Solution thermodynamics of alkyl p-aminobenzoates

Equilibrium solubilities of the first four homologous alkyl p-aminobenzoate esters were determined in methanol, ethanol, and 1-propanol at 25, 33, and 40 degrees; the esters and the alcohols comprise separate homologous series. The solution process of a solute may be considered to be the summation of two sequential steps, melting and mixing, and the magnitude of solubility depends upon temperature and the extent of interactions between solute and solvent molecules. Quantitative solute concentrations, obtained from spectrophotometric analysis, were converted to mole fractions. Statistical analysis of the logarithmic mole fraction solubilities of the aminobenzoates, which were linear with respect to both reciprocal absolute temperature and the logarithm of absolute temperature, generated enthalpies and entropies of solution, respectively. The heats of fusion and the melting points of these aminobenzoates were determined to calculate their ideal solubilities. Excess free energies and partial molal free energies of each solution were calculated from the activity coefficients of the solutes; the thermodynamic elements for these systems are discussed.