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

Article


Firth, A. E. J., Nakasu, P. Y. S., Hallett, J. P. and Matthews, R. P. 2024. Exploiting Cation Structure and Water Content in Modulating the Acidity of Ammonium Hydrogen Sulfate Protic Ionic Liquids. The Journal of Physical Chemistry Letters. 15 (9), pp. 2311-2318. https://doi.org/10.1021/acs.jpclett.3c03583
AuthorsFirth, A. E. J., Nakasu, P. Y. S., Hallett, J. P. and Matthews, R. P.
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.

JournalThe Journal of Physical Chemistry Letters
Journal citation15 (9), pp. 2311-2318
ISSN1948-7185
Year2024
PublisherAmerican Chemical Society (ACS)
Publisher's version
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Anyone
Digital Object Identifier (DOI)https://doi.org/10.1021/acs.jpclett.3c03583
Publication dates
Online22 Feb 2024
Publication process dates
Accepted19 Feb 2024
Deposited12 Mar 2024
Copyright holder© 2024, The Authors
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