TKX-50 is the chemical compound with the formula ; it is a hydroxylammonium salt of 5,5′-bistetrazolyl-1,1′-diolate that forms colorless crystals, and it is a high-performing explosive with superior performance to RDX and HMX while being more resistant to mechanical stimuli. It is also considered an environmentally-friendly replacement for several conventional explosives.
It was invented by Niko Fischer, Dennis Fischer, Davin G. Piercey, Thomas M. Klapötke and Jörg Stierstorfer in Klapötke's research group at LMU Munich. Its development was funded by LMU Munich, the U.S. Army Research Laboratory (ARL), the Armament Research, Development and Engineering Center (ARDEC), the Strategic Environmental Research and Development Program (SERDP) and the Office of Naval Research (ONR).
As of 2014, the US Army was preparing it in 20 kg batches in order to evaluate it as an explosive.
Synthesis
The compound is prepared by reacting 5,5′-bistetrazolyl-1,1′-diol (BTO) with hydroxylamine. The starting compound BTO can be obtained relatively easily from glyoxal, hydroxylamine, chlorine, and sodium azide.Fischer, N.; Klapötke, T.M.; Reymann, M.; Stierstorfer, J.: Nitrogen-Rich Salts of 1H,1'H-5,5'-Bitetrazole-1,1'-diol: Energetic Materials with High Thermal Stability in Eur. J. Inorg. Chem. 2013, 2167–2180, .
Since the initial synthesis of TKX-50, multiple research groups have improved the synthesis to make it more suitable for mass production, including by adding protecting groups to make intermediates safer,Kwon, K.; Kim, S.; Lee, S.; Lee, W. H.: Safe and Scale-up-friendly Synthesis of TKX-50 in Propellants Explos. Pyrotech. 2025, e12073, . and the United States Army Research Laboratory has performed multiple steps via a one-pot synthesis.
Characteristics TKX-50 is a crystalline solid with no melting point. The compound occurs in two polymorphic crystal forms. At about 180 °C, a second-order phase transition with a small heat capacity change of about 0.3 J/mol·K is observed, resulting in a transformation from the low-temperature to a high-temperature crystal form. The crystal system changes from monoclinic with the space group P21/c to triclinic with the space group P1.Zhipeng Lu, Xianggui Xue, Liya Meng, Qun Zeng, Yu Chi, Guijuan Fan, Hongzhen Li, Zengming Zhang, Fude Nie, Chaoyang Zhang: Heat-Induced Solid−Solid Phase Transformation of TKX-50 in J. Phys. Chem. C 121 (2017) 8262–8271, . The compound is thermally unstable. DSC measurements show an exothermic decomposition reaction above 215 °C with a latent heat of decomposition of −2200 kJ/kg and −520 kJ/mol, respectively. The standard enthalpy of formation based on combustion calorimetry measurements is 473 kJ/mol.D. Fischer, V. Golubev, T. M. Klapötke, J. Stierstorfer: Synthesis and Characterization of Novel High-Nitrogen Secondary Explosives. In: Tagungsband die 21. Kalorimetrietage : Braunschweig, 27.-29. Mai 2015 / Veranstalter Gesellschaft für Thermische Analyse e. V., Physikalisch-Technische Bundesanstalt. ISBN 978-3-944659-02-2 (Abstract).
Explosive properties TKX-50 has been found to lead to melt-cast formulations with higher performance than those with HMX.Yu, Y.; Chen, S.; Li, T.; Jin, S.; Zhang, G.; Chen, M.; Li, L.: Study on a novel high energetic and insensitive munitions formulation: TKX-50 based melt cast high explosive in RSC Advances 2017, 31485-31492, . Its detonation velocity, Chapman–Jouguet detonation pressure, and density are also superior to RDX.
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