Amine‐Mediated Bond Cleavage in Oxidized Lignin Models

Introducing amines/ammonia into lignin cracking will allow novel bond cleavage pathways. Herein, a method of amines/ammonia‐mediated bond cleavage in oxidized lignin β‐O‐4 models was studied using a copper catalyst at room temperature, demonstrating the effect of the amine source on the selectivity of products. For primary and secondary aliphatic amines, lignin ketone models underwent oxidative C α −C β bond cleavage and C α −N bond formation to generate aromatic amides. For ammonia, the competition between oxygen and ammonia determined the selectivity between C α −N and C β −N bond formation, generating amides and α‐keto amides, respectively. For tertiary amines, the lignin models underwent oxidative C α −C β bond cleavage to benzoic acids. Control experiments indicated that amines act as nucleophiles attacking at the C α or C β position of the oxidized β‐O‐4 linkage to be cleaved. This study represents a novel example that the breakage of oxidized lignin model can be regulated by amines with a copper catalyst.