(78f) Monomers Via Acidolysis of Lignin Using CO?-Expanded Liquids.

This study investigates the production of aromatic monomers from lignin and lignin model compounds through in situ stabilization of reactive intermediates using CO₂-expanded liquid media. Conventional acidolysis methods, particularly under high-temperature conditions and prolonged solvent exposure, often suffer from low monomer yields due to side reactions such as formaldehyde loss and the formation of unstable phenylethane aldehydes, which readily undergo recondensation in acidic environments. Additionally, the use of strong mineral acids poses environmental concerns due to the need for neutralization and the generation of acidic waste. To address these limitations, we explore the use of CO₂-expanded liquids, specifically water and alcohols, as a tunable and environmentally benign alternative. Upon dissolution, CO₂ reacts with water and alcohols to form carbonic acid and alkyl carbonates, respectively, which dissociate to generate hydronium ions. This in situ acidification facilitates the cleavage of β-O-4 ether bonds in lignin, forming phenylethane aldehydes. To prevent recondensation, these aldehydes are simultaneously stabilized via acetalization with ethylene glycol, forming stable 1,3-dioxolane derivatives directly within the reaction medium.