Thermodynamique de composés azotés. I. Etude calorimétrique des enthalpies de sublimation des trois acides aminobenzoïques

Abstract

The measurement of enthalpies of sublimation of three aminobenzoic acids was made at 367.35, 376.75, and 389.95 K using a Tian–Calvet microcalorimeter equipped with an effusion cell.From the curves (ΔH sub ) m (T) = f(T), it was possible to obtain the values for the standard enthalpies of sublimation of the compounds at 298.15 K: (104.9 ± 1.0), (128.0 ± 3.2), and (116.1 ± 3.7) kJ mol −1 , respectively, for the 2-aminobenzoic acid, the 3-aminobenzoic acid, and the 4-aminobenzoic acid.The experimental (ΔH s ub 0 ) m (298.15 K) values can be accounted for quantitatively from the various contributions (benzene ring, amine, and' carboxylic group) obtained from similar compounds.With the help of structural data, we have tried to explain the differences between the enthalpies of these compounds.We also report here the calculated saturation vapor pressure of these acids, as well as the mean free path of their molecules, at the three temperatures given above.