Hydroformylation Reactions in Alternative Media

HYDROFORMYLATION REACTIONS IN ALTERNATIVE MEDIA 8.3.1 Hydroformylation in Water... 

Because of the generally excellent solubility of metal catalysts in RTILs, many of the reactions studied in these media are homogeneously metal catalysed. For example, rhodium catalysed hydroformylation reactions have been studied at length and a wide variety of phosphine ligands used. This particular reaction in RTILs has just been the subject of an extensive review. In most cases, only minimal leaching of the catalyst out of the ionic liquid phase is observed and the catalysts can be very effectively recycled. These efforts are necessary because the industrial aqueous-biphasic process (Chapter 10) only works effectively for smaller olefins and therefore alternative approaches are needed for more hydrophobic, higher-mass olefins. 

Likewise, a thermoregulated phase transfer process within the aqueous/organic two-phase system has been reported by Jin and co-workers (cf. Section 3.1.1.1) [290]. A water-soluble supramolecular Rh catalyst based on functionalized /1-cyclodextrin was also described [291]. In a two-phase system this catalyst may function as a carrier for the transfer of both the starting material and the product between the different phases. As an alternative to polar media for biphasic hydroformylation, Chauvin et al., used ionic liquids based on imidazolium salts which are well known for dimerization reactions (cf. Sections 2.3.1.4 and 3.1.1.2.2) [270, 271, 292]. For introduction into technical processes the currently availability and price of ionic liquids could be a drawback, especially for bulk chemicals such as 0x0 products. 

The homogeneous hydroformylation could take place both in conventional and environmentally benign (green) reaction media. The solubility of the catalyst is primarily determined by the applied ligand due to its polarity and/or functionality. The unmodified catalysts can be dissolved in the hydrocarbons such as alkanes and toluene, or in industrial scale the reaction is performed in the crude olefin mixtures (downstream) containing different unsaturated hydrocarbons. The solubility of the modified catalyst in the alternative reaction media is easily affected by the ligand variation of the metal complex for example... 

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