Thermo Physical Properties ofBronsted Acidic Ionic
Liquids Based on Quaternary Ammonium CationBinary
Mixtures with Waterat various temperatures from
(293.15 to 363.15) K
Zeinab Heidari Pebdani1*, Abdol Reza Hajipour1 and Yosofe Ghayeb1
1Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan 84156, IR Iran
Zeinab Heidari Pebdani, Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan University of Technology,
Isfahan 84156, IR Iran; E-mail: @
Received: April 04, 2019; Accepted: June 01, 2019; Published: June 11, 2019
Citation: Zeinab Heidari P, Abdol Reza H, Yosofe G (2019) Thermo Physical Properties of Bronsted Acidic Ionic Liquids Based on Quaternary Ammonium CationBinary Mixtures with Waterat various temperatures from (293.15 to 363.15) K. Int J Anal Medicinal
Chem. 2(1): 1-8.
The Bronsted Acidic Ionic Liquids (BAILs)[Bu3NH]H2PO4, [Bu3NH]
HSO4, [Bu3NH]NO3, [Bu3NH]Cl,were synthesized and characterized
using TLC, FT-IR,1H-NMRand elemental analysis. Experimental
densities (??), dynamic viscosities (?), surface tension (s), electrical
conductivity (?), refractive indices (nD) and thermal conductivity (?),
that were investigated as a function of temperature under (293.15to
363.15) K conditions, for binary systems with water ionic liquids at
atmospheric pressure. A common and effective way to evaluate the
acidity ofBronsted acids was the Hammett method (Ho) which can
use them for BAILs, pHandpKa. Also densities, dynamic viscosity,
surface tension, ionic conductivity, refractive indices and thermal
conductivity deviations, and dynamic viscosity deviations in for the
binary systems with water were fitted to a Vogel-Fulcher-Tammann
(VFT) equation. The present synthesized ionic liquids show a weak
temperature dependency on physical properties. To conclude, there
were some explanations on the structure effect of the ILs on the
physical properties, the quality of this study would be substantially
promoted as follow: [Bu3NH][H2PO4]?[Bu3NH][HSO4]?[Bu3NH]
Key Words:Bronsted Acidic Ionic Liquids (BAILs); Room
Temperature Ionic Liquids (RTILs); Thin Liquid Chromatography
(TLC); Vogel-Fulcher-Tammann (VFT).
One of the main principles of green chemistry is the avoiding
using dangerous solvents in chemical synthesis , and also
decrease employing expensive toxic solvents and the generation
of hazardous wastes . In recent years, ionic liquids (ILs) have
attracted increasing interest and been successfully used in a
variety of reactions as environmentally benign solvents and
catalysts due to their comparatively low viscosities, low vapor
pressure, and high thermal and chemical stability . Room
temperature ionic liquids (RTILs) are novel and new class of
substances with high potential to substitute many traditional
organic solvents in reaction and separation processes . In spite
of their importance and attention, accurate values for many of the
basic physical-chemical properties of this ionic liquid are either
in short supply or absent .
To devise any process involving ionic liquids on an industrial
level, it is essential to know a series of physical properties
including viscosity, density, surface tension, refractive Index,
ionic conductivity, thermal conductivity, etc. Furthermore, the
presence of water in the ionic liquid phase can considerably affect
their physical properties . In spite of the interesting feature and
practical importance of ILs, there are limited literature reports
for the accurate measurements of many of their fundamental
physical and chemical properties at various temperatures .
Thus, in this paper we wish to report the results of our studies on
the physical, thermodynamic and transport properties of BAILs.
Properties such as dynamic viscosity, density, surface tension,
refractive Index, thermal stability, ionic conductivity, thermal
conductivity Hammett value (Ho) and pH, for various ionic
liquids including,[Bu3NH]H2PO4+water, [Bu3NH]HSO4+water,
[Bu3NH]NO3+water, and [Bu3NH]Cl +water were determined as a
function of the temperature in the range of(293.15,363.15) K and
Preparation of ionic liquids and Pyritization of ILs
Materials: Water used was freshly deionized and distilled before
use. Tributylamine was purchased from the Sigma-Aldrich. (>99
% of purity), Sulfuric acid (98%) and nitric acid (78%) and
phosphoric acid (99%) and Choleric acid (37%) were purchased
from Merck. The purity of the ILs were confirmed by FT-IR and
1H-NMR spectroscopy and elemental analysis. The BAILs were
prepared from the corresponding chlorides according to the
procedures reported in literature .
Synthesis of ILs: [Bu3NH]H2PO4, [Bu3NH]HSO4, [Bu3NH]
NO3,[Bu3NH]Cl. Initially, tri-butylammine Chloride was added in
to a round-bottom flask, dichloromethane was added and stirred
thoroughly, and then concentrated Bronsted acids in to 1:1
Scheme 1: Two steps preparation of ionic liquids
[Bu3NH]H2PO4, FT-IR (NaCl): 3000, 2962, 2875, 2388, 2340,
1472, 1105, 962, 741, 522, cm-1. 1H-NMR (400MHz, DMSO-d6): d
9.36 (s, 1H, NH), 2.84 (t, 6H, J=7.2, CH2), 1.56 (m, 6H, CH2), 1.27
(m, 6H, CH2),0.89(m, 9H, CH3)ppm.
[Bu3NH]HSO4FT-IR (NaCl): 3433, 2938, 2875, 2875, 2801, 2558,
2801, 1381, 1645, 1234, 1041, 853, 740, 582 cm-1. 1H-NMR
(400MHz, DMSO-d6): d7.11 (s, 1H), 2.99 (t, 6H, J=7.6, CH2), 1.59
(m, 6H, CH2), 1.27 (m, 6H, CH2), 0.87 (m, 9H, CH3) ppm.
[Bu3NH]NO3.FT-IR (NaCl): 3463, 2962, 2875, 2740, 2561, 1742,
1633, 1469,1294, 1035, 1159, 926, 826, 738, cm-1. 1H-NMR
(400MHz, DMSO-d6): d7.00 (s, 1H, NH), 3.02 (t, 6H, J=7.6, CH2),
1.56 (m, 6H, CH2), 1.34 (m, 6H, CH2), 0.89 (m, 9H,CH3) ppm.
[Bu3NH]Cl.FT-IR (NaCl): 3434, 2960, 2524, 1631, 1379, 1105,
1034, 926, 739, 580, 563, cm-1. 1H-NMR (400MHz,DMSO-d6):
d9.85 (s, 1H, NH), 2.85 (t, J=7.2,6H, CH2), 1.57 (m, 6H, CH2), 1.29
(m, 6H, CH2), 0.89 (m, 9H, CH3) ppm.
Results and DiscussionTop
Determination of water content
Before their use, the ionic liquids samples were dried and
degassed under vacuum (10-3bar)at 85°C during 3 h. After this
treatment, the mass fraction of water determined by coulometric
Karl-Fischer titration using a Metrohm 756 KFCoulometer with
a Hydranal® Coulomat AG reagent.Defined water content (45 ±
10) 10-5w/w that were revealed very low levels of water.
Density was measured by a 25 ml pyknometer.In general,
density precisions are ±0.0005 g cm-3
.The temperature was
maintainedusing thermostatic bath with a precision of ±0.01 K.
All densitymeasurements were repeated at least three times.
Densities of the ILs as a function of temperature are shown in
Fig. 1. As expected, densities decrease linearly with increasing
temperature, and can be well correlated by the linear regression
The temperature-dependent densities (ρ), refractive indices
(nD), surface tension (σ) and thermal conductivity (λ) values
were fitted by the method of least squares using the following
equations (1) .
Where fitting parameters A? (gcm-3
)are related to temperature and extrapolated density
at 0K,respectively and T is the temperature (K). The adjustable
parameters of Eq. (2) for the density of these ILs are summarized
Figure 1: Temperature dependence of density data for the ILs
In our viscosity measurements, BAILs showed no deviation
from Newtonian behavior in the investigated temperature range.
Kinematic viscosities were obtained using a LVDV-I PRIME
model viscometer made of Brookfield Co and capillary tube
deeper in athermostated bath with a precision of ±0.01 K. The
dynamic viscosities were calculated from the densities with a
precisionequal to 0.03 mPa·s. All measurements were repeated
twotimes. Sample viscosities were first determined as a function
of the temperature during a heating cycle from (293.15 to 363.15)
K.Data on viscosity and density for the ILs at temperatures
ranging from (293.15 to 363.15) K.are shown in Figs. 2. The
temperature dependency of the dynamic viscosity values fit well
to the Vogel-Tammann-Fulcher (VTF) equation (2) .
Where is the absolute temperature
, , and are adjustable
parameters. The (cP), B , and parameters aregiven
in Table 2.Commonly used equation to correlate the variation of
viscositywith temperature is the Arrhenius-like law Eq (3) .
Viscosity at initial temperature and the activation energy (Ea) are
characteristics parameters generally adjusted from experimental
data. Table 3 lists the parameters for both equations with the
standard relative deviation (S. D.) Eq (4):
Where zexp and zcal are the values of the experimental
andcalculated property, n is the number of experimental data of
parameters. Table 2 Table 3
A comparison between the experimental data for the physical
properties of the studied ABILs at 25°C has also made in Table 3.
To the best of our knowledge, no literature data on densities (??),
dynamic viscosities (?), surface tension (s), electrical conductivity
(?), refractive indices (nD) and thermal conductivity (?), were
not previously available for four studied ILs. As is obvious from
Table 3, the experimental data for [Bu3NH]H2PO4, [Bu3NH]HSO4,
[Bu3NH]NO3, and [Bu3NH]Cl. Figure 2
An Abbe Refractometer Model ATAGO-T3 programmable
digital with a measuring accuracy of(4 10-5) was used to
measure the refractive index ofvarious ILs in a temperature
range of (298.15 to 363.15) K. Thetemperature was controlled
with an accuracy of (0.05) K. The apparatus was calibrated and
checked before each series of measurements using pure organic
solvents (ethanol) with known refractive indices . Refractive
Indicescan be well fitted by Eq (1). Table 4
Figure 2: Dynamic viscosity (?) as a function of temperature for ILs
Figure 3 shows temperature dependence of refractive index
for the studied ILs have refractive indices >1.4. As it can be seen
from Fig3, for all three ILs, there fractive index decreases linearly
with increasing temperature. Figure 3.
We used Stalagmometer dope of falling for estimated surface
tension ILs. The surface tension of the ILs has been measured as
a function of temperature. The experimental data decrease with
increase in temperature in Fig 4. These values were compared
with those obtained with [Bu3NH]NO3 has high surface tension
than ILs. Based on these data, it appears that the surface tension
lowly decreases with increases temperature. The relationship
between surface tension and temperature of can be fitting by the
Eq (1). Table 5
The present synthesized ionic liquids show a weak temperature
dependency on the surface tension Figure 4. Figure 4
The thermal conductivity was measured by using a KD2
thermal property meter (decagon, Canada), which is based on the
transient hot wire method. The KD2 meter has a probe with 60
mm length and 0.9 mm diameter, which integrates in its interior
a heating element and a thermo-resistor and is connected to a
microprocessor for controlling and conducting the measurements.
The KD2 meter was calibrated by using distilled water and
standard ethylene glycol before any set of measurements. In
order to study the effect of temperature, a thermostat bath was
used, which was able to keep the temperature regularity within
the range of ±0.1 K. At least five measurements were taken for
each temperature to make sure the uncertainty of measurements
Figure 5 shows the thermal conductivity of ILs as a function of
temperature. Figure 5.
Figure 3: Refractive Index (nD) as a function of temperature for ILs
Figure 4: Surface tension (σ) as a function of temperature for ILs
Figure 5: Thermal conductivity (λ) as a function of temperature for ILs
The relationship between thermal conductivity (λ) and
temperature of can be fitting by the Eq (1) and fitting parameters
listed in table 6. Table 6.
Electrical conductivity is one of the most main properties
of ILs as electrolyte materials . The electrical conductivity
(?) of the ionic liquids was analytically measured with a
conductivity meter CTR80(ZAG-CHEMIE). Electrical conductivity
was measured by means of the complex impedance method, using
a thermometer, under atmosphere for determined temperature.
The cell constant was determined by calibration after each
sample measurement using an aqueous 0.02M KCl aqueous
solution. The ?data for the considered aqueous RTIL systems
were measured for temperatures ranging from (293.15 to
348.15) K at normal atmospheric pressure. Table 7 presented the
obtained ? measurements. Molar conductivity of the ionic liquids
? (m2Smol-1) was calculated from the ionic conductivity s (Sm-1)
and the molar concentration C (kmolm-3) according to the Eq (5).
The electrical conductivity presents linearly behaviour
with temperature for all ILs measured. Electrical conductivity
(?) values were fitted by the method of least squares using the
following equations (6) .
The plots showing the behaviour of the present ? data for
the studied solvent systems: [Bu3NH][H2PO4] + H2O, [Bu3NH]
[HSO4] + H2O, [Bu3NH][NO3] + H2O, [Bu3NH][Cl] + H2O are shown
in Figure 6. Figure 6
The acidic scale of the RTILs was measured using a titration
pH- metre with volume of NaOH indicator and the pKa data of
RTILs listed on table 8. Table 8
Figure 6: Electrical conductivity (?) as a function of temperature for ILs
Table 8: The pKa data of RTILs at 25°C
Determination of Ho values of Bronsted acidic ILs
A common and effective way to evaluate the acidity of
Bronsted acids was the Hammett method . 1 In reported
papers, the measurement of the acidic scale of these acidic
Bronsted ILs was conducted on a UV-Vis spectrophotometer
with a basic indicator (para-nitroaniline).Increasing the acidic
scale of the acidic IL, the absorbance of the un protonated form
of the basic indicator was decreased, whereas the protonated
form of the indicator was not observed because of its small molar
absorptive and its wavelength. Thus [I]/[HI] (I representsthe
indicator) ratio was determined from the measured absorbance
differences afteraddition of an acidic Bronsted IL, and then the
Hammett function, Ho, was calculated by using Eq 7.
This value was regarded as the relative acidity of the IL. 
Where pK(I) aq was the pKa value of the indicator, [I] and [HI]
were, respectively, the molar concentrations of the unprotonated
and protonated forms of the indicator, determined by UV-visible
When an acidic IL was added, the absorbance of the
unprotonated form of the indicator decreased. The acidities of the
four ionic liquids were examined using 4-nitroaniline as indicator
in dichloromethane.We obtained the acidity order of several ILs
with the Ho values thatare shown in Table 9.
Table 9: Ho Values of Ionic Liquids in CH2Cl2 at Room Temperature
Under the same concentration of 4-nitroanline (10 mg/L,
pK(I)aq=pKa= 0.99) and BAILs (0.1 mmol/L) in dichloromethane,
H0values of all Bails were determined. The maximal absorbance
of the unprotonated form of the indicator was observed at 350 nm
indichloromethane. When the BAIL was added, the absorbance of
the unprotonated form of the basic indicator decreased (Figure 7
and Table 9). Figure 7
Hammett acidity (H0) of these BAILs was calculated using
equations (7). As shown in Figure 7. Calculations suggest that
the Hammett acidity (H0) of these ionic liquids follows the order:
[Bu3NH][H2PO4]> [Bu3NH][NO3]> [Bu3NH][HSO4]> [Bu3NH][Cl].
Figure 7: UV-Vis absorption spectra of ILs
Due to the development of green chemistry in recent years,
researchers have been interested in the application of ionic
liquids can apply as green catalysts, Room temperature ionic
liquids (RTILs). Regard to these unique features, In spite of the
interesting feature and practical importance of ILs, there are
limited literature reports on the accurate measurements of many
of their fundamental physical and chemical properties at various
Size particle affected on properties physical chemistry of ILs.
Weight particle influenced on properties physical chemistry of
Structure ILs impacted on properties physical chemistry of
Hydrogen bonding internal molecular inclined on properties
physical chemistry of ILs.
Electrical charge particle subjective on properties physical
chemistry of ILs.
Temperature affected on properties physical chemistry of ILs.
Principle HARD and SAFT influenced on properties physical
chemistry of ILs.
The data of physical properties on ionic liquids are necessary
for both theoretical research and industrial application. The
establishment of the databases in this respect will certainly
support the study and advance of ionic liquids. Thus, in this work,
we have carefully measured several significant physical properties
of ionic liquids: tri-butyl ammonium chloride [Bu3NH][Cl], tributyl
ammonium nitrate [Bu3NH][NO3], tri-butyl ammonium
hydrogen sulfate [Bu3NH][HSO4] and tri-butyl ammonium
di-hydrogen phosphate [Bu3NH][H2PO4]over a wide range of
temperature from (293.15 to 363.15 K). Clearly, much more
attention should be paid on the measurement of physicochemical
properties of ionic liquids.
The measured densities, ??, and the dynamic viscosities, ?, for
the binary mixtures of [Bu3NH][H2PO4] with water at T = (293.15to
363.15) Cover the whole composition range are listed in Tables 1
and 2.As can be seen, the density of all of the mixtures always
decreases with temperature. A very decent linear correlation is
observed for all compositions (r = 1), this linear behavior with
The experimental viscosity results of [Bu3NH][Cl], [Bu3NH]
[NO3], [Bu3NH][HSO4], [Bu3NH][H2PO4]from this study are
in respectable agreement with the very scarce data from the
literature and are well represented by the VTF equation. At the
same temperature, [Bu3NH][H2PO4] have high very significantly
the viscosity of other tri ILs. Presence oxygen atoms perhaps
make up high viscosity this IL than other ILs.Since the viscosities
of ILs are essentially effective by the van derWaals interactions
and H bonding,have reported the influence of oxygen, wateron
the physical properties of [Bu3NH][H2PO4]. It hasbeen shown that
the presence of even low concentrations of oxygen in the [Bu3NH]
[H2PO4] substantially increases the viscosity.
Figure 5 shows the thermal conductivity of ILs as a function
of temperature.It can be seen that the thermal conductivity of
[Bu3NH][H2PO4] is 0.67 Wm-1 K-1. This indicates that [Bu3NH]
[H2PO4] is a relatively poor thermal conductor with the thermal
conductivity approximately of that of water at the room
temperature. Initially, the temperature-independent thermal
conductivity of the [Bu3NH] [H2PO4] was thought to be due
to the inappropriate method of measurements as both the
thermal probe and the liquid are electrically conductive. It was
alsohypothesised that the temperature-independent behaviour is
associated with the high viscosity of the ionic liquids.
Future Prospective of this work is following:
Application as specific lubricants for engineering fluids.
Electrochemical Applications Ionic liquids, as possible
replacements for organic solvents in lithium ion rechargeable
batteries for laptops, mobile phones, biosensors, actuators,
solvents for electrochemical devices, super capacitors fuel
cells, dye-sensitized solar cells, and polymer electrolytes.
Coefficients of thermal expansion are defined by the following
Bronsted Lewis acidic ionic liquids were used as solvents and
catalysts in many organic reactions such as etherification,
polymerization, alkylation, acylation, carbonylation, aldol
condensation, pinacol rearrangement, nitration, Koch reaction,
oxidation of alcohols.
Acidic Bronsted ionic liquids as environmental-friendly
solvents and catalysts with high activity and selectivity and
easily recovered were used to replace traditional liquid acids,
such as sulphuric acid and hydrochloric acid, in chemical
processes, especially acid catalysed.
Speeds of Sound (u).
Chronoamperograms for ferrocene.
Excess Molar Volumes VE.
Self-diffusion coefficient of Cation and anion in ionic liquid
To recap, in comparison with the other BAILs in that how
do the thermo physical properties and the most benefits and
the dominance of these classifications when compared to the
ones conveyed in the literature being easily made and recycled
in the various temperature, and the structure effect of the ILs
on the physical properties, the quality of this study would be
substantially promoted as followed:
[Bu3NH][H2PO4]? [Bu3NH][HSO4]? [Bu3NH][NO3]? [Bu3NH]
We gratefully acknowledge the funding support received for
this project from the Isfahan University of Technology (IUT), IR
Iran, (Y.GH) and (A.R.H.), Grants.
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