Thermodynamic Study on the Sublimation of Five Aminomethoxybenzoic Acids

Abstract

The Knudsen mass-loss effusion technique was used to measure the vapor pressures at different temperatures of the following aminomethoxybenzoic acids: 2-amino-3-methoxybenzoic acid, between (349.12 and 369.18) K; 2-amino-5-methoxybenzoic acid, between (353.13 and 375.17) K; 3-amino-4-methoxybenzoic acid, between (379.67 and 399.18) K; 3-amino-5-methoxybenzoic acid, between (380.16 and 400.18) K; and 4-amino-3-methoxybenzoic acid, between (373.14 and 395.17) K. From the temperature dependences of the vapor pressure of the crystalline compounds, the standard (p degrees = 10(5) Pa) molar enthalpies and Gibbs energies Of Sublimation, at T = 298.15 K, were derived. The results allowed the estimation of these two thermodynamic properties for two isomers not Studied in this work-2-amino-6-methoxybenzoic acid and 3-amino-2-methoxybenzoic acid. Differential scanning calorimetry was Used to measure the temperature and molar enthalpy of fusion of the studied isomers.