Separation of Hydrophobic Compounds Differing in a Monounsaturated Double Bond Using Hydrophilic Ionic Liquid/Water Mixtures as Extractants

Abstract

Effective separation of analogues structurally differing in a monounsaturated double bond remains challenging. In this study, hydrophilic ionic liquid (IL)/water mixtures were investigated as extractants for the extractive separation of hydrophobic analogues capsaicin and dihydrocapsaicin. A useful “diluent-swing” effect was introduced into the IL-based extraction and the recovery of solute for recycling the extractant. The extractive separation was performed at high IL concentrations where water behaves as a co-solvent, and back-extraction of the solute from the IL/water mixture was performed at low IL concentrations where water acts as an anti-solvent. The influences of IL structures (cations, anions, and substituent groups) and concentration, as well as the analogues concentration, on the separation efficiency were fully investigated. Selectivities of capsaicin versus dihydrocapsaicin of >2.0 were achieved by a number of IL/water mixtures, mainly because of the enhanced dipolarity/polarizability caused...