Thermodynamic Investigation of Uracil and Its Halo Derivatives. Enthalpies of Solution and Solvation in Methanol

The enthalpy of solution of uracil, 5-fluorouracil, 5-chlorouracil, 6-chlorouracil, 5-bromouracil, 5-iodouracil, and 5-(trifluoromethyl)uracil in methanol at 298.15 K using the isoperibol solution calorimeter has been determined in the range of concentration (0.472 to 1.848) × 10 -3 /mol·kg -1 . The enthalpies of solvation were determined from the experimentally obtained enthalpies of solution and the previously determined enthalpies of sublimation for aqueous and methanol solutions. The transfer enthalpies of solution Δ tr H m for water−methanol, and the enthalpy of cavity formation Δ cav H m, the enthalpy of solute−solvent interaction Δ int H m were calculated. The enthalpy of solvation Δ solv H m, sublimation, interaction Δ int H m, and transfer Δ tr H m were correlated with the values of the surface-accessible areas of the compounds investigated.