Microwave-Promoted Synthesis of n-Propyl Propionate using Homogeneous Zinc Triflate Catalyst

The esterification of propionic acid with 1-propanol to produce n-propyl propionate was studied under microwave and conventional heating conditions using a variety of homogeneous and heterogeneous catalysts looking for possible rate enhancement. Direct evaluation of the heating methods was done by comparing the ester yields after 30 min of equimolar reaction at 100 °C. Several catalysts were found to produce more product than the ion-exchange resin Amberlyst 46 under both heating methods and the same catalyst loading. From these catalysts, Zn triflate proved to be more effective under microwave heating conditions producing 40% more ester compared to the conventionally heated experiment. FT-IR spectra showed that there were no changes in the chemistry of the components and that hydrolysis of Zn triflate into triflic acid, which could promote the reaction, is not likely to occur.