Catalyzed Formation of Organic Carbonates

Organic carbonates can be roughly classified into three groups (Structures 25-27). 

Linear dialkyl carbonates and in particular dimethyl carbonate (DMC) are used in many industrial applications in the industry [70, 71], The usual way of synthesizing carbonates involves reactive Ci agents such as phosgene or CO [72]. Although these methods are from an economical viewpoint more than profitable, the development of an environmentally friendly industrial process involving CO2 as a Cl-building block attracts an ever-increasing interest. 

The second class of catalysts are zinc(II) mono- or dialkoxides obtained from polyhydric phenols and dialkylzinc with partly polymeric stmctures. This system, extensively studied by Kuran [84], is an optimization of the water/diethylzinc and polyphenol/diethylzinc systems developed by Inoue [85]. The use of soluble zinc phenoxides and their analogous cadmium complexes as catalyst for the copolymerization of CO2 and epoxide was studied extensively by the Darensbourg group [86]. This work focused on the use of mononuclear phenoxide derivatives with bulky substituents, e. g., phenyl- and fe/t-butyl groups, on the aromatic ring to a homogeneous catalytic system and thus enhance the activity of the Zn phenoxides. The catalysts developed are stabilized through ancillary neutral 

Both catalytic systems, alkoxides and carboxylates, are often described as efficient catalysts for the copolymerization of CO2 and epoxides but some drawbacks which hamper a widespread industrial utilization need to be pointed out. The phenoxides, though displaying good selectivities, have up to now only been tested with model substrates, e. g., propylene- and cyclohexene oxides, and the carboxylates, though active, present low-to-fair selectivities. Cyclization 

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