Protic Ionic Liquids and Ionicity
Bharathi Nuthakki A , Tamar L. Greaves A , Irena Krodkiewska A , Asoka Weerawardena A , M. Iko Burgar B , Roger J. Mulder A and Calum J. Drummond A C DA CSIRO Molecular and Health Technologies (CMHT), Clayton VIC 3169, Australia.
B CSIRO Manufacturing & Materials Technology (CMMT), Clayton South VIC 3169, Australia.
C CSIRO Industrial Physics (CIP), Lindfield NSW 2070, Australia.
D Corresponding author. Email: calum.drummond@csiro.au
Australian Journal of Chemistry 60(1) 21-28 https://doi.org/10.1071/CH06363
Submitted: 10 October 2006 Accepted: 11 January 2007 Published: 29 January 2007
Abstract
Protic ionic liquids (PILs) are a subset of ionic liquids formed by the equimolar mixing of a Brønsted acid and a Brønsted base. PILs have been categorized as poor ionic liquids. However, the issue of assessing the ionicity of PILs is still a matter of debate. In this work we studied some physicochemical properties of three chosen PILs, namely, ethanolammonium acetate (EOAA), 2-methylbutylammonium formate (2MBAF), and pentylammonium formate (PeAF), at the initial equimolar (stoichiometric) acid/base ratio and in the presence of excess acid and base. DSC phase-transition studies along with NMR, IR, and Raman spectroscopy were performed on the chosen PILs. The results are discussed in terms of the degree of ionization (extent of proton transfer from the Brønsted acid to Brønsted base), and the possibility of the formation of polar 1:1 complexes and larger aggregates in the neat stoichiometric PILs.
Acknowledgments
C.J.D. is the recipient of an Australian Research Council (ARC) Federation Fellowship. This work was partly supported by ARC Discovery Project grant DP0666961. We thank Dr Fiona Scholes (CMMT) for assistance with Raman spectroscopy.
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