One-pot oxidation-acetalization strategy for photocatalytic cleavage of C-C bonds in lignin model compounds over phosphorus-doped carbon nitride

Abstract

Photocatalytic depolymerization of lignin into aromatic compounds is of great significance but extremely challenging, hindered by the stable interunit C-C bonds with high dissociation energies. Herein, we develop a novel oxidation acetalization strategy for the phtocatalytic cleavage of C-C bond in lignin model compounds while simultaneously reducing aldehyde condensation. Phosphorus-doped carbon nitride (Px-CN) was synthesized for the selective cleavage of Cα-Cβ bonds under visible light at room temperature. This approach achieves a nearly complete conversion (>99.9%) of 2-phenoxy-1phenylethanol, along with high yields of benzaldehyde dimethyl acetal (91.1%) and benzyl formate (56.3%). Mechanistic investigations reveal that the activation of the Cβ-H bond by photogenerated holes is crucial for the transformation to occur.Meanwhile, the introduction of phosphorus accelerates the separation efficiency of charge carriers, thereby enhancing the photocatalytic performance of the Px-CN. This work demonstrates the potential of phosphorus-doped carbon nitride for the high-selectivity photocatalytic cleavage of the C-C bond in lignin to aromatic chemicals.