Surface-active ionic liquids materials

A second and somewhat simpler approach that can be applied to obtain supported ionic liquid catalyst systems involves the treatment of a solid, porous carrier material by a substantial amount of a catalytically active ionic liquid, allowing the reaction to take place in the dispersed phase. In these systems the ionic liquid phase can itself act as the catalytically active component or it may contain other dissolved compounds or reagents, for example, transition metal complexes, which function as the catalytically active species (i.e. generating SILP catalysts). Importantly, the ionic liquid catalyst phase in these SILP catalyst systems are confined to the carrier surface only by weak van der Waals interactions and capillary forces interacting in the pores of the support. In special cases electrostatic attachment of the ionic liquid phase may also be applied. Usually, the catalysts are prepared by traditional impregnation techniques, where a volatile solvent is used initially to reduce viscosity for the impregnation process and is finally removed by evaporation leaving the ionic catalyst solution dispersed on the support. 

Supporting ionic liquids in the pores of solid materials offers the advantage of high surface areas between the reactant phase and that containing the supported liquid catalyst. This approach is particularly useful for reactants with less than desired solubility in the bulk liquid phase. Another incentive for using such catalysts is that they can be used in continuous processes with fixed-bed reactors (26S). The use of an ionic liquid in the supported phase in addition to an active catalyst can help to improve product selectivity, with the benefit being similar to what was shown for biphasic systems. However, care has to be taken to avoid leaching the supported liquids, particularly when the reactants are concentrated in a liquid phase. 

In summary, the Kobayashi solution to the development of a SILP for catalytic applications in liquid biphasic conditions implies the adoption of a more robust anchoring technique of the catalytically active species to the solid support and of a IL/solvent pair as far as possible in terms of mutual solubility, namely water and [dbim][SbF6]. The role of the IL impregnated on the solid support is that of creating a hydrophobic environment on the surface of the silica material where the catalyst, ionically bound to the organic spacer, exerts its role promoting the desired reaction. Since the catalyst is easily separated from water, the system could be easily optimised for recycle. 

Supported ionic liquid catalysis is one of the main examples of SLPC adopted [120] to take advantage of ionic liquid properties without the drawbacks evidenced in Section 2.3.6. The viability of this concept has been confirmed by several studies that have successfully confined various ionic phases to the surface of support materials and explored their potential catalytic applications. Although most of the evaluated supports were silica based, several studies have focused on polymeric materials, including membranes. These materials were prepared by using two different immobilization approaches. The first involves the covalent attachment of ionic liquids to the support surface whereas the second simply deposits the ionic liquid phases containing catalytically active species on the surface of the support. 

On the other hand, polymer-supported task-specific ILs in which the imidazolium cations couple L-proline via the ionic-pair interaction have also been synthesized and applied in metal scavenging and heterogeneous catalysis. The novel materials displayed considerable ability for metal scavenging onto their surface [e.g., Cul, Pd(OAc)2, Pd and IrCh] without the aid of a non-immo-bilized ionic liquid. Moreover, attempts to use these materials in the Cul-cat-alyzed N-arylation of nitrogen-containing heterocycles revealed that these systems are characterized by a much higher activity and recycling ability than... 

Tbe basis Tor (be separation by bubbles and foam (adsorptive bubble separalion) is the difference in the surface activities of the various materials present in the solution or the suspension of interest. The material mey be cellular or colloidal substances, crystals, minerals, ionic or molecular compounds, precipitates, proteins, or bactemi, but in any case it must be surface active at the air-liquid interface (Fig. 17.1-1) These surface-active meterials tend to attach preferentially to (he air-liquid interfaces of the bubbles or fonme, As the bobbies or fonms rise throngh the columa or pool oftiquid, the attached material is removed. When this combination reachas the surface, the meierial can be removed in the relatively smell volume or collapsed foam or surface "scum. ... 

This modern method, commonly known supported ionic liquid phase catalysis, is based on the simple chemical attachment of ILs to the support surface or the simple deposition of the catalytically active speciesmain idea for the preparation of these alternative materials is to avoid or at least decrease the deactivation of the catalyst after reactions as well as to minimize the amount of IL used in each process. In addition, the SILP method provides some advantages compared to other catalytic systems. For example, SILP catalytic systems offer the elimination/reduction of mass transfer limitations and give access to more robust/recyclable catalysts with an easy separation after reactions. In other words,... 

Seki, S. Kobayashi, Y Miyashiro, H. Ohno, Y Usami, A. Mita Y Watanabe, M. Terada, N., Highly reversible lithium metal secondary battery using a room temperature ionic liquid/ lithium salt mixture and a surface-coated cathode active material, Chem. Commun., 2006, 544-545. 

The link between the self-organisation of ionic liquids and the synthesis of nanostructured materials was established in a series of contributions. Dupont discussed the effect of the three-dimensional nanoscale arrangement of ionic liquids on the production and stabilisation of transition metal nanoparticles [65]. As shown also by Santini and co-workers, metal nanoparticles of several metals can be synthesised in situ in ionic liquids, leading to narrow size distributions and spontaneously stable suspensions without the need for additional surface-active agents [66]. 

The formation of particles in polymer colloids ordinarily is accomplished by the free radical polymerization of an organic monomer in a liquid which is a non-solvent (diluent) for the polymer. A surface active material, such as a soap or other amphipathic molecule, is usually added to stabilize the colloidal particles as they are formed. The particle size distribution varies from very narrow to extremely broad depending primarily upon the solubility of the monomer in the diluent, the stabilizer concentration and the ionic strength. 

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