In search of the most thermally stable 1,1,1-trinitrocompounds, several well-known and new energetic 1,2,4,5-tetrazines have been synthesized. The thermal stability of obtained compounds has been investigated by the methods of isothermal and non-isothermal kinetics. The introduction of the OCH2 or NHCH2 bridge between the heterocycle and the trinitromethyl moiety has been confirmed to result in a significant increase in thermal stability. An increase in stability is accompanied by a decrease in the C–NO2 bond length by 0.025–0.029 Å. An additional increase in the thermal stability of 1.1,1-trinitro derivatives is possible due to the creation of high-melting compounds, the decomposition of which proceeds before melting. Trinitroethylamine derivatives are most preferred due to the strong hydrogen bonds of the NH group. However, in some cases, the actual stability of a substance is reduced by the appearance of autocatalysis. On the basis of experimental data of manometry, analysis of condensed decomposition products by HPLC and IR spectroscopy, a mechanism for the decomposition of 1,1,1-trinitrocompounds was proposed. The compounds studied were found to have favorable detonation properties, which were close to those of RDX, a commonly used explosive. At the same time, some of the obtained polynitro compounds have increased burning rates in comparison with the known nitramines HMX and RDX.

A method for the thermal cyclization of tetrazol-5-ylamino-1,2,4,5-tetrazine has been developed, leading to the formation of a new heterocyclic system based on 1,2,4-triazole and 1,2,4,5-tetrazine, a fused tricyclic compound, from which a number of other tricyclic derivatives containing nitramine, nitro, and keto groups have been obtained. Based on experimental studies and quantum-chemical calculations enthalpies of formation of the new fused energetic materials in the solid state have been found. The enthalpy of formation of the new fused tricyclic compound bis [1, 2,4] triazolo [1,5-b:5',1'-f] [1,2,4,5] tetrazine-2,7-diamine, DATC, (3505 kJ kg(-1)) exceeds the enthalpies of formation of diaminotetrazine (2652 kJ kg(-1)) and 5-aminotetrazole (2442 kJ kg(-1)), which makes the resulting framework one of the most energetic heterocyclic compounds. In addition, DATC and its derivatives turned out to be low-sensitive and thermally stable explosives, the stability of which is comparable to the known thermostable explosives TATB and TACOT, but with higher detonation characteristics. N,N'-(bis([1,2,4]triazolo) [1,5-b:5',1'-f] [1,2,4,5]tetrazine-2,7-diyl)dinitramide was used as a starting acid to obtain salts with organic bases. The hydroxylamine salt, H(2)DNATC, turned out to be the most powerful compound, comparable in detonation characteristics (D = 9020 m s(-1)) to HMX, but having a higher burning rate (54 mm s(-1) at 10 MPa), and therefore it may be of interest as a high-energy fast-burning filler for composite propellants and gunpowder. Thermocouple-aided studies in the H(2)DNATC combustion wave made it possible to estimate the enthalpy of dissociation of the salt into gaseous components and to establish the combustion mechanism. The demonstrated thermal cyclization method for the preparation of fused tricyclic tetrazines provides new insights into the design of HEDMs, which may be useful for practical applications.

By replacing the pyrazolyl fragment in 3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazine with 3-nitro-1,2,4-triazol-5-one (NTO), both mono- and disubstitution products have been synthesized. Further interaction of the obtained compounds with O- and N-nucleophiles led to the preparation of a number of polynitrogen tetrazine derivatives, including 2-[6-amino-1,2,4,5-tetrazin-3-yl]-5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one and 5-nitro-2- [6-(1H-tetrazol-5-ylamino)-1,2,4,5-tetrazine-3-yl]-2,4-dihydro-3H-1,2,4-triazol-3-one. The reactions of nucleophilic substitution of symmetrically substituted tetrazine were shown to proceed more selectively. The resulting compounds were identified using H-1, (CNMR)-C-13 spectroscopy, FTIR, LC-MS, and elemental analysis, as well as using X-ray diffraction analysis. The thermal stability of the new compounds was evaluated under isothermal and non-isothermal conditions and their energy characteristics were calculated. An unusual drop in stability was found on going from symmetrically substituted tetrazines to asymmetric ones.

The thermal stability of 1,3,5,5- tetranitrohexahydropyrimidine (TNDA) in liquid phase under isothermal conditions was studied. It was established that the TNDA decomposition (k(liq)=3.1 . 10(21).exp(-26865/T), E-a=223.4 kJ mol(-1)) is accompanied by strong autocatalysis (k(cat)=9.8 . 10(14).exp(-18056/T), E-a=150.2 kJ mol(-1)). The mechanism of autocatalysis was proposed. The essence of autocatalysis is the oxidation of TNDA by decomposition products, followed by the destruction of the molecule. An unusual feature of this autocatalysis is that, in contrast to autocatalysis of nitroesters, the process does not disappear at high temperatures, but rather determines the kinetics of heat release in the combustion wave. The surface temperature and combustion mechanism of TNDA were established through thermocouple studies. It was shown that the autocatalysis reaction at the surface temperature controls the burning rate.

Based on the deoxygenation reaction of 1-(1-tert-butyl-3-nitroazetidine-3-yl)-1H-1,2,3-triazoles a new method for the synthesis of substituted 1-(1H-imidazole-4-yl)-1H-1,2,3-triazoles has been developed. Fungicidal activity of these compounds has been investigated at a range of phytopathogenic fungi.

The substitution of pyrazolyl moiety in 3-(3,5-dimethyl-1 H -pyrazol-1-yl)-1,2,4,5-tetrazine with N-nucleophiles provided a series of highnitrogen tetrazine derivatives, including 2-nitro-1-(1,2,4,5-tetrazin-3-yl)guanidine, N -(1 H -tetrazol-5-yl)-1,2,4,5-tetrazin-3-amine, N -(1,2,4,5-tetrazin-3-yl)-1,2,4,5-tetrazin-3-amine, N , N '-di(1,2,4,5-tetrazin-3-yl)-1,2,4,5-tetrazine-3,6-diamine, N -(1,2,4,5-tetrazin-3-yl)-[1, 2, 4]triazolo[4,3- b ][1, 2, 4, 5]tetrazin-6-amine, and tritetrazinylamine. The thermal stability of these new compounds was evaluated by differential scanning calorimetry and their energetic characteristics were calculated.

Considerable recent attention has been focused on research and development of high-nitrogen energetic materials. Among polynitrogen energetic materials, 1,2,4,5-tetrazine derivatives are of particular interest owing to their high density, thermostability, and remarkable insensitivity to electrostatic discharge, friction, and impact. The purpose of the present work is to analyze possible application areas of different types of tetrazine-based energetic materials reasoning from their peculiar combustion properties. Study of thermal stability of tetrazine derivatives has shown that, in most cases, the stability of the substance is determined by decomposition of the less stable substitute rather than the tetrazine cycle itself. Combustion and thermocouple-aided studies have revealed that tetrazines are mostly low-volatile substances with high burning surface temperatures that, in turn, predetermine the condensed-phase combustion mechanism. The lack or low content of oxygen in tetrazine-based energetic materials results in formation of high-enthalpy species among combustion products, thus preventing from full release of energy stored in the material.

A convenient method was developed for the synthesis of 6-(1H-1,2,3-triazol-1-yl)-4,7-dihydro-1,3,5-dioxazepines, using deoxygenation of 1-(5-nitro-1,3-dioxan-5-yl)-1H-1,2,3-triazoles with triethyl phosphite.

The peculiarities of the nitration reaction under acidic conditions were studied for a series of alkylamino-1,2,4,5-tetrazines. It was found that the extent of N,N'-dialkyl-1,2,4,5-tetrazine-3,6-diamine nitration was determined by the concentration of nitric acid and the selection of alkyl substituents at the exocyclic nitrogen atom. A new method was developed for the preparation of unsymmetrically substituted N,N'-dialkyl-1,2,4,5-tetrazine-3,6-diamines from N-nitro derivatives of N-alkyl-1,2,4,5-tetrazin-3-amines.

Noncatalytic and Cu(I)-catalyzed dipolar cycloadditions of heterocyclic a-nitro azides to substituted alkynes were studied. Catalytic cyclization gave 1,4-disubstituted triazoles only. The effect of the substituents in alkynes and that of the nature of the starting heterocycles on the isomer ratio of triazoles were examined. New representatives of 1,2,3-triazoles were obtained; their physicochemical properties were studied. A comparative analysis of the spectral characteristics of the resulting regioisomeric triazole derivatives was performed.

The thermal stability of 3,6-dihydrazino-1,2,4,5-tetrazine (DHT) and 3,6-bis(1H-1,2,3,4-tetrazol-5ylimino)-1,2,4,5-tetrazine (BTATz) have been examined by isothermal and nonisothermal methods. The research conducted allow considering that the first stage of DHT decomposition is an unique, from viewpoint of thermal decomposition, redox process, in which tetrazine ring is reduced by hydrazine group forming diaminodihydrotetrazine and molecular nitrogen. In the case of BTATz, the decomposition begins with less thermostable tetrazole fragments, which captures the tetrazine ring also. The presence of preliminary reactions of isomerization during tetrazole ring decomposition is the reason for the large observable activation energy of decomposition (240.6 kJ/mol or 57.5 kcal/mol) in the temperature interval 250-334 degrees C. In the combustion wave at higher temperatures, the activation energy of BTATz decomposition has considerably lower value (128.4 kJ/mol or 30.7 kcal/mol), which is close to theoretically calculated one. Burning characteristics of DHT and BTATz have been investigated. The temperature distribution in the combustion waves of DHT and BTATz have been measured at low pressures, which allows obtaining the surface temperature dependence vs. pressure. The research conducted allow considering that the burning of investigated compounds controls by a combustion model with leading reaction in the condensed phase. (C) 2012 Elsevier B.V. All rights reserved.