Palladium-catalyzed aryl-aryl coupling in water using molecular hydrogen: Kinetics and process optimization of a solid-liquid-gas system

Coupling of substituted chlorobenzenes to the respective biphenyls is effected in water, using hydrogen gas and NaOH in the presence of catalytic PEG-400 and Pd/C. The catalyst can be efficiently recycled. The competing reduction process (e.g. of chlorobenzene to benzene) can be minimized by altering reaction conditions. The roles of the hydrogen, the hydroxide, the Pd catalyst, and the PEG are discussed.