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Updated: Jul 2, 2025
Determination of the Gas-phase Acidities of Oligopeptides
Published on: June 24, 2013
Exploiting Cation Structure and Water Content in Modulating the Acidity of Ammonium Hydrogen Sulfate Protic Ionic
Anton E J Firth1, Pedro Y S Nakasu1, Jason P Hallett1
1Department of Chemical Engineering, Imperial College London, London SW7 2AZ, U.K.
Abstract:
In this paper, we investigated the effect of cation structure and water content on proton dissociation in alkylammonium [HSO4]- protic ionic liquids (ILs) doped with 20 wt % water and correlated this with experimental Hammett acidities. For pure systems, increased cation substitution resulted in a reduction in the number of direct anion-anion neighbors leading to larger numbers of small aggregates, which is further enhanced with addition of water. We also observed spontaneous proton dissociation from [HSO4]- to water only for primary amine-based protic ILs, preceded by the formation of an anion trimer motif. Investigation using DFT calculations revealed spontaneous proton dissociation from [HSO4]- to water can occur for each of the protic ILs investigated; however, this is dependent on the size of the anion aggregates. These findings are important in the fields of catalysis and lignocellulosic biomass, where solvent acidity is a crucial parameter in biomass fractionation and lignin chemistry.
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