Nitramino Groups Research Articles

A density functional theory investigation of the substituent effect on acyclovir and guanine derivatives for applications on energetic materials

The main challenge in designing new energetic materials is to find a good balance between four seemingly incompatible requirements, namely, high-energy content, low sensitivity, low production costs and less-polluting content. Fused nitrogen heterocycles of imidazole and pyrimidine, such as acyclovir and guanine, may offer interesting features due to the combination of a coplanar framework and a large conjugate system, which contribute to a reduced sensitivity, and a number of energetic bonds that can be increased by the introduction of explosophore substituents. In this work, to evaluate the potential of acyclovir and guanine derivatives as energetic materials, density functional theory (DFT) calculations were carried out to investigate the influence of the type and position of the explosophore substituent groups –NO2, –NHNO2, –N3, –ONO2, –CN, −N=N−, and −N=N(O)− on the energetic properties and chemical reactivity of 91 acyclovir- and guanine-based molecules, including thirty one nitramines, three nitroheterocycles, seventeen azides, seventeen nitrate esters, seventeen nitriles, three azo and three azoxy compounds. Several molecular properties were computed, including the chemical reactivity, the heat of formation and the detonation velocities and pressures using semiempirical equations. Among the molecules with no bridge groups, we found that, except for cyano group, position 4 were the most stable for acyclovir derivatives, whereas, except for the azido group, position 2 and 5 provided the most stable compounds for guanine derivatives. Among the bridged derivatives, depending on the molecule and positions, the nitrate esters and the nitro derivatives were more stable. In comparison with the parent compounds, calculations showed that the heat of formation (HOF) increased the most with azido and cyano groups, the density increased substantially with nitrate esters, nitro and nitramino groups, and the detonation velocities and pressures increased the most with nitrate ester, nitro and nitramino groups. Although azo groups resulted in higher HOFs than azoxy groups, azoxy derivatives showed superior values in terms of density, heat of maximum detonation, detonation velocity and pressure. Four nitrate esters (GD134, GD245, AZOXYGD13 and AZOXYGD25) displayed higher values of detonation velocity and pressure than RDX. The designed nitramines are less sensitive to impact than RDX. Except for GD134 and GD245, all guanine-based nitrate esters, with no bridge linkages, are expected to be less sensitive to impact than TNT. Due to the combination of good performance and stability, the compounds GD25, GD13, GD45, GD34, and GD14 have considerable potential as energetic materials. Therefore, their synthesis and further investigation are recommended.

Theoretical study of effects of introducing varying linkages into bis-triazoles on energetic performance.

A series of novel bis-triazole compounds was designed by combining high-energy functionalities (nitro and nitramino groups) as substituents with each triazole and incorporating of varying linkages into the bis-triazoles. Then, their heats of formation (HOFs), energetic properties, HOMO-LUMO, electrostatic potential, and impact sensitivity were studied theoretically to facilitate further developments. In general, all the designed compounds possess much higher HOFs than RDX, -CH2-CH2-, -N=N-, or -NH-NH- linkages contribute to increase the HOFs, while incorporation of the bridge group -O-CH2-CH2-O- shows negative effect on HOFs. Detonation properties of most of the designed compounds can be comparable with or even better than ones of RDX, suggesting that designing the bridged bis-triazoles-based derivatives with energy-rich substituents is an efficient method to obtain potential energetic compounds. Considering the detonation performance and impact sensitivity, -NH-(I), -N=N- (V), and -NH-NH- (VI) are favorable bridged groups between energetic moieties for designing efficient energetic materials (EMs).

Delving into Autocatalytic Liquid-State Thermal Decomposition of Novel Energetic 1,3,5-Triazines with Azido, Trinitroethyl, and Nitramino Groups.

Thermal decomposition of 1,3,5-triazines with azido, trinitroethyl, and nitramino groups, the three important energetic functionalities, has been studied with a range of thermal analysis tools. The involved compounds melt under heating with the following mass loss and heat and gas release in the course of thermal decomposition. Model-fitting kinetic analysis resulted in formal reaction schemes with two general stages. In case of the least energetic 6-azido-2,4-bis(2,2,2-trinitroethylamino)-1,3,5-triazine, the first reaction is a first-order reaction followed by a third-order reaction. Alternatively, for 6-azido-2,4-bis(2,2,2-trinitroethylnitramino)-1,3,5-triazine and 2,4,6-tris(2,2,2-trinitroethylnitramino)-1,3,5-triazine, the first step comprises the autocatalytic reaction. The activation energy for the first decomposition step drops from 141 to 122 kJ mol-1 due to the inductive influence of a β-nitramino group. The second general reaction for all species obeys the third-order reaction model with activation energies in the range 112-126 kJ mol-1. On the basis of the analysis of the kinetic data and temporal behavior of the evolved gases, a similar primary decomposition channel, the homolytic cleavage of a C-NO2 bond, has been proposed for all investigated substances.

Energetic furazan-triazole hybrid with dinitromethyl and nitramino groups: decreasing sensitivity via the formation of a planar anion.

Energetic salts (4, 5 and 7-11) of 3-(3-dinitromethanide-1H-1,2,4-triazol-5-yl)-4-nitraminofurazanate and the azo compound (15) as well as its ammonium (14), hydrazinium (16) and hydroxylammonium (17) salts were synthesized and fully characterized. The structures of 5 and 15 were confirmed by single crystal X-ray diffraction analysis. The hydroxylammonium salt (5) has a high measured density (1.85 g cm-3) and shows promising properties as a replacement for the traditional explosive (RDX). The anion is planar which suggests that a combination of two heterocyclic five-membered rings with nitramino and dinitromethyl groups could open a new avenue to advanced energetic materials with high detonation performance and good sensitivities.

Theoretical studies on a new furazan compound bis[4-nitramino-furazanyl-3-azoxy]azofurazan (ADNAAF).

Bis[4-nitraminofurazanyl-3-azoxy]azofurazan (ADNAAF), synthesized in our previous work [1], contains four furazan units connected to the linkage of the azo-group and azoxy-group. For further research, some theoretical characters were studied by the density functional theoretical (DFT) method. The optimized structures and the energy gaps between the HOMO and LUMO were studied at the B3LYP/6-311++G** level. The isodesmic reaction method was used for estimating the enthalpy of formation. The detonation performances were estimated with Kamlet-Jacobs equations based on the predicted density and enthalpy of formation in the solid state. ADAAF was also calculated by the same method for comparison. It was found that the nitramino group of ADNAAF can elongate the length of adjacent C-N bonds than the amino group of ADAAF. The gas-phase and solid-phase enthalpies of formation of ADNAAF are larger than those of ADAAF. The detonation performances of ADNAAF are better than ADAAF and RDX, and similar to HMX. The trigger bond of ADNAAF is the N-N bonds in the nitramino groups, and the nitramino group is more active than the amino group (-NH2).

Enhancing Energetic Properties and Sensitivity by Incorporating Amino and Nitramino Groups into a 1,2,4-Oxadiazole Building Block.

A single nitrogen-rich heterocyclic ring with many energetic groups is expected to exhibit excellent detonation performance. We report an effective approach for the synthesis of 3-amino-5-nitramino-1,2,4-oxadiazole, which has nitramino and amino groups in the same building block. The single-crystal X-ray structure shows layered hydrogen-bonding pairs as well as the presence of a water molecule which ensure insensitivity. Through incorporation of a cation, the hydrazinium or hydroxylammonium salts exhibit good energetic performance and acceptable sensitivities.

Enhancing Energetic Properties and Sensitivity by Incorporating Amino and Nitramino Groups into a 1,2,4‐Oxadiazole Building Block

AbstractA single nitrogen‐rich heterocyclic ring with many energetic groups is expected to exhibit excellent detonation performance. We report an effective approach for the synthesis of 3‐amino‐5‐nitramino‐1,2,4‐oxadiazole, which has nitramino and amino groups in the same building block. The single‐crystal X‐ray structure shows layered hydrogen‐bonding pairs as well as the presence of a water molecule which ensure insensitivity. Through incorporation of a cation, the hydrazinium or hydroxylammonium salts exhibit good energetic performance and acceptable sensitivities.

Energetic Materials Based on 5,5'-Diamino-4,4'-dinitramino-3,3'-bi-1,2,4-triazole.

A simple and straightforward synthesis of 5,5'-diamino-4,4'-dinitramino-3,3'-bi-1,2,4-triazole by the selective nitration of 4,4',5,5'-tetraamino-3,3'-bi-1,2,4-triazole is presented. The interaction of the amino and nitramino groups improves the energetic properties of this functionalized bitriazole. For a deeper investigation of these properties, various nitrogen-rich derivatives were synthesized. The new compounds were investigated and characterized by spectroscopy ((1)H and (13)C NMR, IR, Raman), elemental analysis, mass spectrometry, differential thermal analysis (DTA), X-ray analysis, and impact and friction sensitivities (IS, FS). X-ray analyses were performed and deliver insight into structural characteristics with which the stability of the compounds can be explained. The standard enthalpies of formation were calculated for all compounds at the CBS-4M level of theory, revealing highly positive heats of formation. The energetic performance of the new molecules was predicted with the EXPLO5 V6.02 computer. A small-scale shock reactivity test (SSRT) and a toxicity test gave a first impression of the performance and toxicity of selective compounds.

Cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), its properties and initiation reactivity

Using the 15N NMR chemical shifts of nitrogen atoms in nitramino groups of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (bicyclo-HMX or BCHMX) and additional 10 nitramines, we have assessed its reactivity in detonation, under the influence of impact, and by action of electric spark. It is stated that the thermal stability of BCHMX is higher than that of 1,3,5-trinitro-1,3,5-triazinane (RDX). The longest N N bond in the BCHMX molecule (1.412(4) Å) is the cause for its higher impact reactivity, which is at the level of that of penterythritol tetranitrate (PETN). In the experimentally determined detonation velocity, BCMX can be slightly better performing than RDX. From the standpoint of friction sensitivity, BCHMX is similar to 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Attention was also focused on the solubility-temperature dependence of BCHMX in acetone, acetonitrile, ethyl acetate, dimethyl sulfoxide, tetrahydrofurane, and nitromethane. X-ray crystallographic study of BCHMX (C 4H 6N 8O 8, M r = 294.17), has been carried out at the temperature of 150 K with the following results: a = 8.5430(8), b = 6.9480(6), c = 8.7780(8) Å, α = 90.0(7)°, β = 102.452(11)°, γ = 90.0(9)°, V = 508.777(8) Å 3, Z = 2, D x = 1.920 g cm −3, λ(Mo Ka) = 0.71073 Å, μ = 0.169 cm −1, F(000) = 856, final R = 0.0414 for 1254 independent observed reflections. In the BCHMX crystal there were found more short contacts in the molecular crystal of BCHMX data of Gilardi creating extensive supramolecular architecture.

N-(3H-thiazol-2-ylidene)nitramine and N-methyl-N-(thiazol-2-yl)nitramine.

The geometries of the thiazole ring and the nitramino groups in N-(3H-thiazol-2-ylidene)nitramine, C3H3N3O2S, (I), and N-methyl-N-(thiazol-2-yl)nitramine, C4H5N3O2S, (II), are very similar. The nitramine group in (II) is planar and twisted along the C-N bond with respect to the thiazole ring. In both structures, the asymmetric unit includes two practically equal molecules. In (I), the molecules are arranged in layers connected to each other by N-H...N and much weaker C-H...O hydrogen bonds. In the crystal structure of (II), the molecules are arranged in layers bound to each other by both weak C-H...O hydrogen bonds and S...O dipolar interactions.

Structure and properties of some nitro derivatives of N-methyl-N-phenylnitramine

Ten mono-, di- and tri-nitro derivatives of N-methyl-N-phenylnitramine were prepared and investigated using spectral and electrooptical methods. Three of them, viz. N-(2, 5-dinitrophenyl)-N-methylnitramine (monoclinic, P21/c, a=8.248(2), b=11.655(2), c=10.404(2)Å,β=102.57(2)°), N-(2,3-dinitrophenyl)-N-methylnitramine (monoclinic, P21/c, a=9.224(2), b=7.222(2), c=15.458(4)Å,β=101.08(2)°)) and N-(3,5-dinitrophenyl)-N-methylnitramine (monoclinic, P21/n, a=9.814(2), b=12.000(2), c=8.865(2)Å,β=114.94(2)°) were examined by the X-ray diffraction method. The nitramino group is nearly planar with the short N(7)–N(8) bond and strongly electron deficient N(8) atom. The nitramino group is twisted vs. the aromatic ring, there is no conjugation between the nitro and nitramino groups across the ring. The nitramino group is an electron withdrawing substituent due to the inductive effect. The number and positions of the Ar-nitro groups have no influence on the N-nitro group. Its migration ability cannot be explained in terms of the interaction between the migration origin and the ring substituents.

Multinuclear magnetic resonance and x‐ray diffraction studies of aminonitropyridines

AbstractThe 15N NMR spectra for 21 aminonitropyridines were measured and their chemical shifts assigned. The 1H and 13C NMR chemical shifts and spin–spin coupling constants were also determined for 16 compounds of this series. In order to relate the structural properties of nitramino groups and their 15N NMR chemical shifts in 2‐ and 4‐nitramino‐3‐nitropyridines, which differ remarkably from all other amino groups studied, low‐temperature 1H NMR, 17O NMR, comparative INEPT and IR spectroscopic studies were carried out. In addition, the x‐ray crystal structure of 2‐nitramino‐3‐nitropyridine was determined. Comparative spectroscopic studies showed that the nitramino derivatives exhibit different characteristics to the other compounds studied. Based on the x‐ray structural data, the nitramino group differs markedly from separate aryl‐bound amino and nitro groups. The nitramino group does not exhibit prototropic tautomerism in the crystalline state. This is in agreement with the small variation in the 15N NMR chemical shifts of the pyridine nitrogen, which excludes the prevalence of pyridinium ions. Among the four NMR nuclei studied, 15N seems to possess the best predictive power regarding the exceptional properties of the nitramino group.

NITRIMINO-(1H)PYRIDINIUM AND NITRIMIN0-(3H)THIAZOLIUM INNER SALTS: THE STRUCTURE OF SOME NITRIMINES IN THE LIGHT OF INFRARED STUDY

Compounds previously known as nitraminopyridines and 2-nitraminothiazoles are formulated as nitrimino-(1H)pyridinium and 2-nitrimino-(3H)thiazolium inner salts on the basis of the infrared study. In the solid state, the three isomer nitriminopyridines do not exhibit any infrared absorption of the —NH group in the region 3400–3200 cm.−1 but show a wide band at lower frequencies in the region 2880–2550 cm−1. 2-Nitriminothiazole shows only a wide band between 3140 and 2270 cm.−1. These shifts of absorption bands can be correlated with structures derived from the classical nitrimino tautomeric forms in which the resonance effect stabilizes (1H)pyridinium and (3H)thiazolium cations, and a nitrimino group carrying a negative charge. n-Butylnitramine, a non-resonating compound, absorbs strongly at 3300 cm.−1, indicating that nitramino groups are not associated.