Organic solutions of amines are being used increasingly to separate organic acids from aqueous mixture solutions via reactive extraction. The design of an amine extraction process requires kinetic data for the acid + amine + solvent system that is used. Kinetic studies for the extraction of propionic acid from aqueous solution with Alamine 336 diluted in toluene were conducted using a stirred cell for kinetic studies. Equilibria for propionic acid extraction by Alamine 336 in toluene as a diluent have been determined. All measurements were conducted at a temperature of 298.15 K. The extent to which the organic phase may be loaded with propionic acid is expressed as a loading ratio (Z). Calculations based on the stoichiometry of the reactive extraction and the equilibria that are involved indicated that more propionic acid is transferred to the organic phase than would be expected from the 1:1 stoichiometry of the reaction. The equilibrium data were also interpreted by a proposed mechanism of three reactions of complexation by which 1:1 and 2:1 acid-amine complexes are formed. The kinetics of extraction of propionic acid by Alamine 336 in toluene has also been determined. The results of the liquid-liquid equilibrium measurements were correlated by a linear solvation energy relationship (LSER) model, which takes into account physical interactions. From the regression coefficients, information on the solvent-solute interaction is obtained and solvation models are proposed.