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.

Automated summary

A green method for the one-pot electrochemical synthesis of a novel highly oxygenated heterocycle dye, PSO, has been successfully developed. The synthesis was performed using anodic oxidation of DHP in the presence of BSA, with the proposed mechanism supported by electrochemical evidence. The synthesis was conducted under environmentally friendly conditions, achieving high yields of PSO.