The photostability and degradation pathways of TKX-50 as a representative of nitrogen-rich energetic salts in aqueous solution

The dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50), as an outstanding representative of nitrogen-rich energetic salts, has recently attracted increasing interest due to its excellent performances. However, it is unclear about the photostability and degradation pathways of TKX-50 in aqueous solution. In this paper, the photostability and the degradation process of TKX-50 in aqueous solution have been comprehensively studied for the first time. TKX-50 can keep stable toward visible light. However, it presented a rapid degradation with rate constant of 0.0054 s⁻¹ under 254-nm light irradiation. TKX-50 also demonstrated much faster photodegradation than traditional nitro explosives. Further, degradation products of TKX-50 were analyzed by high-resolution mass spectrum with theoretical calculations. The photodegradation pathways are proposed that 5,5′-bistetrazole-1,1′-diolate (BTO) anion of TKX-50 can been fragmented into the nitrile by losing N₂ and HNO, and then hydroxylammonium (NH₃OH⁺) from TKX-50 reacts with the nitrile through the nucleophilic addition. Besides as a solvent, water also may accelerate the photodegradation of TKX-50 probably by hydrolyzing the intermediary nitrile products. In a word, this study provides comprehensive understanding about the photostability of TKX-50 in aqueous solution, and it is helpful to study the photochemistry of other energetic ionic salts based on BTO.