Ames Laboratory-USDOE and Department of Chemistry, Iowa State University, 1605 Gilman Hall, Ames, IA 50011, USA.
Ames Laboratory-USDOE and Department of Chemistry, Iowa State University, 1605 Gilman Hall, Ames, IA 50011, USA.
J Chromatogr A. 2022 Mar 29;1667:462871. doi: 10.1016/j.chroma.2022.462871. Epub 2022 Feb 3.
Choline chloride-based deep eutectic solvents (DESs) are immensely popular in organic synthesis, catalysis, electrochemistry, and separation science. A popular choice of hydrogen bond donor (HBD) among these DESs consists of both straight-chain and branched polyols that can incorporate additional functional groups, such as ether linkages. Previous studies have shown that the extraction efficiency is significantly altered when the molar ratio of HBD in choline chloride-based DES systems is varied, but no study has been able to relate it to their solvation characteristics. This is largely due to the limited sensitivity of existing solvatochromic dye techniques to detect minor changes in solvation interactions when the DES composition is varied. In this study, inverse gas chromatography was employed for the first time to investigate the variation in solvation properties for DESs comprised of choline salts as hydrogen bond acceptors (HBAs) and polyols as HBDs when their HBA/HBD ratio is systematically altered. Unlike many organic solvents, DES systems investigated in this work possessed a significant hydrogen bond character. It was observed that the hydrogen bond basicity generally plateaued at higher molar ratios of HBD while the hydrogen bond acidity was observed to be the highest at HBA/HBD ratios of 1:10 in all DESs. Amongst all solvents, neat HBDs (triethylene glycol and 1,8-octane diol) possessed the weakest hydrogen bond basicity since they lack the chloride anion that acts as the primary hydrogen bond acceptor. Results from this study demonstrate that the solvation characteristics of DESs are largely different from their starting materials while the HBA/HBD ratio further influences their solvation interactions that can in turn impact important parameters such as extraction yields.
氯化胆碱基深共晶溶剂（DESs）在有机合成、催化、电化学和分离科学中非常受欢迎。这些 DES 中，氢供体（HBD）的一个热门选择是直链和支链多元醇，它们可以引入额外的官能团，如醚键。以前的研究表明，当氯化胆碱基 DES 体系中 HBD 的摩尔比发生变化时，萃取效率会显著改变，但没有研究能够将其与它们的溶剂化特性联系起来。这主要是由于现有的溶剂化变色染料技术的灵敏度有限，无法检测到 DES 组成变化时溶剂化相互作用的微小变化。在这项研究中，首次使用反气相色谱法研究了当 HBA/HBD 比系统改变时，由胆碱盐作为氢键受体（HBAs）和多元醇作为 HBD 组成的 DES 的溶剂化性质的变化。与许多有机溶剂不同，这项工作中研究的 DES 系统具有显著的氢键特征。结果表明，氢键碱性通常在 HBD 的更高摩尔比下达到平台，而在所有 DES 中，氢键酸性在 HBA/HBD 比为 1:10 时最高。在所有溶剂中，纯 HBD（三乙二醇和 1,8-辛二醇）的氢键碱性最弱，因为它们缺乏作为主要氢键受体的氯离子。这项研究的结果表明，DES 的溶剂化特性与它们的起始材料有很大的不同，而 HBA/HBD 比进一步影响它们的溶剂化相互作用，这反过来又会影响萃取产率等重要参数。
