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Issue 42, 2014
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Brønsted acids in ionic liquids: how acidity depends on the liquid structure

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Abstract

Gutmann Acceptor Number (AN) values have been determined for Brønsted acid–ionic liquid mixtures, over a wide compositional range. Four systems of general formula [C2mim][A]–HA (A = bistriflamide, [NTf2]; triflate, [OTf]; mesylate, [OMs]; or acetate, [OAc], [C2mim]+ = 1-ethyl-3-methylimidazolium cation) were studied. A library of Brønsted acidic systems of varying acidity was constructed and the AN parameter was found to be a convenient approach for quantifying their acidity. HOAc, HOMs and HOTf, when dissolved in ionic liquids, were found to associate with the respective anions to form hydrogen-bonded anionic clusters, [A(HA)x]. In contrast, HNTf2 was solubilised as a discrete, undissociated molecule. AN values were sensitive to the presence of anionic clusters; acidity could be buffered to a particular AN by binding the solubilised acid in the anionic cluster form. Overall, a simple way to manipulate and quantify the Brønsted acidity of acid–ionic liquid mixtures was demonstrated, and measured AN values were related to liquid speciation.

Graphical abstract: Brønsted acids in ionic liquids: how acidity depends on the liquid structure

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Publication details

The article was received on 20 Jul 2014, accepted on 11 Sep 2014 and first published on 11 Sep 2014


Article type: Paper
DOI: 10.1039/C4CP03217A
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Phys. Chem. Chem. Phys., 2014,16, 23233-23243

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    Brønsted acids in ionic liquids: how acidity depends on the liquid structure

    J. A. McCune, P. He, M. Petkovic, F. Coleman, J. Estager, J. D. Holbrey, K. R. Seddon and M. Swadźba-Kwaśny, Phys. Chem. Chem. Phys., 2014, 16, 23233
    DOI: 10.1039/C4CP03217A

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