Ionic liquids as solvents

Because of their potential for easy recycle and low catalyst losses, Pd- 

From reviewing much of the literature it is easy to conclude that ionic liquids are excellent solvents for catalysts and reagents but not for products, which is obviously not the case. Whilst some products can be decanted from the liquid and others can be recovered by distillation, there are many useful reactions in which removal of the product (or residual reactants) from the ionic liquid is challenging. Extraction with an organic solvent, or even water, would reduce the overall eco-efficiency. Initial 

Before leaving ionic liquids it is worth mentioning their potential value in separation processes. Organic solvents are frequently used in multiphase extraction processes and pose the same problems in terms of VOC containment and recovery as they do in syntheses, hence ionic liquids could offer a more benign alternative. Interesting applications along this line which have been studied include separation of spent nuclear fuel from other nuclear waste and extraction of the antibiotic erythromycin-A. 

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Why use Ionic Liquids as Solvents for Transition Metal Catalysis ... 

Ionic liquid as solvent and ligand/ligand precursor... 

Although a great deal of excitement has surrounded the use of ionic liquids as solvents for organic synthesis, the rational synthesis of inorganic and organometallic compounds in ionic liquids has remained largely unexplored. 

Some halogenometalate species have been observed to have formed spontaneously during spectroelectrochemical studies in ionic liquids. For example, [MoCl ] (which is hydrolyzed in water, is coordinated by solvent in polar solvents, and has salts that are insoluble in non-polar solvents) can only be observed in basic (X(A1C13) < 0.5 chloroaluminate ionic liquids [1]. FFowever, this work has been directed at the measurement of electrochemical data, rather than exploitation of the ionic liquids as solvents for synthesis [2]. It has been shown that the tetrachloroa-luminate ion will act as a bidentate ligand in acidic X(A1C13) > 0.5 chloroaluminate ionic liquids, forming [M(AlCl4)3] ions [3]. This was also the result of the spontaneous formation of the complexes, rather than a deliberate attempt to synthesize them. 

Giirtler and Jautelat of Bayer AG have protected methods that use chloroalumi-nate(III) ionic liquids as solvents for both cyclization and polymerization reactions of acyclic dienes [52]. They employed the neutral ionic liquid [EMIM][G1-A1G13]... 

The controlled synthesis of polymers, as opposed to their undesired formation, is an area that has not received much academic interest. Most interest to date has been commercial, and focused on a narrow area the use ofchloroaluminate(III) ionic liquids for cationic polymerization reactions. The lack of publications in the area, together with the lack of detailed and useful synthetic information in the patent literature, places hurdles in front of those with limited loiowledge of ionic liquid technology who wish to employ it for polymerization studies. The expanding interest in ionic liquids as solvents for synthesis, most notably for the synthesis of discrete organic molecules, should stimulate interest in their use for polymer science. 

Ionic liquids as solvents for extraction Ionic liquid/aqueous Rogers et al. Dietz et al. Dai et al. 12, 13, 14, 15 16 17... 

In this manuscript, we will chronicle the discoveiy and development of these non-alkyl halide containing processes for the rhodium catalyzed carbonylation of ethylene to propionic acid and methanol to acetic acid when using ionic liquids as solvent. 

Hydroxycoumarins and 4-hydroxyquinolinones have also been applied as 1,3-dicarbonyl compounds. Using these compounds, Raghunathan and coworkers prepared pyrano[3,2-c]coumarins [387] and pyranoquinolinones [388] under traditional conditions, while the group of Yadav synthesized similar pyrano[3,2-c]coumarins employing ionic liquids as solvents [389]. 

The advantages of using ionic liquids as solvents for Diels-Alder reactions are exemplified by the scandium triflate catalysed reactions [14] in [bmim][PFg], [bmim][SbF6] and [bmim][OTf] for the reaction shown in Scheme 7.6. Whilst the nature of the anion seems to have little effect, all these solvents give rate enhancements for a range of Diels-Alder reactions compared to when the reactions are carried out in dichloromethane (DCM). Also, the selectivity towards the endo product is higher than in conventional solvents. As well as the enhanced rates and selectivities, the products can also be removed by extraction with diethyl ether and the ionic liquid and catalyst can immediately be reused. Experiments... 

Also the use of moisture stable ionic liquids as solvents in the Diels-Alder reaction has been carried out, and in all examples an enhanced reaction rate was observed [182,183]. The application of pyridinium-based ionic liquids allowed the utilization of isoprene as diene [184]. The chiral ionic liquid [bmim][L-lactate] was used as a solvent and accelerated the reaction of cyclopentadiene and ethyl acrylate, however, no enantiomeric excess was observed [183]. In addition several amino acid based ionic liquids have been recently tested in the Diels-Alder reaction. Similar exo. endo ratios were found but the product was obtained as racemate. The ionic liquids were prepared by the addition of equimolar amounts of HNO3 to the amino acids [185]. Furthermore, an enantiopure imidazolium salt incorporating a camphor motive was tested in the Diels-Alder reaction. No enantiomeric excess was found [186]. 

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