Solid-Liquid Phase Equilibria of N,N′-[l,3-Phenylenebis(methylene)]-bis(phosphoramidic acid) P,P,P′,P′-Tetraphenyl Ester in 10 Pure Solvents

N,N'[1,3-Phenylenebis(methylene)]bis(phosphoramidic acid) P,P,P',P'-tetraphenyl ester (PNBE) was synthesized and characterized by elemental analysis, mass spectrometry, and IR and NMR spectroscopy. The melting point and the enthalpy of fusion of PNBE were obtained by differential scanning calorimetry, and the thermal stability of PNBE was measured by thermogravimetric analysis. The solubilities of PNBE in selected solvents were determined by a gravimetric method. The experimental data were correlated with the Wilson, nonrandom two-liquid (NRTL), and universal quasichemical (UNIQUAC) equations. The calculated results showed good agreement with the experimental data. Among them, the Wilson model gave the best description of the solubility data. The solubility parameter of PNBE was evaluated using the Scatchard-Hildebrand model. The data presented in this work will be helpful for the choice of solvents for the solution-casting process and optimization of the dissolution or purification of PNBE.