New green solvents for high dissolution and the mechanism of strongly hydrogen-bonded explosives

Abstract. Hydrogen bonds play an important role on improving the safety of energetic materials. Nowadays, there is a tendency to develop strongly hydrogen-bonded explosives including 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105), and 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide (ICM-102). However, the solubilities of these explosives are severely inhibited by strong hydrogen bonds. For example, the solubility of TATB is 70 ppm in dimethyl sulfoxide (DMSO). Low solubility poses a huge obstacle for the recrystallization, purification and recycling of these explosives. Deep eutectic solvents (DESs) are regarded to be new generation of green solvents because of unique advantages including low cost, simple preparation, and easy biodegradation. The exchange of hydrogen bonds can occur between liquid DESs and other hydrogen-bonded materials to break and rearrange their hydrogen bonds, so DESs show potential dissolution toward most of poorly soluble materials. In this study, a series of new DESs based on tetra-nalkylammonium have been prepared and characterized for the dissolution of strongly hydrogen-bonded explosives. The DESs are liquid at room temperature, which is beneficial to dissolve solid explosives. Meanwhile, these solvents display high dissolution toward TATB with maximum solubility of 13 wt%, which is almost 2000 times higher than DMSO. The dissolution of TATB in DESs is fast, and solid TATB is completely dissolved within 2 min. The DES solvents also have good dissolution toward LLM-105 and ICM-102. The dissolution mechanism has been investigated by experimental characterizations and theoretical calculations. Hydrogen bonds of these explosives are disrupted through forming Zundel-type complexes between TATB and the anions in DESs, and then the complexes are surrounded by the cations in DESs through self-assembly of electrostatic interaction to avoid the disrupted TATB reconnecting with coriginal networks. Therefore, this work provides a valuable strategy for designing new solvents to dissolve strongly hydrogen-bonded explosives and performing various applications such as the purification, recycling and recrystallization.