Structural features of ionic liquids: consequences for material preparation and organic reactivity

Abstract

Ionic liquids have been proposed as functional replacements for harmful and hazardous volatile organic solvents. However, limiting their use in this way does not fully explore the potential chemical benefits of their solvating properties, which stem from the inherent differences between ionic liquids and single molecule solvents. These differences can be used to facilitate alternative and improved reaction outcomes. This review will highlight a range of examples, involving materials preparation and organic synthesis, in which substantial progress towards the understanding and targeted application of ionic liquids is demonstrated. In addition, a number of studies will be cited where unanticipated outcomes have been observed and the relationships between these outcomes and ionic liquid structural effects will be analysed, casting new light onto these studies.

Insights into Ionic Liquid/Aromatic Systems from NMR Spectroscopy: How Water Affects Solubility and Intermolecular Interactions

“…The imidazolium cations also have an aromatic structure due to the lone pair of the nitrogen, but their smaller effective positive charge leads to a lower aromatic solubility . An increase in the alkyl chain length promotes cation‐anion separation and enhances the hydrocarbon solubility because of the decrease in the polarity of the ionic liquid cation, the increase in its asymmetry, and the free volume of the IL . An evaluation of the chemical environment of the IL protons at the highest hydrocarbon concentration has been made by 1 H NMR spectroscopy.…”

“…The ionic nature of the ILs and the aromaticity of the solutes are responsible for LC formation, but more complex interactions are present in these systems as well. The IL structure is dominated by Coulombic interactions and it can support many types of solvent‐solute interactions, such as electrostatic, ionic, hydrogen‐bond donation and accepting, induction and dispersion forces, van der Waals interactions, and dipolar and quadrupole moments, with the latter the main determinants of aromatic solubility in ILs …”

Photopolymerization of coordinated ionic liquid monomers: Realizing the benefits of structured media using only common reagents

“…32,33 Formation of localized structures in ILs has been utilized in several chemical processes including the production of nanomaterials and chemical synthesis. 34,35 ILs have also been examined as solvents for radical polymerization reactions. 36,37 In studies involving both styrene and methyl methacrylate (MMA), the use of ILs as reaction media resulted in improvements in both the reaction kinetics (e.g., propagation and termination rate constants) as well as the molecular weight of the resulting polymers.…”

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

“…In the next step, a variety of ionic liquids are obtainable by anion exchange, either through direct treatments with Lewis acids or by anion metathesis [29]. There are several reviews detailing these synthetic procedures [30–31]. …”