Extraction and separation characteristic stilbene compounds from pigeon pea leaves using V-type thymol-based natural deep eutectic solvent systems

In this study, a V-type deep eutectic miniature solvent composed of thymol/coumarin was designed based on the principle of similitude compatibility and π-π conjugate effect for the extraction of stilbene structure compounds from pigeon pea leaves. According to Hansen solubility parameter theory, the optimal DES type and composition molar ratio were screened out. The optimal extraction conditions were thymol/coumarin ratio 2:1, ultrasonic power 200 W, ultrasonic time 20 min, liquid-solid ratio 50:1 (mL/g). According to the hydrophobic DES form hydrogen bond position, we found that add a small amount of ammonia solution can effectively destroy DES hydrogen bonding structure, which reduces the target product solubility in the solvent, combined with macroporous resin adsorption process can be quickly and efficiently recycling target component and separation solvent. Through the rotary evaporator to remove water, HBAs and HBDs are recombined to form DES, which can be directly used for secondary extraction. After three cycles of DES, the rate of recovery of DES was over 80%. Moreover, the FT-IR, UV–vis and NMR were applied to investigate physicochemical properties of DES and extraction mechanism. This study provides a new solvent screening idea for the extraction and separation of natural products, and designs a green and sustainable extraction and separation process of natural products, and provides a new idea for the recycling of hydrophobic DES.