The essential role of hydrogen-bonding interaction in the extractive separation of phenolic compounds by ionic liquid

Separating phenols or even their homologs is an important process in environmental conservation and biomass utilization, and it has become one fascinating application of ionic liquids (ILs). Nevertheless, its underlying mechanism still needs to be elucidated at the molecular level. This work conducted a theoretical study on the interaction between ILs and phenols by quantum chemical calculations, using tocopherols as model compounds. Calculation results from geometry, electrostatic potential, natural bond orbital, atoms in molecules and energy analyses and their accordance with extraction experiments indicated the essential role of hydrogen-bonding interaction in extracting tocopherols and distinguishing the homologs by IL. The polarizable continuum model and conductor-like screening model for real solvents studies showed that the mechanism still holds when considering the solvation effect. Furthermore, with the aid of theoretical calculation, more efficient extractants, 1-ethyl-3-methylimidazolikum glycinate ([emim]Gly) and 1-ethyl-3-methylimidazolikum alaninate ([emim]Ala), were developed for the separation of tocopherol homologs. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1657–1667, 2013