Understanding the Role of Protic Ionic Liquids (PILs) in Reactive Systems: Rational Selection of PILs for the Design of Green Synthesis Strategies for Allylic Amines and β‐Amino Esters

Abstract

The reactive behaviour of protic ionic liquids (PILs) has been shown to be governed not only by their chemical structures but also by their global compositions, which include the presence of free acids and bases at equilibrium with ionic pairs. Six PILs composed of primary, secondary, or tertiary alkyl ammonium cations with two couterions, nitrate or acetate, were tested in model reactions with unsaturated substrates. The free species that were naturally present in these liquids were identified by cyclic voltammetry. Only tributylammonium nitrate was found to be mostly composed just of the ionic pair; the other five PILs also contain variable amounts of free acid and amine. In reactive systems, these free species determine the products of the reaction. In particular, allylic amines and β‐amino esters were obtained in good yields (91 and 75 %, respectively) by reaction of conjugated dienes and acrylates in the presence of PILs. By taking into account the actual composition of each PIL, it was possible to direct the reaction path towards a specific product with good yields, to ensure acid catalysis, to avoid polymerization of the substrate, and to promote phase transfer of products. These results establish some useful guidelines for the rational design of new PIL‐based one‐step synthetic strategies.

Phase and Chemical Equilibria of Biphasic Protic Ionic Liquid: Triethylamine–Acetic Acid

“…Interestingly, in some cases, the different solubility of molecular and ionic species in different environments may result in the formation of a biphasic PIL . Ionicity, which is usually defined as the degree of proton transfer of a PIL, − not only affects the physicochemical properties of a PIL − but also governs its suitable applications. − The quantitative study on the ionicity of biphasic PILs can provide useful information on both phase and proton-transferring equilibria in these systems.…”

Insights on the catalytic behaviour of sulfonic acid-functionalized ionic liquids (ILs) in transesterification reactions – voltammetric characterization of sulfonic task-specific ILs with bisulfate anions

“…For example, it was recently reported that alkylammonium-derived ILs synthesized by acid-base addition contain the acid and base precursors in autoprotolysis equilibrium with the ionic pairs. 23 The particular combination of ions and neutral species determines the properties of the synthesized IL, and then its performance in an application is influenced by all the interactions that are established within the reactive system.…”

“…Electrochemical techniques are being intensely used for exploiting the outstanding properties of ILs as electrolytes, 26 and particularly cyclic voltammetry has shown to be extremely useful as a detection technique for revealing the presence of free species other than the ionic pair. 21,23 Thus, in this work the monitoring of ILs by cyclic voltammetry was carried out in order to perceive the effect of the IL synthesis conditions and parameters (synthesis reaction time, purification steps) on the amounts of these species. Our hypothesis is that a specific behaviour of a sulfonic TSIL in a reactive system cannot be attributed solely to the presence of the SO 3 H groups that functionalize the TSIL structure.…”

Analysis of the Relationship between the Composition of a Bronsted Acidic Task-Specific Ionic Liquid: 1-(4-Sulfonic Acid)-butyl-3-Methylimidazolium Hydrogen Sulfate ([bsmim] [HSO4]), and Its Behavior on Reactive Systems

“…The aim is to optimize the selection of TSIL to achieve a specific property and analyze the effect of the decoration of structure of imidazolium cation with a sulfonic group. In this direction, the synthesis of a TSIL was developed by decorating the structure of the 1butyl-3-methyl imidazolium (bmim) cation with an acid sulfonic group, to obtain 1-(4-sulfonic acid)butyl- 3 [4]. According to what was observed and in order to correlate results, the ILs were applied in two reactive systems: synthesis of dibenzoxanthenes and esterification reactions.…”