Thermodynamic properties of glycolic acid and glycolide

The values of combustion and formation enthalpy for glycolic acid (I) and glycolide (II) were determined by calorimetry. The temperature dependence of vapor pressures of I and II was obtained using the transpiration method, and the sublimation enthalpies were obtained. The enthalpy of melting of I was found by differential scanning calorimetry. Stable conformers were determined by the ab initio (DFT) method, and combinations of the fundamental oscillations and inertia momenta of I and II conformers were calculated. The full and relative energies of the compounds most stable conformers were found by a composite G3MP2 method, and the enthalpies of formation of I and II in the gaseous state were estimated. The values of the thermodynamic properties in the ideal gas state were determined over the range of 0–1500 K. A thermodynamic analysis was performed for the process of preparation of II from I and the formation of polyglycolide (III) from I and II.