Issue 7, 2010
From the journal:

Physical Chemistry Chemical Physics

Preparation of protic ionic liquids with minimal water content and 15N NMR study of proton transfer†

Geoffrey L. Burrell,*a   Iko M. Burgar,b   Frances Separovicc  and  Noel F. Dunlopd  

* Corresponding authors

a School of Chemistry, The University of Melbourne, Melbourne, Australia

b CSIRO Materials Science & Engineering, Clayton, Australia

c School of Chemistry, The University of Melbourne, Melbourne, Australia
E-mail: fs@unimelb.edu.au

d Orica Ltd., Melbourne, Australia

Abstract

Low-molecular-weight Brønsted acids and amine bases were used to reproducibly prepare very dry, high-purity room-temperature protic ionic liquids (PILs). A series of eight amine bases and six Brønsted acids were combined to produce 48 mixtures, of which 18 were liquid at room temperature. The phase transitions and thermal decomposition temperatures were determined for each mixture; whereas viscosity, density and conductivity were determined for the room-temperature liquids. By utilising 15N NMR it was possible to distinguish between neutral and ionised amine bases (ammonia vs. ammonium-type ion), which indicated that the protic ionic liquids were completely ionised when made as a stoichiometric mixture. However, a Walden plot comparison of fluidity and molar conductivity indicated the majority of PILs had much lower conductivity than predicted by viscosity unless the base contained excess proton-donating groups. This disparity is indicative of protic ionic molecules forming neutral aggregates or non-Newtonian fluid hydrogen-bonded networks with a secondary Grotthuss proton-hopping mechanism arising from polyprotic bases.

Graphical abstract: Preparation of protic ionic liquids with minimal water content and 15N NMR study of proton transfer

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Article information

DOI
https://doi.org/10.1039/B921432A
Article type
Paper
Submitted
13 Oct 2009
Accepted
27 Nov 2009
First published
12 Jan 2010

Phys. Chem. Chem. Phys., 2010,12, 1571-1577

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Preparation of protic ionic liquids with minimal water content and 15N NMR study of proton transfer

G. L. Burrell, I. M. Burgar, F. Separovic and N. F. Dunlop, Phys. Chem. Chem. Phys., 2010, 12, 1571 DOI: 10.1039/B921432A

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