Exploration of the reaction activity, process hazard and mechanism of m-xylene nitration catalyzed by imidazolium hydrogen sulfate ionic liquids: Combining experiments and ab initio molecular dynamics simulations

Background Nitro-m-xylene (NMX) is an important intermediate in the production of fine chemicals. Ionic liquids (ILs) are emerging solvents and catalysts. Investigating the exothermic characteristics and catalytic mechanism of IL-catalyzed synthesis of NMX is of great significance for the development of safe, efficient, and green nitration processes. Method The thermal stability and acid strength of the six imidazolium hydrogen sulfate ILs containing different cations were characterized by TGA and UV–vis. The effect of ILs on the exothermic behavior of MX nitration was characterized by reaction calorimeter. Quantum chemical and ab initio molecular dynamics simulations (AIMD) were combined to reveal the catalytic mechanism. Significant findings ILs all exhibited high thermal stability, [MIMBs]HSO 4 showed relatively higher acid strength and catalytic activity, with MX conversion and NMX yields of 99.3% and 98.1% under catalytic conditions, respectively. The introduction of different ILs reduced the heat accumulation during nitration. The anions and sulfonic acid groups of the ILs could serve as catalytic sites with NO 2 + , promoting their reaction with MX. AIMD calculations revealed the reaction pathway and free energy barriers by which the ILs promoted protonation of HNO 3 and facilitated the NO 2 + attack on MX.