A liquid-liquid extraction equilibrium model was developed describing the extraction of aqueous 4-cyanopyridine with the reactive solvent 4-nonylphenol. The model describes the capacity of the solvent up to an equilibrium aqueous phase concentration of 20 g/L within a temperature interval of 25 to 80 degrees C. This model describes the transfer of 4-cyanopyridine from the aqueous to the 4-nonylphenol phase and takes into consideration the complexation in the solvent phase through hydrogen bonding of 4-nonylphenol with both functional groups of 4-cyanopyridine, as well as the oligomerization of 4-nonylphenol. The thermodynamic equilibrium parameters were regressed to the experimental data with good accuracy, the largest error at the confidence limit of the estimated parameters being 4%. The obtained results were in good agreement with the literature on the complexation of pyridines with phenols. The mean relative error between the model and the experimental data obtained in this work was 3.8%. (C) 2012 Elsevier Ltd. All rights reserved.