Synthesis of 4-sulfonatooxy-2,2,6,6-tetramethylpiperidine-1-yloxyl derivatives for investigation of ionic liquids

Direct sulfonation of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-yloxyl using chlorosulfuric acid trimethylsilylester results in 4-sulfonatooxy-2,2,6,6-tetramethylpiperidine-1-yloxyl in 94% yield that is the basis for the synthesis of potassium 4-sulfonatooxy-2,2,6,6-tetramethylpiperidine-1-yloxyl and sodium 4-sulfonatooxy-2,2,6,6-tetramethylpiperidine-1-yloxyl. These nitroxides can be employed as spin probes to investigate properties of ionic liquids in the molecular domain.