Effect of simple electrolytes on the thermodynamic properties of room temperature ionic liquids in aqueous solutions

Density, sound velocity and conductivity measurements are carried out on 1-heptyl-3-methylimidazolium bromide ([C₇mim][Br]) in pure water and in aqueous solutions of sodium di-hydrogen citrate, di-sodium hydrogen citrate and tri-sodium citrate over a range of temperatures at atmospheric pressure. The experimental density and sound velocity data are used to calculate the apparent molar volume and isentropic compressibility as a function of temperature and concentration. The effects of temperature and charge on the anion of sodium citrate salts on the apparent molar volume and isentropic compressibility of [C₇mim][Br] are studied. It was found that both of the apparent molar volume and isentropic compressibility of [C₇mim][Br] in aqueous sodium citrate solutions are larger than those in pure water and increase by increasing temperature. The effects of temperature and charge on the anion of sodium citrate salts on the conductivity behavior of the investigated IL solutions are also studied.     

(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.     

Effect of alkyl chain length and temperature on the thermodynamic properties of ionic liquids 1-alkyl-3-methylimidazolium bromide in aqueous and non-aqueous solutions at different temperatures

The alkyl chain length of 1-alkyl-3-methylimidazolium bromide ([Rmim][Br], R = propyl (C₃), hexyl (C₆), heptyl (C₇), and octyl (C₈)) was varied to prepare a series of room-temperature ionic liquids (RTILs), and experimental measurements of density and speed of sound at different temperatures ranging from (288.15 to 308.15) K for their aqueous and methanolic solutions in the dilute concentration region (0.01 to 0.30) mol · kg^?1 were taken. The values of the compressibilities, expansivity and apparent molar properties for [C_nmim][Br] in aqueous and methanolic solutions were determined at the investigated temperatures. The obtained apparent molar volumes and apparent molar isentropic compressibilities were fitted to the Redlich–Mayer and the Pitzer’s equations from which the corresponding infinite dilution molar properties were obtained. The values of the infinite dilution molar properties were used to obtain some information about solute–solvent and solute–solute interactions. The thermodynamic properties of investigated ionic liquids in aqueous solutions have been compared with those in methanolic solutions. Also, the comparison between thermodynamic properties of investigated solutions and those of electrolyte solutions, polymer solutions, cationic surfactant solutions and tetraalkylammonium salt solutions have been made.     

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.     

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.     

(Liquid + liquid) equilibrium of (imidazolium ionic liquids + organic salts) aqueous two-phase systems at T = 298.15 K and the influence of salts and ionic liquids on the phase separation

(Liquid + liquid) equilibrium for the {1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim]BF₄)/1-propyl-3-methylimidazolium tetrafluoroborate ([C₃mim]BF₄) + organic salt + H₂O} aqueous two-phase systems (ATPSs) have been experimentally ascertained at T = 298.15 K. Three empirical equations were used to correlate the binodal data. On the basis of the empirical equation of the binodal curve with the highest accuracy and lever rule, the (liquid + liquid) equilibrium data were calculated by MATLAB. The reliability of the tie line compositions was proved by the empirical correlation equations given by the Othmer–Tobias and Bancroft equations. The effective excluded volume (EEV) values obtained from the binodal model for these systems were determined. The EEV and the binodal curves plotted in molality both indicate that the salting-out abilities of the four salts follow the order: Na₃C₆H₅O₇ > (NH₄)₃C₆H₅O₇ > Na₂C₄H₄O₄ ≈ Na₂C₄H₄O₆, while the phase-separation abilities of the investigated ILs are in the order of [C₃mim]BF₄ > [C₂mim]BF₄. In the systems investigated, the effect of salts on the phase-forming capability was also evaluated in the shape of the salting-out coefficient obtained from fitting the tie-line data to a Setschenow-type equation. The phase-forming ability increases with the increase of salting-out coefficient.     

Solubility,volumetric properties and viscosity of the sustainable systems of liquid poly(ethylene glycol) 200 with imidazolium- and phosphonium-based ionic liquids: Cation and anion effects

In this work, solubility, volumetric and viscosity behavior were studied for the systems containing the environmentally acceptable compounds: liquid poly(ethylene glycol) (PEG200) and three ionic liquids: 1-butyl-3-methylimidazolium dicyanamide ([C₄mim][dca]), trihexyltetradecyl phosphonium dicyanamide ([P_6,6,6,14][dca]) and 1-hexyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ([C₆mim][NTf₂]). The studies were performed in a temperature range (288.15 to 328.15) K and at a pressure of 0.1 MPa. For the only system that evidenced limited miscibility, namely (PEG200 + [P_6,6,6,14][dca]), the temperature-composition phase diagram at 0.1 MPa was determined, mapping the existing one- and two-phase regions. In the homogeneous region of this diagram, densities and viscosities were measured and the excess molar volumes, as well as deviations in viscosity were calculated. For the other two systems, as they are always homogeneous in the temperature ranges of the present work, these measurements and calculations were performed in the full range of compositions. The molecular interactions in the studied systems were scrutinized using the obtained excess molar volumes, deviations of viscosity, as well as Kamlet–Taft parameters of PEG200 and the ionic liquids. In addition, the excess molar Gibbs free energies of activation of viscous flow and the related enthalpies and entropies were calculated and introduced to take into consideration the differences in size of the molecules.     

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 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.     

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.     

288.15-318.15K温度范围内离子液体[C5mim][Pro]水溶液的体积和表面性质

在288.15-318.15 K温度范围内,测定了不同浓度离子液体1-戊基-3-甲基咪唑丙酸盐([C5mim][Pro])水溶液的密度和表面张力,计算了不同温度下不同浓度的溶液热膨胀系数、表观摩尔体积和溶液等张比容;根据密度实验数据计算得到溶质表观膨胀率,并与Harned和Owen提供的理论方程计算结果作了比较,两者计算结果能够很好一致;另外,本文还验证了预测溶液表面张力的经验方程,用其预测溶液的表面张力,不仅与溶液表面张力实验值在误差范围内很好一致,也与用等张比容方法预测的结果一致.     

Effect of tri-potassium phosphate on volumetric,acoustic, and transport behaviour of aqueous solutions of 1-ethyl-3-methylimidazolium bromide at T = (298.15 to 318.15) K

Density, sound velocity, and viscosity of 1-ethyl-3-methylimidazolium bromide, [Emim][Br], in aqueous solutions of tri-potassium phosphate with salt weight fractions (w_s = 0.00, 0.10, 0.15, and 0.20) have been measured as a function of concentration of [Emim][Br] at atmospheric pressure and T = (298.15, 303.15, 308.15, 313.15, and 318.15) K. The apparent molar volume, isentropic compressibility, apparent isentropic compressibility, and relative viscosity values have been evaluated from the experimental data. The partial molar volume and isentropic compressibility at infinite dilution, and viscosity B-coefficient obtained from these data have been used to calculate the corresponding transfer parameters for the studied IL from water to the aqueous tri-potassium phosphate solutions. Also, an empirical equation was satisfactorily used to correlate the experimental viscosity data.     

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.     

Interactions of glycine,L-alanine and L-valine with aqueous solutions of trisodium citrate at different temperatures: A volumetric and acoustic approach

Densities, ρ, and speed of sound, u for glycine, L-alanine and L-valine in (0.2, 0.4, 0.6, and 0.8) mol · kg⁻¹ aqueous solutions of trisodium citrate at T = (288.15, 298.15, 308.15 and 318.15) K have been measured. The different parameters such as apparent molar volume, limiting apparent molar volume, transfer volume, have been derived from density data. Experimental values of the speed of sound were used to estimate apparent molar apparent molar isentropic compression, limiting apparent molar isentropic compression, and transfer parameter. The pair and triplet interaction coefficient have been calculated from transfer parameters.     

Volumetric and compressibility behaviour of poly(propylene glycol) – Amino acid aqueous solutions at different temperatures

Precise density and sound velocity measurements have been carried out for aqueous solutions of PPG725 in the absence and presence of (0.2 and 0.5) mol · kg⁻¹ amino acids: alanine, glycine, serine and proline, and also for aqueous solutions of these amino acids in the absence and presence of 0.01 w/w PPG725 at T = (288.15, 293.15, 298.15, 303.15 and 308.15) K. From the experimental density and sound velocity values, the apparent molar volume and isentropic compressibility have been obtained and extrapolated to infinite dilution. The infinite dilution apparent molar properties for transfer of PPG from water to aqueous amino acids solutions and also those for transfer of amino acids from water to aqueous PPG solutions have been studied. Temperature dependency of the infinite dilution apparent molar volume was utilised to determine structure-breaker or structure-maker effects of the solutes. Hydration numbers of the amino acids in the investigated aqueous solutions have been evaluated from the volumetric and compressibility properties. All results are discussed based on the salting-out aptitude of the amino acids (hydrophilic + hydrophobic) interactions and (hydrophobic + hydrophobic) interactions occurred between PPG and the investigated amino acids.     

Isobaric vapor–liquid equilibria for ethanol–water system containing different ionic liquids at atmospheric pressure

Isobaric vapor–liquid equilibrium (VLE) data for ethanol–water systems containing ionic liquids (ILs) 1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) at atmospheric pressure (101.32 kPa) were measured with a circulation still. The results showed that the VLE of ethanol–water systems in the presence of different ILs was obviously different from that of the IL-free system. All ILs studied showed a salting-out effect, which gave rise to a change of the relative volatility of ethanol, and even to an elimination of the azeotropic point. It was found that the salting-out effect followed the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆] and [MMIM][DMP] > [EMIM][DEP], which was ascribed to the preferential solvation ability of the ions resulting from the dissociation of the IL.     

Solubility of high-value compounds in environmentally friendly solvents–liquid poly(ethylene glycol) and ionic liquids: Experimental study and thermodynamic analysis

In this work the (solid + liquid) equilibria (SLE) of the solution of sustainable solvents with five high-value compounds, thymol, ferulic acid, vanillic acid, caffeic acid and caffeine, was investigated. The sustainable solvents studied were liquid poly(ethylene glycol) of average molecular mass 200 and 400 – (PEG200 and PEG400), respectively as well as imidazolium ionic liquids with bistriflamide and triflate anions ([C₄mim][NTf₂] and [C₄mim][OTf]). The obtained SLE data were correlated using the semi-empirical equation proposed by Grant. The activity coefficients of the studied solutes were calculated. Based on these correlations and calculations as well as on the thermo-physical properties of the pure constituents, the SLE behavior of the studied solutions was analyzed and discussed.     

Apparent molar heat capacities and apparent molar volumes of Pr(ClO4)3(aq), Gd(ClO4)3(aq), Ho(ClO4)3(aq), and Tm(ClO4)3(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa

Acidified aqueous solutions of Pr(ClO₄)₃(aq), Gd(ClO₄)₃(aq), Ho(ClO₄)₃(aq), and Tm(ClO₄)₃(aq) were prepared from the corresponding oxides by dissolution in dilute perchloric acid. Once characterized with respect to trivalent metal cation and acid content, the relative densities of the solutions were measured at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa using a Sodev O2D vibrating tube densimeter. The relative massic heat capacities of the aqueous systems were also determined, under the same temperature and pressure conditions, using a Picker Flow Microcalorimeter. All measurements were made on solutions containing rare earth salt in the concentration range 0.01 ⩽ m/(mol · kg⁻¹) ⩽ 0.2. Relative densities and relative massic heat capacities were used to calculate the apparent molar volumes and apparent molar heat capacities of the acidified salt solutions from which the apparent molar properties of the aqueous salt solutions were extracted by the application of Young's Rule. The concentration dependences of the isothermal apparent molar volumes and heat capacities of each aqueous salt solution were modelled using Pitzer ion-interaction equations. These models produced estimates of apparent molar volumes and apparent molar heat capacities at infinite dilution for each set of isothermal V_φ,2 and C_pφ,2 values. In addition, the temperature and concentration dependences of the apparent molar volumes and apparent molar heat capacities of the aqueous rare earth perchlorate salt solutions were modelled using modified Pitzer ion-interaction equations. The latter equations utilized the Helgeson, Kirkham, and Flowers equations of state to model the temperature dependences (at p=0.1 MPa) of apparent molar volumes and apparent molar heat capacities at infinite dilution. The results of the latter models were compared to those previously published in the literature.Apparent molar volumes and apparent heat capacities at infinite dilution for the trivalent metal cations Pr³⁺(aq), Gd³⁺(aq), Ho³⁺(aq), and Tm³⁺(aq) were calculated using the conventions V₂^∘(H⁺(aq)) ≡ 0 and C_p2^∘(H⁺(aq)) ≡ 0 and have been compared to other values reported in the literature.     

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.