Homogeneous thermomorphic solvent systems

The idea to use solvent systems enabling homogeneous reaction conditions at elevated temperatures and liquid/liquid phase separation at lower— preferably room—temperature seems to be obvious. Nevertheless, it is only recently that thermomorphic solvent systems gain attention [30-33] for product separation or multiphase catalysis [34,35]. The main reasons for the delayed engagement is that an efficient choice of a useful solvent system is not easy to achieve. There is also a lack of experience with thermomorphic systems in general. Reactions are optimized to be carried out in solvents having certain distinct solubility and polarity characteristics. A thermomorphic solvent system of choice will have to fulfill these requirements and to show the thermomorphic effect in addition. 

On the other hand thermomorphic solvent systems can be used for industrial applications within existing equipment. In principal, it is also possible to use unmodified ligands and catalyst complexes for homogeneously catalyzed reactions. Therefore, the economic hurdles to use the system in industrial practice are not very high. 

The use of thermomorphic systems has recently been studied as a way of achieving catalyst separation in homogeneous catalysis. For example, a biphasic hydroformylation catalyst system was developed to take advantage of the unusual solvent characteristics of perfluorocarbons combined with typical organic solvents (4). Fluorous/organic mixtures such as perfiuoromethylcyclohexane... 

Batch Experiments with Thermomorphic Systems. As a reference, we tested the hydroformylation of 1-octene in a completely homogeneous system using the same rhodium triphenylphosphine catalyst that is used for hydroformylation of lower aldehydes. This is sample R39 in Table 28.1, and gives us a baseline to compare the performance of our systems in terms of conversion and selectivity. To maintain consistency, we performed all the reactions at 100°C using the same amounts of reactants, catalysts and solvents. Under these conditions we only detected aldehyde products no alcohol or alkene isomers were formed. 

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