Investigation on the dissolution behavior of 2HNIW·HMX co-crystal prepared by a solvent/non-solvent method in N,N-dimethylformamide at T = (298.15–318.15) K

Abstract

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexazisowurtzitane (HNIW)·1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) co-crystal in a 2:1 molar ratio was prepared by a solvent/non-solvent method, and the co-crystal has been characterized by several methods. The enthalpies of dissolution of 2HNIW·HMX co-crystal in N,N-dimethylformamide at different temperatures were measured by a DC08-1 Calvet microcalorimeter under standard atmospheric pressure, and it is indicated that the dissolutions are exothermic process. The empirical formulae for the calculation of the molar enthalpy ( $$\Delta_{\text{diss}} H$$ ) of dissolution, relative partial molar enthalpy ( $$\Delta_{\text{diss}} H_{\text{partial}}$$ ), relative apparent molar enthalpy ( $$\Delta_{\text{diss}} H_{\text{apparent}}$$ ), and enthalpy of dilution ( $$\Delta_{\text{dil}} H_{1,2}$$ ) at 298.15 K are obtained. The differential enthalpies ( $$\Delta_{\text{dif}} H$$ ) and kinetic equations describing the dissolution process at different temperatures are deduced. Furthermore, the apparent activation energy E = 10.54 ± 0.22 kJ mol-1 and pre-exponential constant A = 0.34 ± 0.03 s−1 of 2HNIW·HMX co-crystal are obtained. The standard molar Gibbs free energy of activation ( $$\Delta G_{ \ne }^{\theta }$$ ) at different temperatures is 86.44 ± 0.02 kJ mol−1 (298.15 K), 88.02 ± 0.03 kJ mol−1 (303.15 K), 89.61 ± 0.01 kJ mol−1 (308.15 K), 91.18 ± 0.01 kJ mol−1 (313.15 K), and 92.75 ± 0.02 kJ mol−1 (318.15 K), respectively. The standard molar entropy of activation ( $$\Delta S_{ \ne }^{\theta }$$ ) and standard molar enthalpy of activation ( $$\Delta H_{ \ne }^{\theta }$$ ) are − 262.55 ± 0.72 J mol−1 K−1 and 7.98 ± 0.22 kJ mol−1, respectively.