Preparation Methods for Supported Ionic Liquids

Commercially available siHca materials (e.g., Merck Silica 60 and 100) are the support of choice mainly because of practical reasons such as favorable particle size distribution for apphcation in bench-top reactors, while other inorganic supports (AljOj, Ti02, Zr02, etc.) are used less frequently. These materials are resorted to when stability at high pH values is necessary. Other catalyst support materials such as carbon nanofibers [8], membranes [9], and porous polymers [10] have been used as well, albeit sparingly. In an elegant example, Virtanen et al. [11] immobilized an IL on an activated carbon doth. 

A number of synthetic methodologies have been developed in order to synthesize SILP and SCILL-type materials. The simplest of these methods rehes on physisorp-tion in order to generate the material. Various techniques have been developed to disperse the IL evenly onto the supporf s surface. 

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A simple and efficient method for the preparation of a-diazo- i-hydroxy esters by the condensation of aldehydes with ethyl diazoacetate using chloromethy-lated polystyrene SIL as a heterogeneous catalyst in water was developed [66]. Moderate to excellent yields of the corresponding a-diazo-jl-hydroxy esters were obtained. The catalyst was separated by filtration and reused in five consecutive cycles without any appreciable loss of activity. Later MacMillan s imidazolidinone was noncovalently immobihzed in the pores of siHca gel with the aid of IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (Mac-SILC) (SILC, supported ionic liquid catalyst) [67]. The Mac-SILC as an SIL catalyst was utilized for the enantioselective Diels-Alder reaction of cyclopentadiene and cinnamaldehyde. The Mac-SILC was more active, especially to an electron-rich dienophile, than its homogeneous counterparts, and the reaction could proceed under mild conditions. 

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,... 

These materials are prepared by the covalent attachment of ionic hquids to the support surface or by simple deposition of the ionic liquid phases containing catalytically active species on the surface of the support (usually silica-based or polymeric materials including membranes). In various cases, the procedure involves the simple dissolution of a sulfonated phosphine-modified rhodium catalyst into a supported ionic liquid, while the alkene constitutes the organic phase. This method reduces the amount of ionic liquid and allows for a facUe and efficient separation of products from catalyst. In comparison to traditional biphasic systems, higher catalytic activity and lower metal leaching can be obtained by appropriately tuning the experimental conditions [35—41]. 

Chapters 1 and 2 have been reorganised and updated in line with recent developments. A new chapter on the Future of Purification has been added. It outlines developments in syntheses on solid supports, combinatorial chemistry as well as the use of ionic liquids for chemical reactions and reactions in fluorous media. These technologies are becoming increasingly useful and popular so much so that many future commercially available substances will most probably be prepared using these procedures. Consequently, a knowledge of their basic principles will be helpful in many purification methods of the future. 

The chloroaluminate catalysts prepared according to method 2 show even higher activity in Friedel-Crafts reactions. This can be explained by the fact that here an ionic liquid is simulated on the surface of the support. The hydroxyl groups on the surface of the support, which would otherwise react with AICI3 are now used for the grafting of the organic cation. As shown in Figure 2, this is supported by NMR data t9,10l... 

A series of supported chiral VO(salen) complexes anchored on silica, single-wall carbon nanotube, achvated carbon or ionic liquids have been prepared through the simple methods based on the addition of mercapto groups to terminal C=C double bonds (Scheme 7.17) [58]. The four recoverable catalysts and the standard VO(salen) complex 37 were tested for the enantioselechve cyanosilylation of benzaldehyde using trimethylsilyl cyanide (Table 7.9). It should be noted that the ionic liquid-supported IL-VO(salen) showed the highest catalyhc achvity, though the ee-value was considerably reduced compared to the soluble 37 in [bmim][PF6] (entries 4 and 5). 

Different methods for the preparation of Novel Lewis-Acid Catalysts (NLACs) consisting of ionic liquids immobilised on mesoporous support materials are presented. The focus will be placed on materials bound to the carrier via the organic cation of the ionic liquid, either by grafting or by the preparation of organically modified HMS. After addition of aluminium(III)chloride the materials were used as catalysts e.g. in Friedel-Crafts alkylations, in which they displayed high activities and selectivities. 

Imidazolium-styrene copolymers were prepared by copolymerization of 1-vi-nyl-3-butylimidazolinm-based ionic liquids ([VBImJX, X=C1 , BF ", and PFg) with styrene, which were used as polymeric supports to immobilize Pd(OAc)2 using a method of alcohol reduction [22]. It was demonstrated that Pd existed in the form of Pd nanoparticles (NPs) on these imidazolium-styrene copolymers. Using the [VBIm]Cl-styiene copolymer as a support, Pd NPs of less than 6 nm were formed, which was particularly interesting, as usually only a Pd carbene complex was formed when Pd(OAc)2 was treated with 1,3-dialkyimidazolium ionic liquids containing a halide anion. The copolymer-supported Pd catalysts were found to be efficient and reusable catalysts for the Heck reaction in water in the absence of a phosphine ligand and phase-transfer catalyst. 

Geraldine Merle, A. C. de Ven, E. V. Nijmeijer, K., An easy method for the preparation of anion exchange membranes Graft-polymerization of ionic liquids in porous supports. Journal of Applied Polymer Science 2013, 129, 1143-1150. 

The field of liquid chromatography is well established, and reliable methods have been developed for analytical and preparative separations. Column miniaturization improves performance for analytical separations. Numerous stationary phases have been developed to separate analytes based on a wide variety of molecular properties including hydrophobicity, ionic interactions, and molecular size. Mobile-phase modifiers can be used to aid in the niinumzation of unwanted interactions with the solid support. Although the field is well established, current research continues to improve separations for both microscale analytical and larger preparative separations. Recent publications will be highlighted that demonstrate the developments toward integrating HPLC components and separation techniques onto microfabricated devices. 

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