Vaporization and Sublimation Enthalpies of Acetanilide and Several Derivatives by Correlation Gas Chromatography

The vaporization and fusion enthalpies of acetanilide and several of its derivatives have been measured and combined to provide their corresponding sublimation enthalpies. Since all of the materials examined are solid at T = 298.15 K, the vaporization enthalpies measured by correlation gas chromatography at this temperature are for the subcooled liquid state. Fusion enthalpies have also been adjusted to T = 298.15 K. The compounds examined and their vaporization enthalpies measured at T = 298.15 K include the following values (in kJ·mol−1): acetanilide (82.1 ± 3.0), 4-methylacetanilide (86.2 ± 3.2), 4-methoxyacetanilide (92.0 ± 3.4), 3-ethoxyacetanilide (94.1 ± 3.5), and 4-ethoxyacetanilide (94.8 ± 3.5). The following fusion enthalpies (kJ·mol−1) and fusion temperatures (onset temperatures, K) were measured by differential scanning calorimetry (DSC): acetanilide (22.1 ± 0.1), (386.9 ± 0.1), 4-methylacetanilide (29.4 ± 0.2), (421.3 ± 0.3), 4-methoxyacetanilide (25.4 ± 0.3), (398.2 ± 1.2), 3-ethoxyacetanilide (28.9 ± 0.4), (368.0 ± 0.4), 4-ethoxyacetanilide (32.0 ± 0.1), (407 ± 0.1), and benzanilide (31.2 ± 0.7), (435 ± 0.3). Sublimation enthalpies calculated from vaporization and fusion enthalpies at T = 298.15 K compared favorably with available literature values. ■ INTRODUCTION Acetanilide and some of its derivatives have found applications as analgesics and antipyretics. The thermochemical properties of many of these materials have been the subject of numerous studies. This work complements existing measurements by reporting vaporization and fusion enthalpies of acetanilide and several of its derivatives at T = 298.15 K, allowing an evaluation of their sublimation enthalpies by completing thermochemical cycles as summarized by eq 1. The vaporization enthalpies were evaluated by correlation gas chromatography and the fusion enthalpies by differential scanning calorimetry (DSC). The compounds evaluated include acetanilide, 4-methylacetanilide, 4-methoxyacetanilide, 3-ethoxyacetanilide, and 4-ethoxyacetanilide (phenacetin). The structures of all the compounds included in this study are provided in Figure 1. Δ = Δ − Δ H H H (298 K) (298 K) (298 K) vap sub fus (1) Table 1 lists the sublimation, vaporization, and fusion enthalpies currently available in the literature for both the compounds under investigation and those used as standards. Tables 2, 3, and 4 adjust these phase enthalpies to T = 298.15 K when necessary. Equations 2 to 4 were used for these adjustments. The quantities Cp(l) and Cp(cr) in these equations refer to the heat capacity of the liquid and solid phases, respectively, at T = 298.15 K. Both were estimated by group additivity.