Top-Down and Bottom-Up evaluation of thermochemistry of α,ω-alkanediols

Abstract

At vapor-liquid equilibrium, the thermodynamic properties of the liquid and vapor phases are intrinsically linked through the thermodynamics of vaporization. However, the standard enthalpies of formation and vaporization of α,ω-alkanediols reported in the literature to date are inconsistent with this fundamental thermodynamic relationship. The aim of this work is to evaluate the existing data and provide recommendations for standard enthalpies of formation and standard enthalpies of vaporization for technical applications. For this purpose, available data are critically analyzed using a "top-down/bottom-up" approach based on gas-phase properties and a bottom-up approach starting from the liquid phase. For those α,ω-alkanediols where discrepancies remain, the relevant thermodynamic properties were re-determined with a combination of combustion calorimetry, vapor pressure measurements and quantum chemical calculations. Based on the comprehensive evaluation, it was shown that the thermodynamic properties of α,ω-alkanediols deviate from the regular trends typically expected for homologous series. Due to the significant contribution of intramolecular hydrogen bond conformers in the gas-phase population, the properties of 1,2-ethanediol, 1,3-propanediol and 1,4-butanediol exhibit distinct particularities compared to long-chained α,ω-alkanediols. Starting from 1,5-pentanediol, the enthalpies of vaporization and the standard enthalpies of formation in the gas phase follow a regular linear trend, attributed to the predominance of conformers without intramolecular hydrogen bonding. The recommended accurate thermodynamic data provide the basis for the development of technical processes utilizing diols from renewable sources in future work.