A new model of the liquid/liquid equilibrium of butyric acid (BA) and water extraction from aqueous solutions to an organic solvent containing phosphonium ionic liquid and dodecane has been derived. It has seven fitting parameters and describes experimental data well. Reactive extraction with formation of the (p, 1) acid-IL complexes with p <= 11 acids on one hand and their aggregation by water bridges on the other hand refer to the dualistic character of the extraction process and the developed model. The values of two equilibrium constants characterizing the stability of hydrogen bonds between acid and IL anion are 3 and 2 orders of magnitude larger as compared with constants characterizing stability of acidacid H-bonds. Water is extracted via two reactive mechanisms. The first is a competitive extraction of acid and water which results in the release of water from the solvent as the BA extraction proceeds. The second mechanism is coextraction of water with BA. At the acid loading of IL above 3, this mechanism dominates and the water loading increases linearly with the increasing acid loading. These mechanisms suggest that two types of water exist in the solvents with IL. Water associated directly to IL and hydration water associated with acid molecules in the complexes.