Hydroxyl-Functionalized 1-(2-Hydroxyethyl)-3-methyl Imidazolium Ionic Liquids: Thermodynamic and Structural Properties using Molecular Dynamics Simulations and ab Initio Calculations

Abstract

The influences of hydroxyl functional group (-OH) on the thermodynamic and structural properties of ionic liquids (ILs) composed of 1-(2-Hydroxyethyl)-3-methyl imidazolium ([C2OHmim](+)) cation and the six different conventional anions, including [Cl](-), [NO3](-), [BF4](-), [PF6](-), [TfO](-), and [Tf2N](-) have been extensively investigated using classical molecular dynamics (MD) simulations combined with ab initio calculations over a wide range of temperature (298-550 K). The volumetric thermodynamic properties, enthalpy of vaporization, cohesive energy density, Hildebrand solubility parameter, and heat capacity at constant pressure were estimated at desired temperature. The simulated densities were in good agreement with the experimental data with a slight overestimation. The interionic interaction of selected ILs was also computed using both the MD simulations and ab initio calculations. It was found that the highest association of cation and anion is attributed to [C2OHmim][Cl] followed by [C2OHmim][NO3], and [C2OHmim][Tf2N] with the bulkiest anion has the weakest interionic interaction among chosen ILs. The similar trend of interactions energies was nearly observed from cohesive energy density results. Additional structural details were comprehensively yielded by calculating radial distribution functions (RDFs) and spatial distribution function (SDFs) at 358 K. The most stable configurations of isolated and dimer ion pairs of these ILs were in excellent consistency with RDFs and SDFs results. Significant changes in arrangement of anions around the [C2OHmim](+) cation in comparison with conventional imidazolium-based ILs can be inferred from the MD simulations and ab initio results. Also, microscopic structural properties disclosed that the most strong cation-cation interaction is ascribed to the hydroxyl-functionalized ILs composed of bulkier anions, whereas ILs incorporating [Cl](-) and [NO3](-) anions are mainly involved in cation-anion interactions. The formation of the intramolecular hydrogen bonding in the [C2OHmim](+) cation is another interesting result of the present study.

Cholinium-amino acid based ionic liquids: a new method of synthesis and physico-chemical characterization

“…This confirm the reproducibility of our synthetic method considering that viscosity is very sensitive to the presence of impurities and water. The presence of side groups that can give rise to van der Waals, stacking and hydrogen bonding interactions in the studied AAs makes it difficult to obtain a single trend but 50 we identified two could be due to its special feature of having the amino group included in a cyclic structure.…”

“…Besides, we can also explain the low value with respect to the AAs series with non-polar chains. In fact, if the increase of viscosity in the non-polar chain AAs series 50 is a consequence of the increase of van der Waals interactions by increasing the length of the alkyl side chain, we should consider that, due to the higher molecular weight of sulfur with respect to carbon, in terms of length of the chains Met should be better compared with Ile, Nle and Leu (four terms side chains). If this 55 correction is made we see that viscosity of [Ch][Met] becomes very similar to those of these three AAs and can be included in the non-polar chain AAs series.…”

“…In particular for ILs, the formation of H-bonds between the ether groups and the acidic 45 hydrogen atoms of the imidazolium ring results in a denser packing than for the non-functionalized ILs. 44 50 sulfur atom should not be much greater than about 20 % with respect to that of a methylene group while the molecular weight of sulfur is about 128 % higher than that of a methylene group, 46 the presence of sulfur could give an important contribution to the overall density of the ILs. Using the values of the van der Waals 55 volume of free amino acids in solutions, 4748 65 with respect to that formed by the classical hydroxyl group, 25 does not seem to give a significant contribution to the density values.…”

“…Then, Liu et al exploited these ILs for the selective extraction of lignin from lignocellulosic materials obtaining excellent results using the [Ch][Gly] IL as a solvent. 10 Therefore, to study the potential of such AAILs to be applied in various 50 fields of chemical industry, the knowledge of their physicochemical properties is very important. In their work, Liu et al reported data on glass transition temperature (T g ), decomposition temperature (T d ) and viscosity (η) of 18 [Ch][AA] ILs.…”

Self-Assembly of Cations in Aqueous Solutions of Hydroxyl-Functionalized Ionic Liquids: Molecular Dynamics Studies

“…20,22 There have been several computational studies on aqueous solutions of alkylimidazolium ionic liquids without any functionalization. [23][24][25][26][27] Even though few computational studies are reported on the thermodynamic and structural properties of HFILs in pure liquid form, [28][29][30] to the best of our knowledge, there have been no reports of computational studies on the solution structure of HFILs in water. In the present study, we have investigated the atomic-level details of the effect of the presence of a hydroxyl group attached to one of the two alkyl chains in dialkylimidazolium based ILs, on the bulk solution structure.…”