Abstract
By using the isothermal saturation method, the solid-liquid equilibrium of 2-nitro-p-phenylenediamine in pure organic solvents of methanol, ethanol, n-propanol, isopropanol, N-methyl-2-pyrrolidone, acetonitrile, ethyl acetate, toluene and 1,4-dioxane and liquid mixture of (N-methyl-2-pyrrolidone+methanol) was obtained experimentally at the temperatures ranging from (283.15 to 318.15)K under atmospheric pressure, and the solubility of 2-nitro-p-phenylenediamine in the selected solvents was determined by a high-performance liquid chromatography (HPLC). Within the studied temperature range, the 2-nitro-p-phenylenediamine solubility in mole fraction in these solvents increased with increasing temperature. The descending order of the mole fraction solubility in pure solvents was as follow: (N-methyl-2-pyrrolidone, 1,4-dioxane)>ethyl acetate>acetonitrile>methanol>ethanol>n-propanol>isopropanol>toluene, and for the (N-methyl-2-pyrrolidone+methanol) mixture with given initial composition, the mole fraction solubility of 2-nitro-p-phenylenediamine increased with increasing temperature and mass fraction of N-methyl-2-pyrrolidone. The values of solubility for 2-nitro-p-phenylenediamine in pure solvent were correlated and calculated with the modified Apelblat equation, λh equation, Wilson model and NRTL model; and in the binary solvent mixture of (N-methyl-2-pyrrolidone+methanol), the Jouyban–Acree model, modified Apelblat–Jouyban–Acree model and Sun model. For the pure solvents, the largest values of the relative average deviation (RAD) and root-mean-square deviation (RMSD) obtained by the four models were 1.17% and 6.80×10−4, respectively; and for (N-methyl-2-pyrrolidone+methanol) mixture, they were a larger, which were 3.59% and 19.12×10−4. In general, the selected thermodynamic models were all acceptable for describing the solubility behaviour of 2-nitro-p-phenylenediamine in the solvents. In addition, the mixing properties including the mixing Gibbs energy, mixing enthalpy, mixing entropy, activity coefficient at infinitesimal concentration (γ1∞) and reduced excess enthalpy (H1E,∞) were calculated for 2-nitro-p-phenylenediamine in pure solvents. Knowledge of the solubility and thermodynamic studies is essential in optimizing the purification process of 2-nitro-p-phenylenediamine.
Published Version
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