An improved synthesis of 3,6-diamino-1,2,4,5-tetrazine. I

Treatment of 1,3-diaminoguanidine monohydrochloride ( 1 ) with 2,4-pentanedione ( 2 ) in alcohols under carefully controlled conditions gave 3,6-diamino-1,2-dihydro-1,2,4,5-tetrazine monohydrochloride ( 3 ) in 45-50% yields along with 3,5-dimethyl-1H-pyrazole ( 4 ) and its hydrochloride 5 . Oxidation of 3 with sodium perborate produced 3,6-diamino-1,2,4,5-tetrazine ( 6 ) in quantitative yield.     

An improved synthesis of 3,6-diamino-1,2,4,5-tetrazine. II. From triaminoguanidine and 2,4-pentanedione

A new synthesis for the title compound that gives an 80% overall yield was developed. Treatment of triaminoguanidine monohydrochloride ( 1 ) with 2,4-pentanedione ( 2 ) gave 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine ( 3 ) in 80–85% yield. Oxidation of 3 with nitric oxide or nitrogen dioxide to 3,6-bis(3,5-dimethyylpyrazol-1-yl)-1,2,4,5-tetrazine ( 4 ) followed by ammonolysis of 4 gave 3,6-diamino-1,2,4,5-tetrazine ( 5 ) in guantitatively yields.     

Basicity of 3,6-diphenyl-1,2,4,5-tetrazine

We have determined the basicity of 3,6-diphenyl-1,2,4,5-tetrazine in aqueous solutions of sulfuric acid (pK_BH+ is –4.8). According to quantum chemical calculations done by the MNDO method and theab initio method in a 6-31G++ basis, the tetrazine ring is a nonpolar, highly aromatic system similar to benzene. The aromaticity of the tetrazine hererocycle decreases significantly upon protonation, which considerably destabilizes the protonated form.St. Petersburg State Technological Institute, St. Petersburg 198013, Russia, Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 34, No. 1, pp. 120–123, January, 1998.     

X-ray studies of three 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine cocrystals: an unexpected molecular conformation stabilized by hydrogen bonds

The results of the X-ray structure analysis of three novel 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine cocrystals are presented. These are 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine–2,4,6-tribromophenol (1/2), C₁₂H₈N₆·2C₆H₃Br₃O, 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine–isonicotinic acid N-oxide (1/2), C₁₂H₈N₆·2C₆H₅NO₃, and 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine–4-nitrobenzenesulfonamide (1/1), C₁₂H₈N₆·C₆H₆N₂O₄S. Special attention is paid to a conformational analysis of the title tetrazine molecule in known crystal structures. Quantum chemistry methods are used to compare the energetic parameters of the investigated conformations. A structural analysis of the hydrogen and halogen bonds with acceptor aromatic tetrazine and pyrazine rings is conducted in order to elucidate factors responsible for conformational stability.     

Synthesis of the bi-heterocyclic parent ring system 1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine and some 3,6-disubstituted derivatives

The synthesis of the previously unknown parent ring system was developed. Treatment of 3-hydrazino-1,2,4,5-tetrazine ( 4 ) with diethoxymethyl acetate gave the parent ring system. Similar treatment of 3-(3,5-dimethylpyrazol-1-yl)-6-hydrazino-1,2,4,5-tetrazine ( 2 ) with one carbon cyclizing reagents gave 3,6-di-substituted derivatives of the 1,2,4-triazolo-1,2,4,5-tetrazine ring system.     

3,6-二叠氮基-1,2,4,5-四嗪的合成及理论研究

以3,6-双(3,5-二甲基吡唑基)-1,2,4,5-四嗪为原料, 经过肼解反应和重氮化反应, 制得了3,6-二叠氮基-1,2,4,5-四嗪(DAT). 在DFT-B3LYP/6-31G*水平下求得了DAT的分子几何、IR光谱和热力学性质. 计算模拟IR光谱和实测IR光谱的对比表明DAT在固态下不发生叠氮-四唑互变异构反应. 根据IR光谱计算了DAT的热容、焓、熵等热力学参数, 也给出了这些参数和温度T之间的函数关系. 在不破坏四嗪环和叠氮基的原则下通过构建等键反应求得了DAT的精确生成热为1088 kJ•mol^—1. 爆轰性能计算表明DAT爆速D＝8.45 km•s^－1, 爆压P＝31.3 GPa, 高于TNT和HMX.     

Dihydro- und Tetrahydroderivate des 3,6-Dimethyl-1,2,4,5-tetrazins

The scheme 1 shows those tetrahydro- and dihydroderivatives of the 3,6-dimethyl-1,2,4,5-tetrazine (or s-tetrazine), 8 , which are theoretically possible without considering cis-trans isomerism, together with the reaction pathways. We did not succeed in synthetizing the 3,6-dihydroderivative, 7 , and could not isolate the 1,2-dihydrocompound, 4 , the latter being probably easily convertible to the thermodynamically more stable 1,4-dihydro-s-tetrazine, 5 , via their common conjugate base 4,5B . The 1,4-dihydro-s-tetrazine, 5 , gives with 3,6-dimethyl-s-tetrazine 8 , a charge transfer complex, 15 . The same compounds form in acidic or basic aquious solution stable radicals, 16B and 16S . The mode of formation of these radicals and the subsequent reactions are depicted in scheme 2.     

A polymeric sodium complex of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine

The ligand 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine forms a 1:1 complex with Na[BPh4], which has been structurally characterised as a one-dimensional polymeric system with an unusual coordination geometry about the sodium.     

Synthesis and inverse electron demand Diels-Alder reactions of 3,6-bis(3,4-dimethoxybenzoyl)-1,2,4,5-tetrazine

The synthesis of 3,6-bis(3,4-dimethoxybenzoyl)-1,2,4,5-tetrazine (2) and the scope of its reactivity in inverse electron demand Diels-Alder reactions are disclosed representing the first systematic study of the [4 + 2] cycloaddition reactions of 3,6-diacyl-1,2,4,5-tetrazines.     

Synthesis, Crystal Structure Analysis and DFT Calculation of 1-Benzoyl-3,6-diphenyl-1,4-dihydro-1,2,4,5-tetrazine

The new title compound, 1-benzoyl-3,6-diphenyl-1,4-dihydro-1,2,4,5-tetrazine (C21H16N4O, Mr = 340.38), has been prepared and its crystal structure can not be confirmed by the results of MS, elemental analysis, IR spectrum and 1H NMR spectrum, but determined by X-ray diffraction. The title compound crystallizes in an orthorhombic space group P212121 with a = 7.1100(19), b = 12.115(3), c = 19.884(6), V = 1712.7(8)3, Z = 4, Dc = 1.320 g/cm3, F(000) = 712, μ = 0.085 mm-1, MoKa radiation (λ = 0.71073), R = 0.0334 and wR = 0.0845 for 2254 observed reflections with I 2σ(I). X-ray diffraction analysis reveals that the central tetrazine adopts an unsymmetrical boat conformation. According to the bond lengths of tetrazine ring, the molecule should be 1,4-dihydro-1,2,4,5-tetrazine, rather than 1,2-dihydro-1,2,4,5-tetrazine. The crystal structure is stabilized mainly by intermolecular N–H···O hydrogen bonds.     

Synthesis, characterization and quantum chemistry study of 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine

3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)- 1,2,4,5-tetrazine (BTATz) was synthesized by the condensation of triaminoguanidinium nitrate with 2,4-pentanedione, followed by oxidation and substitution reaction. The product was characterized by elemental analysis, IR, NMR spectrometry and DSC analysis. Instead of nitrogen dioxide/N-methylpyrrolidone, acetic acid/sodium nitrite was used as the oxidizer during the oxidation. Thus, the cost was reduced and the process was simplified. The theoretical properties of BTATz were estimated by a B3LYP method based on a 6-31G(d,p) basis set, and the stable geometric configuration and bond order were obtained. The vibrational frequencies, IR spectrum and thermodynamic properties under different temperatures were obtained from vibrational analysis and the relationship between temperature and thermodynamics properties was deduced. Pyrolysis mechanism of BTATz was discussedand the transition state and activation energy of ring opening reaction of the tetrazole were deduced. __________ Translated from Chinese Journal of Organic Chemistry, 2008, 28(3) (in Chinese)     

3,6-双(1氢-1,2,3,4-四唑-5-氨基)-1,2,4,5-四嗪的合成与表征

研究了低感度高氮化合物3,6-双(1氢-1,2,3,4-四唑-5-氨基)-1,2,4,5-四嗪的合成,其结构经元素分析,IR,^1H NMR和^13C NMR表征。     

3,6-二肼基-1,2,4,5-四嗪的晶体结构及理论研究

通过缓慢蒸发溶剂法培养得到3, 6-二肼基-1, 2, 4, 5-四嗪(DHT)的单晶, 用X-射线单晶衍射仪进行了结构测定. 该晶体属于单斜晶系, P2(1)/c空间群, a=4.032 (4) ?, b=5.649 (6) ?, c=12.074 (14) ?. β=99.32°, Z=2, V=271.4(5) ?3. DHT分子中肼基N原子与四嗪环基本位于同一平面呈现轴对称结构, 分子中的大量氢键使之形成箭尾形排列的三维网络结构. 通过实验测得DHT的燃烧热为1787kJ?mol-1, 5s爆发点为454 K. 在DFT-B3LYP/6-311G*水平下对DHT的电子结构和自然键轨道进行了分析. 通过原子化能的方法计算得到DHT的标准生成热为1075 kJ?mol-1, 与实验值接近. 爆轰性能计算表明, DHT在密度为1.64 g?cm-3时, 爆速和爆压分别为9.27 km?s-1和36.02 GPa, 高于TNT和HMX.     

Synthesis and characterization of novel polyurethanes,polypyridazine, and polyamide based on s-1,2,4,5-tetrazine

The synthesis and analysis of new polymeric materials based on 1,2,4,5-tetrazine are discussed in this study. Tetrazine was mixed with thermoplastic polyurethane in dimethylformamide (DMF) as solvent and dibutyl tin dilaurate as catalyst at 50°C for 24 h to create brush polyurethane-urea, which was then reacted with an unsaturated center in dimethyl sulfoxide as solvent at 60°C for 48 h made of either polyenol or thermoplastic polyurethane through π–π interaction. Because 1,2,4,5-tetrazine (red color) is known to act as an electron-deficient dine in inverse electron demand Diels–Alder reactions and can be easily converted to pyridazine (peach color) via [4 + 2] cycloaddition with suitable followed by expulsion of molecular nitrogen (cycloreversion), we observed a highly colored red shift to peach and this monitor for this reaction. Additionally, polyamide was prepared via reaction of 3,6-diamino-1,2,4,5-tetrazine with terephthaloyl chloride in DMF as a suitable solvent and triethylamine as basic catalyst at 0°C for 3 h and then 36 h at room temperature. The new polymers that were produced were elucidated by spectral data.     

3,6-双(1H-1,2,3,4-四唑-5-氨基)-1,2,4,5-四嗪的合成、表征及量子化学研究

以三氨基胍硝酸盐、戊二酮为起始原料, 经缩合、氧化、取代等反应合成了3,6-双(1H-1,2,3,4-四唑-5-氨基)-1,2,4,5-四嗪(BTATz), 并通过元素分析、红外、核磁、差示扫描量热法(DSC)等分析手段对其进行了表征. 采用亚硝酸钠/乙酸代替了二氧化氮/N-甲基吡咯烷酮, 改进了氧化步骤, 降低了成本, 简化了合成工艺. 用B3LYP方法, 在6-31G(d,p)基组水平上对其性能进行了计算, 得到了其稳定的几何构型和键级; 在振动分析的基础上求得体系的振动频率、IR谱及不同温度下的热力学性质, 并得到了温度对热力学性能影响的关系式; 探讨了其热解机理, 推断出四唑环开环时的过渡态和活化能.     

Crystal Structures,Thermal Behavior Analysis and Thermal Safety of Two Energetic Salts of Hydrazinyl-1,2,4,5-tetrazine with 3,5-Dinitrosalicylic Acid

Two energetic salts, DPHT·DNS·H₂O(1) and DHT·2DNS·2H₂O(2)[DPHT=3-(3,5-dimethyl-1H-pyrazol-1-yl)-6-hydrazinyl-1,2,4,5-tetrazine; DHT=3,6-dihydrazinyl-1,2,4,5-tetrazine], were synthesized from S-tetrazine with 3,5-dinitrosalicylic acid(DNS). Compounds 1 and 2 were structurally characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction. The thermal behavior of the title compounds was studied by differential scanning calorimetry(DSC) and thermogravimetry(TG). The non-isothermal decomposition kinetics of compound 2 were investigated. The self-accelerating decomposition temperature, thermal ignition temperature, and critical temperatures of thermal explosion were obtained to evaluate the thermal safety of compound 2. The results show compounds 1 and 2 decompose at 150.8 and 179.2℃, respectively. The T_SADT and T_b of compound 2 are higher than those of DHT, which indicates compound 2 is a potential candidate for energetic materials that have good thermal stability.     

Cycloaddition reactions of cyclic ketene-N,S-acetals with 1,2,4,5-tetrazines

Reaction of 3,6-diphenyl-, 3,6-bis(2-pyridyl)- and the unsubstituted 1,2,4,5-tetrazine with 4,5-dihydro-1-methyl-2-(methylthio)pyrrole ( 2 ) and 1-raethyl-2-(methylthio)-4.5,6,7-tetrahydroazepine ( 3 ) gives 4,7-di-R-2,3-dihydro-1-methylpyrrolo[2,3-d]pyridazine ( 4 , R = phenyl, 2-pyridyl, hydrogen) and 6,9-di-R-1-methyl-2,3,4,5-tetrahydropyridazino[4,5-6]azepine ( 5 ), R = phenyl, 2-pyridyl, hydrogen), respectively, in reasonable to good yields. The compounds 4 (R = phenyl, hydrogen) are converted into their corresponding 1-methylpyrrolo-[2,3-d]pyridazines 6 by reaction with potassium permanganate in butanone. Reaction of 3-phenyl-1,2,4,5-te-trazine with 2 and 3 leads to the exclusive formation of the 7-phenyl isomer 4d and 9-phenyl isomer 5d , respectively, indicating that the cycloaddition is regiospecific. The mechanism is discussed.     

Crystal and electronic structure of heteromolecular complexes of 3,6-bis(3,5-dymethylpyrazole-1-yl)-1,2,4,5-tetrazine with azoles

X-ray crystallography is used to investigate heteromolecular crystals of 3,6-bis(3,5-dimethylpyrazole-1-yl)-1,2,4,5-tetrazine with NH-donating azole derivatives. The effect is studied of the structure of azole on molecular packing in the crystal and the characteristics of covalent bonds in the molecule of 3,6-disubstituted tetrazine. The distribution of electron density critical points inside crystal cells is analyzed to identify and quantitatively describe the intermolecular interactions underlying the formation of lateral and stacking motifs.     

SN(ANRORC) mechanism XX. Degenerate ring transformations in reactions of 1,2,4,5-tetrazines with hydrazine

Evidence is presented that the hydrazinolysis of 3-amino- (5) and 3-bromo-6-methyl-1,2,4,5-tetrazine ( 7 ) into the 3-hydrazino-6-methyl-1,2,4,5-tetrazine ( 6* ) with ¹⁵N-labelled hydrazine leads to incorporation of ¹⁵N in the 1,2,4,5-tetrazine ring. Thus in the hydrazino-deamination and hydrazino-debromination a S_N(ANRORC) mechanism is operative. Based on quantitative mass spectrometry it was found that 20-25% of both 5 and 7 reacts according to this S_N-(ANRORC) mechanism. The mechanism of these degenerate ring transformations is discussed.     

Synthesis of 5-amino-6-nitro-1,2,3,4-tetrazine 1,3-dioxide

5-Amino-(tert-butyl-NNO-azoxy)-1,2,3,4-tetrazine 1,3-dioxide reacts with nitronium tetra-fluoroborate to give 5-amino-6-nitro-1,2,3,4-tetrazine 1,3-dioxide. This compound is of interest as a new energetic material. A plausible reaction mechanism involves electrophilic substitution of the tert-butyl-NNO-azoxy group by the nitro group.