Pseudoternary Systems of Deep Eutectic Solvents + tert-Butanol + Water at T = 288.15 K, 298.15 K, and 308.15 K: Liquid–Liquid Equilibrium and Ability for Syringic Acid/Eugenol Separation

Abstract

Aiming at developing more biocompatible and economic separation platforms, aqueous biphasic systems (ABS) composed of deep eutectic solvents (DES) and tert-butanol were proposed for the first time. The effects of key factors such as the hydrogen-bond donor (HBD) properties and temperature on the phase-forming ability of DES/tert-butanol ABS were investigated. Meanwhile, syringic acid and eugenol mixtures were selected as model biomolecules to evaluate the efficiency of DES/tert-butanol ABS to use as liquid−liquid extraction systems. The results indicated that DES components migrated preferentially to the bottom phase while tert-butanol was concentrated in the top phase. The more hydrophilic HBD or lower temperature was responsible for greater efficiency to induce the formation of DES/tert-butanol ABS. The reason for phase separation was the incompatibility of the hydrogen-bond acceptor (HBA) and HBD with tert-butanol in aqueous solution, where the higher hydrophilic HBD enriched favorably in the lower phase, allowing for the formation of the DES/tert-butanol ABS. The selective separation of syringic acid and eugenol was a consequence of the HBD characters, temperature, and tie-lines length of the ABS, and they could be greatly separated by using the ABS composed of betaine-xylitol (DES) and tert-butanol at 298.15 K. The highest extraction efficiency of syringic acid and eugenol was 91.64 and 97.62%, respectively. Further, syringic acid and eugenol as well as DES can be recovered and reused by using water as the antisolvent and the vacuum distillation method. This study may be expected to lay a solid foundation for the expansion of DES-based ABS and selective separation of similar biomolecules.

Liquid–Liquid Equilibrium Data for Novel Aqueous Two-Phase Systems Composed of Betaine-Xylitol Deep Eutectic Solvent + Alcohol (1-Propanol/2-Propanol/tert-Butanol) + Water

“…The phase diagrams for the ATPS formed by DES and alcohol (1-propanol/2-propanol/tert-butanol) were investigated using our previous method. 27 Briefly, aqueous solutions of alcohol at 80 wt % were prepared and then added dropwise to aqueous DES solution until the detection of a slightly turbid liquid corresponding to the biphasic region. Afterward, a repetitive dropwise addition of water to the above mixture under stirring until a colorless solution was formed again.…”

“…Furthermore, the tie-lines (TLs), i.e., the composition of each component in the two phases, were measured based on an HPLC method previously reported by us with some modifications. 27 In general, six points with known composition were chosen for each DES/alcohol ATPS at the two-phase region. Typically, 6 g of DES, alcohol, and water were added to centrifuge tubes (10 mL), vigorously stirred, and further kept still in a microthermal bath at (298.15 ± 0.1) K for 12 h to achieve complete phase equilibrium.…”

“…The molar ratio of HBA to HBD was 1:1, and the water content was 30 wt %. The phase diagrams for the ATPS formed by DES and alcohol (1-propanol/2-propanol/ tert -butanol) were investigated using our previous method . Briefly, aqueous solutions of alcohol at 80 wt % were prepared and then added dropwise to aqueous DES solution until the detection of a slightly turbid liquid corresponding to the biphasic region.…”

“…Furthermore, the tie-lines (TLs), i.e., the composition of each component in the two phases, were measured based on an HPLC method previously reported by us with some modifications . In general, six points with known composition were chosen for each DES/alcohol ATPS at the two-phase region.…”

“…Furthermore, Ghaffari et al found that the drugs lamotrigine, salicylic acid, and acetaminophen could be completely separated using the ATPS constituted by choline chloride/fructose-based DES and PPG400. More recently, our team proposed the ATPS constituted by DES and small-molecular alcohols for the first time. − We prepared large amounts of DES using betaine and choline chloride as the HBA while sucrose, glucose, fructose, sorbitol, xylitol, urea, etc. as the HBD, and then focused on the influence of HBD properties on the efficiency to form ATPS.…”