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

The vaporization enthalpies and liquid vapor pressures at  T /K = 298.15 have been evaluated by correlation gas chromatography for the following fatty acids (Δ lg H m (298.15 K)/kJ·mol –1 ; 10 8 · p l298 /Pa): (9 Z )-hexadecenoic acid (palmitoleic acid) (123.0 ± 6.4); (6900 ± 4200), (6 Z )-octadecenoic acid (petroselinic acid), (131.2 ± 2.1); (1130 ± 1000), (9 Z )-octadecenoic acid (oleic acid), (132.6 ± 6.6); (1010 ± 600), (5 Z ,8 Z ,11 Z ,14 Z )-eicosatetraenoic acid (arachidonic acid), (145.3 ± 6.8); (65 ± 37), (11 Z )-eicosenoic acid (gondoic acid), (143.5 ± 2.2); (118 ± 105), (4 Z ,7 Z ,10 Z ,13 Z ,16 Z ,19 Z )-docosahexenoic acid (cervonic acid), (162.9 ± 2.3); (2.2 ± 2.0), (15 Z )-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 ( T fus /K; Δ crl H m ( T fus )/kJ·mol –1 ; Δ crg H m (298.15 K)/kJ·mol –1 ; 10 10 · p cr298 /Pa): (15 Z )-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  T b ) are also derived.