Vapor-liquid and liquid liquid equilibrium of quaternary systems that can form in the production of cyclohexanone by oxidation of cyclohexene in the presence of different solvents water + dimethylformamide (dimethyl sulfoxide, dimethylacetamide) were studied using mathematic modeling and NRTL model. The experimental and calculated data were found to be in a good agreement. The analysis of phase diagrams showed that the simplest diagram (two binary szeotropes and one distillation region) is observed for systems containing dimethyl sulfoxide and dimethylacetamide. It makes possible to separate cyclohexanone from catalyst and high boiling solvents by distillation.