THERMAL-DECOMPOSITION PATHWAYS OF 1,3,3-TRINITROAZETIDINE (TNAZ), RELATED 3,3-DINITROAZETIDINM SALTS, AND N-15, C-13, AND H-2 ISOTOPOMERS

The thermal decomposition of 1,3,3-trinitroazetidine (TNAZ) and relate d 3,3-dinitroazetidium (DNAZ(+)) salts was examined neat and in soluti on. TNAZ kinetics were found (160-250 degrees C) to be first-order and nearly identical neat and in benzene, with an activation energy of 46 .6 kcal/mol (195 kJ/mol). The DNAZ(+) salts were less thermally stable than TNAZ, and neat did not decompose in a first-order fashion. Howev er, in aqueous solution the DNAZ(+) salts did decompose following firs t-order kinetics; their rates were similar with minor differences appa rently related to the strength of the anion as a conjugate base. Like simple nitramines such as dimethylnitramine, TNAZ tended to form N2O r ather than N-2, but unlike other nitramines it formed about as much NO as N2O. TNAZ isotopomers labeled with C-13 and with N-15 were prepare d and used to identify the origin of the decomposition gases and the i dentity of the condensed-phase products. Early in the decomposition of TNAZ, most of the NO came from the nitro group attached to the azetid ium ring nitrogen. Most of the N2O was the result of the nitro groups interacting with each other, while the majority of the N-2 contained o ne nitrogen from the ring. Many condensed products have been identifie d, but five stand out because they are formed in the thermolysis of TN AZ and the three DNAZ(+) salts [NO3-, Cl-, N(NO2)(2)(-)]. These are 3, 5-dinitropyridine (M, always a minor product), 1-formyl-3,3-dinitroaze tidine (L), 1,3-dinitroazetidine (K), 1-nitroso-3,3-dinitroazetidine ( E), and 1-nitroso-3-nitroazetidine (G); the identity of the first four has been confirmed by use of authentic samples. Of these five, the la st four have been shown to interconvert with TNAZ and each other under the conditions of these experiments. This study confirms the presence of two competitive TNAZ decomposition pathways. Under the conditions of this study, N-NO2 homolysis is slightly favored, but products, such as K, resulting from C-NO2 scission, are also well represented.