Formation of Diaryl Carbonates

Some novel procedures have been introduced for the synthesis of diaryl carbonates, substances of interest in polymer chemistry. Unsymmetrical compounds in the series have been obtained by the slow addition over 5 hours at OX of 

4-methoxyphenol (ArOH) to a stirred suspension of N-(dichloromethylene)dimethyl ammonium chloride in dichloromethane followed by treatment of the mixture with phenol and continuation of stirring for 10 hours. 4-Methoxyphenyl phenyl carbonate was produced in 80% yield and by similar processes, thiocarbonates and carbamates were derived (ref. 14). 

Transesterification of dimethyl carbonate by phenol, catalysed with dioctyl tin oxide and titanium tetra-isopropoxide, has been effected by passage of the mixture through 5A molecular sieve at 175-185°C under pressure (203 Bar). Unreacted starting materials were removed separately by heating at 185-195X for 2 hours to give diphenyl carbonate in 85% yield (ref. 15). 

A similar technology for diphenyl carbonate with di(2,2,2-trifluoroethyl) carbonate and phenol in refluxing heptane containing sodium methoxide has been patented (ref. 16). 

Phenyl chloroformate and phenol in 1,2-dichlorobenzene containing a little triphenylphosphine after reaction at 150X until hydrogen chloride was no longer evolved, which was approximately 24 mins., gave an 84% yield of diphenyl carbonate (ref. 17). 

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