Thermodynamics of Ionic Liquid Cosolvent Mixtures Using Molecular Dynamics Simulation: 1-Ethyl-3-methylimidazolium Acetate

Abstract

Molecular dynamics (MD) simulations were conducted to calculate the binary mixture properties (excess molar heats and volumes) of 1-ethyl-3-methylimidazolium acetate [EMIM][Ac] with six polar covalent molecules (acetic acid, acetone, chloroform, dimethyl sulfoxide, isopropyl alcohol, and methanol) over the entire composition range. All of the binary mixtures of [EMIM][Ac] with cosolvents reported negative volumes of mixing over the entire composition range while releasing heat (exothermic heats of mixing), except for the acetone mixture, which had miscibility issues at higher concentrations (x acetone ≥ 0.6). These results were attributed to the nature, size, and structure of the molecules as well as the nature of the interaction between the mixture components. Further, aggregation of the ionic liquid (IL) at higher concentrations of the cosolvent added to the above observed effects, except for the acetic acid mixture. These results have been interpreted in terms of hydrogen-bonding and intermolecular interactions among the binary mixture components via radial distribution functions. The results showed that hydrogen-bonding interactions between the IL and cosolvent play a major role in the volumetric and energetic properties of the mixtures. In the case of the acetic acid mixture, aggregation of acetic acid molecules is reported at lower concentrations of acetic acid (x acetic acid = 0.1), while [EMIM][Ac] molecules were completely solvated at higher concentrations of acetic acid (x acetic acid = 0.9). Mixtures of [EMIM][Ac] with methanol showed isolated methanol molecules at lower concentrations of methanol (x methanol = 0.1), whereas IL ions aggregated to form pairs at higher concentrations of methanol.

The Dependence of Ionic Liquid Solvent Effects on the Nucleophilic Heteroatom in SNAr Reactions. Highlighting the Potential for Control of Selectivity

“…Whilst the origin of this change is not clear, it both greatly simplified analysis and suggests that there is a distinct difference in solvent interactions when using 7 compared to [Bmim][N(SO 2 CF 3 ) 2 ] 6 . Such observations are not unusual for S N Ar reactions; it has been well documented that changing the nature of the solvent can affect the observed reaction outcome by changing, for example, the rate determining step ,…”

Use of Nonideality Parameters for the Analysis of the Thermodynamic Properties of Binary Mixtures

“…In many instances, variation of a thermodynamic property with the composition of a binary mixture is recorded in relative values, as excess differences from the ideally expected values. Thus, plots of viscosities, 1,9 excess molar volumes, 4,6,8,19,20 isentropic compressibilities, 4,19,20 refractive indices, 19,21 or enthalpies 5,20,22 are encountered, where the experimental data are fitted with equations derived from different models, with variable success. Such plots are not amenable to an analysis based on their NIIs, since this index was defined as a ratio between two areas, NII = A 1 /A 2 (see Figure 1), and A 2 = 0 in these excess plots.…”

The Coiling Effect in Ether Ionic Liquids: Exploiting Acetate as a Probe for Transport Properties and Microenvironment Analysis

“…This preferential interaction in the bidentate form corroborates previous observations in mixtures of ILs with imidazolium cations in the presence of water or methanol, where acetate favors concurrent interactions with solvent molecules and C(2)−H of the imidazolium cation. 47,68 In contrast, the acetate anion predominantly interacts in a monodentate manner in dialkylpyrrolidinium ILs, which do not have acidic hydrogens. However, an increase in water content within the mixture promotes a bidentate acetate coordination.…”