Screening of functional solvent system for automatic aldehyde and ketone separation in aldol reaction: A combined COSMO-RS and experimental approach

An integrated reaction-separation process based on only solvents is presented, and thus without the need for related technical equipment (reactor-separator). Both product purification and reactant recovery are achieved automatically for an asymmetric aldol reaction employing a biphasic solvent system as compartmentalizing soft matter. Firstly, COSMO-RS based simulation is introduced as a theoretical guidance in the solvent selection for the reactant 3-chlorobenzaldehyde and non-solvent selection for the R-aldol product, (R)-4-(3-chlorophenyl)-4-hydroxybutan-2-one. This encompasses solubility as core critical parameter, as well as chemo-physical properties and environmental profiling. Such criteria-cascaded screening could effectively reduce a 7665 solvents-database into 1 candidate solvent, which is dodecane, before experimental process assessment. Secondly, this screening's top candidate was validated as the best reaction solvent by first a solubility test and then by a batch reaction, in which a conversion of 69% was achieved. As desired, the mono-phase reaction yielded spontaneously the product layer and the separate dodecane phase as the second layer, which indeed allowed facile separation of the product from the residual reactant. In a third step, a segmented flow process was developed giving a highest product yield of 63% and a total conversion 92% respectively after a 2 h residence time.