Thermodynamic study on the sublimation of succinic acid and of methyl- anddimethyl-substituted succinic and glutaric acids

The Knudsen mass-loss effusion technique was used to measure the vapour pre ssures at different temperatures of the following crystalline dicarboxylic acids: succinic acid, between T = 360.11 K and T = 375.14 K; methylsuccinic acid, between T = 343.12 K and T = 360.11 K; 2,2-dimethylsuccinic acid, be tween T = 350.11 K, and T = 365.11 K; 2-methylglutaric acid, between T = 33 8.38 K and T = 347.63 K; and 2,2-dimethylglutaric acid between T = 342.18 K and T = 352.66 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius-C lapeyron equation and the molar entropies of sublimation at equilibrium pre ssures were calculated. Using estimated values for the heat capacity differ ences between the gas and the crystal phases of the studied compounds, the standard, p(o) = 10(5) Pa, molar enthalpies, entropies and Gibbs energies o f sublimation at T = 298.15 K, were derived: (C) 2001 Academic Press