The influence of heat capacity assumptions on the estimation of solubility parameters from solubility data

Abstract

Regular solution theory indicates that solubility parameters of crystalline organic compounds can be estimated from solubilities in London solvents. The equation for this purpose is: where X2 is the mole fraction solubility of a compound in a solvent with a solubility parameter of [delta]1. With the exception of [Delta]Cp, all parameters in the equation necessary to estimate the solute parameter, [delta]2, can either be suitably approximated or readily determined experimentally. In order to use the equation, simplifying assumptions have been made concerning [Delta]Cp, namely: [Delta]Cp = 0 or [Delta]Cp = [Delta]Sf, the entropy of fusion. In the present work, we have considered the extent to which these assumptions influence the magnitude of solubility parameters estimated from solubilities in n-hexane, n-heptane, n-dodecane, cyclohexane, carbon tetrachloride, toluene and benzene. Using n-alkyl p-aminobenzoates as test compounds, it is shown that solubility-based solubility parameters are relatively insensitive to the form of the equation used to calculate [delta]2. Specifically, solubility parameter estimations based on the two simplifying assumptions differ by no more than 0.2 (cal/ml)1/2, an increment of the order of the presumed inherent error of estimation.