Fluid Phase Equilibria 334 (2012) 157–165
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Fluid Phase Equilibria
j our na l ho me page: www.elsevier.com/locate/fluid
Densities, speeds of sound and
1
H NMR spectroscopic studies for binary mixtures
of 1-hexyl-3-methylimidazolium based ionic liquids with ethylene glycol
monomethyl ether at temperature from T = (288.15–318.15) K
Amalendu Pal
∗
, Bhupinder Kumar
Department of Chemistry, Kurukshetra University, Kurukshetra 136119, Haryana, India
a r t i c l e i n f o
Article history:
Received 3 April 2012
Received in revised form 29 June 2012
Accepted 1 August 2012
Available online 10 August 2012
Keywords:
Room temperature ionic liquids
Ethylene glycol monomethyl ether
Density
Speeds of sound
1
H NMR
a b s t r a c t
Physical properties such as densities and speeds of sound of 1-hexyl-3-methylimmidazolium based room
temperature ionic liquids (RTILs); with bromide (Br), tetrafluoroborate (BF
4
), hexafluorophosphate (PF
6
),
as anions in ethylene glycol monomethyl ether (EGMME), over the whole composition range were mea-
sured at T = (288.15–318.15) K and at atmospheric pressure. Experimental densities were used to obtain
excess molar volumes, V
E
. The V
E
values for each of the mixture studied were negative and decreased
with increase in temperature with the following order: [PF
6
] > [BF
4
] > [Br]. Deviations in isentropic com-
pressibility,
S
were calculated from the experimental speeds of sound and densities. The
S
values
were negative over the entire range of composition for all mixtures with the exception of ILs contain-
ing [Br] and [BF
4
] anions, which changes sign from negative to positive at low temperatures. Both V
E
and
S
were fitted to the Redlich–Kister polynomial equation to obtain the binary coefficients and the
standard errors. The molecular scale interactions between (ILs) and EGMME were investigated through
1
H NMR spectroscopy. NMR chemical shifts for various protons of (ILs) or EGMME molecules and their
deviations show hydrogen bonding interactions of varying strengths between (ILs) and EGMME in their
binary mixtures.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Ionic liquids (ILs) considered as the potential greener replace-
ments for commonly used volatile organic compounds (VOCs) and
have received attention in many scientific investigations due to the
large variety of applications of this new class of liquids in industry
and applied chemistry [1–6]. Also, the properties of such liquids can
be varied by changing their anions or cations and hence are termed
as designer solvents. Moreover, we can enhance their properties
by addition of a co-solvent which can be effectively used in vari-
ous industrial applications. Despite their importance and interest,
detailed knowledge of the thermodynamic behavior of the mix-
tures of ionic liquids with organic solvents, which is of immense
importance in various chemical processes, is still limited. On the
other hand, alkoxyalkanols, which are amphiphilic organic sol-
vents have been used in many chemical processes. It is of great
importance to understand the mixing behavior of ILs in the organic
solvents and to provide accurate physicochemical data. Therefore,
∗
Corresponding author. Tel.: +91 1744 239765; fax: +91 1744 238277.
E-mail address: palchem@sify.com (A. Pal).
thethermodynamic behavior of the mixtures of ILs with organic
solvents is rapidly gaining importance [7–12].
From our earlier studies we have found that various types of
interactions prevail in the binary mixtures of RTILs and organic sol-
vents. Many thermodynamic and spectroscopic properties such as
density, speed of sound, UV–vis, FT-IR, Fluorescence,
1
H NMR have
been studied to understand the exact nature of the solute–solvent
interactions for different ILs with alkoxyalkanols [13–17]. In
the present work, the procedure to synthesize some ionic liq-
uids of different anions, such as 1-hexyl-3-methylimidazolium
bromide [C
6
mim][Br], 1-hexyl-3-methylimidazolium tetrafluo-
roborate [C
6
mim][BF
4
], 1-hexyl-3-methylimidazolium hexaflu-
orophosphate [C
6
mim][PF
6
], is described. Physical properties
such as density and speed of sound of three ILs with ethy-
lene glycol monomethyl ether [EGMME] have been measured at
T = (288.15–318.15) K. Molecular structure and molecular weight
of (ILs) and EGMME is given in Scheme 1. This study examines how
the changes in the anions without changing the alkyl chain length
of the ILs affect the volumetric and derived properties of binary
mixtures involving 1-hexyl-3-methylimidazolium based ILs. There
are certain changes in excess properties with temperature, compo-
sition and anions from which we have analyzed and presented the
influence of these factors on the thermodynamic and spectroscopic
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http://dx.doi.org/10.1016/j.fluid.2012.08.002