Toward radiation-resistant ionic liquids. Radiation stability of sulfonyl imide anions

Room-temperature hydrophobic ionic liquids (ILs) are considered for processing of spent nuclear fuel, including as possible replacements for molecular diluents in liquid-liquid extraction. This application requires radiation stability of the constituent ions. Previous research indicated that most of the anions that are currently used in the synthesis of ILs are prone to fragmentation under prolonged radiation exposure, which causes deterioration of the corresponding ILs. An exception to this general rule is phthalimide; unfortunately, this anion is too basic to be useful for extraction solvents, as these separations involve acidic conditions. The acidity of the imide can be increased by replacing the carbonyl groups by sulfonyl groups, which incidentally transform these imides into familiar artificial sweeteners such as saccharin. In the present study, we use electron paramagnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry to assess the radiation stability of ILs based on such "sweet" sulfonyl imide anions. Our results suggest that saccharinate and o-benzenedisulfonimide are remarkably stable to radiation-induced fragmentation.