TKX-50

TKX-50 is the chemical compound with the formula C₂H₈N₁₀O₄. It is a hydroxylammonium salt of 5,5′-bistetrazolyl-1,1′-diolate. It forms colorless crystals. It is a high-performing explosive with performances higher than RDX and HMX while being safer towards mechanical stimuli. It is also considered an environmentally-friendly replacement for several conventional explosives.^[1][2] As of 2014, the US army was preparing it in 20 kg batches in order to evaluate it as an explosive ^[3] It was invented by Niko Fischer, Dennis Fischer, Davin G. Piercey, Thomas M. Klapötke and Jörg Stierstorfer in the research group of Thomas M. Klapötke at the Ludwig Maximilians-Universität München.^[4] Its development was funded by the Ludwig-Maximilian University of Munich (LMU), 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)

TKX-50

Names
IUPAC name Dihydroxylammonium-5,5′-bistetrazolyl-1,1′-diolate
Other names Dihydroxylammonium-5,5′-bistetrazolyl-1,1′-diolate, Dihydroxylammonium-5,5′-bistetrazolyl-1,1′-dioxide,
Identifiers
CAS Number	1403467-86-6 Y
3D model (JSmol)	Interactive image
PubChem CID	139051543
InChI InChI=1S/C2N8O2.2H4NO/c11-9-1(3-5-7-9)2-4-6-8-10(2)12;2*1-2/h;2*2H,1H3/q-2;2*+1 Key: UHTGTYVZCBKFMU-UHFFFAOYSA-N
SMILES [NH3+]O.[NH3+]O.[O-]N1N=NN=C1C2=NN=NN2[O-]
Properties
Chemical formula	C2H8N10O4
Molar mass	236.15 g/mol
Appearance	colorless crystals
Density	1.92 g/cm3
Explosive data
Shock sensitivity	20 J
Friction sensitivity	120 N
Detonation velocity	9698 m/s
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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.^{[5] [6]}

TKX-50 synthesis

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^[7] and the United States Army Research Laboratory by performing multiple steps of the synthesis in a 1-pot reaction.^[8]

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⁻¹·K⁻¹is 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 P 2 ₁ /c to triclinic with the space group P 1.^[9] 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 ⁻¹ and −520 kJ mol ⁻¹ , respectively .^[10][11] The standard enthalpy of formation based on combustion calorimetry measurements is 473 kJ mol⁻¹ .^[12]

Explosive uses

TKX-50 has been found to lead to melt-cast formulations with higher performance than those with HMX^[13]