US Patent 7498399 Method of preparing ester-substituted diaryl carbonates

An improved method for the preparation of ester-substituted diaryl carbonates prepared by reacting phosgene with recycle streams of ester-substituted phenols from reaction processes using a tetraalkyl ammonium hydroxide catalyst, a tetraalkyl phosphonium hydroxide catalyst, or both, where at least one alkyl group of the tetraalkyl ammonium hydroxide or the tetraalkyl phosphonium hydroxide is a methyl group. The improvement includes the step of treating the recycle stream to reduce the concentration of a trialkyl amine, trialkyl phosphine, or both, if present, from the recycle stream prior to reacting it with phosgene to form the ester-substituted diaryl carbonate.