The Importance of Biphasic Catalysis

Supercritical fluids, another class of alternative reaction medium, have been used as solvents in catalysis for many years. Ipatiev reported the isomerisation of cyclohexane to methylcyclopentane under supercritical conditions using A1203 as the catalyst1151 and shortly afterwards communicated the oligomerisation of supercritical ethylene catalysed by AICI3.1161 However, it took another 60 years before supercritical fluids were used as solvents for 

Ionic liquids continue to receive increasing interest as alternative solvents for catalysis and the historical developments in the field are described in Section 1.4. 

Ever since the plant went online, a great deal of fundamental research has been conducted, the process has been scaled-up further and new plants have come into operation. The economic and environmental benefits of the Ruhrchemie-Rhone-Poulenc process have been closely scrutinised. Overall the cost of the production is reduced, but it is the benefits to the environment 

Not surprisingly, the most well developed biphasic system is that using water and organic solvents, despite the first industrial biphasic process involving only organic solvents. Obviously, water is the solvent of choice as it is abundant, cheap, non-flammable, non-toxic and has many other desirable properties such as being polar (and therefore relatively easy to separate from apolar compounds), high thermal conductivity, heat capacity and heat of evaporation. Nevertheless, alternative solvents to water for applications in biphasic catalysis are needed for several reasons  

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. 

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