Acidic anions of ionic liquids have been demonstrated as efficient catalysts for the cleavage of the β-O-4 ether linkage prevalent in the lignin superstructure. Through the use of lignin model compounds with varying functionality and by monitoring reaction kinetics, a full mechanistic investigation into the hydrolysis of the β-O-4 linkage in acidic ionic liquid solutions is reported. Hammett acidities are reported for different 1-butyl-3-methylimidazolium hydrogen sulfate [C₄C₁im][HSO₄] ionic liquid systems with varying acid and water concentrations and were correlated to substrate reactivity. Results show that the rate of ether cleavage increases with an increase in acidity and the initial dehydration of the model compound is the rate-determining step of the reaction. The Eyring activation parameters of the reaction in hydrogen sulfate ionic liquids with a variety of cations are reported, indicating a consistent E1 dehydration mechanism. Hydrogen bonding in protic ionic liquids was shown to significantly influence anion–cation interactions, consequently altering the solvation of the protonated starting material and therefore the overall rate of reaction. Comparison of reaction rates in these ionic liquids with results within aqueous or aqueous/organic media indicate that the ionic liquids facilitate more rapid cleavage of the β-O-4 ether linkage even under less acidic conditions. All the reported results give a complete overview of both the mechanistic and solvation effects of acidic ionic liquids on lignin model compounds and provide scope for the appropriate selection and design of ionic liquids for lignin processing.

The role of hydrogen bonding, π ⁺ –π ⁺ stacking and anion–π ⁺ interactions on the structure of ionic liquid mixtures has been elucidated through a combined theoretical and experimental approach.

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.

SAXS, ¹²⁹ Xe NMR and PALS were used to interrogate the relationship between the structure, free volume and physicochemical properties of ionic liquid mixtures.

Confinement effects offer unique opportinuties to facilitate reactions in a way to favor sustainability... in an almost magical way.