Design of the reversible biphasic arrangement in the microfluidic chip reactor for asymmetric hydrogenation reactions
Abstract
Design of the reversible biphasic system for a practical use in asymmetric hydrogenation performed in a microfluidic chip reactor is reported. Methylacetoacetate (MAA) was transformed to (R)-methylhydroxybutyrate over optically pure (R)-Ru-BINAP as a model reaction.
The study was an iteration towards the design, description and optimization of the temperature driven reversible biphasic system in the mixed [N-R,N-222][Tf2N]/methanol/water phase by varying the parameter of the structure of the ionic molecule, starting from [NH4][Tf2N] up to [N-14,N-222][Tf2N]. At temperatures, and other conditions providing high conversions and optical yields, the reaction mixture was monophasic.
At lower temperatures, the mixture became biphasic for ionic liquids with long alkyl chains (namely [N-14,N-222][Tf2N]) due to their strong non-polar character. The formed ionic liquid phase accommodated the chiral Ru complex, the water/methanol phase the reaction products.
After the reaction, when the mixture was cooled, over 90% of the catalytic complex was kept in the ionic liquid phase. Viscosity and density data were also discussed.
It seems the reversible biphasic system offers a way to facilitate the separation of the chiral Ru-complex from the reaction mixture. Due to high sensitivity of the complex to handling conditions, its reuse still requires further optimization. (C) 2019 Institution of Chemical Engineers.
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