Selective Synthesis of Hydroquinone via the Liquid-phase Oxidation of Benzene over Cu(II)-2,2’-bipyridine Complexes in a Slug Flow Reactor

The liquid-phase oxidation of benzene using Cu(II)-2,2’-bipyridine complexes as catalysts and molecular oxygen as oxidants has been investigated. The reaction activity of three types of catalysts with one, two, and three bipyridine molecules coordinated to Cu(II) ions was compared in a batch reactor, and [Cu(bipy)Cl2] with coordination of one bipyridine molecule obtained the highest yield of hydroquinone. The coordination structure of the complexes and ease of ligand desorption are speculated to have influenced the reaction activity. The reactor was changed from a batch reactor to a slug flow reactor to investigate the effect of different reactors on the reaction. The results indicate that the reaction in the slug flow reactor obtained a hydroquinone yield that was 5.7 times higher than that in the batch reactor. The formation of the slug flow is assumed to have continuously supplied oxygen to the liquid phase efficiently, which improved the hydroquinone yield.