An ionic liquid according to the invention is substantially halogen-free, has a low viscosity and is stable to hydrolytic degradation under test conditions. The ionic liquid is a compound of the formula (cation) (R′—O—SO3), (cation) (R′—SO3), or a mixture of the two compounds. It can be used in processes for the chemical conversion and separation of materials by employing the ionic liquid as a solvent, solvent additive, extraction agent or phase-transfer catalyst. It can also be used in a heat exchange device wherein the ionic liquid serves as a heat carrier or heat carrier additive.