Validation of the Vaporization Enthalpies of Some Simple Aliphatic Amides and Their Use in the Evaluation of the Vaporization Enthalpy of Valpromide and Valnoctamide

摘要

The vaporization enthalpy of valpromide and both diaster-iomers of valnoctamide have been evaluated by correlation gas chromatography as has the fusion and sublimation enthalpy of valpromide. Values of [(18.6 ± 1.8), (83.6 ± 2.5), and (102.2 ± 3.1)] kJ·mol~(-1) at T/K = 298.15 have been evaluated for the fusion, vaporization, and sublimation enthalpies of valpromide (2-ethylpentanamide), respectively, and [(82.3 ± 2.5) and (82.7 ± 2.5)3 kJ·mol~(-1) have been obtained for the vaporization enthalpy of valnoctamide ((2SR,3SR) and (2SR,3RS) 2-ethyl-3-methylpentanamide), respectively. The vaporization enthalpies have been determined using sublimation and fusion enthalpies from the literature of a series of primary amides. Also evaluated in this process were group values of 102 J·mol~(-1)·K~(-1) and 47.1 kJ·mol~(-1) for the estimation of the heat capacity and vaporization enthalpy of a liquid primary amide (R-CONH2). The fusion enthalpies of 2-methyl- propanamide, hexanamide, heptanamide, and 2-ethylpentanamide have been measured by differential scanning calorimetry (DSC) and the values compared to existing literature values where available; the following, fusion enthalpies were measured (kJ·mol~(-1), T_(fus)/K): (19.9 ± 0.1, 401.6 ± 0.4); (16.8 ± 0.3, 372.4 ± 1.4); (16.2 ± 0.2, 368.6 ± 0.5); (22.5 ± 0.6, 398.2 ± 0.1), respectively. Solid-solid phase transitions (kJ·mol~(-1), T_(trs)/K) were also observed for hexanamide (5.1 ± 0.1, 306.1 ± 0.2), heptanamide (7.5 ± 0.3, 319 ± 0.8; 3.4 ± 0.1, 356.1 ± 0.2), and valpromide (1.75 ± 0.2, 360.6 ± 0.4). The crystal structure and powder pattern of heptanamide are also reported.