Dehydrogenation of hydroxymatairesinol to oxomatairesinol over carbon nanofibre-supported palladium catalysts

Dehydrogenation of the naturally occurring lignan hydroxymatairesinol to oxomatairesinol was performed over carbon nanofibre supported palladium catalysts (Pd/CNF) under nitrogen flow at 70 °C. To study the influence of support acidity on the catalyst performance, the amount of acid sites on the catalysts surface was varied by heat-treatment in nitrogen flow. It was concluded that both activity and selectivity to oxomatairesinol increased when the concentration of acid sites increased. The selectivity to oxomatairesinol was over 70% (at 4 h with 50% yield) when 2-propanol was used as solvent and the major by-product was 7-iso-propoxymatairesinol resulting from interactions with the solvent. In 2-pentanol, the selectivity increased to 90% (at 4 h with 50% yield). It was demonstrated that only one of the two diastereomers of hydroxymatairesinol preferentially yields oxomatairesinol. Quantum chemical calculations were performed as an attempt to explain this behaviour and to understand the role of acid sites.

Two diastereomers of the lignan hydroxymatairesinol, (7R,8R,8′R)-(−)-7-allo-hydroxymatairesinol (HMR 1) and (7S,8R,8′R)-(−)-7-hydroxymatairesinol (HMR 2), were dehydrogenated to 7-oxomatairesinol (oxoMAT) over carbon nanofibre supported palladium catalysts under nitrogen flow at 70 °C. Matairesinol (MAT) was formed as a by-product through hydrogenolysis of HMR. When 2-propanol was used as solvent, 7-iso-propoxymatairesinol was obtained as a by-product. Figure optionsDownload as PowerPoint slide