Ionic liquids structural properties

Ionic Liquids Structure, Properties and Major Applications in Extraction/Reaction Technologf 1229... 

Quite recently, a series of N-alkyl substituted imidazolium salts has been evaluated for additive effects on the mesomorphic behavior and ensuing optical properties of HPC aqueous solutions, followed by characterization of the thermotropicity of novel cellulose derivatives with such an ionic liquid structure in the side-chains [193]. 

However, there are still some problans to be solved, since most information of ionic liquids are not well known up to now and most of works are only performed in laboratory. The relationships between the properties and the structure of ionic liquids are not well understood. Variafions in cafions and anions can produce a large number (10 ) of ionic liquids, and properties of ionic liquids depend on the structure of ions. 

A complementary study of steel/steel contacts (100Cr6) [47] used an oscillation wear and friction tester to screen ionic liquids in the boundary lubrication regime at 30, 100 and 170°C at 200 N load. Results are summarized as follows (i) some promising ionic liquids gave lower friction and wear at all temperatures, compared to reference lubricants, (ii) chemical structures of ionic liquids have a high impact on their physico-chemical as well as on tribological properties and (iii) careful selection of both cation and anion, as a tailor-made ionic liquid, enables adaptation of ionic liquid structures to specific applications. 

Nucleophilic substitution reactions in ionic liquids have recently been the subject of both synthetic [33] and kinetics and mechanistic studies [34]. Ionic liquids may be efficient promoting media for nucleophilic displacement reactions and important information about the ionic liquid properties has been obtained from the study of these reactions. The kinetic investigation of bimolecular substitution reactions of the halides on methyl p-nitrobenzenesulfonate, recently carried out by Wdton et al. [34] in several ionic media characterized by the same anion, [Tf2N] , and different cations ([BMIM]+, [BMMIMJ+ and [BMPY]+) or by the same cation, [BMIM] and different anions ([BF4] , [PFs] , [SbF ] and [Tf2N] ), has shovrathat the halides nucleophilicities depend on the ionic liquid structure (Scheme 5.1-7). 

As a consequence of these findings, the vapor pressure of an ionic liquid can no longer be considered to be zero. As, from a physicochemical perspective, all matter (even a stone ) has some vapor pressure, this former perception was questionable anyway. However, Rebelo s study also showed that the vapor pressure of ionic liquids is indeed negligible at near-ambient conditions. For applications under harsh temperature and high vacuum conditions, however, the vapor pressure of the applied ionic liquids will have some relevance and should be known. Thus, we expect that in the future the vapor pressure of ionic liquid structures will be determined experimentally and that these data will just add to the property and application profile of each specific ionic liquid. 

C. Chiappe, A. Sanzone, D. Mendola, F. Castighone, A. Famulari, G. Raos, A. Mele, Pyrazolium- versus imidazolium-based ionic liquids structure, dynamics and physicochemical properties, J. Phys. Chem. B 117 (2) (2013) 668—676. 

Lorbeer C, Cybinska J, Mudring AV (2011) Europium(in) fluoride nanoparticles from ionic liquids structural, morphological, and luminescent properties. Cryst Growth Des 11 1040-1048... 

The following discussion concerns the thermal liquidus ranges available in different ionic liquids, as functions of cation and anion structure and composition. In particular, those structural features of cation and anion that promote these properties (while providing other desirable, and sometimes conflicting characteristics of the liquid, such as low viscosity, chemical stability, etc.) and variations in liquidus ranges and stabilities are the focus of this chapter. 

In addition to the obvious structural information, vibrational spectra can also be obtained from both semi-empirical and ab initio calculations. Computer-generated IR and Raman spectra from ab initio calculations have already proved useful in the analysis of chloroaluminate ionic liquids [19]. Other useful information derived from quantum mechanical calculations include and chemical shifts, quadru-pole coupling constants, thermochemical properties, electron densities, bond energies, ionization potentials and electron affinities. As semiempirical and ab initio methods are improved over time, it is likely that investigators will come to consider theoretical calculations to be a routine procedure. 

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. 

Ionic liquids have been described as designer solvents [11]. Properties such as solubility, density, refractive index, and viscosity can be adjusted to suit requirements simply by making changes to the structure of either the anion, or the cation, or both [12, 13]. This degree of control can be of substantial benefit when carrying out solvent extractions or product separations, as the relative solubilities of the ionic and extraction phases can be adjusted to assist with the separation [14]. Also, separation of the products can be achieved by other means such as, distillation (usually under vacuum), steam distillation, and supercritical fluid extraction (CO2). 

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