Effect of N, N'-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) schiff base on the thermophysical properties of ionic liquids in N, N -dimethylformamide solutions at 298.15 K

Article abstract of DOI:10.1021/je2006117

Various thermophysical properties, densities, electrical conductances, viscosities, and refractive indices of two ionic liquids, 1-pentyl-3- methylimidazolium bromide ([PnMIm]Br) and 1-propyl-3-methylimidazolium bromide ([PMIm]Br, in the presence of N,N'-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base in N,N-dimethylformamide (DMF) solutions have been measured at 298.15 K. These data have been used to calculate the standard partial molar volumes, V_φ⁰, partial molar volumes of transfer, Δ_trV_φ⁰, ion association constants, K_a, limiting molar conductivities, λ₀, viscosity B-coefficients, and molar refractions, R_D, for the solutions studied. These parameters decrease with increasing BPIE concentration and increase with increasing alkyl chain length of ionic liquids. The results were interpreted in terms of cosphere overlap model and solute-solvent interactions. In general, it is concluded that there is an enhancement in the nonpolar-nonpolar interactions between the BPIE Schiff base and the ionic liquid.

Full text of DOI:10.1021/je2006117

ARTICLE
pubs.acs.org/jced
0
Effect of N,N -Bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE)
Schiff Base on the Thermophysical Properties of Ionic Liquids in
N,N-Dimethylformamide Solutions at 298.15 K
,†
‡
‡
Hemayat Shekaari,* Abolfazl Bezaatpour, and Maryam Khoshalhan
†
Department of Physical Chemistry, University of Tabriz, Tabriz, Iran
‡
Department of Chemistry, University of Mohaghegh Ardabili, Ardabil, Iran
ABSTRACT: Various thermophysical properties, densities, electrical conductances, viscosities, and refractive indices of two ionic
liquids, 1-pentyl-3-methylimidazolium bromide ([PnMIm]Br) and 1-propyl-3-methylimidazolium bromide ([PMIm]Br, in the
0
presence of N,N -bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) Schiff base in N,N-dimethylformamide (DMF) solutions
0
have been measured at 298.15 K. These data have been used to calculate the standard partial molar volumes, V , partial molar
volumes of transfer, Δ V , ion association constants, K , limiting molar conductivities, Λ , viscosity B-coefficients, and molar
ϕ
0
tr
ϕ
a
0
refractions, R , for the solutions studied. These parameters decrease with increasing BPIE concentration and increase with
D
increasing alkyl chain length of ionic liquids. The results were interpreted in terms of cosphere overlap model and soluteꢀsolvent
interactions. In general, it is concluded that there is an enhancement in the nonpolarꢀnonpolar interactions between the BPIE Schiff
base and the ionic liquid.
’
INTRODUCTION
convenient experimental procedure for a suitable biphasic reu-
10
sable catalytic system.
Schiff bases or imines, R C = NR, are the condensation
2
The efficiency of the Schiff base catalyst/IL system is strongly
dependent on the various molecular interactions of the ILs and
Schiff bases. The thermophysical properties such as the volumetry,
viscometry, and conductometry of these compounds in the presence
of ILs can provide important information about soluteꢀsolvent
and soluteꢀsolute interactions occurring in these types of
products of aldehydes, ketones, and β-diketones reacting with
primary amines and related derivatives and are considered an
important class of ligands in coordination chemistry. They have
extensive application in different fields such as the novel tetra-
dentate N O Schiff base as a chromogenic reagent for the
determination of nickel in some natural food samples and the
polydentate Schiff base compounds containing aminic nitrogens
2
2
1
1,12
systems.
However, there are no reports in literature. In our
13
1
ꢀ3
previous paper the partial molar volumes of salen Schiff base in
various organic solvents have been measured without using ILs at
different temperatures.
as corrosion inhibitors for mild steel in acidic media.
Schiff
bases are more selective in various reactions such as oxidation,
hydroxylation, aldol condensation, and epoxidation. For exam-
ple, the Schiff base metal complexes of pyridyl bis(imide) and
pyridine bis(imine) have been used as catalysts in the polymer-
ization of ethylene and propylene. In oxidation catalysis, the
choice of a suitable ligand is often delicate because it must also be
resistant toward the oxidant. The most efficient Jacobsen's and
Katsuki's catalysts have evolved as standard reagents for asym-
metric epoxidation reactions due to the ease of the Schiff base
synthetic generation. In recent years, several works have been
reported on the Schiff bases and its metal complexes in the
presence of ionic liquids. It was found that the activity of these
types of catalysts was increased by adding ionic liquids (ILs) to
In the present work, the ILs based on the imidazolium cation
ꢀ
with a fixed anion (Br ), 1-propyl-3-methylimidazolium bro-
4,5
mide ([PMIm][Br]), 1-pentyl-3-methylimidazolium bromide
0
(
[PnMIm][Br]), and N,N -bis(2-pyridylmethylidene)-1,2-diimi-
noethane (BPIE) Schiff base (Figure 1) were synthesized. The
experimental densities, d, viscosities, η, molar conductivities, Λ,
and refractive indices, n , of ILs in the BPIE + N,N-dimethyl-
D
6
ꢀ8
formamide (DMF) binary solutions have been measured to
obtain various thermophysical properties at T = 298.15 K. The
apparent molar volumes, V , of ILs were calculated using density
ϕ
data and used to calculate the standard partial molar volumes,
0
ϕ tr ϕ
0
9
V , and the partial molar volumes of transfer, Δ V , of the
the reaction mixture. ILs derived from the 1,3-dialkylimida-
ILs from DMF to the BPIE + DMF binary solutions. Molar
conductivities have been used to obtain the ion association
constants, K , and limiting molar conductivities, Λ , of the ILs.
zolium cation have been found to be convenient reaction
media for green chemistry, avoiding the use of volatile organic
compounds and making possible in some cases the recovery of
the catalyst. These neoteric solvents have received increased
attention in many fields and as new solvents for applications
in organic, inorganic, and polymer chemistry due to their neg-
ligible vapor pressure, high thermal stability, and nonflamm-
ability. As a result, a better immobilized catalyst in the IL with
the adequate ionic structure would permit developing a
a
0
The viscosity B-coefficients were calculated by using the
1
5
JonesꢀDole equation. The results are discussed in terms of
Received: July 8, 2011
Accepted: September 27, 2011
Published: October 20, 2011
r 2011 American Chemical Society
4164
dx.doi.org/10.1021/je2006117
|J. Chem. Eng. Data 2011, 56, 4164–4172

Journal of Chemical & Engineering Data
ARTICLE
was obtained and recrystallized from diethyl ether. Yield, 36 %.
1
HNMR(CDCl versus TMS): δ=4.06(s, 4H,dNCH CH Nd),
3
2
2
7
.30 (m, 2H, —NdCH-py), 7.73 (m, 2H, py), 7.98 (m, 2H, py), 8.42
(
m, 2H, py), 8.63 (m, 2H, py).
Apparatus and Procedure. The solutions were prepared in
0
Figure 1. Chemical structure of N,N -bis(2-pyridylmethylidene)-1,2-
diiminoethane (BPIE) Schiff base.
glass vials and in molal base concentrations by weighing using an
analytical balance (Sartorius, AG TE214S, Switzerland) with an
ꢀ
4
uncertainty of ( 1 10 g and closed tightly. The uncertainty for
3
ꢀ
4
ꢀ1
molalities of the solutions is less than 2.0 10 mol kg . The
sample densities were measured with a vibrating-tube densimeter
Table 1. Physical Properties of Pure N,N-Dimethylforma-
mide (DMF) at T = 298.15 K
3
(
Anton Paar, DMA 4500M, Austria). The apparatus was cali-
ꢀ3
3
brated with doubly distilled deionized and degassed water and
dry air at atmospheric pressure. The density is extremely sensitive
d/g cm
10 η/Pa s
n
D
3
3
ꢀ
3
exp.
lit.
exp.
lit.
exp.
lit.
to temperature, so it was kept constant within ( 1.0 10
K
3
a
b
a
a
b
c
using the Peltier technique built-in densimeter. The accuracy of
apparatus performance was also tested with the density of a
known molality of aqueous NaCl using the data given by Pitzer
et al. The uncertainty of density measurements of the solutions
was better than ( 4.0 10 g cm and for the other solutions
0.94388
0.94380
0.8608
0.8605
1.4285
1.4267
1.4276
1.4275
0
0
0
.94406
c
.9445
20
d
.94446
ꢀ4
ꢀ3
a
b
c
d
3
3
ꢀ3
Reference 11. Reference 13. Reference 32. Reference 33.
ꢀ5
studied was ( 4.0 10 g cm
.
3
3
Conductance measurements were carried out on a digital
conductivity meter (Metrohm model 712, Switzerland) with a
sensitivity of 0.1 % and a dipping-type conductivity cell with
various soluteꢀsolvent interactions occurring between the IL
and the Schiff base.
ꢀ1
platinized electrodes with a cell constant of 0.824 cm under
nitrogen atmosphere and at a frequency of 1 MHz. The cell
constant was calibrated with aqueous KCl (0.01 M) solution.
About 50 mL of solvent was placed in the conductivity cell, and
the cell was closed. Weighed pure IL was added with a syringe to
the cell containing solvent. To maintain temperature in a stable
state, water was circulated from a thermostat bath around the
sample holder with a double wall. The conductivity cell was
purged with nitrogen during each run. The temperature was kept
constant using a thermostat bath (Julabo NP, Germany) with a
temperature stability of ( 0.01 K.
’
EXPERIMENTAL SECTION
Materials. The chemicals used in this work were N-methyli-
midazole (> 99 %), 1-bromopropane (> 99 %), 1-bromopentane
> 99 %), N,N-dimethylformamide (guaranteed reagent (GR)
grade, > 99.8 %), ethyl acetate (> 99 %), pyridine-2-aldehyde
> 99.8 %), and ethylenediamine (> 99.9 %), which were purchased
from Merck. N-Methylimidazole was freshly distilled at reduced
pressure, and the other reagents were used without further purifica-
tion. The purity of DMF was checked by measurement of its
density, viscosity, and refractive index given in Table 1 which were
in agreement with those reported in literature values.
Synthesis of ILs and the BPIE Schiff Base. The ILs, 1-propyl-
-methylimidazolium bromide ([PMIm][Br]) and 1-pentyl-3-
methylimidazolium bromide ([PnMIm][Br]), were prepared
and purified by using the procedure previously described in the
(
(
The viscosities were measured using an Ubbelohde-type
viscometer, which has a flow time of about 200 s for water at
298.15 K. The viscometer was calibrated with doubly distilled
deionized water. The viscosity of the solution, η, is obtained by
the following equation:
3
1
4,15
η
K
literature.
Briefly, ILs were synthesized by direct alkylation of
¼ Lt ꢀ t
ð1Þ
d
N-methylimidazole with an excess of 1-bromoalkane in a round-
bottom flask at 353 K for 48 h under a nitrogen atmosphere. The
crude product was separated from reagents and then washed
three times with fresh ethyl acetate. The removal of residual
volatile unreacted reagents from synthesized ILs was accom-
plished using a rotary evaporator for at least 4 h at reduced
pressure at 333 K. The obtained IL has a purity greater than 0.99
in mass fraction. The IL was used after vacuum desiccated for
at least 48 h to remove a trace amount of moisture. The water
content found by the Karl Fischer method in the ILs was less
than 0.05 %. These synthesized ILs were analyzed by H NMR
Bruker Av-300) and FT-IR (Perkin-Elmer, Spectrum RXI) to
confirm the absence of any major impurities, and they were found
to be in good agreement with those reported in the literature.
where d is the density, t is the flow time of the solution, and L and
K are the viscometer constants. A digital stopwatch with a
resolution of 0.01 s has been used for the measurement of flow
time. The estimated uncertainty of the experimental viscosity was
(
0.002 mPa s.
3
Refractive indices of the studied solutions were determined
using a digital refractometer (ATAGO-DRA1, Japan) with an
ꢀ
4
uncertainty of ( 1 10 . The instrument was calibrated with
3
doubly distilled water before each series of measurements. A
procedure called “zero setting” was always performed before the
actual measurements of the sample's refractive index, to ensure
that the refractometer is working properly. The calibration was
checked with pure liquids of a known refractive index. The
temperature was controlled using a circulating bath thermostat
1
(
16ꢀ18
0
N,N -Bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) was
synthesized according to literature. The pyridine-2-aldehyde
0.6 mol) was added slowly to the ethylenediamine (0.3 mol) in
19
(
Julabo NP, Germany) with a temperature stability of ( 0.01 K.
(
ethanol solution. After stirring the mixture gently for 1 h and the
removal of the ethanol by rotary evaporation, an orangeꢀyellow
residual liquid product was obtained. The product was extracted
with hot hexane several times. After cooling, an orange product
’
RESULTS AND DISCUSSION
Volumetric Properties. The measured densities of IL + DMF
binary solutions and BPIE + IL + DMF ternary solutions at
4
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Journal of Chemical & Engineering Data
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Journal of Chemical & Engineering Data
ARTICLE
0
0
Table 3. Standard Partial Molar Volumes, V , and Slopes, S , Partial Molar Volumes of Transfer, Δ V , Correlation Coefficients,
ϕ
v
tr ϕ
2
R , and Standard Deviations, σ(V ), for the ILs in BPIE Schiff Base + DMF Solutions at 298.15 K
ϕ
6
0
6
0
m
BPIE
10 V
ϕ
10 S
v
tr ϕ
Δ V
ꢀ1
3
ꢀ1
3
ꢀ2
2
3
ꢀ1
system
mol kg
m
mol
m
mol kg
R
σ(V
ϕ
)
m mol
3
3
3
3
3
[
[
[
[
[
[
[
[
[
[
PnMIm]Br + DMF
0.0000
172.64 ( 0.41
171.57 ( 0.50
170.51 ( 0.75
169.72 ( 0.57
169.08 ( 0.65
134.90 ( 0.04
134.13 ( 0.56
133.41 ( 0.31
132.90 ( 0.89
132.56 ( 1.01
15.10 ( 0.05
18.89 ( 0.06
22.18 ( 0.09
26.29 ( 0.07
27.28 ( 0.08
20.49 ( 0.05
20.59 ( 0.07
24.75 ( 0.04
26.52 ( 0.11
31.06 ( 0.13
0.9941
0.9944
0.9909
0.9962
0.9960
0.9970
0.9940
0.9969
0.9910
0.9916
0.07
0.09
0.13
0.10
0.12
0.07
0.10
0.09
0.16
0.18
PnMIm]Br + DMF + BPIE
PnMIm]Br + DMF + BPIE
PnMIm]Br + DMF + BPIE
PnMIm]Br + DMF + BPIE
PMIm]Br + DMF
0.0410
0.0728
0.1205
0.1553
0.0000
0.0484
0.0941
0.1508
0.1820
ꢀ1.07
ꢀ2.12
ꢀ2.91
ꢀ3.56
PMIm]Br + DMF + BPIE
PMIm]Br + DMF + BPIE
PMIm]Br + DMF + BPIE
PMIm]Br + DMF + BPIE
ꢀ0.77
ꢀ1.42
ꢀ2.00
ꢀ2.34
to Masson's equation:
0
Vϕ ¼ Vϕ þ Svm
ð3Þ
0
where Vϕ is the partial molar volume at infinite dilution that
21
0
equals the standard partial molar volume. The values of Vϕ
and S along with their standard errors are listed in Table 3.
v
0
The Vϕ values reflect the presence of soluteꢀsolvent interac-
tions, while S values show that the nature of the soluteꢀsolute
v
2
2,23
interactions.
The apparent molar volumes of [PMIm]Br and
[
PnMIm]Br at 0.04 molality of BPIE Schiff base in DMF solu-
tions have been compared in Figure 2 which have the following
order: [PMIm]Br < [PnMIm]Br.
It can be also seen that the standard partial molar volumes, V ,
0
ϕ
for the ILs decrease with an increase concentration of BPIE due
to the stronger intractions of BPIE and IL. The values of S for all
v
studied solutions are positive, which indicates the presence of
soluteꢀsolute interactions in the investigated systems. The
Figure 2. Comparison of apparent molar volumes of [RMIm]Br in
BPIE +DMF) solutions with a molality of 0.04 of BPIE: (, [PnMIm]Br;
, [PMIm]Br at 298.15 K.
(
2
values of S increase with increasing molality of the BPIE
v
Schiff base in solutions containing ILs, which indicates that the
strength of soluteꢀcosolute interactions (Schiff baseꢀIL) is
increasing at higher concentrations of BPIE.
different molalities of BPIE are presented in Table 2. The
Standard thermodynamic properties of transfer yield qualita-
tive and quantitative information regarding the interactions of a
cosolvent and a solute without having to take into account the
effects of soluteꢀsolute interactions as at infinite dilution which
apparent molar volumes V were calculated by the following
ϕ
equation
ꢀ
ꢁ
M
d
1000ðd ꢀ d Þ
the interactions between solute molecules are negligible. The
0
Vϕ ¼
ꢀ
ð2Þ
0
partial molar volumes of transfer, Δ V , for the ILs from DMF
mdd
tr ϕ
0
to BPIE + DMF solutions were calculated as follows:
where M is the molar mass of IL, d and d are densities of the
0
ΔtrVϕ0 ¼ Vϕ ðBPIE þ DMFÞ ꢀ Vϕ ðDMFÞ
0
0
ð4Þ
solutions (BPIE + IL + DMF) and reference solvent (desired
molality of BPIE in DMF), respectively, and m denotes the
molality of the IL in reference solvent (BPIE + DMF). The
0
ϕ
The values of Δ V are given in Table 3. As shown in this table,
tr
0
calculated apparent molar volumes V for the solutions of
the Δ V values have negative values for IL + Schiff base + DMF
ϕ
tr ϕ
[
PnMIm]Br and [PMIm]Br at different molal concentrations
ternary solutions and decrease with increasing concentration
of BPIE.
The types of interactions present in the studied solutions
are as in the following:
of BPIE Schiff base in DMF solutions are also given in Table 2.
The data in Table 2 shows that the apparent molar volumes of
[PnMIm]Br in DMF slightly decreased by increasing the BPIE
molality approximately from m = (0.0, 0.04, 0.08, 0.12, and
(a) Polarꢀionic group interactions between the N groups of
BPIE Schiff base and the ions of [RMIm]Br.
(b) Polarꢀpolar group interactions between the polar groups
of BPIE Schiff base and the imidazolium ring of [RMIm]Br
through the hydrogen bonding.
BPIE
ꢀ
1
0
.16) mol kg at 298.15 K. As can be seen from this table, there
3
is a linear correlation between apparent molar volumes and
molality of IL at T = 298.15 K. Therefore, the infinite dilution
0
ϕ
apparent molar volume, V , was obtained by least-squares fitting
4
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Journal of Chemical & Engineering Data
Table 4. Molar Conductivities, Λ, of ILs in BPIE Schiff Base + DMF Solutions at Different Molalities of ILs, m , at 298.15 K
ARTICLE
IL
3
a
4
3
4
3
4
3
4
1
0 mIL
10 Λ
10 mIL
10 Λ
10 mIL
10 Λ
10 mIL
10 Λ
ꢀ1
2
ꢀ1
ꢀ1
2
ꢀ1
ꢀ1
2
ꢀ1
ꢀ1
2
ꢀ1
mol kg
S m mol
mol kg
S m mol
mol kg
S m mol
mol kg
S m mol
3
3
3
3
3
3
3
3
3
3
3
3
[
PnMIm]Br
b
ꢀ1
ꢀ1
ꢀ1
ꢀ1
m
BPIE = 0.0000 mol kg
m
BPIE = 0.0362 mol kg
m
BPIE = 0.0725 mol kg
m
BPIE = 0.1157 mol kg
3
3
3
3
0
1
2
3
3
4
5
6
7
8
.7182
98.08
87.89
82.93
79.26
77.27
75.59
73.84
71.25
69.49
67.83
0.8197
1.7019
2.4749
3.4351
4.3329
5.3947
6.4018
7.3543
8.2053
8.9860
85.38
79.91
76.61
74.08
71.66
68.00
66.07
63.97
61.73
60.52
0.9252
1.9288
2.8462
3.7478
4.5555
5.4258
6.1079
6.8292
7.5506
8.8835
75.86
73.69
71.36
69.58
68.43
67.23
66.76
66.33
65.71
64.97
0.9912
1.7947
2.9436
3.8823
4.7158
5.5793
6.2702
6.9835
7.7344
9.0711
71.15
70.04
68.92
67.96
66.99
66.42
65.53
64.98
64.29
63.51
.5506
.3422
.1991
.8436
.6436
.4026
.2922
.1735
.0223
[
PMIm]Br
ꢀ1
ꢀ1
ꢀ1
ꢀ1
m
BPIE = 0.0000 mol kg
m
BPIE = 0.0362 mol kg
m
BPIE = 0.0766 mol kg
m
BPIE = 0.1197 mol kg
3
3
3
3
1
2
3
4
5
7
8
9
.0796
.3726
.5946
.7691
.9436
.2960
.6010
.7992
83.29
77.03
71.56
67.89
64.99
62.17
60.22
58.74
56.94
54.80
1.0826
2.3604
3.5894
4.9257
6.0961
7.6274
8.7686
10.1146
11.4607
12.8457
69.33
67.04
64.71
62.61
61.23
59.56
57.91
56.71
55.23
1.4018
2.9541
4.2806
5.4471
6.6043
7.8179
9.0974
10.2827
11.4587
12.6723
62.41
61.43
60.54
59.59
58.95
58.28
57.38
56.87
56.48
56.22
1.7652
3.5596
5.0030
6.3391
7.6264
8.9527
10.2986
11.5274
12.7172
13.9264
57.98
57.33
56.82
56.35
55.97
55.45
54.92
54.60
54.37
54.19
1
1
1.187
3.0854
54.43
b
a
m
IL is the molality of IL where the solvent is (DMF + BPIE). mBPIE is the molality of BPIE where the solvent is DMF.
0
24
interactions of types c and d should lead to negative Δ V . An
tr
ϕ
increase in the concentration of cosolute (BPIE) results in more
0
ϕ
negative Δ V , indicating an enhancement in the nonpo-
tr
larꢀnonpolar interactions between the BPIE Schiff base and
0
the IL. The Δ V values for the [PnMIm]Br are more negative
tr
ϕ
rather than [PMIm]Br solutions. This trend shows that the
nonpolarꢀnonpolar interactions between the BPIE Schiff and
[
PnMIm]Br stronger than [PMIm]Br.
Conductometric Results. Conductivity measurements yield
both the association constant as well as information about the
25
relative solvating ability of solvents for the various ions. Recently,
the low concentration chemical model (LcCM) of the conduc-
tivity equation is widely applied for the correlation of conduc-
2
6
tance data in aqueous and nonaqueous electrolyte solution.
Figure 3. Comparison of molar conductivities of [RMIm]Br in (BPIE +
DMF) solution with a molality of 0.04 of BPIE: 2, [PnMIm]Br; 4,
The conductivity equation of the lcCM is the FuossꢀOnsager
type equation. The calculated molar conductivities Λ of ternary
solutions at several concentrations of BPIE are given in Table 4.
The calculated molar conductivity Λ has an uncertainty better
than 1%. It is shown that the molar conductivity, Λ, decreases
with increasing IL concentration. Increasing IL concentration
causes the formation of ion pair in the dilute region. This table
also represents that the molar conductivity, Λ, values decrease
with increasing BPIE concentration. The increasing Schiff base
concentration causes stronger interactions between the alkyl
chain of IL and the pyridinyl group of Schiff base, thus leading to
a decrease in molar conductivity of [RMIm]Br.
[PMIm]Br at 298.15 K.
(
(
c) Polarꢀnonpolar group interactions between the N group
of BPIE Schiff base and the nonpolar groups (alkyl chain)
of [RMIm]Br.
d) Nonpolarꢀnonpolar group interactions between the
nonpolar groups of BPIE and alkyl group attached to
imidazolium ring of [RMIm]Br.
Taking the cosphere overlap model as a guideline, the a and b
0
types of interactions should lead to positive ΔtrVϕ values, and
4
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Journal of Chemical & Engineering Data
Table 5. Ion Association Constants, K , Limiting Molar Conductivities, Λ , Walden Products, Λ η , Distance Parameters, R, and
ARTICLE
a
0
0 0
Standard Deviations σ(Λ) of [RMIm]Br at Several Concentrations of BPIE Schiff Base + DMF Solutions at 298.15 K
4
7
10
m
BPIE
K
a
10 Λ
0
10 Λ
η
0 0
10 R
ꢀ1
3
ꢀ1
2
ꢀ1
2
ꢀ1
system
mol kg
dm mol
S m mol
S m mol Pa s
m
σ(Λ)
3
3
3
3
3
3
3
3
[
[
[
[
[
[
[
[
PnMIm]Br + DMF
0.0000
96.62
82.20
24.80
19.90
73.05
38.23
13.95
10.76
100.65
89.40
76.09
72.91
88.20
72.51
64.24
58.58
86.64
76.96
65.50
62.76
75.92
62.42
55.30
50.43
18.9
1.88
0.68
0.79
0.13
1.02
0.20
0.17
0.18
PnMIm]Br + DMF + BPIE
PnMIm]Br + DMF + BPIE
PnMIm]Br + DMF + BPIE
PMIm]Br + DMF
0.0362
0.0725
0.1157
0.0000
0.0400
0.0766
0.1197
18.49
16.37
9.99
20.07
14.36
0.13
PMIm]Br + DMF + BPIE
PMIm]Br + DMF + BPIE
PMIm]Br + DMF + BPIE
15.66
The molar conductivity values of [PMIm]Br and [PnMIm]Br
where n and p show the number of the experimental data and
parameters, respectively.
ꢀ
1
in 0.04 mol kg of BPIE in DMF solutions have been compared
3
together in Figure 3. This shows that the molar conductivity
values of [PnMIm]Br in DMF + BPIE solutions are more than
As it is seen from Table 5, the Λ values for ILs decrease
0
with the increase concentration of BPIE Schiff base in BPIE +
IL + DMF ternary solutions. This can be ascribed to the facts
that (i) with the increasing concentration of Schiff base BPIE,
the dielectric constant of solution decrease and electrostatic
attraction between the ions increases, and hence the ions in
the free state decrease; (ii) with the increase in microscopic
viscosity of solutions, the mobility of ions decrease. This
result supports the conclusion obtained by considering volu-
[
PMIm]Br IL. An analysis of conductivity data in the framework
of the LcCM uses the set of equations:
1
=2
3=2
Λ ¼ α½Λ0 ꢀ SðcαÞ
þ Ecα lnðcαÞ þ J1cα þ J2ðcαÞ
ꢁ
ð5Þ
where the ion association constant, Ka
metric results. The values of K decrease with increasing alkyl
1
ꢀ α
a
Ka ¼
ð6Þ
chain length ILs and show that the interactions between the
cation and the anion ILs decreased; thus, the ion association
was reduced.
2
2
α cγ
(
where
kq
þ kR
To eliminate the influence of viscosity on the ionic mobility,
the viscosities of the solutions were determined using the method
ln γ( ¼ 1
ð7Þ
ð8Þ
ð9Þ
27
reported in the literature. The values of the Walden product,
Λ η , were calculated which are included in Table 4. An increase
2
2
0 0
1
6000N z e αc
2
A
in viscosity leads to a decrease in conductivity. This effect was
formulated quantitatively by the Walden rule which states that
the product Λ η should be approximately constant for a given
k ¼
ε εK T
0
B
0
0
zczae2
electrolyte, irrespective of the nature of the solvent, provided that
q ¼ 8
28
the radius of the ion remains unchanged. As shown in Table 5,
πε0εKT
the absolute values of the Walden product decrease slowly with
increasing BPIE concentration. According to the uncertainties in
the experimental viscosity and conductivity, it can be reasonably
expected that some experimental points will deviate from the
linear relation, but this does not influence the decreasing tendency.
This suggests that these ions do not have the same effective
radius in different solvent compositions and consequently pro-
vides evidence for the desolvation of the ions in solution. This
behavior seems to be caused by the preferential solvation of ions
of IL by Schiff base molecules. This indicates that the interactions
of IL with the Schiff base molecules are stronger than those
of DMF.
Viscometric Results. The measured viscosities η, for (IL +
BPIE + DMF) ternary solutions at 298.15 K are tabulated in
Table 6. This table shows that the values of η for ternary solutions
of (IL + BPIE + DMF) increase with increasing the concentra-
tion of BPIE Schiff base. This phenomenon was interpreted in
terms of stronger contact between the components of solution;
then, the molecules of Schiff base tend to congregate together to
induce the increase in the viscosity.
where Λ and Λ are the molar conductivity and limiting molar
0
conductivity, respectively, at molarity c, 1 ꢀ α is the fraction of
oppositely charged ions acting as ion pairs, K is the ion
a
association constant of [RMIm]Br, R is the distance parameter,
and γ is the corresponding mean activity coefficient of the free
(
ions. The coefficients of eq 5 reflect the relaxation and electro-
phoretic effects. In eq 5, S is the coefficient of DebyeꢀH €u ckelꢀ
Onsager, and E depends only on the properties of the solvent and
the charge of the ions, while J and J depend on the same
1
2
parameters and also on the distance parameter, R. The coefficients
26
E, J , and J required for calculations were taken from literature.
1
2
k is the reciprocal Debye radius of the ion cloud, and N is
A
Avogadro's number. Three-parameter fits of molar conductiv-
ity data yields the association constant, K , the limiting molar
a
conductivity, Λ , and distance parameter, R, by nonlinear
0
least-squares iteration. K , Λ , and R parameters are summar-
a
0
ized in Table 5.
The standard deviation σ(Λ) of the measured Λ(exp) and the
calculated one Λ(calc) was computed as follows:
Experimental values of viscosity were then correlated by using
the JonesꢀDole equation which is widely used for the description
2
1=2
σðΛÞ ¼ ð ½ΛðexpÞ ꢀ ΛðcalcÞꢁ =ðn ꢀ pÞÞ
ð10Þ
29
∑
4
169
dx.doi.org/10.1021/je2006117 |J. Chem. Eng. Data 2011, 56, 4164–4172

Journal of Chemical & Engineering Data
ARTICLE
Table 6. Viscosities, η, of Ternary ([RMIm]Br + BPIE + DMF) Solutions at 298.15 K
a
m
IL
η
m
IL
ꢀ1
η
m
IL
ꢀ1
η
m
IL
η
m
IL
ꢀ1
η
ꢀ
1
ꢀ1
mol kg
mPa s
mol kg
mPa s
mol kg
mPa s
mol kg
mPa s
mol kg
mPa s
3
3
3
3
3
3
3
3
3
3
[
PnMIm]Br + BPIE + DMF
b
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
m
BPIE = 0.0000 mol kg
m
BPIE = 0.0401 mol kg
m
BPIE = 0.0728 mol kg
m
BPIE = 0.1205 mol kg
mBPIE = 0.1553 mol kg
3
3
3
3
3
0
0
0
0
0
0
0
0
0
0
.0201
.0409
.0618
.0853
.1009
.1186
.1433
.1610
.1798
.2050
0.877
0.890
0.899
0.912
0.925
0.942
0.957
0.965
0.982
0.991
0.0233
0.0408
0.0602
0.0814
0.0999
0.1205
0.1386
0.1603
0.1820
0.1966
0.890
0.0244
0.0428
0.0628
0.0812
0.1001
0.1223
0.1405
0.1617
0.1793
0.2000
0.901
0.0237
0.0482
0.0602
0.0853
0.0990
0.1253
0.1441
0.1617
0.1843
0.2034
0.920
0.0231
0.0405
0.0613
0.0858
0.0994
0.1228
0.1410
0.1618
0.1848
0.1953
0.945
0.903
0.917
0.927
0.936
0.951
0.965
0.979
0.992
1.003
0.910
0.928
0.938
0.948
0.962
0.978
0.987
0.997
1.010
0.928
0.932
0.940
0.951
0.962
0.968
0.990
1.010
1.018
0.955
0.968
0.981
0.986
0.997
1.012
1.023
1.035
1.050
[
PMIm]Br + BPIE + DMF
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
m
BPIE = 0.0000 mol kg
m
BPIE = 0.0484 mol kg
m
BPIE = 0.0941 mol kg
m
BPIE = 0.1508 mol kg
mBPIE = 0.1820 mol kg
3
3
3
3
3
0
0
0
0
0
0
0
0
0
0
.0268
.0444
.0628
.0851
.1030
.1256
.1396
.1656
.1826
.2057
0.880
0.889
0.897
0.905
0.917
0.923
0.936
0.956
0.966
0.975
0.0271
0.0417
0.0599
0.0842
0.1015
0.1251
0.1403
0.1558
0.1800
0.2033
0.893
0.0282
0.0431
0.0603
0.0850
0.1029
0.1263
0.1439
0.1639
0.1829
0.2017
0.909
0.0283
0.0433
0.0618
0.0865
0.1043
0.1221
0.1447
0.1603
0.1864
0.2104
0.935
0.0228
0.0436
0.0617
0.0834
0.1031
0.1262
0.1442
0.1620
0.1830
0.2024
0.943
0.902
0.915
0.924
0.934
0.947
0.959
0.969
0.998
0.989
0.922
0.932
0.946
0.955
0.968
0.980
0.986
0.995
1.013
0.940
0.949
0.969
0.979
0.988
0.998
1.006
1.016
1.031
0.952
0.961
0.972
0.984
0.995
1.008
1.018
1.030
1.036
a
b
m
IL is the molality of IL where the solvent is (DMF + BPIE). mBPIE is the molality of BPIE where the solvent is DMF.
Table 7. Values of Viscosity B-Coefficients, Standard Devia-
tions σ(η), and Solvation Number B/Vϕ for BPIE + DMF +
where η and η are the viscosities of (Schiff base + IL + DMF)
0
0
ternary solutions and reference solvent (Schiff base + DMF),
respectively, and c is the molar concentration of ILs in the solution.
The A-coefficient, whose value generally is positive, is a measure of
soluteꢀsolute interactions, and the B-coefficient is an empirical
constant which depends on soluteꢀsolvent interactions and can
have positive or negative values. The calculated viscosity B-coeffi-
cients are given in Table 7 obtained from fitting the experimental
viscosity data to the JonesꢀDole equation. The viscosity B-coeffi-
cient is valuable to provide information concerning the solvation of
the solutes and their effects on the structure of the solvent in the near
environment of the solute molecules. The viscosity B-coefficient is a
measure of the effective solvodynamic volume of solvated species
and depends on the basis of shape, size, and soluteꢀsolvent
[
RMIm]Br Ternary Solutions at 298.15 K
3
m
BPIE
10 B
ꢀ1
3
ꢀ1
0
3
mol kg
m
mol
B/V
ϕ
10 σ(η)
3
3
[
PnMIm]Br
ꢀ3
ꢀ3
ꢀ3
ꢀ3
ꢀ3
0
0
0
0
0
.0000
0.802 ( 3.74 10
4.64
4.49
4.32
3.75
3.67
5.44
3.31
2.37
5.02
3.30
3
.0410
0.770 ( 2.30 10
3
.0728
.1205
.1553
0.736 ( 1.66 10
3
0.637 ( 4.94 10
3
0.615 ( 2.31 10
3
30
[
PMIm]Br
interactions. The viscosity B-coefficients are positive and decrease
with increasing the concentration of BPIE and shortening alkyl
chain length of ILs. Positive values of B-coefficients suggest the
presence of soluteꢀsolvent interactions. But these types of interac-
tions are weakened with an increase of Schiffbase concentration. On
other hand, the viscosity B-coefficients for [PMIm]Br are less than
those values for [PnMIm]Br. It means that DMF molecules have
ꢀ
3
0
0
0
0
0
.0000
.0484
.0941
.1508
.1820
0.622 ( 49 10
4.61
4.59
4.49
4.40
4.35
3.56
2.75
3.74
3.66
2.93
3
ꢀ
3
3
3
3
0.616 ( 2.65 10
3
ꢀ
ꢀ
ꢀ
0.607 ( 2.65 10
3
0.586 ( 2.57 10
3
0.577 ( 2.05 10
3
strong interactions with [PnMIm]Br rather than other ILs. Further,
0
of viscosity behavior in dilute electrolyte solutions;
the calculated solvation number, B/V , in DMF + Schiff base
ϕ
solutions are given in Table 7. The solvation number of ILs in IL +
DMF + Schiff base solutions decreases with increase in the amount
of Schiff base. These results further support our earlier conclusions
η
1=2
¼
1 þ Ac þ Bc
ð11Þ
η0
4
170
dx.doi.org/10.1021/je2006117 |J. Chem. Eng. Data 2011, 56, 4164–4172

Journal of Chemical & Engineering Data
ARTICLE
Table 8. Refraction Indices, n , and Molar Refractions, R , of BPIE + [RMIm]Br + DMF Solutions at 298.15 K
D
D
a
m
IL
n
D
R
D
m
IL
n
D
R
D
m
IL
n
D
R
D
m
IL
n
D
R
D
m
IL
n
D
R
D
[
PnMIm]Br
b
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
m
BPIE = 0.0000 mol kg
m
BPIE = 0.0401 mol kg
m
BPIE = 0.0728 mol kg
m
BPIE = 0.1205 mol kg
mBPIE = 0.1553 mol kg
3
3
3
3
3
0
0
0
0
0
0
0
0
0
0
.0201
.0409
.0618
.0853
.1009
.1186
.1433
.1610
.1798
.2050
1.4291
1.4297
1.4299
1.4309
1.4312
1.4317
1.4320
1.4323
1.4329
1.4333
20.0405
20.1031
20.1540
20.2235
20.2683
20.3339
20.3794
20.4267
20.498
0.0233 1.4307 20.0747 0.0244 1.4311 20.0825 0.0237 1.4322 20.1052 0.0231 1.4340 20.1263
0.0408 1.4313 20.1222 0.0428 1.4315 20.1250 0.0482 1.4325 20.1391 0.0406 1.4346 20.1886
0.0602 1.4316 20.1854 0.0628 1.4320 20.1789 0.0602 1.4328 20.198
0.0613 1.4352 20.2586
0.0814 1.4319 20.2316 0.0812 1.4326 20.2383 0.0853 1.4334 20.2481 0.0858 1.4356 20.3003
0.0999 1.4323 20.2865 0.1001 1.4332 20.3039 0.0990 1.4338 20.3140 0.0994 1.4359 20.3566
0.1205 1.4326 20.3324 0.1223 1.4337 20.3585 0.1253 1.4342 20.3666 0.1228 1.4365 20.4155
0.1386 1.4329 20.3859 0.1405 1.4344 20.4266 0.1441 1.4348 20.4239 0.1410 1.4369 20.4726
0.1603 1.4333 20.4427 0.1617 1.4348 20.4769 0.1617 1.4352 20.4841 0.1615 1.4373 20.5345
0.1820 1.4339 20.4959 0.1793 1.4352 20.5322 0.1843 1.4356 20.5379 0.1848 1.4376 20.5673
0.1966 1.4345 20.0747 0.2000 1.4355 20.0825 0.2034 1.4362 20.1052 0.1953 1.4380 20.1263
20.0405
[
PMIm]Br
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
m
BPIE = 0.0000 mol kg
m
BPIE = 0.0484 mol kg
m
BPIE = 0.0941 mol kg
m
BPIE = 0.1508 mol kg
mBPIE = 0.1820 mol kg
3
3
3
3
3
0
0
0
0
0
0
0
0
0
0
.0268
.0444
.0628
.0851
.1030
.1256
.1396
.1656
.1826
.2057
1.4289
1.4296
1.4302
1.4307
1.4309
1.4312
1.4317
1.4321
1.4328
1.4336
20.0338
20.0787
20.1244
20.153
0.0271 1.4307 20.0622 0.0282 1.4318 20.0885 0.0283 1.4334 20.1124 0.0228 1.4340 20.1367
0.0417 1.4311 20.0949 0.0431 1.4324 20.1160 0.0433 1.4338 20.1499 0.0436 1.4349 20.1778
0.0599 1.4314 20.1551 0.0603 1.4326 20.177
0.0618 1.4342 20.1947 0.0617 1.4354 20.2153
0.0842 1.4322 20.1995 0.0850 1.4336 20.2131 0.0865 1.4346 20.2437 0.0834 1.4357 20.252
20.1917
20.2284
20.2749
20.3241
20.3851
20.0338
0.1015 1.4328 20.2391 0.1029 1.4338 20.2563 0.1043 1.4353 20.273
0.1251 1.4331 20.2772 0.1263 1.4342 20.3129 0.1221 1.4357 20.326
0.1403 1.4336 20.3117 0.1439 1.4351 20.3522 0.1447 1.4362 20.366
0.1558 1.4340 20.3602 0.1639 1.4355 20.3929 0.1603 1.4367 20.416
0.1031 1.4359 20.296
0.1262 1.4362 20.34
0.1442 1.4368 20.3808
0.1620 1.4375 20.4255
20.4254 0.1864 1.4369 20.4744 0.1830 1.438 20.4776
0.1800 1.4345 20.4005 0.1829 1.436
0.2033 1.4348 20.0622 0.2017 1.4362 20.0885 0.2104 1.4379 20.1124 0.2024 1.4387 20.1367
a
b
mIL is the molality of IL where the solvent is (DMF + BPIE). mBPIE is the molality of BPIE where the solvent is DMF.
regarding the behavior of these systems (BPIE + IL + DMF) from
values of Vϕ and B.
Refractometric Results. Experimental refractive index data,
nD, for [PMIm]Br or [PnMIm]Br + BPIE Schiff base + DMF
ternary solutions were measured as a function of the IL con-
fer have been computed from the experimental density data. It has
been observed that these parameters decrease with increasing BPIE
concentration and increase with increasing alkyl chain length of ILs.
The variation of these parameters indicate an enhancement in the
nonpolarꢀnonpolar interactions between the BPIE Schiff base and
the IL and these types of interactions between the BPIE Schiff base
and [PnMIm]Br stronger than [PMIm]Br. Electrical conductances
of ILs at several concentrations of BPIE have been used for the
0
centration, and m is the molality of IL where solvent is (DMF +
IL
BPIE) at 298.15 K. The molar refraction, R , is calculated using
D
3
1
the LorentzꢀLorenz equation according to
!
determination of ion association constants, K , and limiting molar
ꢀ
ꢁ
a
3
ðnD ꢀ 1Þ
xiMi
d
conductivities, Λ , using the lcCM of conductance equation. These
0
RD ¼
ð12Þ
∑
2
parameters decrease with increasing the concentration of BPIE due
to the dielectric constant and microscopic viscosity of the solutions
ðnD þ 2Þ
i¼1
studied. The values of K increase with increasing chain length ILs
and show that ion association increases with increasing chain length
where x and M are the mole fraction and molecular weight of
a
i
i
components, respectively, and d is the density of IL + Schiff base
DMF solutions at a fixed concentration of Schiff base. The
alkyl of ILs. The Walden product Λ η values decreased with
+
0 0
increasing BPIE molality for both ILs, which is ascribed to the
preferential solvation of the ions by BPIE molecules. The values of
viscosity B-coefficients decrease with increasing concentration of
BPIE in (BPIE + ILs + DMF) ternary solutions, which indicates the
calculated molar refractions of the investigated solutions are
given in Table 8.
’
CONCLUSIONS
nonpolarꢀnonpolar interactions between BPIE and IL. The R
D
The effect of BPIE Schiff base on the thermodynamic and
values increase with an increasing amount of BPIE in the ternary
solutions studied.
thermophysical properties of two ILs, 1-pentyl-3-methylimidazo-
lium bromide and 1-propyl-3-methyl imidazolium bromide, in the
N,N-dimethylformamide solutions was investigated at T= 298.15 K.
The density, electrical conductance, viscosity, and refraction index
data were measured for ternary (IL + BPIE + DMF) solutions at T=
’
AUTHOR INFORMATION
Corresponding Author
*Tel.: 984113393139. Fax: 984113340191. E-mail address:
hemayatt@yahoo.com (H.S.).
2
98.15 K and at atmospheric pressure. The apparent molar volumes,
standard partial molar volumes, and partial molar volumes of trans-
4
171
dx.doi.org/10.1021/je2006117 |J. Chem. Eng. Data 2011, 56, 4164–4172

Journal of Chemical & Engineering Data
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