Electroreduction of lichexanthone

This paper reports the first study on the electrochemical reduction of lichexanthone (1H) (1-hydroxy-3,6-dimethoxy-8-methylxanthen-9-one) on glassy carbon (GC) electrodes in DMSO, using cyclic voltammetry, rotating disc and ring electrodes, and long-term controlled-potential electrolysis. Parameters involving data from cyclic voltammetry and rotating disc electrodes, such as current functions, E_pc1 vs. log ν, E_pc2 vs. log ν, E_pc/2,1 − E_pc1, −I_pc1ox/I_pc1red, I_pc2/I_pc1, E_1/2 vs. log ω, and collection efficiency (rotating disc and ring electrode data), were used to elucidate the reduction mechanism of 1H that involves two one-electron transfers (two reduction peaks in the voltammograms), the first of which, with reversible characteristics, involves electroreduction of 1H, producing a radical anion 1H⁻, whereas the second, with irreversible characteristics, involves electroreduction of 1H⁻, producing a dianion 1H²⁻. Both transfers appear to involve an E_rC_slow-type mechanism with a chemical step consisting of breakage of a bond followed by protonation of residual water, or parent compound, or solvent, etc., to yield 2-hydroxy-4-methoxy-6-methylphenyl 2-hydroxy-4-methoxyphenyl ketone (1H₃), directly, in the case of 1H²⁻ involved. Compound 1H₃ was elucidated by 1D- and 2D-NMR methods. D₀ = 2.66 × 10⁻⁶ cm² s⁻¹ was found for the electrochemical reduction of 1H.