Finding suitable biobased solvents for extractions from water

Abstract

Solvent usage is one of the most critical factors for the carbon footprint of the chemical and pharmaceutical industries. Therefore, finding suitable green solvents that can be sourced from biomass is necessary for more sustainable manufacturing processes. One of the greenest solvents is water, and chemical transformations in aqueous solution play an increasingly important role. To guide the search for suitable green solvents for extractions from aqueous solution, eleven biobased solvents were systematically evaluated with 132 absolute free energy calculations based on 1728 molecular dynamics simulations. These kinds of calculations are used in modern computer-aided drug discovery for protein–ligand binding because of their high accuracy and the ability to account for dynamic changes of heterogenous nanostructures. Based on the calculations, 1-butanol and cyclopentanol are recommended for extractions of hydrophilic molecules with a decadic logarithm of the partition coefficient between 1-octanol and water (log P) below 0.5, while cyclopentyl methyl ether and butyl methyl ether are recommended for hydrophobic solutes with log P > 2.6. Ethyl acetate and 1-pentanol are suitable for solutes in the mid-range. These findings are verified based on experimental extraction efficiencies from an aqueous solution in a micelle-enabled cross-coupling transformation. The extraction yields confirm the computational results, and also show that only the six most hydrophilic solvents lead to a clear phase separation in the presence of residual organic solvents and surfactants. This highlights that aqueous micellar media require special extraction solvents. Overall, both molecular level insight and practical considerations are needed for the selection of suitable green solvents.