Lignin amination valorization: heterogeneous catalytic synthesis of aniline and benzylamine from lignin-derived chemicals

Lignin chemistry is regarded as one of the core components in the field of biomass catalytic conversion. Over the past decade, the catalytic synthesis of value-added chemicals or biofuels via oxidation/reduction depolymerization with lignin as the initial substrate has made extensive progress through ongoing research attempts. However, there are fewer investigations on the conversion of lignin derivatives to nitrogen-containing compounds such as aniline and benzylamine through heterogeneous catalytic amination. On this account, this paper reviews the amination value-added reaction processes of lignin-derived phenols, ethers, carbonyl compounds and alcohols to produce aniline and benzylamine, mainly focusing on cheap catalysts, green solvent systems, nitrogen source systems, and mild reaction conditions, which can provide novel perspectives to promote the processive innovation of a sustainable lignin amination system. The perspectives on the synthesis of lignin-based aniline and benzylamine proposed in this review are intended to offer novel research ideas for further expanding the boundaries of the biomass refining systems involving lignin amination chemistry.