Vaporization, Sublimation, and Fusion Enthalpies of Some Saturated and Unsaturated Long Chain Fatty Acids by Correlation Gas Chromatography

Abstract

The vaporization enthalpies and liquid vapor pressures at T/K = 298.15 have been evaluated by correlation gas chromatography for the following fatty acids (ΔlgHm(298.15 K)/kJ·mol–1; 108·pl298/Pa): (9Z)-hexadecenoic acid (palmitoleic acid) (123.0 ± 6.4); (6900 ± 4200), (6Z)-octadecenoic acid (petroselinic acid), (131.2 ± 2.1); (1130 ± 1000), (9Z)-octadecenoic acid (oleic acid), (132.6 ± 6.6); (1010 ± 600), (5Z,8Z,11Z,14Z)-eicosatetraenoic acid (arachidonic acid), (145.3 ± 6.8); (65 ± 37), (11Z)-eicosenoic acid (gondoic acid), (143.5 ± 2.2); (118 ± 105), (4Z,7Z,10Z,13Z,16Z,19Z)-docosahexenoic acid (cervonic acid), (162.9 ± 2.3); (2.2 ± 2.0), (15Z)-tetracosenoic acid (nervonic acid), (170.6 ± 2.3), (1.0 ± 0.9); n-tetracosanoic acid (lignoceric acid), (170.7 ± 2.3); (1.1 ± 1.0), and n-hexacosanoic acid (cerotic acid, (177.2 ± 2.4); (0.25 ± 0.22). For those fatty acids that are solids at T/K = 298.15, the following fusion temperatures, fusion and sublimation enthalpies, and solid vapor pressures are also reported (Tfus/K; ΔcrlHm(Tfus)/kJ·mol–1; ΔcrgHm(298.15 K)/kJ·mol–1; 1010·pcr298/Pa): (15Z)-tetracosenoic acid (315 ± 0.3); (60.3 ± 0.5), (228.9 ± 2.4), 27; tetracosanoic acid (356.5 ± 0.2); (84.5 ± 0.5); (253 ± 3.2), 0.4, hexacosanoic acid (358.8 ± 0.3); (88.5 ± 1.0); (257.8 ± 3.5), 0.08. Vapor pressures of the solids are believed accurate within a factor of 3. Tetracosanoic acid also exhibited phase transitions: T/K = (347 and 351); (4.94 ± 0.1) kJ·mol–1. The phase transition for hexacosanoic at T/K = (354.3 ± 0.1) was not resolved from the fusion peak; the enthalpy is included in the fusion enthalpy. Equations to evaluate liquid vapor pressures for a series of saturated and unsaturated fatty acids from T/K = (298.15 to Tb) are also derived.