Induced Protic Behaviour in Aprotonic Ionic Liquids by Anion Basicity for Efficient Carbon Dioxide Capture

Darius J. Yeadon, Johan Jacquemin, Natalia V. Plechkova, Manuel Maréchal, Kenneth R. Seddon

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


The interactions between aprotonic tetrabutylphosphonium carboxylate ionic liquids (ILs), [P4 4 4 4][CnCOO] (n=1, 2 and 7), and water were investigated. The cation-anion interactions occur via the α-1H on [P4 4 4 4]+ and the carboxylate headgroup of the anion. Upon addition, H2O localises around the carboxylate headgroups, inducing an electron inductive effect towards the oxygens, leading to ion-pair separation. Studies with D2O and [P4 4 4 4][CnCOO] revealed protic behaviour of the systems, with proton/deuterium exchange occurring at the α-1H of the cation, promoted by the basicity of the anion, forming an intermediate ylide. The greater influence of van der Waals forces of the [P4 4 4 4][C7COO] system allows for re-orientation of the ions through larger interdigitation. The protic behaviour of the neat ILs allows for CO2 to be chemically absorbed on the ylide intermediate, forming a phosphonium-carboxylate zwitterion, signifying proton exchange occurs even in the absence of H2O. The absorption of CO2 in equimolar IL-H2O mixtures forms a hydrogen carbonate, through a proposed reaction of the CO2 with an intermediate hydroxide, and carboxylic acid.
Original languageEnglish
Pages (from-to)1369-1374
Number of pages6
Issue number13
Early online date03 Jun 2020
Publication statusPublished - 02 Jul 2020


  • Physical and Theoretical Chemistry
  • Atomic and Molecular Physics, and Optics


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