Environmentally benign oxidative homo-coupling of aromatic aldehydes to symmetrical carboxylic anhydrides using biodegradable choline peroxydisulfate

Oxidative coupling reactions have become a cornerstone bond-forming strategy in modern organic synthesis. Here, symmetrical aromatic anhydrides were prepared efficiently by oxidative homo-coupling of aromatic aldehydes using biodegradable choline peroxydisulfate (a task-specific ionic liquid oxidant) with catalytic CuCl2 under mild reaction conditions. Reaction progress and structure confirmation of both starting aldehydes and products were tracked in situ by 1H NMR directly in the reaction mixture. This green, mild, and operationally simple protocol minimizes side reactions and avoids volatile organic solvents, delivering a practical route to anhydrides. This method shows broad functional-group tolerance (electron-donating and -withdrawing substituents), uses low catalyst loadings, and features straightforward workup and purification. These attributes make it suitable for rapid library synthesis and scale-up.