Fluorous fluids

Nakano, H., Kitazume, T. Friedel-Crafts reaction in fluorous fluids. Green Chem. 1999, 1, 179-181. 

Some further studies still deal with the Friedel-Crafts acylation in fluorous fluids. These fluids all have very unusual properties such as high density and high stability, low solvent strength and extremely low solubility in water and organic compounds, and, finally, nonflammability. These properties allow their easy handling and reuse. Friedel-Crafts acylation of electron-rich aromatic substrates can be very efficiently performed in a fluorous biphasic system (FBS), which represents a benign technique for phase separation, and catalyst immobilization and recycling. 

These alternative processes can be divided into two main categories, those that involve insoluble (Chapter 3) or soluble (Chapter 4) supports coupled with continuous flow operation or filtration on the macro - nano scale, and those in which the catalyst is immobilised in a separate phase from the product. These chapters are introduced by a discussion of aqueous biphasic systems (Chapter 5), which have already been commercialised. Other chapters then discuss newer approaches involving fluorous solvents (Chapter 6), ionic liquids (Chapter 7) and supercritical fluids (Chapter 8). 

Hobbs, H.R. and Thomas, N.R., Biocatalysis in supercritical fluids, in fluorous solvents, and under solvent-free conditions. Chem. Rev., 2007, 107, 2786-2820. 

As will happen, for example, with perfluorotriethylamine, a substance that is a good alternative reaction medium may be found for reactions and it can be easily recycled by simple extractive workup (Nakano and Kitazume, 1999). One of the most important issues in twenty-first century scientific society is the environmental problem. Thus far, there have been increasing demands for substitutes for toxic and/or harmful solvents like CH2CI2. Recently, inert and less toxic fluorous (perfluorinated) fluids have been recognized and are attracting attention as new alternative solvents (Fish, 1999). This fact shows the need to survey the scope and limitations of the utility of these liquids as alternative reaction media for reactions, which are of great current interest due to their unique reactivities and selectivities. 

Reaction media such as ionic liquids, fluorous solvents and supercritical fluids may offer a solution in avoiding some of the above mentioned problems. In addition to the physicochemical properties of solvents that are crucial when selecting a solvent for a particular task, within the context of producing cleaner chemical processes, other criteria are also important. 

A wide range of fluids with similar physical and chemical properties, including linear and cyclic perfluoroalkanes, linear and cyclic perfluoroethers and polyethers, perfluorotertiary amines and, in a few instances, perfluoroalkylhalides, may be considered to be perfluorinated or fluorous . Solvents within these categories are marketed around the world under a series of brandnames (Table 1). In certain instances, the commercial fluids represent mixtures of similar compounds with... 

In addition to fluorous solvents and ionie liquids, supercritical fluids sc-fluids, scf s), sueh as supercritical carbon dioxide (se-C02), constitute a third class of neoteric solvents that can be used as reaction media. Although sc-fluids have been known for a long time and have been advantageously used as eluants in extraction and chromatography processes (see Sections A.6 and A.7 in the Appendix), their application as reaction media for chemical processes has become more popular only during the last decade. Some of their physical properties and the supercritical conditions necessary for their existence have already been described in Section 3.2 (see Figure 3-2 and Table 3-4) see also references [209, 211-220, 224-230] to Chapter 3 for reviews on sc-fluids and their applications (particularly for SC-CO2 and SC-H2O). 

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