In the light of the novel physical-chemical properties of supercritical water as a green reaction medium, we studied the synthesis of deuterated benzene in supercritical heavy water, in the presence of sodium deutroxide, as a catalyst. The effects of operational parameters including temperature, time, pressure (density), catalyst amount and benzene/D2O volumetric ratio on the degree of deuteriation (D%) and deuterated benzene yield were investigated extensively and the conditions for the highest degree of deuteration and product yield, were optimized. Furthermore, because of the importance of the pressure of solution inside the reaction medium on the HID exchange process as well as the impurity production, which have not been studied thoroughly, estimation of density for the benzene-water mixture under these operational conditions was studied with Aspen software. After comparing with the experimental data, the best equation of state, Soave-Redlich-Kwong with Kabadi-Danner modification (SRK-KD), with lowest amount of temperature-averaged [350 degrees C-400 degrees C] deviation was introduced. (C) 2017 Elsevier B.V. All rights reserved.