Performance of Pd catalysts for aromatic oxidation in acetic acid

Abstract The performance of silica-supported Pd catalysts for the hydroxylation of naphthalene and benzoic acid has been studied in moist acetic acid. The reaction was carried out by feeding hydrogen and oxygen simultaneously to produce hydrogen peroxide in situ . Particular attention was focused on the effect of Cl − ion in the solution. When there is no Cl − , the yield of products is very low; the yield increases drastically upon addition of Cl − . On the other hand, when Cu(II) salt is added to the solution containing no Cl − , the product yield becomes much higher. The behavior of the system in the absence of Cu species closely resembles the formation reaction of hydrogen peroxide, indicating that hydrogen peroxide is the key intermediate. When Cl − is added to a Cu-containing system, the formation of Cu(I)Cl − complex(es), which reduce the reactivity, is indicated. The possibility of a Wacker-type reaction mechanism is excluded in all of our reaction systems.