Vapor Pressures and Gibbs Energies of Formation of the Three Hydroxybenzaldehydes

Abstract

This work reports experimental sublimation and vaporization vapor pressures at different temperatures of the three isomers of hydroxybenzaldehyde. A static method based on capacitance diaphragm manometers was used to measure the vapor pressures of both (crystalline and liquid) condensed phases of ortho, meta, and para hydroxybenzaldehydes, through the temperature ranges T = (264.6 to 341.7) K, T = (324.9 to 419.4) K, and T = (334.9 to 429.4) K, respectively. The Knudsen mass-loss effusion technique was also used to determine the vapor pressures of crystalline meta and para isomers in the temperature intervals T = (309.1 to 331.2) K and T = (319.1 to 341.2) K, respectively. The obtained results enabled the determination of the standard molar enthalpies and entropies of sublimation and of vaporization, at chosen reference temperatures, as well as the (p,T) values of the triple point of the compounds studied. The temperatures and enthalpies of fusion were determined from differential scanning calorimetry. The contributions of the formyl group to the sublimation properties of benzaldehydes were determined, and the standard Gibbs energies of formation in condensed and gaseous phases were calculated.

Pressão de vapor

“…Diagrama de fases do composto p-hidroxibenzaldeído: Verde claro, pressões de vapor da fase líquida (método estático); verde escuro, pressões de vapor do líquido sobrearrefecido (método estático); vermelho, pressões de vapor da fase cristalina (método estático); azul, pressões de vapor da fase cristalina (método de efusão de Knudsen); Estrela, temperatura de ebulição normal (extrapolação da curva do equilíbrio líquido-vapor para p = 1 atm). Coordenadas do ponto triplo determinadas pela intercepção da curva cr-g e da curva liq-g: T = 389.8 K; p = 79.3 Pa. Figura adaptada da ref 17. as determinações de Dalton, muito se alargou o espetro da aplicabilidade de valores de pressão de vapor.…”