Synthesis and Characterization of Diethyl Citrate and Phase Equilibria in Mixtures with Ethanol and Water

In this work, diethyl citrate (DEC) was synthesized and isolated for further physicochemical characterization and phase equilibria study. The synthesis was performed via partial esterification of citric acid with ethanol, and the final product was separated from the resulting mixture using a pH-controlled solvent extraction method. Characterization using ¹H NMR and ¹³C NMR spectroscopy confirmed the presence of both DEC isomers with few impurities. Results indicate that a 6:5 molar ratio of the symmetric to the nonsymmetric ester structures was attained during synthesis. Thermogravimetric analysis and differential scanning calorimetry allowed us to measure, for the first time, glass transition temperature (228 K) and decomposition temperature (493 K) of diethyl citrate. Additionally, P–x data for the vapor–liquid equilibrium of the binary mixtures diethyl citrate + ethanol and diethyl citrate + water were collected at 308 K using an accurate dynamic device. Data were regressed to generate binary interaction parameters for the UNIQUAC equation. The regressed model shows good agreement with experiments, and it can be used for further process design in the esterification of citric acid.