Further insight into the influence of functionalization and positional isomerism of pyridinium ionic liquids on the aqueous two-phase system equilibria

Abstract

Despite a large collection of publications dealing with the characterization of ionic liquid-based aqueous biphasic systems (IL-ABS), a gap still exists regarding the impact of functionalized alkyl side branches and IL positional isomers on phase equilibria. Therefore, this work addresses the investigation of the ability of different methyl substituted pyridinium based ILs on the formation of ABSs with K3PO4. We evaluated the impact of (i) functional groups (hydroxyl or ether) embed in side alkyl chains of pyridinium cations, (ii) positional isomerism of methyl group (ortho, meta and para) and (iii) the IL cation core. Ternary phase diagrams of the ABSs formed by these ILs and K3PO4 and the appropriate tie lines were determined and presented. It is shown that the presence of functionalized alkyl chain largely affects the salting-in behavior of ILs (ILs with the oxygen groups are more difficult to form ABS) while more subtle differences were observed among positional isomers. Based on the obtained results it is concluded that change of biphasic area of ABS is the manifestation of the altered affinity of ILs for water as a consequence of cation structure. Moreover, aiming at gathering a broader picture of the relationship between ILs structure and ABS properties, molecular simulations were performed, and it was showed that the obtained results are consistent with the experimental results.