Gregory H. Imler

A Highly Stable and Insensitive Fused Triazolo–Triazine Explosive (TTX)

A fused-ring conjugated energetic molecule, 4-amino-3,7-dinitro-[1,2,4]triazolo[5,1-c] [1,2,4]triazine (TTX), has been synthesized in good yield in a two-step process starting from the known 5-amino-3-nitro-1H-1,2,4-triazole (ANTA). Characterization of TTX shows that it possesses energetic properties approaching those of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), but with a higher thermal stability and lower sensitivity towards impact and friction.

Pushing the Limits of Oxygen Balance in 1,3,4-Oxadiazoles

Gem-trinitromethyl groups were introduced into a 1,3,4-oxadiazole ring to give the first example of a bifunctionalized single five-membered ring with six nitro groups. 2,5-Bis(trinitromethyl)-1,3,4-oxadiazole (12) has a high calculated crystal density of 2.007 g cm-3 at 150 K (1.941 g cm-3 at 293 K) and a very high positive oxygen balance (39.12%), which makes it a strong candidate as a high energy dense oxidizer. The dihydroxylammonium and dihydrazinium salts of bis(trinitromethyl)-1,3,4-oxadiazole (5 and 6) exhibit excellent calculated detonation properties (5, vD = 9266 m s-1, P = 38.9 GPa; 6, vD = 8900 m s-1, P = 36.3 GPa) and acceptable impact sensitivities (5 20 J, 6 19 J), which are superior to those of RDX (7.4 J) and HMX (7.4 J). Such attractive features support the application potential of the gem-polynitromethyl group in the design of advanced energetic materials. Surprisingly, 2,5-bis(trinitromethyl)-1,3,4-oxadiazole (12) is more thermally stable and less sensitive than its bis(dinitromethyl) analogue, 8.

5-(Dinitromethyl)-3-(trinitromethyl)-1,2,4-triazole and its derivatives: a new application of oxidative nitration towards gem-trinitro-based energetic materials

An excellent method for the preparation of gem-trinitro compounds is destructive nitration based on an active methylene moiety with a neighboring carbonyl structure. Now described is an alternative approach where oxidative nitration was utilized to synthesize gem-trinitro compounds. Using this strategy, 5-(dinitromethyl)-3-(trinitromethyl)-1,2,4-triazole (6) and its ionic derivatives (7–12) were designed, prepared and thoroughly characterized. This family of new energetic materials exhibits excellent densities, good detonation performances and moderate mechanical sensitivities. Interestingly, as supported by the X-ray structure of energetic salt 8, the amine-based fused ring cation induces a face-to-face π–π arrangement thus reducing the sensitivity of the entire molecule, and advancing the further application of similar fused ring ionic stabilizers for polynitro azole anions. These results open a new chapter concerning gem-trinitro compounds in the energetic materials field.

Polynitro-functionalized Dipyrazolo-1,3,5-triazinanes: Energetic Polycyclization toward High Density and Excellent Molecular Stability

A new fused N-heterocyclic framework, dipyrazolo-1,3,5-triazinane, was synthesized and the physiochemical properties of its derivatives were investigated to evaluate the integrated energetic performance. In contrast to 1,3,5-trinitro-1,3,5-triazinane (RDX) featuring a distorted chair confirmation, polynitro-functionalized dipyrazolo-1,3,5-triazinanes have nearly planar backbones, thereby enhancing the density and thermal stability. Among these new energetic tricyclic compounds, 5 a and 12 show favorable crystal densities of 1.937 g cm-3 and 1.990 g cm-3 at 150 K, respectively, which rank highest in triazinane-based energetic compounds. Additionally, this synthetic approach was carried out to form seven-membered and eight-membered rings, giving rise to tetranitro dipyrazolo-1,3,5-triazepane (5 b) and tetranitro dipyrazolo-1,3,5-triazocane (5 c), respectively.

3,4,5-Trinitro-1-(nitromethyl)-1H-pyrazole (TNNMP): a perchlorate free high energy density oxidizer with high thermal stability

A superior oxidizer, a derivative of trinitropyrazole, 3,4,5-trinitro-1-(nitromethyl)-1H-pyrazole (TNNMP), was obtained in good yield by the reaction of ammonium 4-amino-3,5-dinitropyrazolate with bromonitromethane followed by oxidation with a mixture of H2O2/H2SO4. Characterization of TNNMP shows that in addition to having good oxygen balance (+18.3%) and detonation performance (Dv = 8858 m s−1; P = 35.1 GPa), it concomitantly has high thermal stability (Td = 202 °C) and acceptable sensitivities (IS = 14 J; FS = 120 N). These attractive properties suggest TNNMP as a promising perchlorate free high energy density oxidizer and a potential replacement for ammonium perchlorate.

Energetic dinitromethyl group functionalized azofurazan and its azofurazanates

Incorporating explosophore groups such as nitro, dinitromethyl, and azo into furazan results in potential candidates for energetic materials applications. In this study, 3,3′-azofurazan was functionalized with fluorodinitromethyl (2) and dinitromethyl (3) moieties by fluorination and acidification of potassium 4,4′-bis(dinitromethyl)-3,3′-azofurazanate (1), respectively. In addition, 3 was converted to its ammonium (4), hydrazinium (5) and hydroxylammonium (7) salts. All the compounds were fully characterized by multinuclear NMR and IR spectra, and elemental analysis. Compounds 2 and 3 are further supported by X-ray crystallographic analysis. Electronic structures were also studied. In addition, physicochemical properties, such as thermal stability, density, and sensitivity were measured, and energetic properties (e.g., detonation velocities and detonation pressures) were calculated using EXPLO5 code.

Iodobenzene-Catalyzed Synthesis of Phenanthridinones via Oxidative C–H Amidation

We report a novel synthesis of phenanthridinones from N-methoxybenzamides using an oxidative C-H amidation reaction at room temperature in open air with modest to excellent yields. This method demonstrated unprecedented substrate scope. In particular, it solved the long-standing challenge in the synthesis of phenanthridinones with sterically demanding substitutions.

N-Acetonitrile Functionalized Nitropyrazoles: Precursors to Insensitive Asymmetric N-Methylene-C Linked Azoles

Properties of energetic compounds obtained by linking energetic pyrazoles to tetrazoles by means of N-methylene-C bridges can be fine-tuned. Reactions of pyrazole derivatives with chloroacetonitrile followed by conversion of the cyano group to tetrazole using click reactions in the presence of zinc chloride result in asymmetric N-methylene-C bridged azole-based energetic compounds. All the compounds were thoroughly characterized by IR and NMR [1 H, 13 C {1 H}, 15 N] spectroscopy, elemental analysis, and differential scanning calorimetry (DSC), and for two compounds, further supported by single-crystal X-ray diffraction studies. Heats of formation and detonation performances were calculated using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Initial studies show that this new approach is promising for synthesizing less sensitive energetic compounds with fine-tuned properties.

Aminoacetonitrile as precursor for nitrogen rich stable and insensitive asymmetric N-methylene-C linked tetrazole-based energetic compounds

Reaction of aminoacetonitrile with cyanogen azide resulted in acetonitrile derivative of amino(tetrazole), 1, which on further reaction with sodium azide in the presence of ammonium chloride resulted in compound 2 with N-methylene-C bridged tetrazole and amino-tetrazole moieties. Reaction of 2 with 100% nitric acid resulted in N-(1-((1H-tetrazol-5-yl)methyl)-1H-tetrazol-5(4H)-ylidene)nitramide (4) having N-methylene-C bridged nitroimino-tetrazole and tetrazole moieties. Various energetic salts based on these three types of tetrazole derivatives (tetrazole, amino-tetrazole and nitroimino-tetrazole) in 2 and 4 were obtained. All the compounds were thoroughly characterized by IR, NMR [1H, 13C{1H}, 15N], elemental analysis, and differential scanning calorimetry (DSC). Some of them were also structurally characterized with single-crystal X-ray diffraction studies. Heats of formation and detonation performances for all the energetic compounds were calculated using Gaussian 03 and EXPLO5 v6.01 programs, respectively.

Resolving synthetic challenges faced in the syntheses of asymmetric N,N′-ethylene-bridged energetic compounds

Synthetic challenges faced during the syntheses of asymmetric N,N′-ethylene-bridged energetic compounds due to the differences in the reactivity and stability of various types of energetic rings are addressed. The elusive asymmetric compounds, 12 (in which nitramino-pyrazole is bonded to nitroimino-tetrazole via an N,N′-ethylene-bridge), and 15 and 17 (in which azido-pyrazole is bonded to nitroimino-tetrazole via an N,N′-ethylene-bridge), were obtained in good yields. All the compounds were thoroughly characterized using IR, NMR [1H, 13C{1H}, 15N], elemental analysis and differential scanning calorimetry (DSC). The structures of 13 and 14 were further confirmed via X-ray crystal analysis. Heats of formation and the detonation properties of all the energetic compounds were calculated using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Impact and friction sensitivities were determined using the standard BAM technology.