Alkylsulfate Ionic Liquids Research Articles

Experimental device to measure the ionic conductivity anisotropy in liquid crystal hydrogel based in [EMIM] alkyl sulfate Ionic Liquids

We have built an experimental device with the aim to measure the expected electrical conductivity anisotropy in a liquid crystal, obtained from the gelation of the ionic liquid 1-ethyl-3-methyl imidazolium decyl sulfate, [EMIM][DSO4]. This ionic liquid has the particularity that it transits to a semi-solid gel state at room temperature when it contains water, naturally adsorbed from the environment until a balance is reached between the concentration of water in the IL and the atmospheric humidity grade. The quantity of water adsorbed to form the hydrogel at room temperature varies from about 5 to 30 wt%, each composition giving place to different smectic phases. In the gel state, the ionic liquid ions and the water molecules self-organize into micro-sized mesophases that resemble the structures of a liquid crystal. Our device is a closed 2D sample holder (with sides 150 times longer than its thickness), with a single narrow window open to the atmosphere, and four copper contacts on the sides. The dried ionic liquid is tempered at 40 °C to increase its fluidity when injected into the cavity, and then, it can only adsorb water through the narrow opening. Thus, water adsorption is unidirectional and slow, so the transition of the IL to the gel phase happens progressively. A metastable giant mesophase appears as an orientated macrodomain in the form of a striped pattern. In this state, we measure the electrical conductivity of the confined film in directions parallel and perpendicular to the observed strips, finding a difference of up to 26% between both values of the conductivity. If the sample freezes (below 10 °C) or it liquefies (above 50 °C) the meso structure is broken and the observed anisotropy destroyed. We can return the sample to gel state by varying the temperature, but the ordered macroscopic state is no longer recovered. This research must give clues to solve the charge transport mechanism quiz in ionic liquids and semi-solid coductors.

Selective binding and dynamics of imidazole alkyl sulfate ionic liquids with human serum albumin and collagen - a detailed NMR investigation.

The interaction of ionic liquid (IL) with protein is now becoming important as it stabilizes the protein due to the selective cation-anion combination of the IL. The binding and dynamics of the green solvents such as imidazole alkyl sulfate based ILs, viz., 1-butyl-3-methylimidazolium alkyl [where alkyl = hydrogen, methyl, octyl and dodecyl] sulfate, with two distinct model proteins, namely human serum albumin (HSA) and collagen in aqueous solution, have been investigated with the aid of solution nuclear magnetic resonance (NMR). Interactions of ILs with HSA and collagen have been probed at the atomistic level through NMR determined parameters, such as 1H line-shapes, selective and non-selective spin-lattice relaxation times (T1SEL & T1NS) and spin-spin relaxation times (T2). Furthermore, saturation transfer difference (STD) NMR has been used to monitor the spatial proximities of ILs with HSA and collagen. The results indicate that despite the type of protein (HSA or collagen), STD NMR of protein-IL mixtures exhibits responses only from the anionic part of the selected ILs. Also, a combination of T1SEL and T1NS measurements indicates the genuine protein-IL interaction. Furthermore, it was observed that the global binding affinity between IL and proteins is enhanced with an increase in alkyl chain length of the anionic portion of the IL. The present study thus highlights the role of the anionic part of ILs in the interaction with the selected proteins. The outcome of the present study provides an opportunity to design new ILs with a judicious choice of anionic and cationic parts for targeted functionalities.

Imidazolium-based Alkylsulfate Ionic Liquids and Removal of Sulfur Content From Model of Gasoline

Two ionic liquids, butyl-methyl-imidazolium octylsulfate, [BMIM][OCSO4], and ethyl-methyl-imidazolium ethylsulfate, [EMIM][EtSO4], were demonstrated to be effective for the removal of aromatic sulfur compounds such as benzothiophene and thiophene from model of gasoline. Organic compounds with higher aromatic π-electron density were favorably adsorbed by using ionic liquids. It was shown that the extractive ability of the alkylsulfate ILs was dominated by the structure and size of cation and anion. The cation and anion structure and size of ionic liquids are important factors affecting the absorption capacity for aromatic compounds. It is found that [BMIM][OCSO4] has the best effect on the selective removal of sulfur compounds from gasoline. Sulfur extractive selectivity for specified IL followed the order BT>T>3-MT>2-MT.

Electrical Conductivity of Seven Binary Systems Containing 1-Ethyl-3-methyl Imidazolium Alkyl Sulfate Ionic Liquids with Water or Ethanol at Four Temperatures

We present experimental measurements of specific electrical (or ionic) conductivity of seven binary systems of 1-ethyl-3-methyl imidazolium alkyl sulfate (EMIM-C(n)S) with water or ethanol. Electrical conductivity was measured at 298.15 K in all ranges of concentrations and selected mixtures also at 288.15, 308.15, and 318.15 K. The alkyl chains of the anions used are ethyl (EMIM-ES), butyl (EMIM-BS), hexyl (EMIM-HS), and, only for mixtures with ethanol, octyl (EMIM-OS). Let us note that the four ionic liquids (ILs) measured are miscible in water and ethanol at those temperatures and atmospheric pressure in all ranges of concentrations, but EMIM-OS jellifies for a given range of concentration with water. We compare the measured data in terms of the alkyl chain length and solvent nature. Data are compared with previously scarce results for these same systems and also for other aqueous and ethanol mixtures with ILs. In addition, we verify that our data fit the universal theoretical expression with no fitting parameters given by the pseudolattice-based Bahe-Varela model, except for IL concentrated mixtures. To fit well all ranges of concentrations, we add to the original equation two phenomenological terms with one fitting parameter each. Finally, we calculate the molar conductivity and fit it successfully with an expression derived from Onsager theory.

Solubility of gases in 1-alkyl-3methylimidazolium alkyl sulfate ionic liquids: Experimental determination and modeling

The solubility of different gases (carbon dioxide, methane, ethane, carbon monoxide and hydrogen) in ionic liquids with an alkyl sulfate anion has been modeled with the Group Contribution equation of state developed by Skjold-Jørgensen. New gas solubility measurements have been carried out with a high pressure magnetic suspension balance in order to cover pressure and temperature ranges not considered in previous studies and to obtain more experimental information for the correlation of parameters of the equation of state. New solubility measurements include the solubility of carbon dioxide in 1-ethyl 3-methyl imidazolium ethyl sulfate [emim][EtSO4] at temperatures of 298K and 348K and pressures ranging from 0.3MPa to 6.5MPa, the solubility of methane in [emim][EtSO4] at a temperature of 293K and pressures ranging from 0.2MPa to 10.2MPa, and the solubility of ethane in [emim][EtSO4] at temperatures of 323K and 350K and pressures ranging from 0.2MPa to 4MPa. Results show that the Group Contribution equation of state can be used to describe the solubility of gases in alkyl sulfate ionic liquids as well as infinite dilution coefficients of alkanes in the ionic liquids, with average deviations between experiments and calculations ranging from 1% to 10% in the case of mixtures with CO2, CO, CH4 and H2 with the alkyl sulfate ionic liquids to up to 34% in the case of the solubility of ethane in [emim][EtSO4].

Studies on the Solvation Dynamics of Coumarin 153 in 1‐Ethyl‐3‐Methylimidazolium Alkylsulfate Ionic Liquids: Dependence on Alkyl Chain Length

Steady-state and time-resolved fluorescence behavior of coumarin 153 (C153) is investigated in a series of 1-ethyl-3-methylimidazolium alkylsulfate ([C(2)mim][C(n)OSO(3)]) ionic liquids differing only in the length of the linear alkyl chain (n = 4, 6, and 8) in the anion. The aim of the present study is to understand the role of alkyl chain length in solute rotation and solvation dynamics of C153 in these ionic liquids. The blueshift observed in the steady-state absorption and emission maxima of C153 on going from the C(4)OSO(3) to the C(8)OSO(3) system indicates increasing nonpolar character of the microenvironment of the solute with increasing length of the alkyl side chain of the anion of the ionic liquids. The average solvation time is also found to increase on changing the substituent from butyl to octyl, and this is attributed to the increase in the bulk viscosity of the ILs. A steady blueshift of the time-zero maximum of the fluorescence spectrum with increasing alkyl chain length also indicates that the probe molecule experiences a less polar environment in the early part of the dynamics. Rotational dynamics of C153 are also analyzed by using the Stokes-Einstein-Debye (SED), Gierer-Wirtz (GW), and Dote-Kivelson-Schwartz (DKS) theories. Analyses of the results seem to suggest decoupling of the rotational motion of the probe from solvent viscosity.

Structural Study at the Gas‐Liquid Interface of 1‐Alkyl‐3‐Methylimidazolium Alkylsulfates Using Surface Potential Measurements

Sum frequency generation, surface potential, and surface tension measurements have been combined on the pure ionic-liquid-gas interface for 1-alkyl-3-methylimidazolium alkylsulfate ionic liquids. The results show that surface potential of the ionic liquid generally increases as the alkyl chain on the cation or anion increases in length. This is due to the increased ordering of the surface dipole, mostly coming from the terminal methyl group of the alkyl chain. Both sum frequency generation spectroscopy and surface potential measurements suggest that the charged components, that is, the aromatic ring and the sulfate, occupy nearly the same plane at the surface for all ionic liquids studied herein.

Alkylpyridinium Alkylsulfate Ionic Liquids as Solvents for the Deterpenation of Citrus Essential Oil

The ionic liquids 1-methylpyridinium methylsulfate and 1-ethylpyridinium ethylsulfate were tested as solvents for the deterpenation by liquid-liquid extraction of citrus essential oil, simulated as a mixture of limonene and linalool. Liquid-liquid equilibrium data for the ternary systems limonene + linalool + 1-alkylpyridinium alkylsulfate (with the alkyl chain being methyl or ethyl) were determined at 298.15 K and atmospheric pressure, and suitably correlated with the UNIQUAC thermodynamic model. A comparison was established between the performance of these ionic liquids, as well as with others previously reported in the literature, to evaluate the influence of different structural features of the ionic liquids on their deterpenation ability.

Rotational Dynamics of Coumarin-153 and 4-Aminophthalimide in 1-Ethyl-3-methylimidazolium Alkylsulfate Ionic Liquids: Effect of Alkyl Chain Length on the Rotational Dynamics

Rotational dynamics of two neutral organic solutes, coumarin-153 (C-153) and 4-aminophthalimide (AP), with only the latter having hydrogen-bond-donating ability, has been investigated in a series of 1-ethyl-3-methylimidazolium alkyl sulfate ionic liquids as a function of temperature. The ionic liquids differ only in the length of the linear alkyl side chain (alkyl = ethyl, butyl, hexyl, and octyl) on the anionic moiety. The present study has been undertaken to examine the role of alkyl side chains on the rotational dynamics of the two solutes in these ionic liquids. Analysis of the results using Stokes-Einstein-Debye hydrodynamic theory indicates that the rotational dynamics of C-153 lies between the stick and slip boundary condition in the ethyl analogue and finally reaches subslip condition as in case of the octyl substituent. The observed rotational behavior of C-153 has been explained on the basis of an increase in the size of the solvent, which offers lower friction for solute rotation. On the other hand, AP shows superstick behavior in the ethyl system and exceeds the stick limit in the octyl derivative. Superstick behavior of AP has been attributed to the specific hydrogen-bonding interaction between AP and the sulfate moiety. Proton NMR investigation confirms the hydrogen-bonding interaction between the N-H hydrogen of AP and the ionic liquid. The decrease in rotational coupling constant values for AP with increasing length of alkyl side chains has been attributed to the decrease in the solute-solvent-specific interaction with an increase in the alkyl side chain length on the sulfate moiety.

Aqueous biphasic systems involving alkylsulfate-based ionic liquids

The specific effects of K3PO4, K2CO3, Na2CO3, and (NH4)2SO4, as high charge-density inorganic salts and thus inducers of the formation of aqueous biphasic systems (ABS) containing several ethyl-methylimidazolium alkylsulfate ionic liquids, C2MIM CnSO4 (n=2, 4, 6, or 8), have been assessed at T=298.15K. The results are analyzed in the light of the Hofmeister series. The influence of different alkyl chain lengths in the anion, together with the ability of the selected inorganic salts to induce the formation of ABS, is discussed. Phase diagrams have been determined through turbidimetry, including tie lines assignments from mass phase ratios according to the lever – arm rule. The Merchuck equation was satisfactorily used to correlate the solubility curve.

Effect of Cationic and Anionic Chain Lengths on Volumetric, Transport, and Surface Properties of 1-Alkyl-3-methylimidazolium Alkylsulfate Ionic Liquids at (298.15 and 313.15) K

The effect of the alkyl chain of 1-alkyl-3-methylimidazolium alkylsulfate ([Cnmim][CH3SO4] and [Cnmim][C2H5SO4] ionic liquids (ILs) with n between 1 to 8) on density, viscosity, and surface tension has been experimentally determined at (298.15 and 313.15) K. In addition, the quantum-chemical COSMO-RS method is used to extend the analysis of the influence of sulfate alkyl length on density by screening [Cnmim][CmH2m+1SO4] compounds with m between 1 and 8. COSMO-RS is also tested for the first time in the prediction of IL viscosities. Density and surface tension of the ILs studied decrease with the number of carbon atoms in the alkyl substituent of cation, whereas viscosity increases. All of these properties decrease as the temperature increases.

Design of Alkyl Sulfate Ionic Liquids for Lubricants

Abstract Tribological properties of alkyl sulfate ionic liquids have been evaluated; hydrophobicity of ionic liquids significantly influenced the tribological characteristics and combination of phosphonium cation with hydrophobic octafluoropentyl sulfate anion afforded good ionic liquid that showed excellent tribological performance.

Imidazolium dialkylphosphates—a class of versatile, halogen-free and hydrolytically stable ionic liquids

In this article a systematic and detailed study on the synthesis and the properties of dialkylphosphate ionic liquids is presented. This class of halogen-free ionic liquids is easily available in high quality and great variability by direct alkylation of nucleophiles, such as 1-methylimidazole, 1-ethylimidazole, 1-butylimidazole and 1-(2-methoxyethyl)-imidazole with different trialkylphosphates, such as trimethylphosphate, triethylphosphate or tributylphosphate. In general, these dialkylphosphate ionic liquids were found to display very attractive physico-chemical properties with great technical potential, especially in low temperature (<200 °C) applications with water present. For this specific application area, the materials described here clearly show superior properties compared with alkylsulfate ionic liquids due to their obviously much higher hydrolytic stability.

Transesterification of methylsulfate and ethylsulfate ionic liquids—an environmentally benign way to synthesize long-chain and functionalized alkylsulfate ionic liquids

A new environmentally friendly method to synthesize long-chain and functionalized alkylsulfate ionic liquids is reported. The two-step synthesis comprises the synthesis of a methylsulfate or ethylsulfate ionic liquid by direct alkylation in the first step. In the second step, this intermediate is transformed in a transesterification reaction, using different functionalized and non-functionalized alcohols, to the corresponding new alkylsulfate melts. The entire reaction sequence is halide-free and liberates methanol or ethanol as the only by-products. Moreover, it is carried out in a solvent-free manner and scale-up is straight forward.