Electrochemical Oxidation of 2,3-Dihydroxypyridine in the Presence of Benzenesulfinic Acid: A Green Method for the Synthesis of a Novel Heterocycle Dye

A green method for the one-pot electrochemical synthesis of a novel highly oxygenated heterocycle dye, 3,8-dihydroxy-4,9-bis(phenylsulfonyl)dipyrano[2,3-b:2,3 ' -e]pyrazine-2,7-dione (PSO), is reported. The synthesis of this compound was performed by anodic oxidation of 2,3-dihydroxypyridine (DHP) in the presence of benzenesulfinic acid (BSA) in aqueous acetate buffer solution, using a carbon electrode. The cyclic voltammogram of DHP shows an irreversible anodic peak corresponding to two-electron oxidation of DHP to pyridine-2,3-dione (PDO), while, the CV of the mixture of DHP and BSA exhibits a new anodic peak at more positive potentials which is a confirmation of the reaction between electrogenerated PDO and BSA. Based on the electrochemical evidence, a novel mechanism for the synthesis of PSO is proposed. The synthesis of PSO was conducted in aqueous acetate buffer (pH = 4.0, c = 0.2 M), by controlled potential method (at 0.90 V vs Ag/AgCl electrode, yield 69%) as well as by constant current method (at J = 1.12 mA cm(-2), yield 63%) in a divided cell, under green conditions. Furthermore, the pH dependent anodic behavior of 2,3-dihydroxypyridine was investigated. Our data shows that the E-pA-pH diagram indicates the presence of five predominant regions. The predominant species across all regions were identified.