Electrochemical Oxidation Pathways of Hydroxycoumarins on Carbon Electrodes Examined by LSCV and LC–MS/MS

Abstract

It is reported the voltammetric behavior and the identification of the oxidation products of four different hydroxycoumarins, namely, 3-, 4-, 6- and 7-hydroxycoumarin (3HC, 4HC, 6HC and 7HC), on carbon electrodes by performing bulk electrolyses in buffered solutions. LC–MS/MS in high resolution mode is used for the product identification. It was found that the voltammetric behaviours of the four compounds are quite different, as well as the corresponding oxidation products. For 3HC the end product was 2 hydroxymandelic acid [2-hydroxy-2-(2-hydroxyphenyl)acetic acid]: for 4HC, salicylic acid [2 hydroxybenzoic acid]; for 6HC, 2H-1-benzopyran-2,6(8aH)-dione and for 7HC no low-molecular weight products were identified. Based on these products and on the voltammetric results, the overall oxidation pathways are formulated as four-electron processes for 3HC and 4HC, and two-electron processes for 6HC. 7HC oxidation is proposed to be an electropolymerization reaction.