Thermal Behavior and Decomposition Pathway for Nitrophenols and Sodium Nitrophenolates

Nitrophenols and corresponding sodium nitrophenolates are the main side products in the production of mononitrobenzene (MNB). These side products are hazardous due to their thermal instability nature. In this article, the thermal decomposition behaviors of nitrophenols and sodium nitrophenolates were first characterized by differential scanning calorimeter and accelerating rate calorimetry techniques. Then, the influence of phenol and sodium phenolate on the thermal decomposition of MNB was studied to clarify the effect of phenolic hydroxyl groups on the thermal stability of nitrophenols. It was found that compared to nitrophenols, the exothermic peaks of sodium nitrophenolates were more intense and presented strongly autocatalytic features. Sodium phenolate could significantly decrease the decomposition temperature of MNB. Aniline was detected as the unique product in the decomposition processes of pure MNB and MNB/sodium phenolate mixtures, and the nitrosobenzene was verified as the intermediate product. It was experimentally proven that sodium phenolate could catalyze the decomposition of nitrosobenzene (the decomposition intermediate of MNB). The violent decomposition of sodium nitrophenols was caused by the intermolecular catalysis effect of phenoxy groups.