Simple and Effective Catalyst Separation by New CO2 -Induced Switchable Organocatalysts

Abstract

CO₂ -induced switchable tertiary amine-based organocatalysts were investigated for an efficient catalyst and product separation by its different partitioning between an organic and carbonated water phase. In this case study, the switching ability of eight tertiary amine-based catalysts between the organic and water phase by addition or removal of CO₂ was investigated. Here, the catalyst switched both nearly completely (99.9 %) into the aqueous phase by addition of CO₂ and effectively back into the organic phase (99.3 %) by expelling CO₂ . With this technique, the organocatalyst was successfully recovered and reused twelve times without significant loss of activity (up to 90 % enantiomeric excess) for the asymmetric nitroaldol (Henry) reaction. After the first catalyst switch, evaporation of the solvent affords the product in 98 % purity without any further purification steps.

Keywords: biphasic; catalyst recycling; downstream processing; organocatalysis; switchable catalysts.