Properties Of Protic Ionic Liquids Research Articles

Molecular dynamics simulations of ammonium/phosphonium-based protic ionic liquids: influence of alkyl to aryl group.

The variation of the center atom in the cation from an N to a P-atom leads to improved physiochemical properties of protic ionic liquids (PILs) which are suitable for electrolyte applications. We present an atomistic simulations study to compare the effect of an alkyl or aryl group on trioctylammonium triflate ([HN(Oct)3][TFO]) and triphenylammonium triflate ([HN(Ph)3][TFO]) with their phosphonium analogues. We have computed the binding energy from quantum chemical calculations and physical properties such as the viscosity and the electrical conductivity of PILs from molecular dynamics simulations. The influence of the aromatic character in PILs is found to be significant to the physical properties. Gas phase quantum chemical calculations on clusters of ion pairs have revealed the presence of C-H/π interactions in aromatic PILs along with hydrogen bonding. The variation in strength of the ion-pair affinities is examined using electric-current correlation and velocity autocorrelation functions. The qualitative differences observed are due to the aromatic rings and change in the central atom of the quaternary cation from an N to a P-atom, substantiated quantitatively by diffusion coefficients and electrical conductivities. The relatively weaker ion-pair interactions and low binding energy (-73.34 kcal mol-1) lead to the highest electrical conductivity in [HP(Ph)3][TFO].

Effect of Structural Variations on the Thermophysical Properties of Protic Ionic Liquids: Insights from Experimental and Computational Studies

In this work, new protic ionic liquids (PILs) based on 1-methylimidazolium/1-propanenitrileimidazolium cations with hydrogen sulfate, methanesulfonate, trifluoromethanesulfonate, para-toluenesulfonate, trifluoroacetate, and acetate anions were synthesized. The structures and purity of the products were confirmed by using 1H and 13C NMR and CHNS elemental analysis. The effect of structural variations on the thermophysical properties, namely, refractive index, density, and viscosity, was evaluated in a wide temperature range. The viscosity and density values were measured within the temperature range of 293.15–373.15 K. The density values were used further to calculate more properties like thermal expansion coefficient, molecular volume, standard entropy, and the lattice energy. Moreover, the experimental values of viscosity were used for the calculation of activation energy. Refractive indices were measured within the temperature range of 293.15–323.15 K, and these values were also used in the calculation ...

Properties of Protic Ionic Liquids Comprised of N‐Alkyldiethylenetriamine and Their Complexation of Copper(II) Ions

Protic ionic liquids (PILs) comprised of alkylpolyaminium cations, such as monoprotonated N‐hexyldiethylenetriaminium (HHexdien+) and N‐(2‐ethylhexyl)diethylenetriaminium (HEthexdien+), coupled with bis(trifluoromethylsulfonyl)amide (Tf2N–) and trifluoroacetate (TFA–) were prepared, and their properties and interactions with copper(II) ions were studied using differential scanning calorimetry (DSC), visible absorption spectra, and 15N NMR and 13C NMR spectroscopy. The alkyldiethylenetriaminium (triamine) PILs assume a liquid state at lower temperatures than the corresponding alkylethylenediaminium (diamine) PILs, and they exhibit a glass transition without crystallization for all of the systems studied. The protonation of the alkyltriamines predominantly occurs at the N(1) and N(3) amine moieties and depends on the counteranions (Tf2N– or TFA–) and the alkyl moiety (hexyl or ethylhexyl). The polarity parameters, such as ET(30) (or ETN), π*, α, and β, were determined for the triamine PILs, as well as for the diamine PILs, to examine the amine effect. The coordination structure of the copper(II) ion in the present chelate–amine PILs was deduced based on the visible absorption spectra for the isolated copper(II)–alkyldiethylenetriamine complexes and for Cu(ClO4)2 in molecular solvents. The lifetime of the copper(II)–triamine complex formed in the PIL was estimated to be ca. 10–2 s at ambient temperature using the 13C NMR spectroscopic paramagnetic relaxation times.

Properties of protic ionic liquids composed of N-alkyl (= hexyl, octyl and 2-ethylhexyl) ethylenediaminum cations with trifluoromethanesulfonate and trifluoroacetate anion

Protic ionic liquids (PILs) composed of N-alkyl (=hexyl, octyl and 2-ethylhexyl) ethylenediaminum cation with trifluoromethanesulfonate (TFS) or trifluoroacetate (TFA) anion such as HOct(TFA), HEtHex(TFA), HHex(TFS), HOct(TFS) and HEtHex (TFS) were newly synthesized and HHex(TFA) was synthesized according to the method from a literature. Among them, HHex(TFA), HEtHex(TFA) and HEtHex (TFS) are room temperature ionic liquids. The PILs with TFS exhibit more thermostable than the PILs with TFA and their decomposition temperatures are about 250°C and 150°C, respectively. The physical properties such as density, viscosity and electric conductivity of the PILs were studied in the temperature range of (293.15 to 353.15) K. Temperature dependence of the viscosity and the conductivity was discussed using the Arrhenius equation. The relationship between the molar conductivity and the fluidity was described on the basis of the Walden rule. The results show that the PILs with TFS have a larger ionic mobility compared to the PILs with TFA.

The Influence of Cation Structure on the Chemical–Physical Properties of Protic Ionic Liquids

In this study we investigated the influence of five different cations on the physical–chemical properties of protic ionic liquids (PILs) based on bis(trifluoromethanesulfonyl)imide (TFSI–). We showed that the viscosities, ionic conductivities, densities, and thermal properties of these PILs are strongly affected by the structure of the protic cation. Furthermore, the influence of the cation structure on the lithium coordination was investigated by Raman spectroscopy for all investigated PIL-based electrolytes for lithium ion batteries (LIBs). This investigation clearly demonstrates that the lithium average coordination number in PIL-based electrolytes is strongly affected by (ring) size and the number of protons on the cation structure and, more importantly, it might be significantly lower (more than 60%) than that of electrolytes containing aprotic ionic liquids (AILs). Electrochemical performances of these PIL-based electrolytes were then also investigated to address some conclusions on their applicabil...

A pH Scale for the Protic Ionic Liquid Ethylammonium Nitrate.

To quantify the properties of protic ionic liquids (PILs) as acid-base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was found between the 14 pKa values of 12 compounds in EAN and in water. In other words, the pKa value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3 O(+) in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from -1 to 9 on the pH scale based on the pH value in water.

A pH Scale for the Protic Ionic Liquid Ethylammonium Nitrate

AbstractTo quantify the properties of protic ionic liquids (PILs) as acid–base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was found between the 14 pKa values of 12 compounds in EAN and in water. In other words, the pKa value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3O+ in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from −1 to 9 on the pH scale based on the pH value in water.

Investigation of the rheological properties of protic ionic liquids

This paper reports on the synthesis of five protic ionic liquids namely 2‐hydroxy ethylammonium acetate, 2‐hydroxy diethylammonium acetate, 2‐hydroxy ethylammonium propionate, 2‐hydroxy ethylammonium lactate, and 2‐hydroxy diethylammonium lactate and the study of shear and temperature dependency of the viscosity at the range 313.15–343.15 K. 1H nuclear magnetic resonance and Fourier transform infrared spectroscopy spectra establish the simple ionic salt structure of these compounds. Because of their polar character, these protic ionic liquids are able to dissolve polar solvents and inorganic salts, all of them showing high tolerance into hydroxylic media. The experimental results showed that the viscosity of these fluids decreases strongly with increasing temperature, being of non‐Newtonian trend over a range of shear rate. The parameters enthalpy of activation (ΔH*), free energy of activation (ΔG*), entropy of activation (ΔS*), and change in heat capacity of activation (ΔCp*) for their viscous flow were evaluated. The temperature dependence of viscosities was fitted using the power law, Litovitz, Vogel–Fulcher–Tammann, and Ghatee equations. Copyright © 2016 John Wiley & Sons, Ltd.

ChemInform Abstract: Protic Ionic Liquids: Evolving Structure‐Property Relationships and Expanding Applications

AbstractReview: 635 refs.

Protic Ionic Liquids: Evolving Structure-Property Relationships and Expanding Applications.

The thermal and physicochemical properties of protic ionic liquids (PILs) are reported. It is highly evident that there has been an extensive range of alkylammonium, imidazolium, and heterocyclic cations paired with many organic and inorganic anions that have been employed to prepare PILs. There has been strong interest in modifying the properties of PILs through the addition of water or other molecular solvents. For many applications, the presence of some water in the PILs is not detrimental, and instead leads to enhanced solvent properties such as lower viscosity, higher conductivities, and lower melting points. It remains an issue of definition though of how to refer to these resulting protic solutions. There is also an ongoing difficulty surrounding how to describe the proton activity in the PILs, analogous to pH in aqueous systems. For a broad range of applications, it has been reported that the acidity/basicity of the PIL or PIL-solvent system is crucial for their beneficial properties. It is expected that the fundamental properties of PILs will continue to be explored, along with continued interest in many existing and new applications, such as in electrochemistry, organic and inorganic synthesis, and biological applications. In particular, there has been a significant interest in a broad- range of PILs for use as electrolytes and incorporation in polymer electrolytes for fuel cells, and other energy storage devices.

Tribological properties of protic ionic liquid and functionalized copper oxide nanoparticles as additives to base oil

The aim of the present study was to investigate a novel composite as lubricant additive for metal wear parts, composing of protic ionic liquid and functionalized copper oxide nanoparticle composite. A simple and an easy-to-modify synthesis method for the preparation of thiol cov-ered copper oxide nanoparticles was developed. A long process of optimization of reaction parameters was carried out that resulted in preparing non-agglomerated oil dis-persible copper oxide nanoparticles with an estimated av-erage diameter of 60 nanometers based on SEM measure-ments. Novel protic ionic liquid, which dissolves in oil was synthesized. Lubricant tribological experiments with the standardized four-ball-method were conducted with 15 kg. The addition of 3% ionic liquid and 0.5% copper oxide nanoparticles to base oil reduced the wear up to 35% com-pared to base oil without any additives, while 1% of protic IL reduced wear up to 47%. In addition, the novel type lubricant additive has many advantages and can also widen the range of applications, e.g. wider temperature range and preserved functionality at harsh conditions where oil-based lubricants fail.DOI: http://dx.doi.org/10.5755/j01.mech.21.2.11723

Synthesis, characterization and the effect of temperature on different physicochemical properties of protic ionic liquids

In this work, eleven protic ionic liquids (PILs) containing different cations and anions were prepared and their physicochemical properties were measured.

Assessment of the Density Functional Tight Binding Method for Protic Ionic Liquids.

Density functional tight binding (DFTB), which is ∼100–1000 times faster than full density functional theory (DFT), has been used to simulate the structure and properties of protic ionic liquid (IL) ions, clusters of ions and the bulk liquid. Proton affinities for a wide range of IL cations and anions determined using DFTB generally reproduce G3B3 values to within 5–10 kcal/mol. The structures and thermodynamic stabilities of n-alkyl ammonium nitrate clusters (up to 450 quantum chemical atoms) predicted with DFTB are in excellent agreement with those determined using DFT. The IL bulk structure simulated using DFTB with periodic boundary conditions is in excellent agreement with published neutron diffraction data.

Comparative Study on Physicochemical Properties of Protic Ionic Liquids Based on Allylammonium and Propylammonium Cations

Protic ionic liquids (PILs) were prepared by neutralization of a series of allylamines (allyldimethylamine, allyldiethylamine, and diallylmethylamine) with trifluoromethanesulfonic acid, in order to achieve highly conductive PILs, and their physicochemical properties, including thermal and transport properties, were compared with PILs from a series of propylamines (dimethylpropylamine, diethylpropylamine, and methyldipropylamine). The melting point and ionic conductivity of the allylammonium-based PILs were lower and higher than those of the corresponding propylammonium-based PILs having cations with the same number of carbon atoms, respectively. The origin of the difference in the properties of these two series of PILs was investigated based on the evaluation of the molar concentration, self-diffusion coefficient of the cations and anions, and ionicity. The molar concentration and ionicity of the allylammonium-based PILs were higher than those of the corresponding propylammonium-based PILs, whereas the d...

Effect of anion variation on the thermophysical properties of triethylammonium based protic ionic liquids with polar solvent

In this work, we explore the anion effect on the thermophysical properties of protic ionic liquids (PILs) such as triethylammonium acetate [Et3NH][CH3COO] (TEAA), triethylammonium dihydrogen phosphate [Et3NH][H2PO4] (TEAP) and triethylammonium hydrogen sulfate [Et3NH][HSO4] (TEAS) with polar solvent such as dimethylsulfoxide (DMSO). To understand the molecular interactions between DMSO with ILs, densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been measured over whole range of compositions and at three temperatures, 298.15, 303.15, and 308.15K under atmospheric pressure. A second order empirical polynomial and Arrhenius equations were used to correlate the ρ and η as function of temperature, respectively. Sound velocity mixing rules were used on experimental values. Further, the excess molar volume (VE), the deviation in isentropic compressibility (Δκs) and deviation in viscosity (Δη) were calculated using these properties. The obtained VE, Δκs and Δη values were correlated by using the Redlich–Kister polynomial equation.

Electrochemical properties of protic ionic liquids: correlation between open circuit potential for H2/O2 cells under non-humidified conditions and ΔpKa

Electrochemical measurements for a series of protic ionic liquids revealed that open circuit potential (OCP) for H2/O2 cells increases with increasing ΔpKa of the constituent acid and base and passes through a maximum to gradually fall for further increase in the ΔpKa, which indicates the reliance of the electrochemical activity on the persistence of non-ionic species and on the meagre proton activity due to strong N–H bonds.

New for old. Password to the thermodynamics of the protic ionic liquids

Activity coefficients at infinite dilution of some common solvents in a protic ionic liquid ethylammonium nitrate have been measured using well established gas-chromatography-method. This method was possible to apply due to extremely low vapour pressure of ethylammonium nitrate at temperatures below 100 °C. Activity coefficients and separation factors were compared with those for aprotic ionic liquids. A new window for intensive accumulation of thermodynamic properties of protic ionic liquids has been opened.

Preparation and ion transport properties of NaY zeolite–ionic liquid composites

The physicochemical properties of protic ionic liquids (IL)–zeolite (Z) composites were investigated. H-3 methylimidazolium bis(trifluoromethanesulfonyl) imide (TFSI)/NaY zeolite composites with different IL/Z weight ratios were prepared and characterized. X-ray diffraction and FT-Raman measurements show the formation of NaTFSI during the preparation procedure which indicates that an ion exchange reaction is taking place during the composite preparation method. N 2 physisorption shows that the zeolite pores are completely filled when IL/Z ratio is between 0.2 and 0.5. The water adsorption capacity of the samples decreased with IL/Z ratio. The conductivity of the composite pellets increased with temperature and ionic liquid loading, however significant enhancement was detected once the IL/Z weight ratio was higher than a threshold value (∼0.5). Moreover, theoretical calculations were performed using the Effective Medium Theory in order to understand the effect of IL/Z ratio on conductivity. In qualitative agreement with the experimental data, the model shows a sharp increase of the conductivity right above a critical threshold value for the ionic liquid/zeolite mass ratio, followed by a more moderate increase at higher loadings.

Transport properties of protic ionic liquids, pure and in aqueous solutions: Effects of the anion and cation structure

Ionic conductivities of twelve protic ionic liquids (PILs) and their mixtures with water over the whole composition range are reported at 298.15 K and atmospheric pressure. The selected PILs are the pyrrolidinium-based PILs containing nitrate, acetate or formate anions; the formate-based PILs containing diisopropylethylammonium, amilaminium, quinolinium, lutidinium or collidinium cations; and the pyrrolidinium alkylcarboxylates, [Pyrr][C n H 2 n+1 COO] with n = 5–8. This study was performed in order to investigate the influence of molecular structures of the ions on the ionic conductivities in aqueous solutions. The ionic conductivities of the aqueous solutions are 2–30 times higher than the conductivities of pure PILs. The maximum in conductivity varies from w w = 0.41 to 0.74 and is related to the nature of cations and anions. The molar conductance and the molar conductance at infinite dilution for (PIL + water) solutions are then determined. Self-diffusion coefficients of the twelve protic ionic liquids in water at infinite dilution and at 298.15 K are calculated by using the Nernst–Haskell, the original and the modified Wilke–Chang equations. These calculations show that similar values are obtained using the modified Wilke–Chang and the Nernst–Haskell equations. Finally, the effective hydrodynamic (or Stokes) radius of the PILs was determined by using the Stokes–Einstein equation. A linear relationship was established in order to predict this radius as a function of the anion alkyl chain length in the case of the pyrrolidinium alkylcarboxylates PILs.

Physicochemical Properties of Protic Ionic Liquids as Electrolyte for Non-humidified Intermediate Temperature Fuel Cell

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