Date of Award

1972

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Pharmaceutical Sciences

First Advisor

Anthony N. Paruta

Abstract

Equilibrium solubilities of the first four homologous alkyl p-aminobenzoate esters were determined in methanol, ethanol, n-propanol and water at 25°, 33° and 4o° C.; the esters and the alcohols comprise separate but similar 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 by computer 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 in order to calculate their ideal solubilities. Partial molal free energies of each solution were calculated from the activity coefficients of the solutes, i.e., the comparison of ideal to actual solubility. Solubilities of the aminobenzoates are linear with increasing temperature, and directly related to the homologous nature of the esters, i.e., alkyl carbon number. However, these data proved to be of limited utility in the correlation between theoretical and actual solubilities with respect to the polarity differences between solute and solvent.

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