Air oxidation of benzene to biphenyl - A dual catalytic approach

Facile oxidative homocoupling of benzenes to the respective biphenyls is ef fected under moderate conditions, using air or oxygen in the presence of ca talytic PdCl2 and AcOH/AcONa as solvent. The fast regeneration of the activ e Pd2+ species is accomplished by combining several oxygen-binding catalyst s, 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 c atalyst regeneration is faster than the rate of aggregation of the "spent c atalyst", Pd(0), to palladium black. The effects of various process paramet ers are studied and some mechanistic implications are discussed.