Effects of twelve organic solvents on process hazards and reaction selectivity of m-xylene nitration: Combined calorimetric technique and DFT calculations

Selection of appropriate solvents is of great significance for achieving efficient and safe m-xylene nitration. In this study, the exothermic behavior of m-xylene nitration under twelve organic solvents were studied by reaction calorimetry. The process hazards were assessed by calculation of thermal safety parameters. The reaction selectivity was quantified. The anhydrides exhibited the prominent promotion as water absorbent and active reagent in nitration, followed by selected aliphatic hydrocarbons, chlorinated hydrocarbons. While acetic acid, propionic acid and ethyl acetate had negative effects. The maximum yield of 95.6 % was achieved in nitric acid-acetic anhydride (HNO₃-Ac₂O) system. The thermal weight loss of the products appeared at around 150−230 °C by thermogravimetry experiments. The activation energy was determined to be 192.9 kJ/mol through adiabatic kinetic calculations. Furthermore, the solvent effects were analyzed by calculating the solvent polarity and its interaction energy with HNO₃. The different action mechanisms of Ac₂O and Pc₂O on NO₂ ⁺ generation were revealed. The density functional theory calculations were in agreement with the experimental results. These findings can provide guidance for understanding of the solvent effect on the reaction hazards and selectivity of m-xylene nitration, and provide experimental and theoretical basis for solvent screening for the nitration of similar aromatic compounds.