Research Article Open Access
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
*Corresponding author: 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.
AbstractTop
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] [NO3]?[Bu3NH][Cl]

Key Words:Bronsted Acidic Ionic Liquids (BAILs); Room Temperature Ionic Liquids (RTILs); Thin Liquid Chromatography (TLC); Vogel-Fulcher-Tammann (VFT).
IntroductionTop
One of the main principles of green chemistry is the avoiding using dangerous solvents in chemical synthesis [1], and also decrease employing expensive toxic solvents and the generation of hazardous wastes [2]. 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 [3]. 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 [4]. 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 [5].

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 [6]. 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 [7]. 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 atmospheric pressure.
Experimental sectionTop
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 [8].

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
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 (r2> 0.999).

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) [9].
Where fitting parameters A? (gcm-3), A1(gcm-3 K-1)and A2(gcm-3 K-2)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 inTable 1
Figure 1: Temperature dependence of density data for the ILs
Viscosity
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) [10].

Where is the absolute temperature ${\eta }_{°}$ , , 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) [11].

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
Refractive Index
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 [12]. 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.
Surface Tension
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
Thermal conductivity
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 almost±2%.

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
Electrical conductivity is one of the most main properties of ILs as electrolyte materials [13]. 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) [14].
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
Acidity
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
 ILs [Bu3NH]H2PO4 [Bu3NH]HSO4 [Bu3NH]NO3 [Bu3NH]Cl pKa1 3.35 2.26 2.55 1.95 pKa2 5.35 6.33 - -
Determination of Ho values of Bronsted acidic ILs
A common and effective way to evaluate the acidity of Bronsted acids was the Hammett method [15]. 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. [8] 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 spectroscopy.

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
 ILs Amax [I]% [HI]% H0 Para-nitro aniline 1.602 100 - - [Bu3NH]H2PO4 1.409 87.95 12.05 1.85 [Bu3NH]HSO4 1.467 91.57 8.43 2.03 [Bu3NH]NO3 1.433 89.45 10.85 1.92 [Bu3NH]Cl 1.558 97.25 2.75 2.54
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
ConclusionsTop
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 temperatures.

• Size particle affected on properties physical chemistry of ILs.
• Weight particle influenced on properties physical chemistry of ILs.
• Structure ILs impacted on properties physical chemistry of ILs.
• 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 temperature.

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 equation:${\alpha }_{P}=-1/p{\left(\partial \rho /\partial T\right)}_{p}$ .
• 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).
• Cyclic voltammograms.
• Chronoamperograms for ferrocene.
• Excess Molar Volumes VE.
• Self-diffusion coefficient of Cation and anion in ionic liquid (D).

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] [Cl].
• AcknowledgmentsTop
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.
ReferencesTop
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