Electrochemical Oxidation of 7-, 8- and 9-Hydroxy-3-ethoxycarbonyl-2,4-dimethyl coumarin[4,3-b]Pyridine Isomers at Glassy Carbon in Dimethylformamide

Abstract

The oxidation of three synthesized 7-, 8- and 9-hydroxycoumarin[4,3-b] pyridines isomers on glassy carbon electrode (GCE) in dimethylformamide is reported. Voltammetry, chronoamperometry, UV-Visible spectroscopy and spectroelectrochemistry were employed to collect data that permitted us to establish the oxidation behavior of hydroxy-substituted pyridine-fused coumarins. The oxidation of the phenol moiety is irreversible in character and the overall oxidation process involves 2-electrons and 2-protons, to give the corresponding quinone-type derivatives. Furthermore, cyclic voltammetry supports the conclusion of that the oxidation of the 9-hydroxy-substituted derivative occurs in two steps in an ECE mechanism. Chronoamperometry permits us to determine the number of electrons for each step, thus supporting the mentioned ECE mechanism. Additionally, the effect of tetrabutylammonium hydroxide on the oxidation of the compounds was studied through UV-Visible spectroscopy and voltammetry. Spectroelectrochemical data showed that the quinone products of the electrolysis absorb in the range of 337-381 nm. Comparative studies by cyclic voltammetry revealed that hydroxy-substituted coumarin[4,3-b] pyridines are oxidized more easily than 3-acetyl-8-hydroxycoumarin and phenol. © 2011 The Electrochemical Society.