In
order to resolve the existing discrepancies in the mechanism
and key intermediates of oxadiazole thermolysis, the initial decomposition
pathways of oxadiazoles have been studied comprehensively using the
M062X method for optimization and CBS-QB3 and DLPNO-CCSD(T) methods
for energies. The transformation from the furoxan ring to nitro group
was suggested as a potential decay channel of furoxan compounds. Results
of thermochemistry calculations showed that the preferred decomposition
reaction of oxadiazoles is the ring-opening through the cleavage of
the O–C or O–N bond. The introduction of the nitro group
has little effect on the preferential path of oxadiazole thermal decomposition,
but a great impact on the energy barrier. The lowest energy barrier
and bond dissociation energy of NO2 loss of azoles were
comprehensively studied based on the quantum chemistry calculations.
The initial decay steps of 3,4-dinitrofurazanfuroxan and benzotrifuroxan
were also studied to give insights into the mechanism of primary stages
of thermal decomposition of oxadiazoles.