Bi-functionality of organic acids as acid catalysts and hydrogen source for one-pot production of secondary amines from primary amines and aromatic aldehydes over an Au-C3N4 photocatalyst

Abstract

Carbon nitride modified with a gold (Au) cocatalyst (Au-C3N4) was utilized in a one-pot synthesis of N-phenylbenzylamine (PBA) from benzaldehyde (BAD) and aniline (AN) in the presence of an organic acid. In this process, the organic acid fulfilled two functions: 1) as an acid catalyst for the condensation of AN and BAD, producing benzylideneaniline (BAN) in the initial thermal step, and 2) as a hole scavenger (hydrogen source) for the hydrogenation of BAN to PBA in the subsequent photocatalytic step over Au-C3N4. Various organic acids were utilized, and oxalic acid was found to be the most effective due to its capacity to maintain an acidic pH environment as a divalent acid and its ability to effectively capture positive holes as a hole scavenger, resulting in the generation of carbon dioxide. Photoirradiation to the system in an equilibrium in the condensation process induced effective hydrogenation of BAN, resulting in the production of PBA with a yield of >99%. A series of experiments were conducted, including action spectrum, impact of alcohols, reusability, and synthesis of halogen-substituted PBA. The outcomes of this study demonstrate the efficacy of oxalic acid in photocatalytic reactions and the potential of a cocatalyst-loaded C3N4 photocatalyst for organic synthesis.