Prediction of thermophysical properties of novel ionic liquids based on serine [Cnmim][Ser] (n = 3, 4) using semiempirical methods

Two novel ionic liquids based on serine [C_nmim][Ser] (n = 3, 4) were prepared by the neutralization method and their structures were confirmed by ¹H NMR spectroscopy and differential scanning calorimetry (DSC). The density, surface tension, and refractive index of the two ILs were measured from T = (298.15 to 338.15) K. Since these ILs [C_nmim][Ser] (n = 3, 4) could form strong hydrogen bonds with water, small amount of water in the ILs is difficult to removed by common methods. In order to eliminate the effect of trace of water, the standard addition method (SAM) was applied to these measurements. On the basis of the experimental data, the speed of sound (μ), thermal expansion coefficient (α), molecular volume (V_m), standard entropy (S⁰298), entropy of surface (S_a), energy of surface (E_a), parachor (P), molar polarization (R_m), and polarization coefficient (α_p) were calculated, and the relationship between each of these properties of [C_nmim][Ser] (n = 3, 4) and temperatures was discussed. According to the additivity, the average value of anionic parachor, P_−(ave), was 180.81 for [Ser]⁻. At the same time, the surface tension of these serine ionic liquids could be estimated from their parachor and refractive index. The estimated values of the surface tension and the corresponding experimental data were almost identical.     

(Vapour + liquid) equilibria,volumetric and compressibility behaviour of binary and ternary aqueous solutions of 1-hexyl-3-methylimidazolium chloride,methyl potassium malonate,and ethyl potassium malonate

(Vapour + liquid) equilibrium data (water activity, vapour pressure, osmotic coefficient, and activity coefficient) of binary aqueous solutions of 1-hexyl-3-methylimidazolium chloride ([C₆mim][Cl]), methyl potassium malonate, and ethyl potassium malonate and ternary {[C₆mim][Cl] + methyl potassium malonate} and {[C₆mim][Cl] + ethyl potassium malonate} aqueous solutions were obtained through the isopiestic method at T = 298.15 K. These results reveal that the ionic liquid behaves as surfactant-like and aggregates in aqueous solutions at molality about 0.4 mol · kg⁻¹. The constant water activity lines of all the ternary systems investigated show small negative deviations from the linear isopiestic relation (Zdanovskii–Stokes–Robinson rule) derived using the semi-ideal hydration model. The density and speed of sound measurements were carried out on solutions of methyl potassium malonate and ethyl potassium malonate in water and of [C₆mim][Cl] in aqueous solutions of 0.25 mol · kg⁻¹ methyl potassium malonate and ethyl potassium malonate at T = (288.15 to 308.15) K at atmospheric pressure. From the experimental density and speed of sound data, the values of the apparent molar volume, apparent molar isentropic compressibility and excess molar volume were evaluated and from which the infinite dilution apparent molar volume and infinite dilution apparent molar isentropic compressibility were calculated at each temperature. Although, there are no clear differences between the values of the apparent molar volume of [C₆mim][Cl] in pure water and in methyl potassium malonate or ethyl potassium malonate aqueous solutions, however, the results show a positive transfer isentropic compressibility of [C₆mim][Cl] from pure water to the methyl potassium malonate or ethyl potassium malonate aqueous solutions. The results have been interpreted in terms of the solute–water and solute–solute interactions.     

Specific ion effects on the surface tension and surface potential of aqueous electrolytes

The phenomena of electrolytes affecting the surface tension of aqueous solutions and producing measurable surface potentials are reviewed in the light of recent studies of them. The factual information presented includes the molar ionic surface tension increments k_i = lim(c_i → 0)(dσ / dc_i) of many ions and the surface potential increments ∆ χ = χ_E − χ_W of electrolytes involving the cations H⁺, Na⁺, K⁺, and NH₄⁺ and various anions. Gaps in the data that invite filling and inconsistencies in reported data are pointed out. Correlations of k_i with several properties of the ions that should be relevant to their specific effects: their sizes, quantities representing their polarizabilities, their effects on the structure of the water and the binding of water molecules by them, are presented. Correlations of the surface potential increment ∆ χ with the electrolyte surface tension increments and with the differences between the cation and anion increments are shown. Models recently proposed for the rationalization of the observed phenomena and relevant theoretical developments are shown and discussed. The paradox of hydrogen ions not promoting significant charge separation at the interface but yielding large surface potentials is emphasized.     

Thermodynamic studies of the ionic liquid 1-hexyl-3-methylimidazolium chloride [C6mim][Cl] in polyethylene glycol aqueous solutions

Vapour pressure osmometery (VPO) measurements at T = 308.15 K for {[C₆mim][Cl] + water}, {[C₆mim][Cl] + (0.005, 0.0155, and 0.0263) mol · kg⁻¹ PEG2000 + water} and {[C₆mim][Cl] + (0.0017, 0.0052, and 0.0088) mol · kg⁻¹ PEG6000 + water} systems and isopiestic measurements at T = 298.15 K for {[C₆mim][Cl] + PEG2000 + water} and {[C₆mim][Cl] + PEG6000 + water} systems have been carried out. The VPO measurements were carried out at very low concentrations of PEG and from which the values of the water activities, osmotic coefficients, vapour pressure and activity coefficients were obtained. The data obtained from the VPO method show that over the whole concentration range of the ionic liquid (IL), the activity coefficients of [C₆mim][Cl] in the presence of PEG2000 are increased. Although, at high IL concentrations, the values of the activity coefficient of [C₆mim][Cl] in the presence of PEG6000 are also increased, however for low concentrations of IL the values of the activity coefficient of [C₆mim][Cl] in pure water are larger than those in aqueous PEG6000 solutions. For a known IL concentration, the values of water activity coefficient for the binary {[C₆mim][Cl] + water} system are larger than those for the ternary {[C₆mim][Cl] + PEG + water} systems and decrease by increasing the concentration of PEG or decreasing the molar mass of PEG. The constant water activity lines of the all ternary systems obtained from the isopiestic method show positive deviation from the linear isopiestic relation (Zdanovskii–Stokes–Robinson rule) derived using the semi-ideal hydration model. The results have been interpreted in terms of the solute–water and solute–solute interactions.     

Experiments and model for the surface tension of (MDEA + [Bmim][BF4]) and (MDEA + [Bmim][Br]) aqueous solutions

The surface tension (γ) of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]), 1-butyl-3-methylimidazolium bromide ([Bmim][Br]), (N-methyldiethanolamine(MDEA) + [Bmim][BF₄]) and (MDEA + [Bmim][Br]) aqueous solutions were measured by using the BZY-1 surface tension meter. The temperature ranged from (293.2 to 323.2) K. The mass fraction of MDEA ranged from 0.35 to 0.45. A thermodynamic equation was proposed to model the surface tension of (MDEA + ionic liquids) (ILS) aqueous solutions and the calculated results agreed well with the experiments. The effects of temperature, mass fractions of MDEA and ILS on the surface tension were demonstrated on the basis of experiments and calculations.     

Study on the enthalpy of solution and enthalpy of dilution for the ionic liquid [C3mim][Val] (1-propyl-3-methylimidazolium valine)

A new amino acid ionic liquid (AAIL) [C₃mim][Val] (1-propyl-3-methylimidazolium valine) was prepared by the neutralization method. Using the solution-reaction isoperibol calorimeter, molar solution enthalpies of the ionic liquid [C₃mim][Val] with known amounts of water and with different concentrations in molality were measured at T = 298.15 K. In terms of standard addition method (SAM) and Archer’s method, the standard molar enthalpy of solution for [C₃mim][Val] without water, ${\mathrm{\Delta }}_{\text{s}}{H}_{\text{m}}^{\circ }$ = (−55.7 ± 0.4) kJ · mol⁻¹, was obtained. The hydration enthalpy of the cation [C₃mim]⁺, ΔH₊ ([C₃mim]⁺) = −226 kJ · mol⁻¹, was estimated in terms of Glasser’s theory. Using the RD496-III heat conduction microcalorimeter, the molar enthalpies of dilution, Δ_DH_m(m_i → m_f), of aqueous [C₃mim][Val] with various values of molality were measured. The values of Δ_DH_m(m_i → m_f) were fitted to Pitzer’s ion-interaction model and the values of apparent relative molar enthalpy, ^φL, calculated using Pitzer’s ion-interaction model.     

Densities and dynamic viscosities of the binary system (water + 1-hexyl-3-methylimidazolium bromide) at different temperatures

Densities and viscosities were measured for pure ionic liquid [C₆mim][Br] (1-hexyl-3-methylimidazolium bromide) and the binary system (water + [C₆mim][Br]) at 0.1 MPa and in the (293.15 to 333.15) K range. The excess molar volume and viscosity deviation were calculated and correlated by Redlich–Kister polynomial expansions. The fitting parameters and the standard deviations were determined.     

Pd-catalyzed asymmetric alternating co-polymerization of propene with carbon monoxide using ionic liquids

A protocol for Pd-catalyzed stereoselective co-polymerization of propene and carbon monoxide using chiral ligands, such as (2S,3S)-DIOP and (R)-P-Phos in [C₄mim][PF₆]/[C₆mim][PF₆] as an ionic liquid medium was developed. With (2S,3S)-DIOP as chiral ligand and [C₄mim][PF₆] as medium, the Pd-catalyzed co-polymerization of propene and CO gave almost completely regioregular polyketones, and the product polymer showed moderate stereoregularity (61% of ℓ-diads). The highest molar optical rotation = +15.9 and polydispersity = 1.2 were attained when (R)-P-Phos was used as the ligand and [C₆mim]PF₆ as the solvent. The co-polymer exhibited regioregularity of H–H/H–T/T–T (%) = 17:66:17.     

Noncovalent assembly of ferrocene on modified gold surfaces mediated by uracil–adenine base pairs

Redox-active ferrocene was assembled on gold surfaces through the hydrogen bonding interactions between adenine-substituted ferrocene and a uracil-terminated organothiol monolayer. The surface coverage of ferrocene Γ could be varied from ca. 4 × 10^? 11 to 2.0 × 10^? 10 mol cm^? 2 by diluting the thiol-modified uracil derivative with inert 1-octanethiol. A decrease in the apparent electron transfer rate constant for ferrocene, k_app, from ca. 50 to 10 s^? 1 was observed upon increasing Γ.     

Density and surface tension of pure 1-ethyl-3-methylimidazolium l-lactate ionic liquid and its binary mixtures with water

The density and surface tension of 1-ethyl-3-methylimidazolium l-lactate ([emim][l-lactate]) ionic liquid were determined from T = (283.15 to 333.15) K. The coefficients of thermal expansion were calculated from the experimental density results using an empirical correlation for T = (283.15 to 333.15) K. Molecular volume and standard entropies of the IL were calculated from the experimental density values. The surface properties of IL were investigated. The critical temperature and enthalpy of vaporization were also discussed. Density and surface tension have been measured over the whole composition range for {[emim][l-lactate] + water} binary systems at a temperature of 298.15 K and atmospheric pressure. Excess molar volumes V^E and the surface tension deviations δγ have been determined.     

Relative hydrophobicity of equilibrium phases in biphasic systems (ionic liquid + water)

Partition coefficients for a series of dinitrophenylated (DNP) amino acids in biphasic systems composed of hydrophobic ionic liquids and water were experimentally determined. The ionic liquids used were three 1-alkyl-3-methylimidazolium tetrafluoroborates, [C_nmim][BF₄], with alkyl chain substituents hexyl, octyl, and decyl. The liquid–liquid phase diagram for the system ([C₁₀mim][BF₄] + water) was experimentally determined. DNP amino acids distribute preferentially to the IL-rich phase and ([C₁₀mim][BF₄] + water) was found to be the system with the lowest partition coefficients for the solutes studied. The experimental partition coefficients decrease as the size of the alkyl side chain in the ionic liquids increases. The free energy of transfer of a methylene group between phases was calculated through the partition coefficients, which provides a measure of the relative hydrophobicity of the equilibrium phases. It was found that the system ([C₁₀mim][BF₄] + water) presents a lower free energy (and thus a lower relative hydrophobicity) than the system ([C₈mim][BF₄] + water). In order to better understand this result, the micellar behavior of the three ionic liquids was studied. Electrical conductivities of several aqueous solutions of the ionic liquids were measured to determine the critical micelle concentration (CMC) and the degree of micelle ionization, α, of the three ionic liquids. From these two properties it was possible to obtain the free energy of micellization, ΔG_mic, for the ionic liquids.     

Thermodynamic properties and polymorphism of 1-alkyl-3-methylimidazolium bis(triflamides)

Heat capacities in a range of temperatures of (5 to 370) K, enthalpies and temperatures of phase transitions for 1-ethyl-3-methylimidazolium bis(triflamide) ([C₂mim][NTf₂]) and 1-octyl-3-methylimidazolium bis(triflamide) ([C₈mim][NTf₂]) have been determined by adiabatic calorimetry. [C₂mim][NTf₂] has been found to form four crystalline phases with different fusion temperatures. Formation of the phases can be controlled by the temperature of annealing during crystallization. [C₈mim][NTf₂] forms three sequences of crystalline modifications, each including two polymorphs. Based on results of the measurements, thermodynamic functions for the compounds under study have been calculated.A heat-capacity anomaly near T = 230 K reported earlier for [C₄mim][NTf₂] and [C₆mim][NTf₂] have been found in some crystalline modifications of both the studied compounds. The position of the anomaly depends on the temperature of annealing of the crystals.     

Solubility of CO2 in 1-(2-hydroxyethyl)-3-methylimidazolium ionic liquids with different anions

The solubility of carbon dioxide in a series of 1-(2-hydroxyethyl)-3-methylimidazolium ([hemim]⁺) based ionic liquids (ILs) with different anions, viz. hexafluorophosphate ([PF₆]^?), trifluoromethanesulfonate ([OTf]^?), and bis-(trifluoromethyl)sulfonylimide ([Tf₂N]^?) at temperatures ranging from 303.15 K to 353.15 K and pressures up to 1.3 MPa were determined. The solubility data were correlated using the Krichevsky–Kasarnovsky equation and Henry’s law constants were obtained at different temperatures. Using the solubility data, the partial molar thermodynamic functions of solution such as Gibbs free energy, enthalpy, and entropy were calculated. Comparison showed that the solubility of CO₂ in the ILs studied follows the same behaviour as the corresponding conventional 1-ethyl-3-methylimidazolium ([emim]⁺) based ILs with the same anions, i.e. [hemim][NTf₂] > [hemim][OTf] > [hemim][PF₆] > [hemim][BF₄].     

Solubilities of imidazolium-based ionic liquids in aqueous salt solutions at 298.15 K

The solubilities of ionic liquids in the ternary systems (ionic liquid + H₂O + inorganic salt) were reported at 298.15 K and atmospheric pressure. The examined ionic liquids are [C₄mim][PF₆] (1-n-butyl-3-methylimidazolium hexafluorophosphate), [C₈mim][PF₆] (1-n-octyl-3-methylimidazolium hexafluorophosphate), and [C₈mim][BF₄] (1-n-octyl-3-methylimidazolium tetrafluoroborate). The examined inorganic salts are the chloride-based salts (sodium chloride, lithium chloride, potassium chloride, and magnesium chloride) and the sodium-based salts (sodium thiocyanate, sodium nitrate, sodium trifluoroacetate, sodium bromide, sodium iodide, sodium perchlorate, sodium acetate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium tetrafluoroborate, sodium sulfate, and sodium carbonate). The effects of the cations and the anions of the ionic liquids and of the inorganic salts on the solubility of the ionic liquids in the ternary solutions were systematically compared and discussed.     

Densities,excess volumes,isobaric expansivity,and isothermal compressibility of the (1-ethyl-3-methylimidazolium ethylsulfate + methanol) system at temperatures (283.15 to 333.15) K and pressures from (0.1 to 35) MPa

Densities of pure 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid – [C₂mim][EtSO₄] and its mixtures with methanol have been measured with an accuracy of ±0.2 kg · m^?3, over the temperature range (283.15 to 333.15) K and pressure range (0.1 to 35) MPa, using a vibrating tube densimeter. Excess volumes have been calculated directly from the experimental densities. The latter data have been correlated by the Tait equation with the temperature dependent parameters for the pure ionic liquid and by a van Laar-type equation, involving parameters dependent on temperature and pressure for the mixtures. The isobaric expansivity, isothermal compressibility, and related excess properties have been calculated. The exceptionally strong influence of pressure and temperature on these properties has been observed.     

Surface tension and viscosity of molten vanadium measured with an electrostatic levitation furnace

Surface tension and viscosity of molten vanadium were measured over a wide temperature range by the oscillating drop method in an electrostatic levitation furnace. Over the (2023 to 2517) K temperature range, the surface tension can be expressed as γ(T)/(10^?3 N/m) = 1935 ? 0.27 {(T ? T_m)/K} with T_m = 2183 K. Over the same temperature span, the viscosity can be expressed as η(T)/(10^?3 Pa · s) = 1.23exp[2.27 · 10⁴/(RTK^?1)], where R is the gas constant.     

Synthesis,physical, and thermodynamic properties of 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

Synthesis of new ionic liquids (ILs) viz. 1-butyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [BCN³Py][NTf₂], 1-hexyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN³Py][NTf₂], 1-hexyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN⁴Py][NTf₂], and 1-octyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [OCN³Py][NTf₂] were performed. The specific basic characterization of new compounds by NMR spectra, elementary analysis, water content and glass transition temperature as well as melting temperature, enthalpy of fusion and decomposition of compounds TG/DTA determined by the differential scanning calorimetry, DSC is presented. The heat capacity was measured at three temperatures (298.15, 323.15, and 353.15) K and at pressure 0.1 MPa. The effect of temperature on the density and viscosity is reported over the temperature range from (293.15 to 363.15) K and at 0.1 MPa. The density and viscosity correlation for these systems was provided by an empirical polynomial. From the density–temperature dependence, the isothermal expansion coefficient (volume expansivity), α, was calculated. The surface tension of pure ionic liquids was measured at 0.1 MPa at five temperatures (298.15, 308.15, 318.15, 328.15, and 338.15) K. The surface thermodynamic functions such as surface entropy and enthalpy, critical temperatures according to the Eötvös and Guggenheim definition and the total surface energy of the ILs studied were derived from the temperature dependence of the surface tension values. The parachor and speed of sound for pure ionic liquids were described within a range of temperature from (298.15 to 338.15) K. A qualitative analysis on these quantities in terms of molecular interactions is reported.     

Properties of n-butylpyridinium nitrate ionic liquid and its binary mixtures with water

The density and surface tension of the pure ionic liquid n-butylpyridinium nitrate ([BuPy]NO₃) were determined at temperature range from T = (293.15 to 338.15) K. The coefficient of thermal expansion, molecular volume and lattice energy of [BuPy]NO₃ were calculated from the experimental values of density. The surface entropy and enthalpy of [BuPy]NO₃ were investigated. The IL studied show much lower surface enthalpy and lattice energy in comparison with fused salts. The densities and surface tensions of binary mixtures of [BuPy]NO₃ with water have been measured within the whole composition range at T = 298.15 K and atmospheric pressure. Excess molar volumes V^E and surface tension deviations δγ were then deduced from the experimental results as well as partial molar volumes and excess partial molar volumes. Excess molar volumes have a negative deviation from ideal behavior and the surface tension deviations are negative over the whole compositions range. V^E and δγ were correlated with suitable equation respectively.     

Heat capacities and electrical conductivities of 1-ethyl-3-methylimidazolium-based ionic liquids

We present the heat capacities and electrical conductivities of five [Emim] 1-ethyl-3-methylimidazolium-based ionic liquids: [Emim][BF₄] (tetrafluoroborate), [Emim][CF₃SO₃] (trifluoromethanesulfonate), [Emim][C₂N₃] (dicyanamide), [Emim][C₂H₅SO₄] (ethylsulfate), and [Emim][MDEGSO₄] (2-(2-methoxyethoxy) ethylsulfate). The heat capacities were measured using a differential scanning calorimeter (DSC) over the temperature ranging from (303.2 to 358.2) K. The electrical conductivities were measured over the temperature ranging from (293.2 to 353.2) K using a commercial conductivity meter. The estimated uncertainties of heat capacity C_p and electrical conductivity σ measurements were ±0.015 kJ · kg^?1 · K^?1 and ±0.001 mS · cm^?1, respectively. The measured C_p and σ are presented as a function of temperature. The temperature dependency of the C_P value was correlated using an empirical equation. A modified version of VTF-type (Vogel–Tamman–Fulcher) equation was used to describe the temperature dependency of σ values. The correlations give satisfactory results. Also, the results of this study are in good agreement with the available literature data. The heat capacities and electrical conductivities presented in this work are in good agreement with the available literature data. The results of this study can be applied to numerous chemical processes, since C_p and σ data are essential information for rational design.     

Evaluation of the ionic liquids 1-alkyl-3-methylimidazolium hexafluorophosphate as a solvent for the extraction of benzene from cyclohexane: (Liquid + liquid) equilibria

In the catalytic hydrogenation of benzene to cyclohexane, the separation of unreacted benzene from the product stream is inevitable and essential for an economically viable process. In order to evaluate the separation efficiency of ionic liquids (ILs) as a solvent in this extraction processes, the ternary (liquid + liquid) equilibrium of 1-alkyl-3-methylimidazolium hexafluorophosphate, [C_nmim][PF₆] (n = 4, 5, 6), with benzene and cyclohexane was studied at T = 298.15 K and atmospheric pressure. The reliability of the experimentally determined tie-line data was confirmed by applying the Othmer–Tobias equation. The solute distribution coefficient and solvent selectivity for the systems studied were calculated and compared with literature data for other ILs and sulfolane. It turns out that the benzene distribution coefficient increases and solvent selectivity decreases as the length of the cation alkyl chain grows, and the ionic liquids [C_nmim][PF₆] proved to be promising solvents for benzene–cyclohexane extractive separation. Finally, an NRTL model was applied to correlate and fit the experimental LLE data for the ternary systems studied.