The behavior and mechanism of a temperature-responsive ionic liquid and its applications in extracting geniposidic acid from Eucommia ulmoides male flowers

Abstract

A lower critical solution temperature responsive ionic liquid (IL) was fabricated via the neutralization reaction of tetrabutyl phosphine hydroxide ([P4444]OH) and benzimidazole (BzIm) for the ultrasonic extraction of geniposide acid (GPA) from Eucommia ulmoides Male flowers. Temperature-dependence properties of this IL were closely related to its N and P atoms and self-aggregation. GPA extraction was performed to obtain a maximum extraction yield (Y = 0.23 mg/g). The experimental conditions such as IL concentration, solid–liquid ratio, temperature, time, and ultrasonic power were optimized. The separation data showed that the recovery yield (R) and distribution coefficient (K) of GPA in aqueous phase were 91.95% and 3.29, respectively. The simple treated IL could be reused for 5 times for extracting, and RGPA and RIL values were decreased to 87.18% and 78.00%, respectively, indicating that this IL had a nice reusability. Molecular dynamics simulation revealed that H-bonds of [BzIm]–/H2O molecules were seriously destroyed at high temperatures, which was the major driving force for the spontaneous aggregation and liquid–liquid demixing of IL/H2O system. Further, additional H-bonds were generated of GPA and water, prompting the majority of GPA to be enriched in H2O-rich phase. Thus, [P4444][BzIm]/water system is a greenly reusable potential solvent for natural GPA extraction, and these findings are meaningful to further promote the excavation and application of analogous ILs.