Reaction Mechanism of 1,3,5-Trinitro-s-triazine (RDX) Deciphered by Density Functional Theory

Abstract

1,3,5-Trinitro-s-triazine, or cyclotrimethylene trinitramine, or RDX, is a sensitive, secondary explosive, which has been the subject of a number of studies regarding the sensitivity and mechanism of decomposition in energetic materials. Several initial mechanistic steps have been proposed for RDX decomposition, with no conclusive agreement upon any one as the definitive pathway. Our research utilizes density functional theory (DFT)-based calculations and concepts, particularly the nuclear Fukui function, to analyze the effects of additive/depletive electronic perturbation upon vapor conformers and crystal RDX structures. Since the nuclear Fukui function is a measure of the physical stress that a nucleus encounters upon a change in the electron population, it may provide useful information regarding the role of each atom in unimolecular decomposition. The results illustrate that both homolytic cleavage of N-N bonds and elimination of HONO from RDX exhibit favorability as initial steps in the decomposition of RDX in either phase. The nuclear Fukui function proved a valuable tool for gaining insight into the initial steps of unimolecular reactions.

Nuclear fukui functions and the deformed atoms in molecules representation of the electron density: Application to gas‐Phase RDX (hexahydro‐1,3,5‐trinitro‐1,3,5‐ triazine) electronic structure and decomposition

“…The latter has also an appreciable value of G i (0.12697 au). This situation points to a more probable release of the equatorial nitro group in agreement with Swandley and Li [13]. A HONO elimination here seems unlikely because the values of the U i vector of the hydrogen atoms, including the ones closer to the equatorial oxygen atoms, similar to the AAA and AAE conformers, are very small when compared with the AEE conformer that favors this channel, see Discussion in the next paragraph.…”

“…Therefore, gas-phase RDX has probably the three lowest energy conformers-AAE, AAA, and AEE-interconverting among each other. The same energy ordering and similar relative energies were previously obtained by other researchers [13,25].…”

“…Their work brought new insights for the onset of the molecular decomposition processes [13]. They concluded that the NAN homolysis of the AAA conformer is through the NANO 2 bond break.…”

“…To test this approach and compare with previous nuclear Fukui function studies on the same system, on one RDX conformer [12], and on the four [13] conformers of the molecule, we investigated in this work the electronic structure and the onset of dissociation of the four RDX conformers.…”

Preparation and Properties of RDX-Nitrocellulose Microspheres

“…The most common approach to increase the energy of CMDBs is by the addition of nitramine explosives and RDX is the one commonly used to do this [3][4][5][6]. But adding RDX produces many problems, such as higher mechanical sensitivity and worse mechanical properties [7][8][9][10]. Previous research has shown that reducing the size of solid filler particles can solve these problems and also enhance the burning rate of propellants [11][12][13][14].…”