Jean'ne M. Shreeve

Trinitromethyl-Substituted 5-Nitro- or 3-Azo-1,2,4-triazoles: Synthesis, Characterization, and Energetic Properties

Various new polynitro-1,2,4-triazoles containing a trinitromethyl group were synthesized by straightforward routes. These high nitrogen and oxygen-rich compounds were fully characterized using IR and multinuclear NMR spectroscopy, elemental analysis, natural bonding orbital (NBO) analysis, and differential scanning calorimetry (DSC) and, in the case of 12, with single crystal X-ray structuring. The heats of formation for all compounds were calculated with Gaussian 03 (revision D.01) and then combined with experimentally determined densities to determine detonation pressures (P) and velocities (D) of the energetic materials (Cheetah 5.0). They exhibit high density, good thermal stability, acceptable oxygen balance, positive heat of formation, and excellent detonation properties, which, in some cases, are superior to those of TNT, RDX, and HMX.

Bis[3-(5-nitroimino-1,2,4-triazolate)]-Based Energetic Salts: Synthesis and Promising Properties of a New Family of High-Density Insensitive Materials

Bis[3-(5-nitroimino-1,2,4-triazolate)]-based energetic salts were synthesized in a simple, straightforward manner. They exhibit low solubility in available solvents, high hydrolytic stability, excellent thermal stability, high density, positive heat of formation, low shock sensitivity, and excellent detonation properties. The physical and energetic properties of some salts are similar and even superior to those of RDX.

Polyethylene glycol functionalized dicationic ionic liquids with alkyl or polyfluoroalkyl substituents as high temperature lubricants

A series of new polyethylene glycol functionalized dicationic ionic liquids with alkyl or polyfluoroalkyl substitutents (9–17 and 19–24) has been prepared. Important physical properties of these liquids, including glass transition (Tg) and decomposition temperatures (Td), solubility in common solvents, density (d) and viscosity (η), were measured. These ionic liquids show high thermal stability and good lubricity. In general, imidazolium based dicationic liquids have higher Td (>415 °C) than their triazolium analogues. The introduction of polyfluoroalkyl groups boosts antiwear properties but also leads to a decrease in Td. These ionic liquids also exhibit excellent tribological characteristics even at 300 °C, which suggests use as high temperature lubricants.

High-Density Energetic Mono- or Bis(Oxy)-5-Nitroiminotetrazoles†

In the last decade, the investigation of energetic tetrazoles— cyanotetrazole, aminotetrazole, azidotetrazole, nitrotetrazole, and nitroiminotetrazole—has led to major developments in the area of high-energetic materials by many research groups. Several exciting classes of 5-substituted tetrazole moieties are introduced in the literature. Tetrazoles can be protonated to form tetrazolium salts or deprotonated to give tetrazolates. While deprotonation increases the thermal stability of tetrazoles, protonation can lower the decomposition temperature. These energetic materials based on high nitrogen content are derived from their high heats of formation due to the large number of N N and C N bonds. The combination of a tetrazole ring with energetic substituent groups containing oxygen atoms, such as nitro groups, nitrate esters, or nitramine, is of interest leading to excellent oxidizers. Current research issues in the field of high energetic materials include increasing oxygen content, which may result in the replacement of ammonium perchlorate in an effort to decrease pollution. Organic 5-nitrotetrazole derivatives, especially for synthesis of the highly energetic 1-methyl-5-nitrotetrazole, were synthesized in good yields. These were calculated to be endothermic with heats of formation of 2.16 kJg , which was assessed by means of standard tests and quantum chemical calculations. In addition, the highly energetic, nitrogen-rich 1-methyl-5-nitroiminotetrazole and its salts can easily be obtained by nitration of aminotetrazole followed by metathesis reactions using silver 1-methyl-5-nitroiminotetrazolate and the guanidinium family of chlorides in aqueous solution with high yields. Although 5-nitroiminotetrazole derivatives and their salts are energetic materials with high nitrogen content, they show good stabilities towards friction and impact, and good thermal stability. The development of new energetic compounds with similar attractive properties exhibit significant promise in optimizing environmentally benign replacements for toxic materials. In the past few years, the most convenient route to 1substituted 5-aminotetrazole is the addition of amine or hydrazine to cyanogen azide, which was found to be an efficient reagent for the synthesis of readily purified 1substituted 5-aminotetrazoles from primary amines under non-catalytic mild conditions. Nitration of these aminotetrazoles using 100% nitric acid has been shown to form mono-, di-, or trisubstituted nitroiminotetrazole derivatives. With these features in mind, our group became interested in examining the analogous chemistry using alkoxy amine derivatives. Here we describe the work leading to a series of nitroiminotetrazole derivatives of oxy nitroiminotetrazoles and their salts, with potentially significant physical and energetic properties. The aim of our study was to elucidate the structures in the crystalline state using X-ray diffraction analysis and to find new, potent oxygenand nitrogen-rich tetrazoles. Alkoxy 5-nitroiminotetrazolates may be of interest as a new class of ionic energetic materials, which have good thermal stabilities, high densities, good oxygen balance, and high heats of formation and which are realizable in high yields though straightforward routes. The synthesis of 1-methoxy-5-aminotetrazole (2) was achieved from the reaction of cyanogen azide with methoxy amine (obtained by neutralization of 1 with sodium hydroxide) (Scheme 1). At ambient temperature, nitration of amino-

Energetic Nitrogen-Rich Derivatives of 1,5-Diaminotetrazole†

these high-energy-density materials (HEDM). Surprisingly, substitution of the heterocyclic tetrazole ring with amino groups is one of the simplest methods to enhance thermal stability, even though 1 contains 84.0% nitrogen. Nearly 80 years ago 1 was prepared by treatment of thiosemicarbazide with lead(II) oxide and sodium azide. In 1984, further investigation into its synthesis and properties gave 1 in 59% yield. Later, 1 was synthesized by using aminoguanidinium chloride and HNO2. [5] The reaction mixture was carefully brought to pH 8 with sodium carbonate in order to deprotonate the amino-substituted azido guanyl chloride intermediate, which cyclized to form 1 in 58% yield. However, a further report that appeared in the same year recommended special caution in the synthesis of 1. This stated that 1 was pure following ethanol extraction; however, during extraction by ethanol a very shock sensitive alkali metal salt of tetrazolyl azide often was observed as a byproduct, produced by double diazotization of diaminoguanidine with HNO2. In our continuing interest in the development of energetic materials, we have now synthesized derivatives of 1,5diaminotetrazole in situ by reaction of cyanogen azide with monosubstituted hydrazine derivatives (Scheme 2).

3,4,5-Trinitropyrazole-Based Energetic Salts

High-density energetic salts that are comprised of nitrogen-rich cations and the 3,4,5-trinitropyrazolate anion were synthesized in high yield by neutralization or metathesis reactions. The resulting salts were fully characterized by (1)H, (13)C NMR, and IR spectroscopy; differential scanning calorimetry; and elemental analysis. Additionally, the structures of the 3,5-diaminotriazolium and triaminoguanidinium 3,4,5-trinitropyrazolates were confirmed by single-crystal X-ray diffraction. Based on the measured densities and calculated heats of formation, the detonation performances (pressure: 23.74-31.89 GPa; velocity: 7586-8543 ms(-1); Cheetah 5.0) of the 3,4,5-trinitropyrazolate salts are comparable with 1,3,5-triamino-2,4,6-trinitrobenzene (TATB; 31.15 GPa and 8114 ms(-1)). Impact sensitivities were determined to be no less than 35 J by hammer tests, which places these salts in the insensitive class.

Furazan‐Functionalized Tetrazolate‐Based Salts: A New Family of Insensitive Energetic Materials

Insensitive energetic salts: A series of furazan-functionalized tetrazolate-based energetic salts (see figure) were synthesized and characterized. All of the salts exhibit excellent thermal stabilities and high positive heats of formation.Furazan-functionalized tetrazolate-based energetic salts (1-13) were prepared by direct treatment of neutral 4-amino-3-(5-tetrazole)furazan and a Lewis base or by simple metathesis reactions of its barium salt formed in situ with the corresponding sulfate salts in aqueous solution. Key physical properties, such as melting point, thermal stability, density, hypergolicity, and sensitivity to shock, were measured. The relationship between their structures and these properties was determined. Most of salts exhibit better thermal stability than their 5-nitrotetrazolate and 5-nitraminotetrazolate analogues as well as other furazan-based salts. The structures of representative aminoguanidinium (4), carbonic hydrazylhydrazidinium (9), and 1,4-dimethyl-5-aminotetrazolium salts (13) were further confirmed by single-crystal X-ray analysis. Their densities, heats of formation, detonation pressures and velocities, and specific impulses were calculated. All of the salts possess high positive heats of formation. The effect of the furazan ring on these physicochemical properties was examined and discussed.

Ionic liquids as hypergolic fuels.

In propellant systems, fuels of choice continue to be hydrazine and its derivatives, even though they comprise a class of acutely carcinogenic and toxic substances which exhibit rather high vapor pressures and require expensive handling procedures and costly safety precautions. Only recently (2008), ionic liquids (salts with melting points less than 100 °C) with the dicyanamide anion were shown to exhibit hypergolic properties (instantaneous ignition when contacted with oxidizers (100 % nitric acid, WFNA)). Such liquids tend to have low volatilities, and high thermal and chemical stabilities, and often exhibit long liquid ranges which could allow utilization of these substances as bipropellant fuels over a variety of conditions. A new family of dicyanoborates is presented, which can be synthesized in water, with substituted N-acyclic, N-cyclic, and azolium cations has met nearly all of the desired important criteria needed for well-performing fuels.

Hypergolic Ionic Liquids with the 2,2‐Dialkyltriazanium Cation

No flame, no gain: A hypergolic mixture is composed of stable species that readily react/ignite on molecular contact. Both the anion and the cation in an ionic liquid play prominent roles in determining hypergolic properties as well as ignition delay times. With the 2,2-dialkyltriazanium cation, salts with nitrate, chloride, nitrocyanamide, and dicyanamide anions are hypergolic.

Energetic Salts with π-Stacking and Hydrogen-Bonding Interactions Lead the Way to Future Energetic Materials

Among energetic materials, there are two significant challenges facing researchers: 1) to develop ionic CHNO explosives with higher densities than their parent nonionic molecules and (2) to achieve a fine balance between high detonation performance and low sensitivity. We report a surprising energetic salt, hydroxylammonium 3-dinitromethanide-1,2,4-triazolone, that exhibits exceptional properties, viz., higher density, superior detonation performance, and improved thermal, impact, and friction stabilities, then those of its precursor, 3-dinitromethyl-1,2,4-triazolone. The solid-state structure features of the new energetic salt were investigated with X-ray diffraction which showed π-stacking and hydrogen-bonding interactions that contribute to closer packing and higher density. According to the experimental results and theoretical analysis, the newly designed energetic salt also gives rise to a workable compromise in high detonation properties and desirable stabilities. These findings will enhance the future prospects for rational energetic materials design and commence a new chapter in this field.