Computational study on the comparative synthesis of energetic FOX‐7 derivatives

Abstract

Ethene and two kinds of nitrating reagents (HNO 3 and N 2 O 5 ) were included in respective molecular systems, which progressed through a two-stage electrophilic and free radical nitrosubstitution, resulting in the corresponding nitroethene compounds. Subsequent halogenation (using Cl 2 and Br 2 ) and amination (using ammonia) were then performed, also by electrophilic and radical substitution, to produce the target 1,1-diamino-2,2-dinitroethene (FOX-7) derivatives. All transition state species were identified using a two-or three-structure Synchronous Transit-Guided Quasi-Newton between the Cartesian coordinates of the related molecular systems at specific reaction stages. The modeling results suggest that N 2 O 5 is the better agent for nitration and bromine is suitable for use in halogenation. The comparable activation energies throughout the reaction stages were considered to imply the most feasible pathways of FOX-7 synthesis.

Initial decomposition mechanism for the energy release from electronically excited energetic materials: FOX-7 (1,1-diamino-2,2-dinitroethene, C2H4N4O4)

“…Orbitals used for FOX-7 active space are three NO σ nonbonding orbitals nσ NO(1) , nσ NO 2, and nσ NO 3, two π -nonbonding orbitals π NO2(1) and π NO2 2, one σ nonbonding orbital around the whole molecule nσ , one delocalized ONO π -antibonding orbital π ONO *, and one π -antibonding orbital of the whole molecule π * as shown in Figure 1. We tried the Gaussian calculations in larger active spaces such as (14,9), (12,11), (12,10): the values for potential energy surfaces are similar to those found for the (12,8) calculation. To avoid convergence failure problems, a reduced (6,5) active space is also used initially for the excited state calculations: the CASSCF(12,8) is applied to get a more accurate potential energy.…”

“…Equilibrium geometry calculations are conducted taking the total charge as neutral and the spin multiplicity as 1. To explore the excited state potential energy surfaces, the active space comprises 12 electrons distributed in 8 orbitals, denoted as CASSCF (12,8). Orbitals used for FOX-7 active space are three NO σ nonbonding orbitals nσ NO(1) , nσ NO 2, and nσ NO 3, two π -nonbonding orbitals π NO2(1) and π NO2 2, one σ nonbonding orbital around the whole molecule nσ , one delocalized ONO π -antibonding orbital π ONO *, and one π -antibonding orbital of the whole molecule π * as shown in Figure 1.…”

“…FOX-7 contains two symmetric NO 2 groups and to make the calculation converge, a CASSCF(6,5) is employed initially with chosen NO 2 orbitals located only on one NO 2 group. Following this, the (12,8) active space is applied to get a better potential energy surface. To find the transition states and intermediate states along the reaction pathways, a relaxed scan optimization algorithm as implemented is employed in which all geometrical parameters except for the specified bond distance are optimized and electronic energies are monitored as the specified bond is elongated.…”

“…[4][5][6][7][8] FOX-7 is described as a push-pull ethylene with two donor amine groups (-NH 2 ) and two withdrawing nitro groups (-NO 2 ) on the molecular (ethylene) framework: its insensitivity behavior can be explained by its structure. 1,[9][10][11] FOX-7 is stable partially due to the strong intra-molecular hydrogen bonds between nitro oxygen atoms and amino hydrogen atoms, 4,12,13 which are important for its ground and excited electronic state properties. The FOX-7 crystal appears golden yellow and has two-dimensional wave-shaped layers with extensive intermolecular hydrogen bonding within the layers and with weaker van der Waals interactions between the layers.…”

Computational optimum conditions for FOX-7 synthesis – A comparative synthesis route

“…[17,18] Early theoretical work in our lab indicated the feasibility of selecting ethene as the raw material to undergo nitration and halogenation to 1,1-dichloro-2,2-dinitroethene (or 1,1-dibromo-2,2-dinitroethene), followed by amination by ammonia to obtain FOX-7. [19] Corresponding achievements in those researches present the possibility that FOX-7 can be prepared from 1,1-dihalogen-2,2-dinitroethene, regardless of the experiment performed by Baum et al, who did not obtain the desired product from amination of 1,1-diiodo-2,2-dinitroethene [11,20].…”