Abstract: The nitration process of nitrogen-containing heterocyclic aromatics with electron-donating groups, taking 2,6-diaminopyridine and 2,6-dimethoxypyrazine as substrates, is studied. The effects of nitration systems on the yields of 2,6-diaminopyridine and 2,6-dimethoxypyrazine are investigated, respectively. The best nitration system that is suitable for those pyridine and pyrazine compounds which are difficult to be nitrated is determined. On the base of that, some important factors, such as the amount of nitric acid, reaction temperature, ratio of super acid, are further studied, and the optimized reaction conditions are obtained. Yields of 90% and 65% are reached for 2,6-diaminopyridine and 2,6-dimethoxypyrazine, respectively. Finally, the relationship between the difficulty of nitration and the activity of nitrogen-containing heterocyclic aromatics is analyzed through simulated quantum chemistry calculation in the view of electron cloud density and zero point energy. The results show that, with the increase in nitrogen atom number of aromatic, the electron cloud density of carbon atom displays a decreasing trend, the activity of nitrogen-containing heterocyclic aromatics weakens, and then the nitration reaction is restrained. However, as the introduction of electron-donating group, the electron cloud density of carbon atom increases, promoting the nitration reaction.

Key words: ordnance science and technology, nitrogen-containing heterocyclic aromatics, pyridine, pyrazine, nitration process