Electro-oxidation of synthetic lignin with linoleic acid and co-catalyst

Abstract

Linoleic acid (LA) was investigated as an electron transfer catalyst in biomimetic lignin degradation with an electrolytic mediator system (EMS). Initial attempts of electro-oxidations of synthetic lignin, guaiacyl (G)-type dehydrogenation polymer (G-DHP), with LA alone at 0.8 V and 1.8 V, resulted in limited G-DHP conversion, suggesting that LA-mediated EMS is not effective when LA was used alone. Next, electro-oxidations of G-DHP with LA with O₂-sparging as well as in the presence of co-catalysts, such as p-coumaric acid (PCA), tris(2, 2'-bipyridine) iron(II) [Fe(bpy)₃], and 1-hydroxybenzotriazole (HBT) were performed. The combined use of oxygen and co-catalysts appeared to be effective to promote G-DHP conversion. In particular, G-DHP conversion proceeded effectively in the electro-oxidation with LA/HBT at 0.6 V, as demonstrated by structural analysis of the electrolysis residues using nuclear magnetic resonance. HBT was also found to be a vital mediator when used alone in the present system. Overall, the combined use of oxygen and co-catalysts was essential for the EMS oxidation with LA, as reported in laccase mediator system (LMS) oxidation with LA.