Protocatechuic acid has wide pharmacological significance. The separation of protocatechuic acid (0.001-0.01 mol.kg(-1)) from tri-n-octylamine (TOA) (0.3140-2.827 mol.kg(-1)), in petroleum ether, toluene, and isobutyl acetate was investigated at 298 +/- 1 K as well as atmospheric pressure. The equilibrium complexation constant (K-E), extraction efficiency (E), distribution coefficients (K-D) as well as loading ratio (Z) are used to explain the magnitude of protocatechuic acid loading in the organic phase. The best diluent was isobuty acetate having a maximum distribution value as 4.57 and efficiency of 82.06% for 0.01 mol.kg(-1) protocatechuic acid and 2.827 mol.kg(-1) TOA concentration. For the various diluents in TOA, considering K-D and %E the extraction capability was observed in the order isobutyl acetate (82.06%) > toluene (61.21%) > petroleum ether (58.88%). The design parameters for the extraction process, minimum ratio of solvent to feed (S/F-min), and theoretical stages required were calculated. The Langmuir isotherm, mass action law, and relative basicity models represented the reactive extraction equilibrium for protocatechuic acid-TOA-diluent systems. The results of the relative basicity model were found to be near to experimental data with less than 5% error.