Synthesis and Characterization of Binary, Highly Endothermic, and Extremely Sensitive 2,2′-Azobis(5-azidotetrazole)

Abstract

2,2′-Azobis­(5-azidotetrazole) (C2N16, 3), a highly energetic nitrogen-rich binary CN compound was obtained in a three-step synthesis through the formation of 5-azidotetrazole (1), subsequent amination using O-tosylhydroxylamine to give 2-amino-5-azidotetrazole (2), and oxidative azo coupling of 2 using tBuOCl as an oxidant in MeCN. A nitrogen:carbon ratio of 8:1, eight nitrogen atoms in a row, and a nitrogen content of over 90% was unknown for a binary heterocyclic compound until now. The successful isolation was confirmed through X-ray diffraction as well as by vibrational and 13C NMR spectroscopy. C2N16 can explode instantly and shows mechanical sensitivities far higher than quantitatively measurable. Nevertheless, it features interesting energetic performances, which were calculated using different quantum-chemical methods.

1‐Nitrimino‐5‐azidotetrazole: Extending Energetic Tetrazole Chemistry

“…It shows a room temperature density of 1.636 g cm −3 . Therefore, it is 0.1 g cm −3 lower than for its isomer 2‐amino‐5‐azidotetrazole (ρ=1.736 g cm −3 @298 K) [24] and is also below the estimated value [31] . The molecule itself is planar.…”

“…In general, tetrazoles with substitution at N1 are difficult to synthesize as soon as an electron-withdrawing group is located at position C1. Direct reactions of C-electron-withdrawing tetrazolates (e. g. 5-azidotetrazolate, 5-nitrotetrazolate or 5-cyanotetrazolate) with electrophiles always give the derivatives substituted at N2, as has been shown, for amination, [24][25] N-oxidation [21,[26][27] or methylation [28][29] reactions. Consequently, two possible synthesis strategies arise for substitutions for particular tetrazolates at position N1.…”

“…This method provided 1‐nitrimino‐5‐azidotetrazole ( 2 ) in 54 % yield in the form of a viscous oil. The nitration of the recently published isomeric 2‐amino‐5‐azidotetrazole [24] through various methods (N 2 O 5 , NO 2 BF 4 or mixed acid as for 1 ) was not successful since only decomposition products were obtained.…”

Silver-Catalyzed Synthesis of 2-Cyano-5-pyrazolyl-2H-tetrazole: A Promising Precursor to Insensitive Energetic Compounds

“…Yield: 3.10 g (73%). 1 H NMR (500 MHz, DMSO-d 6 ): δ = 13.64 (br), 13.34 (s, 1H), 8.07 (s, 1H), 6.88 (s, 1H) ppm; 13 (5). Compound 4 (2.1 g, 10 mmol) in CHCl 3 (20 mL) was added slowly to a stirring mixture of trifluoroacetic anhydride (8 mL) and 100% HNO 3 (4 mL) at 0 °C, and the temperature was controlled at 0−5 °C during the addition.…”

“…Especially, the research of utilizing nitrogen-rich five-membered heterocycles (tetrazole, triazole, pyrazole, oxadiazole, etc.) as skeletons to assemble polycyclic nitrogen-rich energetic compounds has aroused great interest of researchers in recent years. − A high nitrogen content can improve the enthalpy of formation and detonation performances, but it is also accompanied by an increase in mechanical sensitivity, which causes major safety risks in storage and practical application. Therefore, it is of certain significance to assemble nitrogen-rich heterocycles with different types of single nitrogen-rich heterocycles, which could further achieve a better balance between detonation performances and sensitivities (Figure ).…”