Ionic liquids interact with dissolved salts to give solutions that are completely different to salt solutions in traditional organic solvents or water, say UK scientists.
Ionic liquids are of great interest as green solvents but the way they solvate solutes isn’t well understood. Scientists studying their polarity have produced contradictory results – in some cases they are reported to be highly polar, in others non-polar.
Now Tom Welton and colleagues at Imperial College London say they’ve resolved this contradiction and have revealed a completely new solvent paradigm for salt solutions in ionic liquids.
In contrast to molecular solvents, where the solute cation and anion need to stay close to each other to preserve charge neutrality, ionic liquids solvate individual solute ions, explains Welton. This completely divorces the cations and anions from each other but the ionic liquid itself is capable of preserving the charge neutrality.
The polarity of ionic liquids depends on when you ask, adds Welton. Polarity measurements that record snapshots of the ionic liquid on a short timescale (such as measuring the position of the absorption maximum) ‘freeze out’ ionic movement and so the ionic liquid appears non-polar. Absorptivity measurements involve a longer timescale, allowing ion movement to dominate solvation, yielding a much higher polarity.
Read more in ‘Salts dissolved in salts‘ in Chemical Science.
