*5.2.4 Oxidation*

In oxidation, ether bonds are sliced of the hydroxyl-benzyl group of the lignin structure, resulting to a combination of aromatic ketones and aldehydes that are valuable predecessors to fine chemicals. For example, in an alkaline medium, lignin is oxidized under high-pressure of oxygen for vanillin synthesis. Further, catalysts like Pd/Al2O3 speed up the selective oxygenation of lignin for high yield of vanillin and syringaldehyde [26].
