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. Published by Elsevier B.V. All rights reserved.