A comprehensive study of the dissolution process of N-oxide based explosives in deep eutectic solvents

N-oxide based explosives display better explosive performances than traditional explosives, because of the introduction of N-oxide group with strong hydrogen bonding (H-bonding). However, the strong H-bonding results in poor dissolution of N-oxide based explosives, and thus poses a significant challenge for their potential applications. Deep eutectic solvents (DESs), a new generation of green solvents, display promising dissolution toward strong H-bonding materials in recent years. In this study, 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) was used as a prototype of N-oxide based explosives to study the dissolution in DESs. The dissolution conditions for LLM-105 were optimized by using different types of DESs. The DES-3-2 based on choline chloride and urea displayed higher dissolving capacity with 0.52 g/100 g at 80 °C, which was determined by traditionally gravimetric method. Further, the dissolution process of LLM-105 in DES-3-2 under different temperatures was investigated by comprehensive analysis including ultra-high-performance liquid chromatography, high-resolution mass spectrum and theoretical calculations. The dissolution of LLM-105 under ≤80 °C was demonstrated to be real dissolution referring to the formation of Zundel-type complex and Meisenheimer complex between DES-3-2 and LLM-105. Abnormally high solubility of LLM-105 at >80 °C was attributed to the self-collapse of its H-bonding network by losing a nitro group and an oxygen of N-oxide group.