Thermodynamic study of the sublimation of eight 4- n-alkylbenzoic acids

• Published in: The Journal of chemical thermodynamics 2004-05, Vol.36 (5), p.385-392
• Main Authors: Monte, Manuel J.S., Almeida, Ana R.R.P., Ribeiro da Silva, Manuel A.V.
• Format: Article
• Language: English
• Subjects: Alkylbenzoic acids; Chemical thermodynamics; Chemistry; Elements, mineral and organic compounds; Enthalpies of fusion; Enthalpies of sublimation; Entropies of sublimation; Exact sciences and technology; General and physical chemistry; Knudsen effusion; Liquid crystals; Thermodynamic properties; Vapour pressures
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/j.jct.2004.02.001

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following 4- n-alkylbenzoic acids: 4-methylbenzoic acid, between 319.68 K and 337.33 K, 4-ethylbenzoic acid, between 321.17 K and 335.25 K, 4-propylbenzoic acid, between 331.16 K and 347.16 K, 4-butylbenzoic acid, between 333.16 K and 349.15 K, 4-pentylbenzoic acid, between 341.16 K and 357.16 K, 4-hexylbenzoic acid, between 347.08 K and 363.14 K, 4-heptylbenzoic acid, between 353.16 K and 369.20 K and 4-octylbenzoic acid, between 356.67 K and 371.86 K. From the temperature dependence of the vapour pressure of the crystalline compounds, the standard, p ∘=10 5 Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T=298.15 K, were derived. A d.s.c. study of the crystalline polymorphic transitions, fusion and isotropization of liquid crystals is also presented.