Ionic Liquids and Water: Hydrophobicity vs. Hydrophilicity

Abstract

Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the structure of aqueous solutions of several ionic liquid systems capable of forming multiple solubilizing environments were modeled by molecular dynamics simulations. The effect of small aliphatic chains on solutions of hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide ionic liquids (with alkyl = propyl [C3C1im][NTf2], butyl [C4C1im][NTf2] and isobutyl [iC4C1im][NTf2]) are covered first. Next, we focus on the interactions of sulphonate- and carboxylate-based anions with different hydrogenated and perfluorinated alkyl side chains in solutions of [C2C1im][CnF2n+1SO3], [C2C1im][CnH2n+1SO3], [C2C1im][CF3CO2] and [C2C1im][CH3CO2] (n = 1, 4, 8). The last system considered is an ionic liquid completely miscible with water that combines the cation N-methyl-N,N,N-tris(2-hydroxyethyl)ammonium [N1 2OH 2OH 2OH]+, with high hydrogen-bonding capability, and the hydrophobic anion [NTf2]–. The interplay between short- and long-range interactions, clustering of alkyl and perfluoroalkyl tails, and hydrogen bonding enables a wealth of possibilities in tailoring an ionic liquid solution according to the needs.

Imidazolium based ionic liquid-phase green catalytic reactions

“…[59][60][61][62][63][64][65] The number of water clusters changes the nanostructural organisation of IL spaces and affect the characteristics of this fluid. [66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81] The confined water in some ILs is activated and can act as a base or nucleophile and react, for example, with CO 2 forming carbonates. 82 Keeping track [62][63][64][65] of water content is very important, as the common anions BF 4…”

Effect of cation alkyl chain length on 3-sulfopropylmethacrylate-based draw solutes having lower critical solution temperature

“…71,72 The ionization ability of ILs depends on the hydrophobic alkyl chain length; ILs with longer alkyl chain lengths are likely to lead to weaker solvation of the ILs with water and stronger aggregation of the ILs. [73][74][75][76] Therefore, [P 4444 ][C 3 S], which has more hydrophilic cations due to the alkyl chains being shorter than hexyl, displays a higher osmotic pressure in water than the [P 4446 ][C 3 S] aqueous solutions at all concentrations.…”

Impact of extended long-range electrostatics on the correlation of liquid-liquid equilibria in aqueous ionic liquid systems

“…This is not representative of the reality. The behavior of the attraction of water molecules, mainly by their positive charged hydrogens, to the negatively charged atom of the anion has been studied by several sources, such as Rodrigues et al [88] in the field of Molecular Dynamics (MD). In their work regarding imidazolium cations combined with bis(trifluoromethylsulfonyl)imide anions, it can be seen that water molecules infiltrate the IL and are attracted not only to charged centers, i.e., the imidazolium ring in the cation and the negatively charged nitrogen in the anion, but also to the acidic hydrogens of the cation.…”