Reactions of Lignin Model ß-Aryl Ethers with Acetyl Bromide

The reactivities of several softwood lignin model compounds with acetyl bromide have been examined in a number of good lignin solvents. Primary (y-)alcohols acetylate more rapidly than phenolic hydroxyls, whereas benzylic (α-)hydroxyls are converted to bromides via their acetates. Models treated under mild conditions with acetyl bromide cleanly produced acetylated α-bromo derivatives. Benzyl aryl ethers are cleaved rapidly and quantitatively to yield aryl acetates and acetylated α-bromo products. The rate order for the observed reactions is : primary (γ-)OH acetylation > benzyl aryl ether cleavage/bromination > benzylic secondary (α-)OH acetylation > benzylic acetate to benzylic bromide interconversion >> phenolic OH acetylation. These reactions are synthetically useful and have further potential in analytical methodologies.