Combined thermal calorimetry and quantum chemical evaluation of effect of hydrogen peroxide on the thermal decomposition of N-methylmorpholine-N-oxide

The effect of hydrogen peroxide (H₂O₂) on the thermal decomposition characteristics of N-methylmorpholine-N-oxide (NMMO) was investigated using thermal experiments and quantum chemical calculations. The thermal decomposition characteristics of the NMMO and NMMO/H₂O₂ systems were determined at different heating rates using a microreaction calorimeter. Firstly, H₂O₂ decreased the onset temperature and increased the reaction enthalpy of NMMO decomposition. Secondly, the apparent activation energy decreased from 97.49–76.79 kJ mol⁻¹ to 80.76‒89.87 kJmol⁻¹ based on the Kissinger and Starink models. Finally, density functional theory was used to investigate the effect of H₂O₂ on NMMO decomposition from a microscopic perspective. It was found that the length of the N–O bond in NMMO increased, and the ability of oxygen atoms to obtain electrons was enhanced in the presence of H₂O₂, decreasing the stability of the NMMO molecules. The nucleophilicity of the oxygen atom in the NMMO molecule was enhanced in the NMMO/ H₂O₂ system, which is beneficial for electron transfer to the H₂O₂ molecule. The energy-gap of the frontier molecular orbital decreased under the influence of H₂O₂, intensifying the interaction between H₂O₂ and NMMO to form π bonds. Overall, the stability of the NMMO molecular structure was reduced and the reactivity of NMMO was enhanced at lower temperatures in the presence of H₂O₂, which provides a theoretical reference for the safe production of NMMO.