Preparation and reaction of β-O-4 γ-aldehyde-containing butanosolv lignins

Catalytic processing of lignin predominantly focuses on the most prevalent β-O-4 bonds. During butanosolv pretreatment of lignocellulosic biomass, the β-O-4 unit is modified, which leads to high levels of butanol incorporation at the α-position. This enables oxidation of the γ-hydroxyl without the need for selective oxidation with no additional steps being required in the overall process. Here we take advantage of this to prepare a butanosolv walnut shell lignin in which the β-O-4 γ-hydroxyl has been converted to the corresponding aldehyde. This lignin is relatively stable and has been characterized by 2D heteronuclear single quantum coherence spectroscopy NMR. Subsequent Seyferth-Gilbert reaction of the aldehyde generates the corresponding lignin-bound alkyne which undergoes copper-mediated cycloaddition reactions. This protocol provides rapid access from lignocellulosic biomass to modified lignins.