Ionic liquid phases

The ionic liquid process has a number of advantages over traditional cationic polymerization processes such as the Cosden process, which employs a liquid-phase aluminium(III) chloride catalyst to polymerize butene feedstocks [30]. The separation and removal of the product from the ionic liquid phase as the reaction proceeds allows the polymer to be obtained simply and in a highly pure state. Indeed, the polymer contains so little of the ionic liquid that an aqueous wash step can be dispensed with. This separation also means that further reaction (e.g., isomerization) of the polymer s unsaturated ot-terminus is minimized. In addition to the ease of isolation of the desired product, the ionic liquid is not destroyed by any aqueous washing procedure and so can be reused in subsequent polymerization reactions, resulting in a reduction of operating costs. The ionic liquid technology does not require massive capital investment and is reported to be easily retrofitted to existing Cosden process plants. 

Transfer from an Aqueous/Organic Phase to the Ionic Liquid Phase... 

Grafted Ionic Liquid-Phase-Supported Synthesis... 

Scheme 7.90 Preparation of polyethylene glycol-ionic liquid phases.

In a related study, the group of Bazureau applied their polyethylene glycol-grafted ionic liquid phases (ILPs) to the preparation of 2-thioxotetrahydropyrimidinones [105], After the initial formation of acrylate-bound ILPs utilizing acryloyl chloride in refluxing dichloromethane, several primary amines were attached in a Michael addi-... 

Previous work [111] by our group has demonstrated that RTIL-catalyzed 1,3-dipolar cycloaddition under the action of microwave irradiation leads to dramatically shorter reaction times with better yields of isolated products. We have recently investigated the reactivity of the formyl group covalently grafted on the ionic liquid phase 75 in the Knoevenagel reaction with malonic derivatives 76 [112], as shown in Scheme 8.76. 

Scheme 12.19 Ionic liquid-phase supported synthesis performed with microwave irradiation.

Knoevenagel Reactions on a Grafted Ionic Liquid Phase 289... 

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 ... 

It is important to note that with the phosphinocobaltocenium ligand cdpp the reaction took place almost exclusively in the ionic liquid phase (ca. 0.5% of the Rh was found in the product layer after reaction). The catalyst phase was separated from the product by decantation. Moreover, the recovered ionic catalyst solution could be reused at least once more with similar reactivity to that in the original run. 

Rhodium Catalysed Hydroformylation Using Supported Ionic Liquid Phase SILP) Catalysis... 

The term Supported Ionic Liquid Phase (SILP) catalysis has recently been introduced into the literature to describe the heterogenisation of a homogeneous catalyst system by confining an ionic liquid solution of catalytically active complexes on a solid support [68], In comparison to the conventional liquid-liquid biphasic catalysis in organic-ionic liquid mixtures, the concept of SILP-catalysis offers very efficient use of the ionic liquid. Figure 7.10 exemplifies the concept for the Rh-catalysed hydroformylation. 

Figure 7.10. Supported ionic liquid phase (SILP) catalysis exemplified for the Rh-catalysed hydroformylation reaction...

Two ways of ionic liquid immobilisation have been applied so far a) the approach in which part of the ionic liquid phase is fixed to a support by chemical bonds between either the cation or the anion of the ionic liquid and the support and b) the impregnation approach in which physisorption fixes the ionic liquid onto the support. 

Scheme 7.7. Preparation of surface anchored ionic liquid phases...

BMIM][PF6], while the corresponding sodium salt only dissolved in the [BMIM][BF4] The resulting acetonitrile solutions were combined with the ionic liquid phase (25 wt % loading) and added to the support. After the solvent was removed under reduced pressure, a slightly yellow-coloured powder was obtained. 

Supported aqueous phase (Chapter 3, Section 3.6, Chapter 5, Section 5.2.5) and supported ionic liquid phase catalysts, Chapter 7, Section 7.3) are probably not suitable for use with higher alkenes because the liquid feed slowly dissolves some of the water or ionic liquid changing the nature of the catalyst and leading to catalyst leaching. 

A rather new concept for biphasic reactions with ionic liquids is the supported ionic liquid phase (SILP) concept [115]. The SILP catalyst consists of a dissolved homogeneous catalyst in ionic liquid, which covers a highly porous support material (Fig. 41.13). Based on the surface area of the solid support and the amount of the ionic liquid medium, an average ionic liquid layer thickness of between 2 and 10 A can be estimated. This means that the mass transfer limitations in the fluid/ionic liquid system are greatly reduced. Furthermore, the amount of ionic liquid required in these systems is very small, and the reaction can be carried in classical fixed-bed reactors. 

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