The structure of protic ionic liquids based on sulfuric acid, doped with excess of sulfuric acid or with water

Abstract

Neutron scattering with isotopic substitution was used to study the structure of concentrated sulfuric acid, and two protic ionic liquids (PILs): a Brønsted-acidic PIL, synthesised using pyridine and excess of...

Protic ionic liquids for sustainable uses

“…Utilising sulfuric acid in a χ H 2 SO 4 > 0.50 versus the corresponding amine base resulted in a PIL with an extended anionic hydrogen-bonded network. 64 At χ H 2 SO 4 = 0.67, these PILs showed acidity levels similar to those of analogous PILs based on HOTf. Chrobok and co-workers reported that these PILs outperformed neat sulfuric acid and the product could be easily separated by decantation.…”

“…There have been several excellent fundamental studies, that go beyond comparative reporting of catalytic activity, and draw on a wide range of techniques to understand the mechanistic considerations when using PILs, such as: Andreev et al 82 studying the multimodal influence of [HC 1 im][NCS] on organic transformations, the neutron scattering study on sulfuric acid-based PILs, leading to understanding enhanced phase separation in esterifications, 64 or the combined NMR spectroscopy and DFT investigation of DBU-based PIL in the reaction of CO 2 and propargyl alcohols, proving the cooperative role of both the anion and the cation. 106 These insights have real potential to enable rational design of improved catalytic systems.…”

“…6) has been suggested, while others have proposed a three-dimensional, hydrogen-bonded network with no discrete clustering. 63,64…”

“…Fig.8Hydrogen-bonded chains of [HSO 4 ] − and H 2 O in pyridinesulfuric acid (χ H 2 SO 4 = 0.50), doped with 17 wt% of waterunpublished image from our neutron scattering studies of this system 64. …”

Exploiting Cation Structure and Water Content in Modulating the Acidity of Ammonium Hydrogen Sulfate Protic Ionic Liquids

“…This leads to a systematic reduction in the intensity of ion−ion interactions relative to the anhydrous systems while the main structuring of the individual protic ILs remains intact with water molecules intercalated in the ionic network and unable to form bulk water-like structure, consistent with recent findings from neutron scattering experiments on pyridinium hydrogen sulfate, [Hpy][HSO 4 ], doped with ∼15 wt % water. 45 The effect on structuring and corresponding chemical properties has been previously investigated for several ILs on addition of metal salt dopants 46,47 or water at various concentrations. 48−51 Specifically, addition of metal dopants revealed unsymmetrical anion−metal cation clusters, which directly impacts the transport properties of the metal cations.…”