Abstract:

A new cyclic byproduct was formed during hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) preparation by direct nitration. Silicone column chromatography with acetone and dichloromethane in various ratios as the eluent was used to separate 3, 5-dinitro-1-oxygen-3, 5-diazacyclohexane from the product mixture. A single crystal of 3, 5-dinitro-1-oxygen-3, 5-diazacyclohexane was grown from acetone, and characterized using elemental analysis, Fourier-transform infrared (FTIR) spectroscopy, ¹H nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS). Its structure was determined using an X-ray single-crystal diffractometer. The results indicate that the crystal molecular weight is 178.12. It belongs to the monoclinic system with the space group P121/n1, a = 0.58128(13) nm, b = 1.72389(14) nm, c = 0.71072(6) nm, β = 112.056°, V = 0.66006(16) nm³, Z = 4, D_C= 1.792 g·cm^-3, μ = 0.17 mm^-1, and F(000) = 368.0; the final deviation factor R is 0.0397. Differential scanning calorimetrythermogravimetry (DSC-TG) was used to investigate the thermal behavior of the title compound. Sharp peaks were observed at 383.15 K (melting) and 519.05 K (decomposition). The kinetic parameters were obtained using the Kissinger and Flynn-Wall-Ozawa methods and the TG data at different heating rates. The Coats-Redfern method was used to study the thermal decomposition mechanism of 3, 5-dinitro-1-oxygen-3, 5-diazacyclohexane. The results show that the title compound is a low-melting-point compound with good stability; its apparent activation energy and pre-exponential factor, calculated using the Kissinger equation, are 212.32 kJ·mol^-1 and 6.20×10²⁰ s^-1, respectively. The apparent activation energy, calculated using the Flynn-Wall-Ozawa equation, is 210.39 kJ·mol^-1. G(α) = (1-α)^-1-1 (n = 2) obtained using Coats-Redfern method is regarded as the most appropriate thermal decomposition kinetic equation.

Key words: RDX, 3, 5-Dinitro-1-oxygen-3, 5-diazacyclohexane, Crystal structure, Thermal decomposition kinetics, Apparent activation energy, Mechanism