Measurement and correlation of the solubility of 1-methyl-3,4,5-trinitropyrazole in twelve pure solvents at temperatures from 283.15 K to 323.15 K

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In the present study, the solubility of 1-methyl-3,4,5-trinitropyrazole (MTNP) was determined by a dynamic laser monitoring at T = (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K in twelve pure solvents, including water, benzene (Ph), dimethyl sulfate (DMS), methylbenzene (PhMe), tetrahydrofuran (THF), methanol (MeOH), ethanol (EtOH), 1,2-dichloroethane (DCE), nitromethane (NM), acetonitrile (ACN), ethyl acetate (EA) and formic acid (FA), at atmospheric pressure (P = 0.1 MPa). In the temperature range from 283.15 K to 323.15 K, the mole fraction solubility values of MTNP in water, Ph, DMS, PhMe, THF, MeOH, EtOH, DCE, NM, ACN, EA and FA were 0.000008–0.000072, 0.003495–0.025271, 0.002153–0.037197, 0.001602–0.012304, 0.002103–0.074525, 0.000318–0.001625, 0.003752–0.048205, 0.017836–0.047105, 0.008408–0.016783, 0.003579–0.012367, 0.004460–0.022006 and 0.220917–0.443206. As revealed from the experimental results, the solubility of MTNP in twelve pure solvents increased with the increase in the temperature. The solubility behaviors of MTNP in investigated solvents were analyzed with the Hansen solubility parameter (δd, δp, δh, δt, δv and Δδt). The Kamlet-Taft parameters were calculated to delve into the solvent effect. Subsequently, the measured solubility data was correlated with five thermodynamic models, i.e., the modified Apelblat equation, λh equation, NRTL model, Wilson model and Two-Suffix Margules model. Overall, the NRTL model provided the most satisfactory fitting results. As revealed from the results, the minimum average values of relative mean deviation (102ARD) and root-mean square deviation (104RMSD) were determined with the NRTL model that achieved the values of 2.06 and 1.49. Furthermore, the dissolution thermodynamic parameters, including mixing enthalpy (ΔmixH), mixing entropy (ΔmixS) and mixing Gibbs energy (ΔmixG) were calculated according to the Wilson model, and the relative contributions of enthalpy %ζH and entropy %ζS were also calculated. It can be seen that the dissolution of MTNP in a given solvent is spontaneous and entropy driven.