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.
Subject(s)
Amines , Carbon Dioxide/chemistry , Carbon Dioxide/isolation & purification , Organic Chemicals/chemistry , Amines/chemistry , Catalysis , Cobalt/chemistry , Organometallic Compounds/chemistry , Rhodium/chemistry , Solvents/chemistryABSTRACT
Switchable-hydrophilicity solvents (SHSs) are solvents that can switch reversibly between a water-miscible state to a state that forms a biphasic mixture with water. In this case study, SHSs have been studied for easy product/catalyst separation as well as catalyst recycling. A series of tertiary amine SHSs have been identified for the extraction of the hydrophilic product from the postreaction mixture. Here, we determined high extraction efficiencies for the product (>84%) and low extraction rates for the catalyst (<0.1%). With the catalyst recycling experiments, we isolated the product in high purity (>98%) without further purification steps. At the same time, the catalyst was reused without any loss of activity (>91% enantiomeric excess, >99% yield) four times. Furthermore, we optimized the extraction efficiency by working with a microextractor. In addition, with the use of a falling-film microreactor, we obtained the product with high enantioselectivity by working at ambient conditions.
Subject(s)
Organic Chemicals/chemistry , Solvents/chemistry , Catalysis , Hydrophobic and Hydrophilic InteractionsABSTRACT
A novel strategy for the embedding of quinine-based organocatalysts in polymerized ionic liquids-based hydrogels is presented. With this technique, the encapsulated organocatalyst was successfully recovered and reused for four cycles without any loss of enantioselectivity (up to 91% ee) for the asymmetric nitroaldol (Henry) reaction. In this study, high catalyst leaching was significantly reduced (<0.01%) by controlling the water content. After catalyst removal, evaporation of the solvent affords the product in 98% purity without any further purification.
