Hexafluorophosphate salts with tropine-type cations in the extraction of alkaloids with the same nucleus from radix physochlainae

Abstract

Ionic liquids (ILs) have been widely used in the field of extraction of natural bioactive compounds because of their advantages compared to traditional organic solvents. In this study, the new ‘like dissolves like’ mode was designed and seven types of tropine-based ionic liquids were used to extract tropane alkaloids from radix physochlainae, and then the relationship between their performance and structures together with the effects of main extraction conditions were explored. It was found that 0.05 mol L⁻¹ [C₃tr][PF₆] aqueous solution had the ideal selectivity and high extraction efficiency of 95.1% at 75 °C when the extraction time was 55 min and the solid–liquid ratio was 1 : 35, which was superior to that of 85% ethanol–water and 0.1% hydrochloric acid–water. There was no decomposition and racemization of products occurring in the mixture solution when above extraction solvent was applied. In addition, the extraction behavior and mechanism using an ionic liquid aqueous solution was tentatively studied through thermodynamics experiments, near-infrared/infrared spectroscopy (NIR/IR), scanning electron microscopy (SEM), and thermogravimetric analysis (TG), and subsequent back-extraction could be efficiently used to further separate alkaloids and ILs. In the developed ‘like dissolves like’ mode, the extraction process of target alkaloids was found to be endothermic and spontaneous through the specific interaction between them and the solvent molecules with the same nucleus.