Switchable-Hydrophilicity Solvents for Product Isolation and Catalyst Recycling in Organocatalysis

Abstract

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.

Keywords: catalyst recycling; downstream processing; microreactor; organocatalysis; switchable solvents.