Ionic liquids models

Scheme 7.2 Preparation of /V-methylimidazolium-based ionic liquids - model reaction of case study 2.

The model is certainly complex, but perhaps no more so than previous ionic liquid models described in Sections 5.5.1 and 5.5.2. The initial experience (Selleby 1996) suggests that the number of terms needed to describe a ternary system such as Fe-Mn-S is quite similar for both ionic two-sublattice liquid and associate models (see next section). The modelling of ionic liquids is, in the main, complex and the advantages of the various techniques can only become apparent as they become more commonly used. 

At the time the CLAP force field was proposed, many of the existing ionic liquid models used to borrow parameters from different, not always compatible, sources. For instance, it was common to see parameterizations of the cation and of the anion using information from different force fields [10,11,13], In the development of the CLAP force-field, in order to respect internal consistency, ab initio calculations were used extensively to provide essential data for the development of an internally consistent force field. This included molecular geometry optimization and the description of electron density using extended basis sets, leading to the evaluation of force field parameters such as torsion energy profiles and electrostatic charges on the interaction centers. 

Tay] carried out a reahstic thermodynamic assessment using an ionic liquid model, a sublattice model for the solid phases, with 4, 3 and 2 sublattices for flie spinel, corundum and wuestite phases, respectively. Thermodynamic models were also developed for flie oxidation of alloys in air [2004Gon], and for the desoxidation equilibria in molten steels [2004Jun]. 

Abildskov, J., M. D. Ellegaard, and J. P. O Connell. 2010a. Densities and isothermal compressibilities of ionic liquids-modeling and application. Fluid Phase Equilibria. 295, 215. Abildskov, J., M. D. Ellegaard, and J. P. O Connell. 2010b. Phase behavior of mixtures of ionic liquids and organic solvents. Journal of Supercritical Fluids. 55, 833. 

IONIC LIQUID MODELLING EIGENSCHAFTEN/SEISHITSU/PROPERTIES... 

A well-known effect of water impurities in ionic liquids is the viscosity decrease. " However, also ionic liquids were reported, in which water impurities induces gelation. Spohr and Patey have shown with ionic liquid model systems that water tends to replace the counter ions from the ion solvation shell in ionic liquids with small ion size disparity, leading to a faster diffusion of the lighter ion-water clusters. However, water can increase viscosity of ionic liquids if the ion size disparity is too large, or if strong directional ion pairs are found. Spohr and Patey attributed this behavior to extended water-anion chains and strongly bound water-anion-cation clusters. A classical molecular dynamics study by Raju and Balasubramanian observed that the anion diffuse faster than the cation in water ionic liquid mixtures in contrast to neat ionic liquids. The larger... 

In this chapter, we review the achievements in the area of extractions with boron extractants accomplished in the last five years. The literature on extraction with cobalt bis(dicarbollide) and synergist, the UNEX process, and new boron-selective extractants is ample, and other connected science, such as ion-selective electrodes with boron anions, boron anion room-temperature ionic liquids, modeling of the mechanism of the extraction, IR studies on extracts, the state of CD in water solutions, or a description of some of the new ideas on solvation, resolvation theory, and so on, could not be covered here. 

The liquid is in most cases treated as a substitutional solution. For liquids with very strong short range order the associate model [78Som] or the ionic liquid model [85Hil] has sometimes been used. 

Gillan M 1980 Upper bound on the free energy of the restricted primitive model for ionic liquids Mol. Phys. 41 75... 

In a series of papers published throughout the 1980s, Colin Poole and his co-workers investigated the solvation properties of a wide range of alkylammonium and, to a lesser extent, phosphonium salts. Parameters such as McReynolds phase constants were calculated by using the ionic liquids as stationary phases for gas chromatography and analysis of the retention of a variety of probe compounds. However, these analyses were found to be unsatisfactory and were abandoned in favour of an analysis that used Abraham s solvation parameter model [5]. 

It can easily be shown that the value of K" is inversely proportional to the value of K and that K is dependent on both the cation and the anion of the ionic liquid. Eience, it is entirely consistent with this model that the difference made by changing the anion should depend on the hydrogen bond acidity of the cation. 

Bowron et al. [11] have performed neutron diffraction experiments on 1,3-dimethylimidazolium chloride ([MMIM]C1) in order to model the imidazolium room-temperature ionic liquids. The total structure factors, E(Q), for five 1,3-dimethylimidazolium chloride melts - fully probated, fully deuterated, a 1 1 fully deuterated/fully probated mixture, ring deuterated only, and side chain deuterated only - were measured. Figure 4.1-4 shows the probability distribution of chloride around a central imidazolium cation as determined by modeling of the neutron data. 

The measurement of correlation times in molten salts and ionic liquids has recently been reviewed [11] (for more recent references refer to Carper et al. [12]). We have measured the spin-lattice relaxation rates l/Tj and nuclear Overhauser factors p in temperature ranges in and outside the extreme narrowing region for the neat ionic liquid [BMIM][PFg], in order to observe the temperature dependence of the spectral density. Subsequently, the models for the description of the reorientation-al dynamics introduced in the theoretical section (Section 4.5.3) were fitted to the experimental relaxation data. The nuclei of the aliphatic chains can be assumed to relax only through the dipolar mechanism. This is in contrast to the aromatic nuclei, which can also relax to some extent through the chemical-shift anisotropy mechanism. The latter mechanism has to be taken into account to fit the models to the experimental relaxation data (cf [1] or [3] for more details). Preliminary results are shown in Figures 4.5-1 and 4.5-2, together with the curves for the fitted functions. 

The highly detailed results obtained for the neat ionic liquid [BMIM][PFg] clearly demonstrate the potential of this method for determination of molecular reorienta-tional dynamics in ionic liquids. Further studies should combine the results for the reorientational dynamics with viscosity data in order to compare experimental correlation times with correlation times calculated from hydrodynamic models (cf [14]). It should thus be possible to draw conclusions about the intermolecular structure and interactions in ionic liquids and about the molecular basis of specific properties of ionic liquids. 

In an attempt to study the behavior and chemistry of coal in ionic liquids, 1,2-diphenylethane was chosen as a model compound and its reaction in acidic pyri-dinium chloroaluminate(III) melts ([PyHjCl/AlCb was investigated [69]. At 40 °C, 1,2-diphenylethane undergoes a series of alkylation and dealkylation reactions to give a mixture of products. Some of the products are shown in Scheme 5.1-40. Newman also investigated the reactions of 1,2-diphenylethane with acylating agents such as acetyl chloride or acetic anhydride in the pyridinium ionic liquid [70] and with alcohols such as isopropanol [71]. 

Murray, S.M., O Brien, R.A., Mattson, K.M., Ceccarelli, C., Sykora, R.E. and West, K.N. Jr. (2010) Fluid-mosaic model, homeoviscous adaptation, and ionic liquids dramatic lowering of the melting point by side-chain unsaturation. Angewandte Chemie International Edition, 49 (15), 2755-2758. 

In practical cases, it is the solute charges that are modeled explicitly, and treated as permanent source charges. In contrast, the whole solvent medium is usually treated as a continuum, without any explicit, permanent, source charges. (This is reasonable for a solvent made of small, neutral molecules ionic liquids would obviously need a different treatment.) Since there are no permanent charges in the solvent,... 

The first use of room temperature ionic liquids as potential novel soluble phases for combinatorial synthesis has recently been described. As model reaction the Knoevenagel condensation of salicyl aldehyde grafted on to an imidazolium-derived ionic liquid was studied under the action of microwave irradiation (Scheme 12.19) [66]. Reactions were performed without additional solvent in the presence of a basic catalyst, utilizing microwave irradiation in a designated monomode microwave reac-... 

Liquid-liquid multiphasic catalysis with the catalyst present in the ionic liquid phase relies on the transfer of organic substrates into the ionic liquid or reactions must occur at the phase boundary. One important parameter for the development of kinetic models (which are crucial for up-scaling and proper economic evaluation) is the location of the reaction. Does the reaction take place in the bulk of the liquid, in the diffusion layer or immediately at the surface of the ionic liquid droplets ... 

Temkin was the first to derive the ideal solution model for an ionic solution consisting of more than one sub-lattice [13]. An ionic solution, molten or solid, is considered as completely ionized and to consist of charged atoms anions and cations. These anions and cations are distributed on separate sub-lattices. There are strong Coulombic interactions between the ions, and in the solid state the positively charged cations are surrounded by negatively charged anions and vice versa. In the Temkin model, the local chemical order present in the solid state is assumed to be present also in the molten state, and an ionic liquid is considered using a quasi-lattice approach. If the different anions and the different cations have similar physical properties, it is assumed that the cations mix randomly at the cation sub-lattice and the anions randomly at the anion sub-lattice. 

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