Electrochemical and IR spectroscopic detection of oxidation products of the monomer and dimer of vanillyl alcohol in a sol–gel processed silicate matrix

The electrooxidation of two lignin model compounds – vanillyl alcohol and its dimer 1-(4-benzyloxy-3-methoxyphenyl-2-(2-methoxyphenoxy)-2-hydroxy-1-ethanol were studied. The products of this reaction were identified electrochemically and spectroscopically. For this purpose both compounds were encapsulated as part of two different electrode structures: hydrophobic sol–gel processed film deposited on a gold surface and a heterogeneous bulk electrode composed of hydrophobic silicate and graphite microparticles (carbon ceramic electrode). The electrochemical oxidation of the model compounds in pH 4.8 buffer is irreversible. However, during subsequent scanning a reversible set of voltammetric peaks appeared for vanillyl alcohol and for its dimer. This is attributed to the redox process of 1,2-quinone derivatives and the mechanism of the electrode process is elucidated. The ex situ polarisation modulation infrared reflection–absorption spectroscopy study of the film electrode before and after oxidation revealed that 1,2-quinone derivatives are not the only products produced during the electrooxidation process of both compounds. Oxidation of the monomer and the dimer results in the production of two different sets of products.