Ionic immobilization

Immobilized ionic liquids Chloroaluminate ionic liquids on inorganic supports IGI, UK 2001 27... 

Immobilized ionic liquid-based sfafionary phases... 

Immobilized ionic liquid-based stationary phases for high-temperature separations... 

Figure 4.3 Scheme illustrating the development of immobilized ionic liquids by thermally induced free radical polymerization of vinyl-substituted imidazolium-based monocationic and dicationic monomers. 

Figure 4.4 Flow diagram for choosing the appropriate neat ionic liquid or immobilized ionic liquid composition for a particular analyte separation. Note that the most important characteristics for choosing the appropriate stationary phase are separation selectivity and thermal stability. Both of these properties can be effectively tuned and optimized by controlling the cation and anion combination.

Anderson, J.L., and Armstrong, D.W., Immobilized ionic liquids as high-selectivity/high-temperature/high stability gas chromatography stationary phases. Anal. Chem., 77, 6453-6462,2005. 

There is still another type of internal solid state reaction which we will discuss and it is electrochemical in nature. It occurs when an electrical current flows through a mixed conductor in which the point defect disorder changes in such a way that the transference of electronic charge carriers predominates in one part of the crystal, while the transference of ionic charge carriers predominates in another part of it. Obviously, in the transition zone (junction) a (electrochemical) solid state reaction must occur. It leads to an internal decomposition of the matrix crystal if the driving force (electric field) is sufficiently high. The immobile ionic component is internally precipitated, whereas the mobile ionic component is carried away in the form of electrically charged point defects from the internal reaction zone to one of the electrodes. 

The first polymer-supported reagents were derived from ion-exchange resins by immobilizing ionic reagents on macroporous polystyrene resins [5], This approach enables easy access to many reagents. For preparation, a... 

Lewis acids immobilized on ionic liquids have been used as the acid catalysts for the alkylation of phenols. The catalytic activities of the immobilized ionic liquids were found to be higher than those for the zeolites. Typically, ionic liquids such as butylmethyUmi-dazoUum halides are treated with AICI3 to give the ionic liquids with halogenoaluminates as the counter anions. They show enhanced Lewis acid character and promote predominantly C-alkylation of phenols over O-alkylation. The alkylation of phenol with dodecene, for example, in the presence of these immobilized ionic liquids results in up to 70% of C-alkylated products (ortho and para products) and 30% of O-alkylated product, comparable to zeolite catalysis (equation 23). The rates of alkylation of phenols are slower than those of arenes due to the complexation of the phenolic group with the Lewis acidic ionic liquids. At higher temperatures conversions of up to 99% could be achieved. 

The concept of immobilized ionic liquids entrapped, for instance, on the surface and pores of various porous solid materials (supported ionic liquid phase, SILP) is rapidly become an attractive alternative. In addition, the SILPs can also answer other important issues, such as the difficult procedures for product purification or IL recycling, some toxicity concerns and the problems for application in fixed-bed reactors, which should be addressed for future industrial scale-up. This new class of advanced materials shares the properties of true ILs and the advantages of a solid support, in some cases with an enhanced performance for the solid material. Nevertheless, a central question for the further development of this class of materials is to understand how much the microenvironment provided by the functional surfaces is similar or not to that imparted by ILs. Recent studies carried out using the fluorescence of pyrene to evaluate the polarities of a series of SILPs based on polymeric polystyrene networks reveal an increase in polarity of polymers, whereas the polymer functional surfaces essentially maintain the same polarity as the bulk ILs. However, this is surely not a simple task, in particular if we consider that the basic knowledge of pure ILs is still in its infancy, and we are just starting to understand the fundamentals of pure ILs when used as solvents. 

Table 2.6 The immobilized ionic liquids as the catalysts for eilkylation...

In the alkylation section, it was stated that the immobilized ionic liquids can combine the advantage of green media with solid support materials, which may enable the wide apphcation of precious ionic hquids by the reduchon of usage and also realize the sustainability of the chemical reaction process. The supported ionic hquids (SlLs) catalysts commonly employ the supports such as the macroporous polymer, metal oxide (SiO, AI2O3, etc.), zeohte, clay, and achve carbon, and after the immobilization of the ionic hquids, the ionic hquids still maintain their special solvent effect. Presently, the immobilized ionic hquids have been applied extensively to the alkylation, acylation, hydroformylation, oxidation, esterihcation, hydrolyza-tion, hydrogenahon, and other unit reactions this part of the chapter only discusses the application of immobilized ionic hquids to the acylahon. 

In addition, immobilized ionic liquids have been employed for the 0-acylation and A-acylation. Kara et al. have investigated the reactions that supported ionic liquids in Upase-catalyzed asymmetric acylation of 7-phenylethanol with vinyl acetate in the reaction temperature range of 25-60°C and found that the immobilized [EMlM][NTfJ can stabilize the lipase against inactivation and maintain good enantioselectivity [152]. Furthermore, Paun s group via grafting 7,5-dimethyl-5-(5-triethoxysilylpropyl)-imidazolium tetrafluoroborate or bis (trifluoromethyl)... 

For the application of the immobilized ionic liquids to the acylation (although the advantages are obvious, such as the simplification of the product isolation), the realization of the continuous reactions, the leaching of the ionic liquids, and the inactivation of the catalysts because of carbon distribution are still the problems urgently needed to be resolved. Therefore, the interaction of the ionic liquids with supports, the recovery of the supported catalysts, and so on need the in-depth and intensive research. 

Kumar P, Vermeiren W, Dath JP et al (2006) Production of alkylated gasoline using ionic hquids and immobilized ionic hquids. Appl Catal A Gen 304 131-141... 

The immobilization method was also found to have influence on the membrane stability. A comparative study of the preparation of SILMs by two different methods, under pressure and vacuum were reported by Hemandez-Femandez et al. [26]. They used the ionic liquids, [bmim+][Cl"], [bmim ][BF ], [bmim ][PF "] and [bmim llNTf ] as liquid phase supported on a nylon membrane. Small losses of ionic liquid were observed after 7 days of operation when the ionic liquid was immobilized under pressure in a diffusion cell using n-hexane/n-hexane as surrounding phases. However, the losses of IL were higher when immobilization was carried out under vacuum, especially with the most viscous ionic liquids ([bmim+] [PF ] and [bmim+][CT]). This behaviour was explained by the fact that the higher viscosity of ILs makes difflcult their penetration into the middle of the deeper pores of the membrane, and therefore, the ionic liquid was mainly immobilized on the most external layer of the membrane, and consequently, the immobilized ionic liquid is more easily removed during operation. 

Ion-exclusion chromatography is used for the separation of low molecular weight ions and some neutral substances by a combination of partition, adsorption and ion repulsion [159,428,477-479]. The stationary phase is a high capacity ion exchanger with the same type of immobilized ionic group as the sample ions. Permanent ions with the same charge as the stationary phase are repelled and can only explore the interparticle volume while neutral and partially ionized solutes are retained and separated by partition between the mobile phase trapped in the porous stationary phase and the streaming... 

Supported ionic liquid compositions are also a vivid field of research in which many companies tried to make their claims [88-90]. By immobilizing ionic liquids onto silica- or alumina-based carriers it is possible to obtain new Lewis acid catalysts with interesting characteristics. These are presently preferably used for alkylation and acylation reactions of aromatic compounds [91, 92] or isomerizations. Even the co-immobilization of ionic liquids with transition metal complexes [93] or Lewis acids [94] has been described, and it can be anticipated that this particular field offers many options for future catalyst development. 

Ion-exchange chromatography, used for ionic solutes, involves competition for solute ions between immobilized ionic sites on the stationary phase (e.g., ion-exchange resin) and liquid mobile phase. 

Hydrogen bonds A structural insight into ionic hquids 12CEJ2748. Immobilized ionic liquids in organic chemistry 12COC1680. 

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