Binary Mixtures of Ionic Liquids in Aqueous Solution: Towards an Understanding of Their Salting-In/Salting-Out Phenomena

  • Catarina M. S. S. Neves
  • Teresa B. V. Dinis
  • Pedro J. Carvalho
  • Bernd Schröder
  • Luís M. N. B. F. Santos
  • Mara G. Freire
  • João A. P. CoutinhoEmail author


The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of macromolecules in aqueous solutions is known as the Hofmeister series. Taking into account that ionic liquids (ILs) are constituted by ions, they can exert similar effects on the solubility of other ILs in aqueous media. To expand the knowledge of the salting-in/-out ability of ILs, experimental studies on the solubility of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) in water and in the presence of other IL/salts, were conducted at 298.15 K and atmospheric pressure. Both the impact of the anion and cation of the IL were evaluated with the following ILs/salts: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hydrogensulfate, cholinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, over a wide composition range. As happens with common salts, both salting-in and salting-out effects exerted by ILs were observed, with a higher impact exerted by the IL anion on the salting-out phenomenon. These data allow better understanding of the ILs impact when designing liquid–liquid separation processes.

Graphical Abstract


Ionic liquids Solubility Water Salting-in effect Salting-out effect Hofmeister series 



This work was developed in the scope of the projects CICECO-Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. Catarina M. S. S. Neves and Teresa B. V. Dinis also acknowledge FCT for their grants (SFRH/BPD/109057/2015 and SFRH/BD/130958/2017, respectively). P. J. Carvalho acknowledges FCT for a contract under the Investigador FCT 2015, Contract No. IF/00758/2015. The research leading to reported results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement No. 337753.

Supplementary material

10953_2018_836_MOESM1_ESM.docx (475 kb)
NMR spectra of all ILs, UV calibration curve of [C4C1im][NTf2] and experimental solubility data. Supplementary material 1 (DOCX 474 kb)


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Authors and Affiliations

  1. 1.CICECO - Aveiro Institute of Materials, Department of ChemistryUniversity of AveiroAveiroPortugal
  2. 2.CIQUP-Centro de Investigação em Química da Universidade do Porto, Departamento de Química e Bioquímica, Faculdade de CiênciasUniversidade do PortoPortoPortugal

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