high yields of ester - substituted diary carbonates such as bis - methyl salicyl carbonate were obtained by the condensation of methyl salicylate with phosgene in the presence of a phase transfer catalyst in an interfacial reaction system in which the ph of the aqueous phase was greater than 9 . 3 . using the method of the present invention conversions of greater than 99 % were obtained whereas under standard conditions using triethylamine as the catalyst conversions were limited to 70 - 75 % of the methyl salicylate starting material even with a 20 mole % excess of added phosgene . the optimized conditions of the of the present invention use only a slight excess of phosgene and represent an attractive route for the manufacture of bis methyl salicyl carbonate and ester - substituted diaryl carbonates generally .