Air Oxidation of Benzene to Biphenyl - A Dual Catalytic Approach

Facile oxidative homocoupling of benzenes to the respective biphenyls is effected under moderate conditions, using air or oxygen in the presence of catalytic PdCl₂ and AcOH/AcONa as solvent. The fast regeneration of the active Pd²⁺ species is accomplished by combining several oxygen-binding catalysts, such as Zr(IV), Mn(II), and Co(II) acetates. In this way, it is possible to increase the content of active oxygen in solution so that the rate of catalyst regeneration is faster than the rate of aggregation of the "spent catalyst", Pd(0), to palladium black. The effects of various process parameters are studied and some mechanistic implications are discussed.