Aqueous biphasic hydroformylation and hydroaminomethylation assisted by cyclodextrins: From benchtop to industrial perspective
Résumé
Hydroformylation is an important industrial process that produces aldehydes from alkenes and syngas in accordance with the atom economy principle. Hydroaminomethylation, on the other hand, allows the direct conversion of alkenes into valuable tertiary amines in a sequential one-pot reaction involving hydroformylation followed by hydrogenation of the imine or enamine produced by condensation of the amine with the aldehyde formed by the first hydroformylation step. Recycling of the expensive organometallic catalyst could be achieved by working in aqueous biphasic conditions, with the catalyst immobilised in the aqueous phase by water-soluble ligands, while the reactants and products are in the organic phase. However, for highly hydrophobic substrates like long chain olefins, a mass transfer additive is mandatory in order to obtain high productivity. With this in mind, the use of native and chemically modified cyclodextrins and more sophisticated cyclodextrin-based systems in the aqueous biphasic hydroformylation and hydroaminomethylation are reviewed. The early first results, their developments and the recent advances are discussed. The promotor effect of these cyclodextrins is highlighted by key examples. The main examples have been designed in batch mode, but perspectives in continuous flow are also presented.