Hydroformylation in ionic liquids

Adipic acid is of considerable importance since it is a precursor to nylon and polyester, which are extensively used in many products. Between two and three million tonnes are produced worldwide each year. Currently, its main method of manufacture is a costly, multistep process involving concentrated nitric acid. Nitrous oxide is produced as a by-product in such quantities that they measurably contribute to global warming and ozone depletion [24], A cleaner alternative to this process is clearly highly desirable. 

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Olivier-Bourbigou s group, for example, has recently shown that phosphite ligands can be used in Rh-catalyzed hydroformylation in ionic liquids as well as the well loiown phosphine systems [81]. Since phosphite ligands are usually unstable in aqueous media, this adds (apart from the much better solubility of higher olefins in... 

Figure 18 Ligands for hydroformylation in ionic liquid/organic solvent biphasic system.

Table 4.4 Supported ionic liquid phase hydroformylation in ionic liquids...

Leclercq L, Suisse L, Agbossou-Niedercorn F (2008) Biphasic hydroformylation in ionic liquids interaction between phosphane ligands and imidazolium triflate, toward an asymmetric process. Chem Commun 3 311-313... 

Scheme 2.31 Synthesis of monophosphine ligands designed for the hydroformylation in ionic liquids.

Preliminary mechanistic studies by Fernandez, Peris, and Crudden provided evidence that, under smooth hydroformylation conditions, NHCs remain ligated in the coordination sphere of rhodium [55, 68]. A similar conclusion was drawn by Scholten and Dupont for hydroformylation in ionic liquids [69]. A serious problem sometimes faced is the reductive elimination of carbene ligand from the metal as imidazohum salt under the effect of H2, as found in hydrogenation reactions [70]. 

The observed reaction rates for the hydroformylation in ionic liquids are usually quite superior to those performed in aqueous-phase regimes, and the selectivities are similar to those obtained in homogeneous conditions. 

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