Cation-Anion and Cation-Cation Interactions in Mixtures of Hydroxy-functionalized and Aprotic Ionic Liquids

Unraveling the Morphology of [CnC1Im]Cl Ionic Liquids Combining Cluster and Aggregation Analyses

“…Notably, for n ≥ 4 the polar and nonpolar networks seem to coexist without destructively perturbing each other. This is a sign of stark microheterogeneity in the IL, which has also been observed in prior studies. ,,,,− At this point, it remains unclear what the exact composition of the nonpolar domains in the n = 2–8 systems is.…”

“…Ionic liquids (ILs) constitute a well-established field of research, for example, due to their fascinating physicochemical properties that distinguish them from conventional molecular liquids. − A particularly interesting facet of ILs is their mesoscopic order, also known as nanosegregation, that has been investigated experimentally and computationally in various studies. − Notably, ILs often exhibit a distinct and continuous polar domain comprising the charged (and thus polar) moieties of their constituents. Conversely, the nonpolar moieties tend to form large nonpolar regimes the size of which are dependent on the nature of the IL ions. − The formation of polar and nonpolar domains is primarily driven by favorable electrostatic and noncovalent interactions, respectively, and may be hindered by steric demands of the ions. This mesoscopic order can be controlled by the choice of IL constituents, for example, upon elongation of the alkyl side chains of the IL.…”

Applications of Ionic Liquids in Carboxylic Acids Separation

“…These associations can be obtained as reverse micelles (the ionic liquid act as surfactant due to asymmetrical structure with localized polar charged domains and prolonged cationic alkyl chain [88,89]), which influences water solubility by including it and are broken once the extracted acid concentration increases, or as IL-acid complexes that can exist as clusters due to electrostatic and intermolecular forces [90]. To estimate the ionic liquids phase forming ability, the Kamlet-Taft parameters (a scale based on linear solvation energy relationships measuring solvent hydrogen bond acidity, α-hydrogen bond donating ability, and basicity, β-hydrogen-bond accepting ability, while π* measures solvent dipolarity and polarizability) are usually used [91].…”

“…where k n -stability constants (equilibrium constant), characterizing the stability of the bond between the acid and IL in complexes (1, 1) and (2,1), and between two acids in complexes with n > 2; its values systematically decrease with the increase in extracted acid molecules (n) [88,89].…”

“…When the carboxylic acid is a stronger acid than the hydrophobic acid (e.g., lactic acid extracted with phosphonium IL) from the anionic part of the ionic liquid, this can be exchanged with extracted acid and the hydrophobic acid from the anion is kept in organic phase [89]. The reactive extraction mechanism of carboxylic acids is influenced by aqueous solubility of the IL anion, which can determine the formation of carboxylic acid-ionic liquid complexes that include multiple acid molecules-overloading-strongly influenced by the acid concentration (which also influences the ionic liquid water content: an increased acid concentration determines the decrease) [92].…”