Fluorous solvents, examples

Figure 3.4 Some examples of perfluoroalkyl-substituted molecules suitable for reactions in fluorous solvents...

Fluorous organometallic chemistry, examples, 1, 842 Fluorous solubles, in organometallic synthesis, 1, 81 Fluorous solvents, for hydroformylations, 11, 450 Fluorous tin hydrides, preparation and applications, 9, 346 Fluorovinyl groups, vinylic C-F bond activation, 1, 753 Fluoro vinyltitanocenes, synthesis, 4, 546 g tfZ-Fluorovinyltributylstannane, in carbonylative cross-coupling, 11,413... 

Examples of applying biphasic systems to catalyzed reactions, such as phase-transfer catalysis, overpower the stoichiometric reactions. In a typical catalytic biphasic system, one phase contains the catalyst, while the other phase contains the substrate. In some systems, the catalyst and substrates are in the same phase, while the product produced is transferred to the second phase. In a typical reaction, when the two phases are mixed during the reaction and after completion, the catalyst remains in one phase ready for recycling while the product can be isolated from the second phase. The most common solvent combination consists of an organic solvent combined with another immiscible solvent that, in most applications, is water. However, there are few examples of suitable water-soluble and stable catalysts, and therefore various applications are limited to some extent [192]. Immiscible solvents other than water are recently becoming more applicable in biphasic catalysis because of the better solubility and stability of various catalysts in such solvents. For example, ionic liquids and fluorous solvents have many successful applications in liquid-liquid... 

Finally, it should be noted that Lewis acids and bases can also be used in other non-conventional media, as described in Chapter 7, e.g. fluorous solvents, supercritical carbon dioxide and ionic liquids by designing the catalyst, e.g. for solubility in a fluorous solvent or an ionic liquid, to facilitate its recovery and reuse. For example, the use of the ionic liquid butylmethylimidazolium hydroxide, [bmim][OH], as both a catalyst and reaction medium for Michael additions (Fig. 2.45) has been recently reported [151]. 

Fluorous biphasic catalysis was pioneered by Horvath and Rabai [54, 55] who coined the term fluorous , by analogy with aqueous , to describe highly fluori-nated alkanes, ethers and tertiary amines. Such fluorous compounds differ markedly from the corresponding hydrocarbon molecules and are, consequently, immiscible with many common organic solvents at ambient temperature although they can become miscible at elevated temperatures. Hence, this provides a basis for performing biphasic catalysis or, alternatively, monophasic catalysis at elevated temperatures with biphasic product/catalyst separation at lower temperatures. A number of fluorous solvents are commercially available (see Fig. 7.16 for example), albeit rather expensive compared with common organic... 

Perfluoromethylcyclohexane, PP2 Perfluorohexane, FC-72 Figure 3.1 Examples of fluorous solvents... 

This new experimental technique, using fluorous solvents or fluorous biphasic systems (FBS) with fluorous biphase catalysis (FBC), was developed by Vogt and Kaim [884] and by Horvath and Rabai [885] in 1991 and 1994, respectively. Since then, this method has found many applications in synthetic organic chemistry and has already been reviewed repeatedly [886-893]. Incidentally, temperature-dependent two-phase one-phase transitions are not limited to combinations of fluorous solvents with organic solvents. For example, certain mixtures of water and l-cyclohexylpyrrolidin-2-one form one phase at ambient temperature and a two-phase system at higher temperatures >ca. 50 °C), also allowing interesting separation possibilities. 

One of the first examples of the use of fluorous solvents in reactions was their use in the extraction of photodegraded solid and liquid wastes contaminated with polychlorinated biphenyls (PCBs). Fluorinated ligands and scavengers... 

---