Dimethyl phosgene route

Dimethyl carbonate (DMC) is a colorless liquid with a pleasant odor. It is soluble in most organic solvents but insoluble in water. The classical synthesis of DMC is the reaction of methanol with phosgene. Because phosgene is toxic, a non-phosgene-route may be preferred. The new route reacts methanol with urea over a tin catalyst. However, the yield is low. Using electron donor solvents such as trimethylene glycol dimethyl ether and continually distilling off the product increases the yield. ... 

Diphenol carbonate is produced by the reaction of phosgene and phenol. A new approach to diphenol carbonate and non-phosgene route is by the reaction of CO and methyl nitrite using Pd/alumina. Dimethyl carbonate is formed which is further reacted with phenol in presence of tetraphenox titanium catalyst. Decarbonylation in the liquid phase yields diphenyl carbonate. 

Application The Polimeri/Lummus process is a non-phosgene route using CO, CH3OH (methanol) and 0 to produce dimethyl carbonate (DMC). DMC is a nontoxic intermediate used in the production of polycarbonates, lubricants, solvents, etc., and is also used directly as a solvent or a gasoline/diesel fuel additive. This environmentally safe process can be applied to large capacity plants. 

Diphenyl carbonate can be made from phenol and phosgene, but if it is made by a non-phosgene route, it can avoid the use of the toxic gases phosgene and chlorine. Diphenyl carbonate can be made from dimethyl carbonate. Dimethyl carbonate is available from the reaction of methanol with carbon monoxide [14] or with carbon dioxide [15]. 

Another polyester type, i.e., polycarbonate, is rather seldom solvolytically depolymerized because of losing (at least partially) carbonate groups/bonds obtained via phosgene route synthesis. Troev et al. [29] recently described PC chemical degradation with dialkyl phosphonates (dimethyl or diethyl) or triethyl phosphate. The products, oligomeric carbonates containing phosphorus atoms, can be considered as precursors for the modification of various polymers by improving their flame-retardant properties, thermal stability, and adhesion. 

Both new catalysts and new processes need to be developed for a complete exploitation of the potential of CO2 use [41]. The key motivation to producing chemicals from CO2 is that CO2 can lead to totally new polymeric materials and also new routes to existing chemical intermediates and products could be more efficient and economical than current methods. As a case in point, the conventional method for methanol production is based on fossil feedstock and the production of dimethyl carbonate (DMC) involves the use of toxic phosgene or CO. A proposed alternative production process involves the use of CO2 as a raw material (Figure 7.1)... 

Aromatic polycarbonates are currently manufactured either by the interfacial polycondensation of the sodium salt of diphenols such as bisphenol A with phosgene (Reaction 1, Scheme 22) or by transesterification of diphenyl carbonate (DPC) with diphenols in the presence of homogeneous catalysts (Reaction 2, Scheme 22). DPC is made by the oxidative carbonylation of dimethyl carbonate. If DPC can be made from cyclic carbonates by transesterification with solid catalysts, then an environmentally friendlier route to polycarbonates using C02 (instead of COCl2/CO) can be established. Transesterifications are catalyzed by a variety of materials K2C03, KOH, Mg-containing smectites, and oxides supported on silica (250). Recently, Ma et al. (251) reported the transesterification of dimethyl oxalate with phenol catalyzed by Sn-TS-1 samples calcined at various temperatures. The activity was related to the weak Lewis acidity of Sn-TS-1 (251). 

Application The Polimeri/Lummus process is a phosgene-free route for the production of diphenyl carbonate (DPC)—a polycarbonate intermediate—from dimethyl carbonate (DMC) and phenol. The Polimeri/Lummus DPC process has no environmental or corrosion problems, and the byproduct methanol can be recycled back to the DMC process. 

Because of the toxicity of phosgene, research on nonphosgene routes to isocyanates and polycarbonates has intensified over the past decade. Eni-Chem of Italy has commercialized a process to manufacture dimethyl carbonate (DMC) by oxidative carbonylation of methanol. Dimethyl carbonate can be used as an intermediate for the production of polycarbonates. A description of the nonphosgenation chemistry for producing DMC and polycarbonates is included in Section II.A in this chapter. 

A system has been described for the formation of dimethyl carbonate via the phosgene-free route of oxidative carbonylation of methanol [(Eq. (8)] catalyzed by PdCl2 in [BMIMKPFjj (110 C, total pressure 10 MPa, 1 h) [48]. Conversions were generally low (< 7%) and did not improve with increased reaction time, although the selectivity to dimethyl carbonate dropped. Dimethoxymethane was the major product but selectivities of dimethyl carbonate of up to 25% were possible with an O2/CO2 ratio of 29 71. Neither the pressure nor the temperature had dramatic effects upon the yield or selectivity, although the reaction was slower at lower temperatures. The reaction was repeated three times under the optimum conditions in a repetitive batch process. The rate remained constant, but there was a slight drop in selectivity. 

Carbonic add diesters are very attractive reagents and of great economic interest because they represent safe, nonenvironmentally acceptable alternatives to phosgene for carbonylation and carboxylation reactions. For example, methoxycarboxylation with dimethyl carbonate offers an eco-friendly alternative route for the production of carbamates and isocyanates, which are valuable precursors of ureas (see Sections 4.3.1 and 4.3.2) [781, 782]. The method is comparable, from an environmental point of view, with the transition metal catalyzed carbonylation of nitro compounds and amines with CO. 

Nevertheless, this does not seem to be a useful route from an industrial point of view. Similarly, the use of solid triphosgene, CO(OCCb)2, in place of phosgene in the reaction with amines [12], although useful as far as transport and storage are concerned, does not appear to be a significant solution to the industrial problems. Note that triphosgene is prepared by reaction of chlorine with dimethyl carbonate. 

A new route to dimethyl carbonate is phosgene-free. Chem Eng 106(6) 23, 1999. C VieviUe, JW Yoo, S Pelet, Z Mouloungui. Synthesis of glycerol carbonate by direct carbonatation of glycerol in supercritical CO2 in the presence of zeohtes and ion exchange resins. Catal Lett 56 245-247, 1998. 

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