Removal of phenolic hydroxyl groups in lignin model compounds and its effect on photostability

The phenolic hydroxyl groups in the lignin model compounds, 2-methoxy-4-pro pylphenol and 4-hydroxy-3-methoxyacetophenone, were removed by first conver ting the hydroxyl groups to the trifluoromethanesulfonates (triflates) and then cleaving the triflate substituents via catalytic hydrogen transfer. Th e products, 1-methoxy-3-propylbenzene and 3-methoxyacelophenone: were chara cterized by H-1 and C-13 NMR, mass spectrometry and elemental analyses. The effect of the removal of the phenolic groups on the photostability of the model compounds was evaluated by impregnating the compounds into Whatman fi lter paper sheets, and subjecting them to an accelerated yellowing experime nt in a UV chamber. The removal of the phenolic groups resulted in a signif icant yellowing inhibition, with a higher photostabilizing effect than meth ylation or acetylation of the hydroxyl, particularly for the model compound without an alpha-carbonyl group.