Novel type of heterogenized CuCl2 catalytic systems for oxidative carbonylation of methanol

A novel type of heterogenized CuCl2 catalysts was designed for the oxidativ e carbonylation of methanol to dimethyl carbonate (DMC) taking account of t he plausible reaction mechanism and intermediates. To prevent severe corros ion of the reaction equipment materials due to Cl- while keeping the cataly tic activity of the homogeneous CuCl2 catalyst, we adopted, as supports (or ligands) of CuCl2, four polymers, bearing a 2,2'-bipyridine (bpy) or pyrid ine (py) unit, namely, poly(2,2/-bipyridine-5,5'-diyl) (Pbpy), poly(pyridin e-2,5-diyl) (Ppy), poly(N,N'-bisphenylene-2,2' -bipyridine-4,4' -dicarboxyl ic amide) (Bpya), and poly(4-methyl-4'-vinyl 2,2'-bipyridine) (Pvbpy), toge ther with one chelate compound, 8-quinolinol. The catalytic activity, stabi lity of heterogenized CuCl2 and their corrosivities to stainless steels wer e examined in the liquid-phase reaction of the oxidative carbonylation of m ethanol. These polymer-supported catalysts showed considerable catalytic ac tivity and stability for the DMC synthesis. In particular, the Pbpy-CuCl2 a nd Ppy-CuCl2 catalysts exhibited high DMC yields and selectivity comparable to those of the homogeneous CuCl2 catalyst. This high activity appears to be associated with the presence of the pi -conjugated system in the polymer s, which affect the redox reactions of Cu involved in the catalytic reactio n. All of the polymer-supported CuCl2 catalysts could be easily recycled af ter filtration, and the initial catalytic activity was maintained after thr ee times of use. The corrosive characters of the catalysts were closely rel ated to CuCl2 leaching from the supports, which reflects the ability of sup ports to coordinate Cu. These experimental results suggest that both the el ectronic structure and the coordination ability of the polymer supports are key factors for the development of an effective catalytic system.