Thermal Decomposition Mechanism of HNNO2H Dissociated from Mononitrobiuret and 1,5-Dinitrobiuret.

摘要

Mononitrobiuret (MNB) and 1,5-Dinitrobiuret (DNB) are, tetrazole- free, nitrogen-rich compounds, which have been reported as powerful new explosives. The initiation of thermal decomposition of MNB and DNB was found to involve an intra-molecular transfer of the H-atom from the central NH group to one of the adjacent nitro oxygens to eliminate the unstable intermediate, HNNO2H, which undergoes further decomposition. In this work, we have investigated the thermal decomposition of HNNO2H using multi-reference second- order perturbation theory and coupled-cluster theory. The following HNNO2H decomposition pathways were found to be important. First, a direct N-OH bond fission occurs with a loose saddle point to form OH and cis-HNNO radicals. Second, an inversion of the aminylene H-atom elongates the N-OH bond due to repulsion between the aminylene H-atom and the hydroxyl H-atom, and this leads to N-OH bond fission to form OH and trans-HNNO radicals. Third, the thermodynamically stable products, N2O + H2O, are formed by a complex mechanism, which involves rotation of the N-OH bond, an H-atom shift from the hydroxyl H- atom to the nitric oxygen, and then migration of the aminylene H-atom to the hydroxyl O-atom, resulting in H2O elimination with 50.4 kcal/mol of exothermicity.