Dual Catalytic Activity of an Ionic Liquid in Lignin Acetylation and Deacetylation

An ionic liquid, 1-ethyl-3-methylimidazolium acetate (EmimOAc) better catalyzed the acetylation of the aliphatic hydroxyl groups of lignin than the phenolic hydroxyl groups using isopropenyl acetate as an acetyl donor. However, in situ 1H NMR analyses performed on model compounds revealed that EmimOAc more effectively promoted the acetylation of phenol than 2-phenethyl alcohol. EmimOAc was also found to selectively catalyze the deacetylation of aromatic acetate, and thus the aliphatic hydroxyl groups of lignin were preferentially acetylated.