Why Ionic Liquids in Multiphasic Catalysis

Notwithstanding their very low vapor pressure, their good thermal stability (for thermal decomposition temperatures of several ionic liquids, see [11, 12]) and their wide operating range, the key property of ionic liquids is the potential to tune their physical and chemical properties by variation of the nature of the anions and cations. An illustration of their versatility is given by their exceptional solubility characteristics, which make them good candidates for multiphasic reactions (see Section 5.3.4). Their miscibility with water, for example, depends not only on the hydrophobicity of the cation, but also on the nature of the anion and on the temperature. 

The influence of the nature of cations and anions on the solubility characteristics of the resulting salts with organic substrates is also discussed in Section 5.3.4. It has 

Addition of co-solvents can also change the co-miscibility characteristics of ionic liquids. As an example, the hydrophobic [BMIM][PF6] salt can be completely dissolved in an aqueous ethanol mixture containing between 0.5 and 0.9 mole fraction of ethanol, whereas the ionic liquid itself is only partially misdble with pure water or pure ethanol [13]. The mixing of different salts can also result in systems with modified properties (e.g., conductivity, melting point). 

One of the key factors controlling the reaction rate in multiphasic processes (for reactions taking place in the bulk catalyst phase) is the reactant solubihty in the catalyst phase. Thanks to their tunable solubility characteristics, the use of ionic Hq-uids as catalyst solvents can be a solution to the extension of aqueous two-phase catalysis to organic substrates presenting a lack of solubihty in water, and also to moisture-sensitive reactants and catalysts. With the different examples presented below, we show how ionic liquids can have advantageous effects on reaction rate and on the selectivity of homogeneous catalyzed reactions. 

262 Helene Olii/ier-Bourbigou, Alain Forestiere 1-hexene / IL (wt.%) 

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