Extraction of geniposidic acid and aucubin employing aqueous two-phase systems comprising ionic liquids and salts

Abstract

Ionic liquid aqueous two-phase systems (ILATPS) exhibiting enhanced separation efficiency and selectivity have attracted enormous attention. In this study, diverse ILATPSs comprising 1-alkyl-3-methylimidazolium ([Cnmim]+) and inorganic salts were developed and studied for the extraction of geniposidic acid (GPA) and aucubin (AU) for the first time. The binodal curves were fitted to the nonlinear Merchuk relationship. The ability of these ILs to form ATPS increased as their alkyl side chains increased. Moreover, the performances of the utilized potential salts in the phase separation were compared. The influences of the types and amounts of ILs and salts, extraction temperature and time, and the amount of the initial mixed solution were investigated through single-factor experiments. Under the following optimum conditions: 25% (w/w) K2CO3, 30% (w/w) [Bmim]Br, 1.2 mL of the GPA and AU mixed solution, temperature of 10 °C and extraction time of 360 min, the maximum extraction efficiency (E1AU = 96.95%, E1GPA = 99.99%), partition coefficient (logKAU = 1.54 ± 0.01 and logKGPA = 4.47 ± 0.01), and S (843.57 ± 15.67) were obtained. Afterward, IL could be easily recycled without organic solvents via a metathesis reaction with lithium bis(trifluoromethane)sulfonamide (LiNTf2) during which hydrophilic [Bmim]Br could be converted into hydrophobic [Bmim]NTf2. Furthermore, the density functional theory (DFT) calculations revealed that the H-bond interactions were the main factor that affected this extraction; the H-bond between [Bmim]Br and GPA was stronger than that between [Bmim]Br and AU. This research is expected to avail meaningful theoretical references for the extraction of similar natural products from plants.