The chemistry of 3-mtro-1,2,4-triazol-5-one (NTO): thermal decomposition

Abstract

This paper presents the results from a study of the thermal decomposition and thermal stability of NTO (3-nitro-1,2,4-triazol-5-one). Mass spectra of NTO are presented (electron impact 20 and 70 eV and chemical ionisation spectra). The large abundance of the molecular ion in these spectra shows that NTO is a more stable molecule than TNT or RDX. The data acquired for NTO is summarised as a proposed mass spectral fragmentation path. A number of laser ignition measurements were conducted. These measurements showed a strong pressure dependence, which clearly indicates a multiple phase (condensed and gas phase) ignition. The laser ignition measurements also showed that the sensitivity to ignition is slightly higher than that for TNT. The results of the LI-MS (laser induced mass spectrometry) method applied to NTO imply that the probable decomposition path is an elimination of NO 2 followed by a breaking of the azole ring. The chemiluminescence (CL) method was used for determination of the activation energy and the frequency factor ( E a= 140 kJ and K 0= 5 × 10 6s −1 in the temperature interval 100–140° C). Chemiluminescence data for RDX and TNT was acquired for comparison. The DSC spectrum of NTO showed only one peak, a very strong exothermic peak at 253°C. This study is complemented with some quantum mechanical calculations which were conducted in an attempt to verify the initial steps in the decomposition path and to explain the high stability of NTO. The results were computed with the mopac 6.0 code using the semi-empirical modified neglect of diatomic overlap (MNDO) method with the parametric method 3 (PM3) parameter set at the unrestricted Hartree-Fock level.