The interaction between imidazole-based ionic liquids and the mustard gas simulant CEES and its influence on its solubility

Abstract

Mustard gas (HD) is one of the most dangerous chemical warfare agents, which can cause serious injuries and even deaths. The rapid and efficient degradation of HD is crucial to protect people from hurting by its high toxicity. However, the widely used water-based decontaminants always have limited degradation efficiency for HD due to its poor solubility in water. Therefore, ionic liquids (ILs) hold great potentials as solvents for degradation of HD since they can improve HD’s solubility for an effective degradation. In this study, the solubilities of 2-chloroethyl ethyl sulfide (CEES), a simulant of HD, in nine ionic liquids (ILs) were investigated. Interaction descriptors of the anions, cations, and ILs were computed using quantum mechanics and density functional theory to understand the influence of the IL properties on the solubility of CEES in ILs at the molecular level. The results indicate that CEES solubility depends on cation/anion physical properties and anion–cation and anion/cation/IL–CEES interactions. The cation electron affinity and anion ionization potential are closely related to the solubility of the Lewis acid CEES in the ILs. The anion/cation–CEES interaction energy (IE) exhibits poor correlation with CEES solubility, while the anion–cation IE plays a dominant role. A negative correlation was observed between absolute IL–CEES IEs and CEES solubility. For HCO3¯ anion-based ILs, the interstitial space of the ILs increased with the cationic alkyl side chain length within a specific limit, resulting in more excellent solubility of CEES. For [BMIm]+ cation-based ILs, the anion influenced the cation–anion and cation/anion/IL–CEES IEs, thus affecting the solubility of CEES. In conclusion, this study serves as a guide for designing ILs for dissolving CEES and improving the degradation efficiency of HD by exploring cation–anion and anion/cation/IL–CEES interactions and other interaction descriptors.