Dimethyl carbonate copper catalysts

Dimethyl carbonate [616-38-6] and dimethyl oxalate [553-90-2] are both obtained from carbon monoxide, oxygen, and methanol at 363 K and 10 MPa (100 atm) or less. The choice of catalyst is critical cuprous chloride (66) gives the carbonate (eq. 20) a palladium chloride—copper chloride mixture (67,68) gives the oxalate, (eq. 21). Anhydrous conditions should be maintained by removing product water to minimize the formation of by-product carbon dioxide. 

Today most dimethyl carbonate is made by methanol carbonylation (Equation 3.2) using a copper chloride catalyst with a very long life. This process produces pure dimethyl carbonate, which is not now classified as harmful, and water as a by-product. 

The syntheses of 1 utilized the Ullmann ether synthesis.13 Reaction of 2 mol of 1-bromonaphthalene with 4,4-(hexafluoroisopropylidiene)diphenol afforded the desired product 1. The reaction was carried out in DM Ac at 160°C in the presence of potassium carbonate as the base and copper (I) iodine as the reaction catalyst to yield 1, as depicted in Scheme 1. The reaction proceeded slowly but in good yield with easy isolation of the desired compound. Acylation of 1 with 4-fluorobenzoyl chloride to prepare 2 was carried out under modified Friedel-Crafts reaction conditions14 using dimethyl-sulfone as catalyst moderator. Both 1 and 2 were easily recrystallized to yield high-purity monomers suitable for polymerizations. 

Raw stock for the direct synthesis of methylchlorosilanes, methylchlo-ride, has such impurities as moisture, methyl alcohol, oxygen, sulfur dioxide, methylenechloride, dimethyl ether, carbon oxide and dioxide, etc. Most of them negatively affect the synthesis of methylchlorosilanes harmful impurities are chemisorbed on the active centres of contact mass and foul the copper catalyst, which naturally inhibits the reaction of methyl-chloride with contact mass. A similar situation is observed in the direct synthesis of ethylchlorosilanes. 

Different variations of the Enichem process have been described that may show some improvements in selectivity and efficiency of the catalyst system, but they generally seem to be less attractive from the economic point of view and none of them has been realized until now. For example, since 1986 the Japanese company Daicel especially has applied for numerous patents on modifications of the Enichem process, in which dimethyl carbonate is prepared in the presence of catalyst systems that contain copper and palladium salts and additional modifiers, e. g., quinoid compounds and quatemery phosphonium halides [40-48]. Although Daicel has announced several times the constmction of an industrial plant for the production of dimethyl carbonate, all investment plans now seem to be put aside. The separation of the reaction product from the complicated catalyst system as well as the complete recycling of the palladium compounds, which is a necessary requirement for any economic process design, seem not to be solved sufficiently. 

Workers at Enichem have developed a commercial process for producing dimethyl carbonate by the oxidative car bonylation of methanol using cobalt or copper catalysts (2.7).29... 

A selectivity of 96% was obtained when the reaction was carried out in the gas phase at 130oC with a palladium chloride-copper acetate-magnesium chloride catalyst.30 The reaction has also been run in a eutectic mixture of copper chloride-potassium chloride at 150°C, with 94-96% selectivity to dimethyl carbonate and 2-5% selec-tivty to methyl ether (2.8).31 After the product distils out, the molten salt can be used for the next run. 

Palladium/graphite in combination with copper(ll) chloride and flthium chloride is a good catalytic system for the oxidative dicarbonylation of alkenes using a 20 1 ratio of CO/O2 (Eq. 16). The ratio of diester to dimethyl carbonate is sensitive to the nature of the palladium catalyst precursor (Pd/graphite or PdCl2). 

Tin dioxide, an n-type semiconductor with a wide bandgap (3.6 eV at 300 K), has been widely studied as a sensor, a (photo)electrode material and in oxidation reactions for depollution. The performance of tin(iv) oxide is closely linked to structural features, such as nanosized crystallites, surface-to-volume ratio and surface electronic properties. The incentive for carbon-dioxide transformation into value-added products led to examination of the electroreduction of carbon dioxide at different cathodes. It has been recognised that the faradic yield and selectivity to carbon monoxide, methane, methanol, and formic acid rely upon the nature of the cathode and pH. ° Tin(iv) oxide, as cathode, was found to be selective in formate formation at pH = 10.2 with a faradic yield of 67%, whereas copper is selective for methane and ethene, and gold and silver for carbon monoxide. Nano-tin(iv) oxide has been shown to be active and selective in the carboigrlation of methanol to dimethyl carbonate at 150 °C and 20 MPa pressure. The catalyst was recyclable and its activity and selectivity compare with that of soluble organotins (see Section 21.5). 

Wang, X.J. Xiao, M. Wang, S.J. Lu, Y.X. Meng, YZ. Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol using Supported Copper (Ni, V, O) Catalyst with Photo-Assistance. J. Mol. Catal. A Chem. 2007,278,91-96. 

King [112,113] found that Cu(I)-Y prepared by SSIE was, in contrast to conventionally produced Cu(ll)-Y, an active catalyst for oxidative carbonylation of CH3OH to dimethyl carbonate. The presence of NH3 facilitated the migration of copper ions into the zeolite structure. 

A new heterocyclic system, 3 ,4-dihydro-3//-benzo[4,5]imidazo[l,2-f]oxazol-l-one 462, was synthesized by reaction of 4,4-dimethyl-5-methylene-l,3-dioxolan-2-one with o-phenylenediamine in the presence of copper bromide as catalyst in carbone dioxide at 60-80 °C under high pressure (Equation 217) <1999CHC216>. 

The reduction is usually made in a multi-compartment electrochemical cell, where the reference electrode is isolated from the reaction solution. The solvent can be water, alcohol or their mixture. As organic solvent A,A-dimethyl form amide or acetonitrile is used. Mercury is often used as a cathode, but graphite or low hydrogen overpotential electrically conducting catalysts (e.g. Raney nickel, platinum and palladium black on carbon rod, and Devarda copper) are also applicable. 

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