Mathematical correlation of 4-aminobenzoic acid solubilities in organic solvents with the abraham solvation parameter model

Abstract

The Abraham solvation parameter model is used to calculate the numerical values of the solute descriptors for 4-aminobenzoic acid from experimental solubilities in organic solvents. The mathematical correlations take the form of

where C _S and C _W refer to the solute solubility in the organic solvent and water, respectively, C _G is a gas phase concentration, R ₂ is the solute excess molar refraction, V _x is McGowan volume of the solute,

and

are measures of the solute hydrogen-bond acidity and hydrogen-bond basicity,

denotes the solute dipolarity/polarizability descriptor, and L ⁽¹⁶⁾ is the solute gas phase dimensionless Ostwald partition coefficient into hexadecane at 298 K. The remaining symbols in the above expressions are known solvent coefficients, which have been determined previously for a large number of gas/solvent and water/solvent systems. We estimate R ₂ as 1.0750 and calculate V _x as 1.0315, and then solve a total of 26 equations to yield

,

and

. These descriptors reproduce the observed log(C _S/C _W) values with a standard deviation of only 0.120 log units. The log(C _S/C _G) correlation could not be used in the present study because of lack of experimental vapor pressure data for 4-aminobenzoic acid at 298.15 K.

Keywords:

• 4-Aminobenzoic acid solubilities
• Alcohol solvents
• Partition coefficients
• Molecular solute descriptors
• Solubility predictions

Acknowledgements

Research supported in part by the University of North Texas Research Council. Amanda Charlton and Charlisa Daniels thank the National Science Foundation for support received under NSF-REU grant (CHE-0243795).