Oxidative dehydrogenation of a biomass derived lignan – Hydroxymatairesinol over heterogeneous gold catalysts

Synthesis of the lignan oxomatairesinol via oxidative dehydrogenation of the naturally occurring lignan hydroxymatairesinol was studied over gold catalysts supported on C, TiO2, SiO2, Al2O3, and MgO. In order to investigate the reaction performance over the gold catalyst, synthesis of lignan oxomatairesinol was carried out in different organic solvents/water mixtures under synthetic air and nitrogen atmosphere at 373 K, and using also isolated hydroxymatairesinol isomers as a starting material. The results were compared with those obtained over palladium catalysts. Synthesized supported gold catalysts as well as the corresponding supports were characterized by TEM, XRD, ICP-OES, CO2-TPD, FTIR (using pyridine as a probe molecule), and XPS. Gold catalysts were shown to display superior performance compared with palladium ones: the activity was 4 times higher, with selectivity toward oxomatairesinol being 100%, while 60–85% were obtained over palladium catalysts. In contrast to palladium, the activity of gold catalysts is high in aerobic conditions and water–propan-2-ol mixture. However, activity and selectivity of gold catalysts were shown to be dependent on the electronic state of the metal and, similar to palladium catalysts, on the support acidity.

Synthesis of lignan oxomatairesinol (oxoMAT) via oxidative dehydrogenation of the naturally occurring lignan hydroxymatairesinol (HMR), which exists in nature as a mixture of two diastereomers: (7R,8R,8’R)-(-)-7-allo-hydroxymatairesinol and (7S,8R,8’R)-(-)-7-allo-hydroxymatairesinol, was studied over supported gold catalysts. Applying gold catalysts boosts the selectivity toward oxomatairesinol up to 100%.Figure optionsDownload high-quality image (88 K)Download as PowerPoint slideHighlights
► Oxidation of hydroxymatairesinol–natural lignan.
► Gold catalysts are superior compared with Pd.
► 100% selectivity to oxomatairesinol.
► Activity and selectivity dependent on support acidity.
► Reaction requires water–propanol mixture as solvent.