Choline Saccharinate and Choline Acesulfamate: Ionic Liquids with Low Toxicities

Choline saccharinate and choline acesulfamate are two examples of hydrophilic ionic liquids, which can be
prepared from easily available starting materials (choline chloride and a non-nutritive sweetener). The (eco)toxicity of these ionic liquids in aqueous solution is very low in comparison to other types of ionic liquids.
A general method for the synthesis and purification of hydrophilic ionic liquids is presented. The method
consists of a silver-free metathesis reaction, followed by purification of the ionic liquid by ion-exchange
chromatography. The crystal structures show a marked difference in hydrogen bonding between the two
ionic liquids, although the saccharinate and the acesulfamate anions show structural similarities. The optimized
structures, the energetics, and the charge distribution of cation−anion pairs in the ionic liquids were studied
by density functional theory (DFT) and second-order (Møller−Plesset) perturbation theory calculations. The
occupation of the non-Lewis orbitals was considered to obtain a qualitative picture of the Lewis structures.
The calculated interaction energies and the dipole moments for the ion pairs in the gas phase were discussed.