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, Epc1 vs. log ν, Epc2 vs. log ν, Epc/2,1 − Epc1, −Ipc1ox/Ipc1red, Ipc2/Ipc1, E1/2 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 ErCslow-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.