Solvatochromic probes absorbance behavior in mixtures of 2-hydroxy ethylammonium formate with methanol, ethylene glycol and glycerol

Article abstract of DOI:10.1007/s10953-010-9596-8

Solute-solvent and solvent-solvent interactions were investigated for binary mixtures of an ionic liquid (IL) 2-hydroxy ethylammonium formate as with methanol, ethylene glycol and glycerol. The physicochemical properties of the solvent mixtures at 25 °C, over the whole range of mole fractions, were determined using solvatochromic probes. High normal polarity (E_T ^N) in the alcohol-rich region confirms solute-solvent interactions in this medium. Dipolarity/polarizability (π ^*) show a different trend to E_T^N with a positive deviation from ideal behavior in IL-glycerol mixtures. However, these deviations for other solvent mixtures are insignificant. Contrary to what is observed for E _T^N and π^*, hydrogen-bond donor (HBD) acidity and hydrogen-bond acceptor (HBA) basicity demonstrate similar trends. The applicability of the combined nearly-ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation for the correlation of various parameters provides a simple computational model to correlate and/or predict various solvatochromic parameters for many binary solvent systems.

Full text of DOI:10.1007/s10953-010-9596-8

J Solution Chem (2010) 39: 1509–1519
DOI 10.1007/s10953-010-9596-8
Solvatochromic Probes Absorbance Behavior in Mixtures
of 2-Hydroxy Ethylammonium Formate with Methanol,
Ethylene Glycol and Glycerol
Hadi Salari · Ali Reza Harifi-Mood ·
Mohammad Reza Elahifard ·
Mohammad Reza Gholami
Received: 20 February 2010 / Accepted: 12 May 2010 / Published online: 5 October 2010
© Springer Science+Business Media, LLC 2010
Abstract Solute-solvent and solvent-solvent interactions were investigated for binary mix-
tures of an ionic liquid (IL) 2-hydroxy ethylammonium formate as with methanol, ethylene
glycol and glycerol. The physicochemical properties of the solvent mixtures at 25 °C, over
the whole range of mole fractions, were determined using solvatochromic probes. High
normal polarity (ETN ) in the alcohol-rich region confirms solute-solvent interactions in this
medium. Dipolarity/polarizability (π∗) show a different trend to ETN with a positive de-
viation from ideal behavior in IL-glycerol mixtures. However, these deviations for other
solvent mixtures are insignificant. Contrary to what is observed for ETN and π∗, hydrogen-
bond donor (HBD) acidity and hydrogen-bond acceptor (HBA) basicity demonstrate sim-
ilar trends. The applicability of the combined nearly-ideal binary solvent/Redlich-Kister
(CNIBS/R-K) equation for the correlation of various parameters provides a simple com-
putational model to correlate and/or predict various solvatochromic parameters for many
binary solvent systems.
Keywords Ionic liquids · Solvatochromic properties · 2-Hydroxy ethylammonium
formate · Solute-solvent and solvent-solvent interactions
1 Introduction
During the last decade ionic liquids (ILs) have gathered widespread interest and curiosity as
potential environmentally friendly solvents from both the scientific and engineering commu-
nities. The number of research publications on investigations of ILs for properties, analysis,
and applications has increased many fold [1–7].
H. Salari · M.R. Elahifard · M.R. Gholami (
)
ꢀ
Department of Chemistry, Sharif University of Technology, Azadi Ave., P.O. Box 11365-9516, Tehran,
Iran
e-mail: gholami@sharif.edu
A.R. Harifi-Mood
Department of Chemistry, Tarbiat Moallem University, Mofatteh Ave., P.O. Box 15719-14911, Tehran,
Iran

1510
J Solution Chem (2010) 39: 1509–1519
An ideal solvent should have a very low volatility and should be chemically and physi-
cally stable, recyclable, reusable, and eventually, easy to handle. Moreover, solvents that al-
low more selective and rapid chemical transformations will have a significant impact. Ionic
liquids have been recognized as a novel class of solvents [1].
To increase the efficiency of a process (e.g., separation, extraction, synthesis, etc.), one
would like to “tune” the solvent or solvent mixture by addition of cosolvents. It is beneficial
in many ways to understand how added cosolvents (or impurities) affect the physicochem-
ical properties of ILs [8–10]. Among molecular solvents, alcohols and polyols have gained
interest as cosolvents and for their effects on IL properties [11–16].
Although an abundant chemical literature exists on applications of both ILs and polyols
as solvent media, there are certain drawbacks concerning these solvents which limit their
potential as environmentally friendly solvents. One of the most crucial drawbacks is the
limited solubility of many common solutes in these solvents [1–7]. It is interesting to note,
however, that many solutes that are insoluble or slightly soluble in ILs are soluble in alcohols
or polyols and vise versa. The cost of ILs is another limitation for their large scale usage.
To evaluate the behavior of a liquid as a solvent, understanding the solution interactions
at a molecular level is necessary. In this direction, it is of interest to quantify its most rel-
evant molecular-microscopic solvent properties, which determine how it will interact with
potential solutes. An appropriate method to study solute-solvent interactions is the use of
solvatochromic indicators that reflect the specific and nonspecific solute-solvent interactions
on the UV-Vis spectral band shifts.
2-Hydroxy ethylammonium formate is one of the simplest ILs; it is easily prepared and
its reactants are accessible and relatively inexpensive [17]. Also, this IL is miscible with
many solvents. However, there are few reports on the properties of this IL [15]. Since there
are some structural similarities between this IL and aliphatic alcohols, it is expected that its
mixture with alcohols and polyols will show individual features.
In continuing our studies on ILs [14, 15, 18, 19], the four solvatochromic parameters (i.e.,
ETN , normalized solvent polarity parameter; π∗, dipolarity/polarizability; β, hydrogen-bond
acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mix-
tures of methanol, ethylene glycol and glycerol with 2-hydroxy ethyl ammonium formate
at 25 °C over the whole range of mole fractions. The solvatochromic indicators used are
Reichardt’s betaine dye for solvent polarity (ET (30) scale) [20, 21] as well as 4-nitroanisole
and 4-nitroaniline for measuring the Kamlet-Taft parameters [22–25]. The applicability of
the CNIBS/R-K equation for the correlation of these solvatochromic parameters with sol-
vent composition is also shown for the three binary solvent mixtures.
2 Experimental
2.1 Materials
4-Nitroanisole and 4-nitroaniline (Merck, 99%) were recrystallized from water/ethanol and
water/acetone, respectively. Reichardt’s betaine dye was obtained from Aldrich (>99%) and
was used without further purification. Methanol (99%), ethylene glycol (99%) and glycerol
(99%) were purchased from Merk Company. Ethanol amine and formic acid (Riedel de
Haen) were purified according to the literature [6].

J Solution Chem (2010) 39: 1509–1519
2.2 Methods
1511
The ionic liquid (2-hydroxy ethylammonium formate) was prepared by the dropwise addion
of formic acid to 2-amino ethanol, with equal mole fraction, in a two-necked flask under a
nitrogen atmosphere with vigorous stirring. The flask was mounted in an ice bath. Stirring
was continued for 20 h at room temperature to obtain a viscous clear liquid. The IL was char-
acterized as described in the literature [17]. Ethanolic solutions of the indicators were pre-
pared and stored in a dark glass vial at 4 °C. An aliquot of the solvatochromic probe primary
solution was transferred into a 1 cm quartz cuvette, and its solution was evaporated under
vacuum. The mixture of IL with molecular solvents (methanol, ethylene glycol, glycerol) at
different compositions was gravimetrically prepared ( 0.1 mg) for each binary solvent mix-
ture and was transferred into the quartz cuvette. The solution was vigorously stirred with a
magnetic stirrer, so that a homogenerous solution was prepared. Final probe concentrations
were 0.5–1 × 10−4 mol·dm−3. UV-Vis absorption spectra of the solutions were recorded
in the ranges of λ = 250–400 nm for 4-nitroanisole, 300–450 nm for 4-nitroaniline, and
420–600 nm for Reichardt’s betaine dye, using a GBC UV-Vis Cintra 40 spectrophotome-
ter with a thermocell coupled to it. All of the measurements were performed three times
and the maximum absorption was determined for each probe from the first derivative of the
wavelength scan. The precision of replicated measurements was 1 nm.
3 Results and Discussion
The selected IL is composed of 2-hydroxy ethylammonium as the cation and formate as
the anion. The values of solvatochromic properties (ETN , π∗, α and β) have been deter-
mined in binary mixtures of methanol, ethylene glycol and glycerol with an IL from pure
IL to pure alcohol according to the procedure reported elsewhere (Table 1) [20, 21, 26–29].
Table 1 Solvatochromic parameters
Binary
Ionic liquid mole fraction
mixture
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
N
T
IL + methanol
E
α
β
π
0.76
1.16
0.8
0.88 0.88 0.88 0.89 0.89 0.9
1.48 1.3 1.26 1.3
1.04 0.81 0.81 0.89 0.92 0.95
0.48 0.74 0.79 0.75 0.75 0.75 0.72 0.75 0.83 1.06
0.85 0.86 0.87 0.88 0.89 0.89 0.89 0.89 0.9 0.9
0.89 0.89 0.9
0.9
1.31 1.31 1.33 1.31 1.25 1.09
0.98 0.91 0.66
1
∗
0.58
N
T
IL + ethylene glycol
IL + glycerol
E
α
β
π
0.78
0.9
0.61
1
1.08 1.1
1.11 1.12 1.1
1.1
1.1
0.7
1.14 1.11 1.09
0.76 0.71 0.66
0.72 0.73 0.71 0.72 0.69 0.7
∗
0.94 0.95 0.97 0.99 1.02 1.02 1.03 0.98 1.03 1.06
N
T
a
E
α
β
π
0.81
0.93
0.67
1.04
0.85 0.87 0.88 0.89 0.89 0.89 0.89 0.89 0.89 0.9
a
0.77 0.54 0.56 0.59 0.6
0.61 0.62 0.62 0.62 1.09
0.34 0.01 0.01 0.01 0.03 0.02 0.01 0.01 0.02 0.66
1.39 1.75 1.75 1.73 1.72 1.71 1.71 1.71 1.71 1.06
∗
a
Reference [21]

1512
J Solution Chem (2010) 39: 1509–1519
Equations 1–7 show relationship between the solvatochromic parameters and experimental
values.
ET (solvent) − ET (TMS) ET (solvent) − 30.7
ETN
=
=
(1)
(2)
ET (water) − ET (TMS)
34.12 − νANS
32.4
π∗ =
= 0.427(32.12 − νB)
2.343
31.10 − 3.14π∗ − νANI
β =
(3)
(4)
2.79
α = 0.186(10.91 − νB) − 0.72π∗
in which νB , νANI and νANS are the maximum wavenumbers of betaine dye, 4-nitroaniline
and 4-nitroanisole, respectively, in kK.
The ETN value for the pure IL is close to that in water and far from those in the alcohols.
This behavior is different from ILs based on imidazolium cations, which demonstrates em-
pirical polarities similar to short-chain alcohols [13, 14]. The ETN parameter is a blend of
dipolarity/polarizability and the HBD acidity of the media. This unusually high ETN value
indicates a greater dipolarity/polarizability and/or HBD acidity than those of the alcohols.
Also, the other parameters (α, β and π∗) of 2-hydroxy ethylammonium formate are larger
than general for ILs [14]. The α value is largely determined by the nature of the cation.
The 2-hydroxy ethylammonium cation can act as strong hydrogen bond donor (HBD) due
to strongly acidic O–H and N–H hydrogen atoms. On the other hand, the positive charge on
the nitrogen atom could be one of the reasons for strong HBD. The β value, in contrast to ILs
based on imidazolium and pyridinium cations, is controlled by both cation and anion. The
hydroxide group in the cation structure can participate as a hydrogen bond acceptor (HBA).
The observed ETN values of the pure ILs are higher than those in pure methanol, ethylene
glycol and glycerol indicating higher dipolarity/polarizability and/or HBD acidity of IL rel-
ative to those of the others. As expected, ETN increases with increasing molecular weight
of the alcohols. This is explained by evoking the number of polar OH groups in glycerol
and ethylene glycol as compared to that of methanol. The increasing number of OH groups
results in increasing polarity. In addition, it seems that intermolecular hydrogen bonding in
ethylene glycol and glycerol can be a prevailing factor in decreasing HBD of these liquids.
3.1 Normalized Polarity (ETN )
The ETN parameter of the IL is higher than that of methanol (ETN = 0.9 and 0.76 respec-
tively). When small quantities of an IL are added to methanol, the ETN value increases
sharply and then increases monotonically to the value of the pure IL (Fig. 1). The response
patterns show that the influence of the IL is strong at the lowest IL concentration in all
mixtures. These results can be related to the preferential solvation of the solutes by the
IL through the cation [14, 26]. For dilute probe solutions in the absence of any solute-
solvents and solvent-solvent interactions, an ideal additive ETN value is calculated using
Eq. 5 [30, 31]:
ETN,ideal = xAETN,A + xILETN,IL
(5)
where xA and xIL are the mole fractions of alcohols and IL, respectively. Figure 1 shows the
ideal additive and experimentally obtained ETN values as a function of xIL.
It is notable that the experimental ETN values are greater than the ideal additive values.
The maximum deviation from ideal additive behavior in methanol-IL mixtures is observed in

J Solution Chem (2010) 39: 1509–1519
1513
N
T
Fig. 1
E
parameters for binary mixtures of IL with methanol (1), ethylene glycol (!) and glycerol (P)
(x is the mole fraction of IL)
IL
the methanol-rich region. A careful observation reveals that the deviations in experimental
ETN values from the ideal additive behavior (Eq. 5) are more prominent for methanol-IL
mixtures compared to ethylene glycol and glycerol-IL systems and thus, solvent-solvent
interactions are strongly implied. Investigation of the Kamlet-Taft parameters can prove this
claim. This deviation is small for glycerol-IL mixtures.
3.2 Dipolarity/Polarizability (π∗)
Figure 2 shows that the addition of IL to methanol causes a smooth variation with a S-type
curve. These variations in ethylene glycol-IL mixtures are insignificant. The π∗ trend of
glycerol-IL mixtures demonstrates a positive deviation that increases to the maximum value
at XIL = 0.3. A negative deviation from ideality is observed for IL-ethylene glycol. In
glycerol-IL mixtures, the π∗ values confirm high solvent-solvent interactions. The promi-
nence of the synergetic effect in mixtures with glycerol can be related to hydrogen bonding
interaction between the IL and glycerol to give a complex that is more polar than the indi-
vidual constituents of the mixture [26].
3.3 Hydrogen Bond Donor Acidity (α)
The α value for an IL is high and this parameter for the three molecular solvents is near to
the value in the pure IL. Figure 3 demonstrates that the α values exhibit positive deviations
from ideal behavior in methanol and ethylene glycol-IL mixtures. In addition, a negative
deviation is observed in glycerol-IL mixtures. In glycerol-IL systems the α parameter shows
a maximum negative deviation at XIL = 0.3 (Fig. 3).
This sharp decrease in the α values of the solution can be related to the involvement of
hydrogen bonding between solvent molecules. Glycerol is an interesting solvent because

1514
J Solution Chem (2010) 39: 1509–1519
∗
Fig. 2
π
parameters for binary mixtures of IL with methanol (1), ethylene glycol (!) and glycerol (P)
Fig. 3 α parameters for binary mixtures of IL with methanol (1), ethylene glycol (!) and glycerol (P)
the rotation of two CH2OH groups around the C–C bonds gives rise to three staggered con-
formations, leading to six possible backbone structures [32, 33]. Apart from various struc-
tures of glycerol, a plurality of intermolecular hydrogen bonds between the IL and glycerol
causes significant deviations from ideal behavior. However, the two solvents do not have

J Solution Chem (2010) 39: 1509–1519
1515
Fig. 4 β parameters for binary mixtures of IL with methanol (1), ethylene glycol (!) and glycerol (P)
equal number of acidic hydrogen and the maximum deviation observed is shifted towards
the glycerol-rich region instead of being in the vicinity of the equimolar composition.
3.4 Hydrogen Bond Acceptor Basicity (β)
There is no distinct difference between the trends in the β and α parameters. Similar to
the HBD trend, when the IL is added to methanol or ethylene glycol, the β value increases
smoothly. However, with addition of an IL to glycerol the hydrogen bond acceptor (HBA)
basicity decreases sharply to zero at XIL = 0.3 (Fig. 4). This negative deviation from ideal
behavior is continued to XIL = 0.9 and then the β parameter increases to its corresponding
value in pure IL.
The decreasing β values in glycerol-IL mixtures can be attributed to the same source as
for the α parameter. Intermolecular hydrogen bonds in mixtures of glycerol and IL reduce
the HBA ability over a wide range of compositions.
The general trend of the Kamlet-Taft parameters shows that small additions of IL to
molecular solvents results in dramatic deviations from ideal additive behavior.
This case is particularly observed in glycerol-IL mixtures. It is important to emphasize
that high polarity or low HBD and HBA abilities may be achieved by addition of small
amounts of IL to glycerol. Interestingly, unusual deviation from the ideal additive values in
such mixtures of solvents may have potentially important applications.
4 Theoretical Calculations
The “excess solvatochromic parameters”, SPE (SP is ETN , π∗, α and β) can be calculated
according to Eq. 6 in which the variation of any property is related to the pure and mixed

1516
J Solution Chem (2010) 39: 1509–1519
Fig. 5 Predicted values of the solvatochromic parameters from the correlation equations against their exper-
imental values for binary mixtures of IL with methanol, ethylene glycol and glycerol
solvent properties
2
ꢀ
SPE = SPm −
xiSPoi
(6)
i=1
where SPm and SPi are the corresponding parameters for the solvent mixture and the pure
solvents, respectively, and xi is the mole fraction of one solvent.
The CNIBS/R-K model provides a simple method to correlate and/or predict the excess
molar properties of a solute dissolved in a binary or ternary solvent mixture in terms of the
weighted mole fraction average of solute properties in the pure solvents and contributions
of solute-solvent and solvent-solvent interactions [34–39]. The solvatochromic parameters
(SP) in a binary solvent mixture at a constant temperature can be expressed as in Eq. 7:
k
ꢀ
SPm = x1SP01 + x2SP20 + x1x2
Aj (x1 − x2)j
(7)
j=0
where SPm, SP01 and SP02 are solvatochromic parameters determined in the mixed and pure
solvents 1 and 2, respectively, and x1 and x2 are the mole fractions of the binary solvent
mixture. Aj and j are the equation coefficients and the degree of the polynomial expansion.
The values of j can be varied between 0 and 4 to find an accurate mathematical representa-
tion of the experimental data. A cross-validation method has been applied to predict any of
the parameters. This method is a practical and reliable way to test the predictive significance
when little data are available [40]. In Fig. 5, the predicted values of SP (ETN , π∗, α and β)
obtained by the cross-validation method for various binary solvent mixtures from Eqs. 6 and
7 have been plotted versus the corresponding experimental values, and Eq. 8 is obtained for

J Solution Chem (2010) 39: 1509–1519
1517
Table 2 Average Redlich-Kister coefficients and standard deviation of the excess solvatochromic parameters
for three binary mixtures
A
0
A
1
A
2
A
3
A
4
σ
IL/methanol
N
T
∗
E
0.212
−0.336
0.793
−0.98
−1.881
1.077
0.442
1.575
−0.876
2.128
0.011
0.035
0.036
0.042
π
−5.94
6.462
7.108
α
β
−1.289
−1.754
−3.086
−2.338
0.836
1.794
IL/ethylene glycol
N
T
∗
E
π
α
β
0.156
−0.101
0.147
0.207
−0.568
0.966
−0.4
0.0617
0.021
0016
−0.089
0.394
0.070
−0.236
0.631
−0.382
−0.163
−0.480
−0.146
0.267
0.668
0.022
IL/glycerol
N
T
∗
E
0.147
2.593
−0.091
−1.127
0.607
0.014
4.448
−0.182
4.095
0.0167
0.052
0037
π
α
β
−1.582
−2.544
−2.927
−4.572
−3.219
−3.821
0.932
0.056
this correlation. It is clear that this correlation is reasonable.
SPmcal = 0.9946( 0.00708)SPemxp + 0.00387( 0.00682)
(8)
n = 132,
R2 = 0.993,
σ = 0.02896
Consequently, the R–K coefficients are reported in Table 2, where the standard deviation,
σ, was obtained from Eq. 9:
ꢂ
ꢁ
ꢃ
i=1(SPiexp − SPical
)
n
1/2
2
σ =
(9)
n
where n, SPiexp, and SPcial are the number of the experimental data points, and the exper-
imental and calculated solvatochromic parameters in the binary solvent mixtures, respec-
tively. The solvatochromic parameters and their excess values over the whole range of mole
fractions have been calculated from the coefficients of Eq. 7 given in Table 2.
The model shows a good correlation between predicted and experimentally measured
values, also no correlation and systematic errors were observed. Therefore, the CNIBS/R-K
model is a reasonable one for prediction of the solvatochromic parameters with high confi-
dence in the binary solvent mixtures of IL with methanol, ethylene glycol and glycerol.
5 Conclusions
The solvatochromic parameters have been determined in binary mixtures of 2-hydroxy eth-
ylammonium formate (an IL) with methanol, ethylene glycol and glycerol. This investi-
gation reveals the effect of OH groups in molecular solvents and its influence on solvent-
solvent interactions. All studied system show basically similar ETN response patterns. ETN

1518
J Solution Chem (2010) 39: 1509–1519
increases abruptly to the value of the pure IL upon increasing IL mole fraction. Slower
changes in glycerol-IL mixtures are attributed to increasing dipolarity/polarizability and
synchronously decreasing HBD acidity of the media when the IL is added to the glycerol.
The π∗, α and β values show no distinct deviations from ideal additive behavior. However,
positive deviation in the methanol-IL system confirms that the mixtures of these solvents
have better HBD and HBA values than the neat solvents. On the other hand, because of in-
termolecular hydrogen bonds, the HBD and HBA abruptly decrease in mixtures of glycerol
and IL so that the β value is zero at many mixtures mole fractions.
It was proved that the combined nearly ideal-binary solvent/Redlich-Kister(CNIBS/R-K)
equation can be used with confidence to achieve a correlation between the variation of the
solvatochromic parameters and solvent composition, and this equation is able to predict the
solvatochromic parameters.
References
1. Wasserscheid, P., Welton, T. (eds.): Ionic Liquids in Synthesis. Wiley-VCH, Weinheim (2003)
2. Welton, T.: Room-temperature ionic liquids: solvents for synthesis and catalysis. Chem. Rev. 99, 2071–
2084 (1999)
3. Wasserscheid, P., Keim, W.: Ionic liquids—new “solutions” for transition metal catalysis. Angew. Chem.,
Int. Ed. Engl. 39, 3772–3789 (2000)
4. Sheldon, R.: Catalytic reactions in ionic liquids. J. Chem. Soc., Chem. Commun. 2399–2407 (2001)
5. Ohno, H. (ed.): Electrochemical Aspects of Ionic Liquids. Wiley-Interscience, New York (2005)
6. Rogers, R.D., Seddon, K.R. (eds.): Ionic Liquids as Green Solvents: Progress and Prospects. ACS Sym-
posium Series, vol. 856. American Chemical Society, Washington (2003)
7. Poole, C.F.: Chromatographic and spectroscopic methods for the determination of solvent properties of
room temperature ionic liquids. J. Chromatogr. A 1037, 49–82 (2004)
8. Seddon, K.R., Stark, A., Torres, M.: Influence of chloride, water, and organic solvents on the physical
properties of ionic liquids. J. Pure Appl. Chem. 72, 2275–2287 (2000)
9. Swatloski, R.P., Visser, A.E., Reichert, W.M., Broker, G.A., Farina, L.M., Holbrey, J.D., Rogers, R.D.:
Solvation of 1-butyl-3-methylimidazolium hexafluorophosphate in aqueous ethanol—a green solution
for dissolving ‘hydrophobic’ ionic liquids. J. Chem. Soc., Chem. Commun. 20, 2070–2071 (2001)
10. Swatloski, R.P., Visser, A.E., Reichert, W.M., Broker, G.A., Farina, L.M., Holbrey, J.D., Rogers, R.D.:
On the solubilization of water with ethanol in hydrophobic hexafluorophosphate ionic liquid. Green
Chem. 4, 81–87 (2002)
11. Fletcher, K.A., Pandey, S.: Effect of water on the solvatochromic probe behavior within room-
temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. Appl. Spectrosc. 56, 266–
271 (2002)
12. Fletcher, K.A., Pandey, S.: Solvatochromic probe behavior within binary room-temperature ionic liquid
1-butyl-3-methyl imidazolium hexafluorophosphate plus ethanol solutions. Appl. Spectrosc. 56, 1498–
1503 (2002)
13. Fletcher, K.A., Pandey, S.: Solvatochromic probe behavior within ternary room-temperature ionic liquid
1-butyl-3-methylimidazolium hexafluorophosphate + ethanol + water solutions. J. Phys. Chem. B 107,
13532–13539 (2003)
14. Harifi-Mood, A.R., Habibi-Yangjeh, A., Gholami, M.R.: Solvatochromic parameters for binary mix-
tures of 1-(1-butyl)-3-methylimidazolium tetrafluoroborate with some protic molecular solvents. J. Phys.
Chem. B 110, 7073–7078 (2006)
15. Khodadadi-Moghadam, M., Habibi-Yangjeh, A., Gholami, M.R.: Solvatochromic parameters for binary
mixtures of an ionic liquid with various protic molecular solvents. Monatsh. Chem. 140, 329–334 (2009)
16. Mellein, B.R., Aki, S.N.V.K., Ladewski, R.L., Brennecke, J.F.: Solvatochromic studies of ionic liq-
uid/organic mixtures. J. Phys. Chem. B 111, 131–138 (2007)
17. Bicak, N.: A new ionic liquid: 2-hydroxy ethylammonium formate. J. Mol. Liq. 116, 15–18 (2005)
18. Harifi-Mood, A.R., Habibi-Yangjeh, A., Gholami, M.R.: Solvent effects on kinetics of the reaction be-
tween 2-chloro-3,5-dinitropyridine and aniline in aqueous and alcoholic solutions of [bmim]BF4. Int. J.
Chem. Kinet. 39, 681–687 (2007)
19. Harifi-Mood, A.R., Habibi-Yangjeh, A., Gholami, M.R.: Kinetics study of a Diels–Alder reaction in
mixtures of an ionic liquid with molecular solvents. J. Phys. Org. Chem. 21, 783–788 (2008)

J Solution Chem (2010) 39: 1509–1519
1519
20. Reichardt, C.: Solvatochromic dyes as solvent polarity indicators. Chem. Rev. 94, 2319–2358 (1994)
21. Reichardt, C.: Solvents and Solvent Effects in Organic Chemistry. VCH, Weinheim (1988)
22. Kamlet, M.J., Taft, R.W.: The solvatochromic comparison method. I. The β-scale of solvent hydrogen-
bond acceptor (HBA) basicities. J. Am. Chem. Soc. 98, 377–383 (1976)
23. Taft, R.W., Kamlet, M.J.: The solvatochromic comparison method. 2. The α-scale of solvent hydrogen-
bond donor (HBD) acidities. J. Am. Chem. Soc. 98, 2886 (1976)
24. Kamlet, M.J., Abboud, J.-L.M., Taft, R.W.: The solvatochromic comparison method. 6. The π scale of
∗
solvent polarities. J. Am. Chem. Soc. 99, 6027–6038 (1977)
25. Kamlet, M.J., Abboud, J.-L.M., Abraham, M.H., Taft, R.W.: Linear solvation energy relationships. 23.
∗
A comprehensive collection of the solvatochromic parameters, π , α, and β, and some methods for
simplifying the generalized solvatochromic equation. J. Org. Chem. 48, 2877–2887 (1983)
26. Rosés, M., Ràfols, C., Ortega, J., Bosch, E.: Solute–solvent and solvent–solvent interactions in binary
solvent mixtures. Part 1. A comparison of several preferential solvation models for describing E (30)
T
polarity of bipolar hydrogen bond acceptor-cosolvent mixtures. J. Chem. Soc., Perkin Trans. 2, 1607–
1615 (1995)
27. Buhvestov, U., Rived, F., Ràfols, C., Bosch, E., Rosés, M.: Transfer thermodynamic parameters of local
anesthetic lidocaine in ethanol–water mixtures, effect of preferential solvation. J. Phys. Org. Chem. 11,
185–192 (1998)
28. Herodes, K., Leito, I., Koppel, I., Rosés, M.: Solute-solvent and solvent-solvent interactions in binary
solvent mixtures. Part 8. The E (30) polarity of binary mixtures of formamides with hydroxylic sol-
T
vents. J. Phys. Org. Chem. 12, 109–115 (1999)
29. García, B., Aparicio, S., Alcalde, R., Ruiz, R., Dávila, M.J., Leal, J.M.: Characterization of lactam-
containing binary solvents by solvatochromic indicators. J. Phys. Chem. B 108, 3024–3029 (2004)
30. Suppan, P., Ghoneim, N. (eds.): Solvatochromism. Royal Society of Chemistry, Cambridge (1997)
31. Marcus, Y.: Solvent Mixtures: Properties and Selective Solvation. Dekker, New York (2002) and refer-
ences therein
32. Blackmore, P.R., Williams, J.F., Clark, M.G.: Biological asymmetry of glycerol. J. Chem. Educ. 50,
555–564 (1973)
33. Van Den Enden, L., Van Alsenoy, C., Scarsdale, J.N., Schäfer, L.: Ab initio studies of structural fea-
tures not easily amenable to experiment. Part 26. Conformational analysis and study of the self-induced
molecular asymmetry of glycerol. J. Mol. Struct. Theochem 104, 471–487 (1983)
34. Redlich, O.J., Kister, A.T.: Algebraic representation of thermodynamic properties and the classification
of solutions. Ind. Eng. Chem. 40, 345–348 (1948)
35. Hernández, C.E., Coym, K.S., Roy, L.E., Powell, J.R., Acree, W.E. Jr.: Solubility of pyrene in (binary
alkane + 2-butanol) solvent mixtures. J. Chem. Therm. 30, 37–42 (1998)
36. Al-Sharrah, G.K., Ali, S.H., Fahim, M.A.: Solubility of anthracene in two binary solvents containing
toluene. Fluid Phase Equilib. 193, 191–201 (2002)
37. Iloukhani, H., Rezaei-Sameti, M., Zarei, H.A.: Volumetric and viscometric studies of molecular interac-
tion of the ternary system toluene (1) plus cyclohexane (2) plus n-hexane (3) at 298.15 K. Thermochim.
Acta 438, 9–15 (2005)
38. Wu, J., Wang, J.: Solubility of cefazolin sodium pentahydrate in aqueous 2-propanol mixtures. J. Chem.
Eng. Data 50, 980–982 (2005)
39. Kadam, U.B., Hiray, A.P., Sawant, A.B., Hasan, M.: Densities, viscosities, and ultrasonic velocity studies
of binary mixtures of chloroform with propan-1-ol and butan-1-ol at (303.15 and 313.15) K. J. Chem.
Eng. Data 51, 60–63 (2006)
40. Wold, S., Sjöström, M., Eriksson, L.: PLS-regression: a basic tool of chemometrics. Chemom. Intell.
Lab. Syst. 58, 109–130 (2001)