The electrode reaction of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was investigated in a solvate ionic liquid composed of lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) and tetraglyme (G4), [Li(G4)]TFSA. A quasi-reversible redox reaction of the oxoammonium (TEMPO+) and TEMPO was observed with a formal potential of 0.19 V vs ferrocene|ferrocenium. The diffusion coefficient of TEMPO+ (2.1 × 10-8 cm2 s-1) was smaller than that of neutral TEMPO (1.3 × 10-7 cm2 s-1), reflecting the coulombic interaction between monovalent TEMPO+ and TFSA- in the solvate ionic liquid. The standard rate constant for TEMPO+/TEMPO redox reaction was estimated to be 1.9 × 10-4 cm s-1 at 25 C by electrochemical impedance spectroscopy. The solubility of TEMPO in [Li(G4)]TFSA was found to be 4.4 M at 25 C.
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