Dimethyl carbonate, from polycarbonate

An analogue of the transesterification process has also been demonstrated, in which the diacetate of BPA is transesterified with dimethyl carbonate, producing polycarbonate and methyl acetate (33). Removal of the methyl acetate from the equihbrium drives the reaction to completion. Methanol carbonylation, transesterification using phenol to diphenyl carbonate, and polymerization using BPA is commercially viable. The GE plant is the first to produce polycarbonate via a solventiess and phosgene-free process. 

Phenyl-3,6-dihydro-l,3,4-oxadiazin-2-one (50) is a high temperature blowing agent used primarily for polycarbonates (qv). It is prepared by the reaction of a-hydroxyacetophenone and methyl carbazate (52), made from hydrazine and dimethyl carbonate (175) ... 

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). 

Haba, O. Ueda, M. Kuze, S. Synthesis of polycarbonate from dimethyl carbonate and bisphenol-A through a non-phosgene process. J. Polym. Sci. A, Polym. Chem. 1999,37,2087-2093. 

Diphenyl carbonate can be made from dimethyl carbonate by exchange with phenol (2.9).32 It can also be made directly from phenol (2.10), but the yields are not as high.33 A combination of palladium and manganese catalysts is used. The water formed is sparged out with excess reaction gas to shift the reaction to the desired product. Diphenyl carbonate is preferred over dimethyl carbonate for production of polycarbonates. 

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. 

Con version of dimethyl carbonate to diphenyl carbonate. Po[ycar bo-nates cannot be made directly from DMC. The DMC must first be converted to diphenyl carbonate (DPC). General Electric, a major producer of engineering plastics including polycarbonates, holds several patents for conversion of DMC to diphenyl carbonate (DPC). The first step is reaction... 

Cyclic carbonate synthesis from epoxide and CO2 is one of the few industrial processes that use CO2 as a feedstock. The reaction proceeds in the presence of catalysts that are typically metal halides or tetraalkylammonium halides. The products (e.g. ethylene carbonate, which is an important intermediate of dimethyl carbonate) are utilized for polycarbonate synthesis via a non-phosgene, melt polymerization process. 

In addition to the development of a polymer process which is environmentally benign, an innovative non-phosgene monomer process for producing diphenyl csubonate has been developed via dimethyl carbonate, using carbon dioxide as a raw material. This monomer process, which will be reported in other papers, has also been estimated to be completely competitive with other processes already commercialized or under development Therefore, high-quality polycarbonates are now able to be produced from carbon dioxide and bisphenols. 

Scheme 21.11 Reaction pathways to biphenol-A polycarbonate from dimethyl carbonate and phosgene.

The solventless reaction in the presence of diallq ltin(iv) complexes led to a conversion of 42% with 78% selectivity to diphenyl carbonate. Starting from phenyl acetate, total conversion was obtained at 220 "C with higher selectivity to diphenyl carbonate (95%). Transesterification with higher alcohols was also examined, giving better conversion due to higher nucleophilicity compared to phenol. However, a steric effect was evidenced as fert-butanol was unreactive. Transesterification of ethylene carbonate (l,3-dioxolan-2-one) with methanol to dimethyl carbonate was also reported early. " Today, both transesterifications with methanol and phenol are integrated into the value chain of bisphenol-A polycarbonate production and commercialised by Asahi Kasei Corporation (Scheme 21.12). ... 

The polycondensation of a diol and the diester of a dicarboxylic acid (e.g., the dimethyl ester) can be carried out in the melt at a considerably lower temperature than for the corresponding reaction of the free acid. Under the influence of acidic or basic catalysts a transesterification occurs with the elimination of the readily volatile alcohol (see Example 4.3). Instead of diesters of carboxylic acids one can also use their dicarboxylic acid chlorides, for example, in the synthesis of high-melting aromatic polyesters from terephthaloyl dichloride and bisphenols. The commercially very important polycarbonates are obtained from bisphenols and phosgene, although the use of diphenyl carbonate as an alternative component is of increasing interest (see Example 4.4). Instead of free acids, cyclic carboxylic... 

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