Nonaqueous ionic liquids

The strategy of using two phases, one of which is an aqueous phase, has now been extended to fluorous . systems where perfluorinated solvents are used which are immiscible with many organic reactants nonaqueous ionic liquids have also been considered. Thus, toluene and fluorosolvents form two phases at room temperature but are soluble at 64 °C, and therefore,. solvent separation becomes easy (Klement et ai, 1997). For hydrogenation and oxo reactions, however, these systems are unlikely to compete with two-phase systems involving an aqueous pha.se. Recent work of Richier et al. (2000) refers to high rates of hydrogenation of alkenes with fluoro versions of Wilkinson s catalyst. De Wolf et al. (1999) have discussed the application and potential of fluorous phase separation techniques for soluble catalysts. 

Ionic liquids are also sometimes referred to as molten salts, nonaqueous ionic liquids (NAILs) or room temperature ionic liquids, and all of these names are entirely valid. The term molten salt is now used less frequently, and generally... 

The major problem associated with aqueous catalysis is the limited and often very low solubility of certain organic reactants in water. Much work is needed to find practical solutions for these hydrophobic reactants. Possibilities deserving further attention include the application of fluorous biphasic catalysis or nonaqueous ionic liquid catalysis. The potential of organic reactions compatible with or even promoted by water is not yet fully exploited. 

At present, ionic liquids, also known as room-temperature ionic liquids, nonaqueous ionic liquids, molten salts, liquid organic salts, and fused salts, are considered to be the new generation of solvents. In chemical abstracts, they can be found under the headings ionic liquid or liquids ionic. Publications on ionic liquids are increasing in number. 

Nonaqueous ionic liquids have been used for hydrogenation of arenes and other liquids [67, 68]. By selecting a stable catalyst that is soluble in the ionic phase, purification of products began by separating the liquid products from the ionic liquid containing the catalyst. Because of the expense of nonaqueous ionic liquids, the ability to recover and reuse these materials will be important to control costs if they are to be used on scale. 

Chauvin, Y. Olivier - Bourbigou, H., Nonaqueous Ionic Liquids as Reaction Solvents. CHEMTECH, 1995, 25(9), 26. 

Chauvin Y, Olivier-Bourbigou H (1995) Nonaqueous ionic liquids as reaction solvents. Chem Tech 25 26-30... 

Non-aqueous approaches toward two-phase hydroformylation have been demonstrated by Horvath et al. [16] with the use of a fluorous biphasic system containing a rhodium catalyst bearing partially fluorinated ponytail ligands, and Olivier and Chauvin [17] with TPPMS and TPPTS dissolved in nonaqueous ionic liquids (see Sections 7.2 and 7.3). 

The technique of aqueous catalytic reactions has had such an impact on the field of more general two-phase reactions that scientists have now also proposed and tested other solutions. Fluorous systems (FBS, perfluorinated solvents cf. Section 7.2) and nonaqueous ionic liquids (NAILs, molten salts cf. Section 7.3) meet the demand for rapid separation of catalyst and product phases and, owing to the thermoreversibility of their phase behavior, have advantages in the homogeneous reaction and the heterogeneous separation. However, it is safe to predict that the specially tailored ligands necessary for these technologies will be too expensive for normal applications. Compared to the cheap and ubiquitous solvent water, with its unique combination of properties (cf. Table 1), other solvents may well remain of little importance, at least for industrial applications. Other ideas are mentioned in Section 7.6. 

Last but not least, the success of aqueous-phase catalysis has drawn the interest of the homogeneous-catalysis community to other biphasic possibilities such as or-ganic/organic separations, fluorous phases, nonaqueous ionic liquids, supercritical solvents, amphiphilic compounds, or water-soluble, polymer-bound catalysts. As in the field of aqueous-phase catalysis, the first textbooks on these developments have been published, not to mention Job s book on Aqueous Organometallic Catalysis which followed three years after our own publication and which put the spotlight on Job s special merits as one of the pioneers in aqueous biphasic catalysis. Up to now, most of the alternatives mentioned are only in a state of intensive development (except for one industrial realization that of Swan/Chematur for hydrogenations in scC02 [2]) but other pilot plant adaptations and even technical operations may be expected in the near future. 

Nonaqueous Ionic Liquids (ILs, NAILs) (H. Olivier-Bourbigou) 655... 

As far as nonaqueous ionic liquids (more shortly but erroneously also called ionic liquids , or ILs) are concerned, they were just considered as potential alternatives for multiphase reactions and were mentioned in forward-looking chapters of books dealing with this area, while water was already in key transition metal-catalyzed processes see, for example, [6a, 17, 24, 29] (cf also Chapter 2). Ionic Hquids also have recently attracted much interest it is now possible to buy them, which probably promotes their use, and there are more and more physical data available for these solvents. The range of reactions that have been described in IL media is probably wider than in SCCO2 (and surely wider than in fiuorous Hquids). But it would not be realistic to say that all catalyzed reactions can be transferred to ionic Hquids with benefits. The advantages of using ILs have been weH described for some reactions which will be reported later in this book and just a few of them have been run on micro-pilot or pilot plant scale. 

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