Methylene nitramine

The McGill workers postulated that, in their process, methylene nitramine (CH2=N—N02) is formed as an intermediate, which then tri-merizes to RDX. However, the existence of methylene nitramine has never been proven. Werner Bachmann (Ref 2) of the University of Michigan, during WWII, conceived of a combination process in which the Hale nitrolysis of Hexamine would occur first, and the remaining methylene would be converted to RDX by the Ross-Schiessler route. Using three feed streams Ac20, Hexamine In acetic acid, and AN in nitric acid, the Bachmann process results in an 80% yield of RDX (two moles from one of Hexamine), including a small amount of HMX. 

On synthesis of cyclonite from paraformaldehyde, ammonium nitrate and acetic acid (method 4), products with cyclic structure, chiefly cyclonite and octogen, may arise due to the polymerization of the transiently-formed, hypothetical methylene-nitramine (XXVIII) [67] ... 

It is likely that theoretical methods, both ab initio and MD simulations, will be needed to resolve the complicated chemical decomposition of energetic materials. There are species and steps in the branching, sequential reactions that cannot be studied by extant experimental techniques. Even when experiments can provide some information it is often inferred or incomplete. The fate of methylene nitramine, a primary product observed by Zhao et al. [33] in their IRMPD/molecular beam experiments on RDX, is a prime example. Rice et al. [99, 100] performed extensive classical dynamics simulations of the unimolecular decomposition of methylene nitramine in an effort to help clarify its role in the mechanism for the gas-phase decomposition of RDX. 

Mowrey et al. [103] performed ab initio calculations to determine the structures, energies, and frequencies at the critical point of the possible dissociation pathways for methylene nitramine. There are three possible routes for H2CNN02 decomposition. The calculations predict that simple bond fission... 

A reaction-path based method is described to obtain information from ab initio quantum chemistry calculations about the dynamics of energy disposal in exothermic unimolecular reactions important in the initiation of detonation in energetic materials. Such detailed information at the microscopic level may be used directly or as input for molecular dynamics simulations to gain insight relevant for the macroscopic processes. The semiclassical method, whieh uses potential energy surface information in the broad vicinity of the steepest descent reaction path, treats a reaction coordinate classically and the vibrational motions perpendicular to the reaction path quantum mechanically. Solution of the time-dependent Schroedinger equation leads to detailed predictions about the energy disposal in exothermic chemical reactions. The method is described and applied to the unimolecular decomposition of methylene nitramine. 

As an illustrative example of the semiclassical reaction path dynamics method, we discuss the HONO elimination pathway for the unimolecular decomposition of methylene nitramine,... 

The conclusion drawn that the first two steps in the decomposition of TNAZ involve NO2 loss agrees with the observation by Brill and coworkers [5] that gaseous NO2 was the most abundant species in the initial phases of the thermal decomposition of bulk TNAZ. That the NO2 concentration decreases from its initially observed level in the bulk study is evidence that this species is already undergoing significant secondary reactions at the time of its initial appearance yet the surmisal that the NO2 is a primary product is correct. Additionally, the observation that no methylene nitramine formation occurs agrees with the same conclusion drawn from the bulk study where the N2O/H2CO pair was not present. However, the absence of NO as an initial product in the molecular beam experiment, shows that the NO observed in the bulk decomposition study is not due to gas phase unimolecular nitro-nitrite isomerization followed by NO loss. 

Figure 7. Reaction diagrams for the water-catalyzed concerted reaction for the conversion of methylene-nitramine, CH2NNO2, to CH2O + N2O through the hydrated intermediate CH20HNN(0)0H. In the first concerted mechanism, the CH2NNO2 molecule is hydrated. In the second step, the hydrated molecule is unimolecularly converted to CH2O and N2O. Note that the oxygen atom in the CH2O molecule arises from the water molecule rather than the NO2 group.

---