Determination and Correlation of Solubility Data and Dissolution Thermodynamic Data of L-Lactide in Different Pure Solvents

The solubility of L-lactide in pure ethanol, ethyl acetate, acetone, isopropanol, methanol, and methylbenzene from (278.15 to 338.15) K was determined by dynamic method with a laser monitoring technique. It was found that L-lactide is sparingly soluble in ethanol, isopropanol, methanol, and methylbenzene while it has high solubility in ethyl acetate and acetone. The solubility data of L-lactide in different solvents increase with the increasing of temperature. The measured solubility data of L-lactide were correlated by using the modified Apelblat, Wilson, nonrandom two-liquid (NRTL), and universal quasichemical (UNIQUAC) models, respectively. It was found that NRTL equations give the best correlation results for most solvents except for ethanol. The dissolution enthalpy, entropy of L-lactide, and the free Gibbs energy change of L-lactide in these solvents were obtained by using the van't Hoff equation. From solubility data, melting point, fusion enthalpy, and entropy of L-lactide and D-lactide, it was proven that the thermodynamic data of D-lactide are the same with those data of L-lactide.