Chemical equilibrium (CE) for the quaternary reactive system of acetic acid-n-butanol-n-butyl acetate-water was studied at 308.15 K and atmospheric pressure. The experimental data on CE were considered in comparison with the data on liquid-liquid equilibrium: the CE is reached both in homogeneous and heterogeneous area of reactive mixture compositions. The crossing of CE and binodal surfaces is presented in a composition tetrahedron and a square of transformed composition variables. The thermodynamic constant of CE at 308.15 K was determined with the use of NRTL and UNIQUAC models. (C) 2015 Elsevier B.V. All rights reserved.