Aqueous biphasic hydroformylation of methyl oleate: a green solvent-only strategy for homogeneous catalyst recycling†
An alternative strategy for the Rh-catalysed hydroformylation of technical-grade methyl oleate in aqueous-media has been developed. This is achieved with the water-soluble Rh/NaTPPTS catalyst dissolved in a green polar phase consisting only of the safe and benign solvents water and 2-propanol. This approach allows to completely avoid the use of additional auxiliaries like surfactants, cyclodextrins, or other phase-transfer agents. Along with efficient immobilization and recycling of the catalyst, excellent chemo- (>96%) and regioselectivity (>98%) to the desired branched aldehyde products is achieved. Investigations on the composition- and temperature-dependent phase-behaviour of the multicomponent liquid system water/2-propanol/methyl oleate are carried out in order to optimise all reaction parameters. Beneficially, a pure nonpolar aldehyde product phase is obtained after reaction, containing only low amounts of 2-propanol (<2%) and keeping catalyst leaching very low (<0.5%). After decanting the product phase, the aqueous catalyst phase can be reused, avoiding energy-intensive separation and purification procedures. The catalyst phase is reused in up to 10 recycling runs, reaching accumulated turnover numbers of up to 20 000.