Theoretical studies on synthetic process of lactide were carried out with density functional theory and the geometries of compounds maybe to appear in reactive system were optimized. The changes of enthalpy and Gibbs free energy were computed at B3LYP/6-31G* and B3LYP/6-311＋G* levels of theory, suggesting that the selected model reactions should be endothermal and approximately reversible. The results indicated that control of water in the reaction system was very important to the formation of lactide. By combination of the results of quantum computation with the infrared spectra obtained at various synthetic stage, the possible synthetic mechanism was proposed.

Key words: lactide, density functional theory, infrared spectrum, synthetic mechanism