Fluorous Phase-Separation Techniques in Catalysis

E. de Wolf, G. van Koten and B.-J. Deelman (1999) Chemical Society Reviews, vol. 28, p. 37 - Fluorous phase separation techniques in catalysis . 

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. 

Certain solvents are immiscible at low temperature, but on heating, form a single phase. This allows reactions to be conducted in single phase under homogeneous conditions followed by separation using normal biphasic extraction methods.4 The technique was first recognized in fluorous-organic biphasic catalysis, and has more recently been applied to ionic liquid-aqueous reactions (see below). 

Since the first edition of this book a great number of articles have been published in which the different techniques to separate the catalyst from the products via two liquid phases were applied. Some general review articles in books and journals about multiphase homogeneous catalysis, catalyst recycling and fluid-fluid systems have been published [96-102]. Other review articles concentrate on aqueous organometallic chemistry and catalysis [103-108], on biphasic systems with ionic liquids [109, 110], or on fluorous solvents [111, 112] (cf. Sections 7.2, 7.3). 

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