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 (CC) 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 nu, E-pc2 vs. log nu, E-pc/2,E-1 - E-pc1, - I-pc1ox/I-pc1red, I-pc2/I-pc1, E-1/2 vs. log omega, 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 1H(2-). Both transfers appear to involve an E Gamma Cslow-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 (1H(3)), directly, in the case of 1H(2)- involved. Compound 1H(3) was elucidated by 1D- and 2D-NMRmethods. D-0 = 2.66 x 10(-6) cm(2) s(-1) was found for the electrochemical reduction of 1H. (C) 2008 Elsevier Ltd. All rights reserved.