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

摘要

The vaporization enthalpies and liquid vapor pressures at T/K = 298.15 have been evaluated by correlation gas chromatography for the following fatty acids (Delta H-g(1)m(298.15 K)/kJ.mol(-1); 10(8).p(1)(298)/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 (T-fus/K; Delta H-1(cr)m(T-fus)/kJ.mol(-1); Delta H-g(cr)m(298.15 K)/kJ.mol(-1); 10(10).p(cr)(298)/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 T-b) are also derived.