The carboxylic acids such as ethanoic, propanoic. and butanoic acids are most widely used in pharmaceutical. agricultural, polymer, and chemical industries. The separation of acids from fermentation broth and aqueous waste stream can be intensified by reactive extraction. The reactive extraction of carboxylic acids (ethanoic, propanoic, and butanoic acids) by N,N-dioctyloctan-1-amine (TOA) with six different diluents [decane. benzene, 4-methyl-2-pentanone (MIBK), decan-1-ol, chloroform, and decane (w = 0.725) + decan-1-ol (w = 0.275)] is studied. The physical equilibria using pure diluents with the same conditions are also studied. Distribution coefficients, loading factors, and degree of extraction are calculated as a result of batch extraction experiments. In the present work, a population-based search algorithm, differential evolution (DE), is employed as an optimization routine to estimate the optimum values of equilibrium constants (K(E)) and stoichiometries of reactive extraction (men) through proposed mathematical models. On the basis of stoichiometries, the equilibrium constants (K(11), K(21). and K(31)) for individual complexes between acid and extractant are also estimated. In addition to these parameters, the linear solvation energy relationship (LSER) model is applied to evaluate distribution coefficients, and the I.SER equation is presented for each acid. The extraction power of amine/diluent system increases in the order of chloroform >= decan-1-ol > MIBK > decane (w = 0.725) + decan-1-ol (w = 0.275) >= benzene > decane (w = 0.725) + decan-1-ol (w = 0.275) >= benzene > decane.