Sublimation enthalpies are calculated at T/K = 298.15 by combining both literature and measured vaporization enthalpies with available fusion enthalpies of a series of saturated and unsaturated fatty acids. The results are used to predict vapor pressures of both the subcooled liquid and solid state for those materials that are solids at T/K = 298.15. Equations for the prediction of vapor pressure from T/K = 298.15 to the boiling temperature are provided for all liquid materials studied. The results are compared to vapor pressures in the literature measured by other methods. Vaporization enthalpies were measured for the following compounds by correlation gas chromatography (ΔH vap (298.15 K), kJ•mol −1 ): α-linolenic acid, (136.9 ± 10.4); γ-linolenic acid, (135.9 ± 6.8); linoleic acid, (134.1 ± 10.3); elaidic acid, (133.0 ± 10.3); heneicosanoic acid, (149.2 ± 7.1); erucic acid, (149.2 ± 7.1); and docosanoic acid (154.7 ± 7.3). A solid−solid transition enthalpy and fusion enthalpy, respectively, for docosanoic acid by differential scanning calorimetry (DSC) was also measured (kJ•mol −1 , K): (3.57 ± 0.3, 340.9 ± 0.2); (66.3 ± 0.2, 352.3 ± 0.1). The saturated acids that were studied include tetradecanoic acid through to docosanoic acid.

The vaporization enthalpies of the n-alkanes reported previously in the literature are corrected to 298.15 K and compared to vaporization enthalpies obtained from correlation-gas chromatography. The vaporization enthalpies at 298.15 K for C21−C28 and C30 are critically evaluated, and the accuracy of measurements derived from some recent torsion effusion measurements is questioned. A series of vaporization enthalpies consistent with the gas chromatographic results are obtained which correlate with the number of carbon atoms in the molecule. The following vaporization enthalpies in kJ·mol-1 at 298.15 K are recommended:  heneicosane, 107.3 ± 2.5; docosane, 113.7 ± 0.3; tricosane, 118.5 ± 0.4; tetracosane, 125.6 ± 2.7; pentacosane, 126.9 ± 1.4; hexacosane, 139.1 ± 7.7; heptacosane, 145.6 ± 8; octacosane, 151.4 ± 8.4; triacontane, 162.1 ± 8.0.

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 l g H m (298.15 K)/kJ•mol −1 ; 10 8 •p l 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; Δ cr l H m (T fus )/kJ• mol −1 ; Δ cr g H 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.

The vaporization enthalpy of valproic acid (2-propylpentanoic acid) is reported, and the vapor pressures of a series on aliphatic carboxylic acids are used to evaluate its vapor pressure as a function of temperature. The vaporization enthalpy was derived by correlation-gas chromatography. This resulted in a vaporization enthalpy, ΔH vap (298.15 K) of (74.8 ± 2.4) kJ•mol −1 . Vapor pressures from T/K = 298.15 to boiling temperature of valproic acid are also reported. A normal boiling temperature of T/K = 492.8 (lit., 494−5 K) and a vapor pressure of (2.2 ± 0.3) Pa has been evaluated for valproic acid at T/K = 298.15. This compares favorably with an Environmental Protection Agency estimate of 6.1 Pa.

No abstract