Mechanistic Study of Oxidative Aromatization Using Activated Carbon–Molecular Oxygen System in the Synthesis of 2-Arylbenzazoles:Focus on the Role of Activated Carbon

摘要

Nineteen activated carbons, including sixteen tailor-made and three commercially available ones, were employed toinvestigate their role in the one-pot synthesis of 2-arylbenzazoles starting from 2-aminophenol, 1,2-diaminobenzene, or 2-aminobenzenethiol, and aldehyde via oxidative cyclization of intermediate phenolic Schiff base promoted by the activatedcarbon–molecular oxygen system. Tailor-made activated carbons were prepared from wood, coconut shell, and coal by thesteam activation method or the chemical activation method. All activated carbons were characterized to clarify theirproperties, such as metal contaminants, specific surface area, porosity, and surface functionality. After examining theireffects on reactivity in the oxidative aromatization, we found that the essential role of activated carbon in this oxidationsystem is concerned not with metal contaminants, specific surface area, pore volume, mean pore diameter, and surfaceoxygen groups evolving as CO_2at 900 °C but with surface oxygen groups evolving as CO during heating at 900 °C, suchas carbonyl groups on the surface of activated carbon. Additionally, in the synthesis of 2-arylbenzoxazole, it was foundthat activated carbon would also promote the cyclization of the intermediate Schiff base.