhances. Therefore, [HMIm]Br with a long non-polar alkyl chain is less
solvated by the solvent molecules and has greater ionic mobility. The comparison
between the Λ values of [HMIm]Br and [HMIm]Cl reveals the effect of anion size of
0
ionic liquid on its conductivity. In the studied solutions, the Λ values increase as the
0
−
−
anion size gets larger (Cl < Br ). We observed this result in our previous paper [27],
where we studied the conductivities of these two ionic liquids in aqueous saccharide
solutions. A good reason for this observation is the reduction of the surface electrical

charge density resulted by a rise in the anion size that increases the mobility of the anion
inside a medium with free ions.
4
.2. Ion association constants
The values of ion association constant ( K ) of the ionic liquids in BPIE + MeCN
A
solutions are given in Table 2. Clearly, the K values of each ionic liquid decrease at
A
higher concentrations of BPIE solution. This is due to the strong ion–Schiff base
interactions in the concentrated solutions that reduce the ion-pair formation. At a fixed
molality of BPIE, the values of ion association constant increase with the alkyl chain
length of the cations in the sequence propyl < pentyl < hexyl. As stated above, the cation
with hexyl alkyl chain is less solvated by the solvent (MeCN) molecules and
consequently forms more ion-pairs relative to the two other cations.
0
A
The association constants were used to calculate the standard Gibbs energy ( ∆G )
of ion-association process using the following equation
0
A
(
8)
∆
G = −RT ln K
A
0
A
The obtained values of the standard Gibbs energy are given in Table 2. The ∆G values
are negative and become more negative as the size of cation and anion increases. The
large negative values of the standard Gibbs energy obtained for [HMIm]Br indicates the
more spontaneity and the more feasibility of the association process for this ionic liquid.
5
. Conclusions
The effect of cation and anion size on the conductivity of the ionic liquids 1-
propyl-3-methylimidazolium bromide ([PMIm]Br), 1-pentyl-3-methylimidazolium

bromide ([PnMIm]Br), 1-hexyl-3-methylimidazolium bromide ([HMIm]Br), and 1-hexyl-
-methylimidazolium chloride ([HMIm]Cl) in N,N'-bis(2-pyridylmethylidene)-1,2-
3
diiminoethane (BPIE) Schiff base + acetonitrile solutions was studied at 298.15 K. For
this purpose, limiting molar conductivities (Λ ) and ion association constants ( K ) were
0
A
calculated using low concentration Chemical Model (lcCM) conductivity equation. The
results show that the Λ values decrease as BPIE concentration increases in the solution.
0
Moreover, the limiting molar conductivities increase with the alkyl chain length of the
cation in the order propyl < pentyl < hexyl and also increase with the anion size in the
-
-
order Cl < Br . The K values reduce with the increase of BPIE concentration but
A
increase as the size of cation and anion gets larger. The association constants were used
0
A
to calculate the standard Gibbs energy (∆G ) of ion-pairing association. The obtained
0
A
∆
G values are negative and become more negative as the alkyl chain length of the
cation and the size of anion increase. The large negative values of the standard Gibbs
energy obtained for [HMIm]Br indicates the more spontaneity and the more feasibility of
the association process for this ionic liquid.
Acknowledgment
All the laboratory work of the present paper has been performed in the University
of Mohaghegh Ardabili. The authors would like to thank financial support from the
Graduate Council of this university. The authors also greatly appreciate Dr. A.
Bazaatpour for helping with synthesis of the Schiff base and useful comments in this
project.

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Figure captions
Fig. 1. The structure of N,N'-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff
base.
Fig. 2 Molar conductivities (
Λ
) of [PnMIm]Br in MeCN and in MeCN + BPIE solutions
, 0.0452; □, 0.0991;
with several molalities of BPIE at 298.15 K. Symbols: ♦, 0.0000;
▲
-1
and ∆, 0.1210 mol kg .
Fig. 3. Comparison of molar conductivities (
Λ ) of [RMIm]Br in BPIE +MeCN solution
-1
with 0.04 mol kg molality of BPIE at 298.15 K. Symbols: ●, [PMIm]Br;
PnMIm]Br; and □ , [HMIm]Br.
▲,
[
Fig. 4. Limiting molar conductivities (Λ ) of the ionic liquids against the molality of
0
BPIE Schiff base at 298.15 K. Symbols:
▲, [PMIm]Br; ■, [PnMIm]Br; ○, [HMIm]Br;
and ×, [HMIm]Cl.

Table 1
The molar conductivities (
Λ) of the ionic liquids [PMIm]Br, [PnMIm]Br, [HMIm]Br, and
[
HMIm]Cl in BPIE + MeCN solutions as a function of IL concentration (c ) at 298.15 K.
c
Λ
S cm mol
c
Λ
S cm mol
c
Λ
S cm mol
c
Λ
S cm mol
-3
-3
-3
-3
2
-1
2
-1
2
-1
2
-1
mol m
mol m
mol m
mol m
[
PMIm]Br +BPIE + MeCN
-
1
-1
-1
-1
mBPIE = 0.0000 mol kg
mBPIE = 0.0346 mol kg
mBPIE = 0.0655 mol kg
mBPIE = 0.0959 mol kg
0
1
2
3
4
4
5
6
7
8
9
.4699
.4373
.2205
.1419
.0448
.8004
.6480
.5141
.3250
.1818
.1216
144.10
141.03
139.16
136.48
133.93
132.53
130.08
128.48
126.21
125.34
124.27
0.9785
2.2515
3.3440
4.5031
5.6241
6.9351
8.0276
9.0821
10.2982
11.4097
12.5022
115.98
1.2034
2.6583
4.0773
5.3975
6.9063
8.5408
9.9508
11.5674
13.1121
14.4233
15.7435
101.47
95.82
90.97
88.02
84.03
81.00
78.62
75.72
71.76
69.03
68.70
1.2519
2.9710
4.4168
5.8098
7.1851
8.7719
10.2618
11.9104
13.6560
15.1724
16.8210
99.69
95.96
91.60
89.00
86.28
83.63
79.41
75.94
74.19
72.44
72.30
111.69
107.35
105.30
103.64
101.37
99.75
98.06
95.81
94.02
92.76
[
PnMIm]Br +BPIE + MeCN
-
1
-1
-1
-1
mBPIE = 0.0000 mol kg
mBPIE = 0.0452 mol kg
mBPIE = 0.0991 mol kg
mBPIE = 0.1210 mol kg
0
0
1
2
2
3
3
4
4
5
5
6
.3857
.9316
.4876
.0335
.5494
.0853
.6312
.1471
.7381
.3291
.9202
.5012
163.49
158.56
155.16
150.04
148.00
144.82
140.09
136.99
133.85
131.15
128.58
126.78
0.7691
1.5632
2.3991
3.1431
4.0460
4.8903
5.7011
6.6457
7.4566
8.2006
9.0198
9.8725
143.11
134.51
129.57
126.20
121.10
117.80
114.78
110.88
109.04
107.43
105.66
103.73
1.0198
1.9846
3.0504
4.0335
5.0901
6.0088
7.0838
8.0302
9.1051
10.125
11.0529
11.9625
131.08
128.38
123.29
118.11
113.43
110.30
105.83
103.58
101.38
99.08
1.1148
1.9433
2.8698
3.9318
5.0842
6.0710
6.8769
7.9164
9.0387
10.0555
11.1176
11.9386
120.15
114.47
109.05
103.42
98.49
95.59
93.57
90.83
88.39
86.78
84.88
84.47
97.10
96.07
[
HMIm]Br +BPIE + MeCN
-
1
-1
-1
-1
mBPIE = 0.0000 mol kg
mBPIE = 0.0378 mol kg
mBPIE = 0.0852 mol kg
mBPIE = 0.1130 mol kg
0
0
1
1
2
2
3
3
4
4
5
6
.3186
.8151
.3338
.8376
.3637
.8750
.3493
.7939
.3274
.9053
.7056
.4836
178.54
171.21
166.93
161.59
156.17
152.57
149.45
147.59
143.75
140.00
136.01
132.49
0.6941
1.3425
1.9527
2.6545
3.2037
3.9131
4.6072
5.4616
6.2244
6.9032
7.7499
177.96
169.11
158.82
149.79
142.13
136.16
130.47
124.62
120.34
116.95
114.46
0.7978
1.5026
2.2406
2.9786
3.6834
4.4014
5.1328
5.9107
6.6088
7.3069
7.9984
8.6167
137.85
131.76
124.29
119.24
117.01
113.50
111.18
109.51
108.28
107.14
106.22
104.98
0.8867
1.8660
2.7989
3.5069
4.2216
5.2670
6.0015
6.7889
7.4771
8.3505
9.0784
9.8856
124.60
121.59
119.11
116.68
114.50
112.18
110.59
108.69
107.39
105.08
102.86
100.81
99.69
1
1
0.7193
1.5531
97.95
[
HMIm]Cl +BPIE + MeCN
-1
-1
-1
-1
mBPIE = 0.0000 mol kg
mBPIE = 0.0397 mol kg
mBPIE = 0.0740 mol kg
mBPIE = 0.1107 mol kg

0
1
1
2
3
4
4
5
6
7
.4831
.1507
.8711
.6353
.3381
.0320
.7523
.5429
.3599
.1592
154.77
145.43
140.11
133.44
127.46
122.93
118.37
116.34
114.41
111.42
0.9041
1.8176
2.7027
3.5972
4.4347
5.4053
6.1952
7.0707
7.9557
8.8027
133.65
126.72
120.56
116.18
112.75
109.86
107.18
102.61
100.77
98.23
0.9967
1.9133
2.8121
3.6308
4.5206
5.4283
6.3360
7.0657
7.9556
8.7921
126.40
120.73
114.11
111.38
107.59
104.80
102.10
99.76
1.0811
2.2544
3.3774
4.2993
5.2715
6.1179
7.1236
7.8695
8.9506
9.7887
120.14
113.28
109.87
107.04
103.01
100.54
98.28
96.33
94.65
93.12
97.41
95.46
Table 2
The limiting molar conductivities (Λ0), Walden products (Λ0η), ion association constants (KA),
0
A
standard Gibbs energies of ion-pairing process ( ∆G ), distance parameters (R), and standard
deviations (σ(Λ)) of the ionic liquids in BPIE + MeCN solutions at 298.15 K.
1
0
0
A
mBPIE
Λ
0
Λ0η
KA
10 R
∆G
σ
(Λ)
-1
2
-1
2
-1
3
-1
mol kg
S cm mol
S cm mol mPa s dm mol
-1
m
kJ mol
[
PMIm]Br + BPIE + MeCN
0
0
0
0
.0000
147.97
121.49
108.51
106.92
50.75
43.37
39.82
39.67
15.98
28.31
45.83
35.59
- 6.87
- 8.33
- 8.26
- 7.62
11.82
8.21
14.92
13.27
0.50
0.54
0.64
1.10
.0346
.0655
.0959
[
PnMIm]Br + BPIE + MeCN
0
0
0
0
.0000
.0452
.0991
.1210
170.73
147.15
138.96
123.44
58.56
53.12
51.69
46.29
65.50
52.68
41.54
39.68
- 10.37
- 9.83
- 9.24
- 9.12
16.85
16.14
16.32
17.74
0.87
1.52
1.36
2.36
[
HMIm]Br + BPIE + MeCN
0
0
0
0
.0000
.0378
.0852
.1130
185.33
160.47
144.57
131.72
63.59
57.45
53.49
49.13
85.66
74.29
70.68
31.21
- 11.03
- 10.68
- 10.55
- 8.53
15.50
18.87
8.05
0.55
1.00
1.92
0.62
12.99
[
HMIm]Cl + BPIE + MeCN
0
0
0
0
.0000
.0397
.0740
.1107
160.06
142.83
132.53
54.90
51.27
48.90
46.18
80.72
70.11
49.78
29.88
- 10.88
- 10.53
- 9.69
19.22
15.67
16.99
16.79
1.85
0.71
1.11
1.22
N
N
123.82
- 8.42
N
N
Fig. 1

1
1
1
1
1
1
75
60
45
30
15
00
175
160
145
130
115
100
85
Λ
8
7
5
0
70
0
3
6
9
12
15
cIL/ mol m-3
Fig. 2

1
1
1
55
40
25
155
140
125
110
95
Λ
110
9
8
5
0
80
0
3
6
9
12
15
cIL/ mol m-3
Fig. 3

1
90
190
170
150
130
110
90
170
150
130
Λ
110
9
0
0.00
0.05
BPIE / mol kg
0.10
-1
0.15
m
Fig. 4