pH of Single and Double Salt SO₃H-Functionalized Brønsted Acidic Ionic Liquids

Abstract

Acidic ionic liquids are widely utilized as catalysts in acid-catalyzed reactions. The acidity of SO3H-functionalized Brønsted acidic ionic liquids (S-BAILs) in aqueous solutions was systematically investigated by their pH values. The pH values of single and double salt S-BAILs in aqueous solutions were measured by a pH meter. The dissociation mechanisms of single and double salt S-BAILs in aqueous solutions were proposed. The methods to predict the pH values of single and double salt S-BAILs were also proposed based on the dissociation mechanisms, and the calculated pH values agreed well with the experimental results. The dissociation mechanism of S-BAILs in aqueous solutions is further explained by the dissociation fraction of ionic liquids, and a method to estimate the dissociation fraction of S-BAILs in dilute aqueous solutions was proposed.

Studies on the Stability and Deactivation Mechanism of Immobilized Ionic Liquids in Catalytic Esterification Reactions

“…As we know, the Brønsted acidity of an immobilized ionic liquid comes from the protons of anions (e.g., HSO 4 – and H 2 PO 4 – ) or functional groups of cations (e.g., −SO 3 H and −CO 2 H). − Due to the positive charge of cations, many ionic liquid cations may tend to be deprotonated and result in the dissociation of protons in functional groups. Unfortunately, the releasable proton may be able to bond with an anion to form a free molecule, which will leach out into the solvent.…”