Vapor Pressures and Enthalpies of Vaporization of Malic Acid Esters

Transpiration method is used to determine the vapor pressures of diesters of malic acid and linear alcohols (C1–C5) over the 303–369 K range of temperatures. The enthalpies of vaporization of the esters at 298.2 K are calculated from the resulting data. Correlations between the enthalpies of vaporization, the Kovats indices, and the number of carbon atoms are derived. The contributions from hydroxyl groups and intermolecular hydrogen bonding \({{\Delta }_{{{\text{vap}}}}}H^\circ (298.15~\;{\text{K}})\) to the overall enthalpy are determined. A modified version of the established QSPR procedure is developed for calculating the enthalpies of vaporization of hydroxy acid esters.