Guiding the synthesis of pentazole derivatives and their mono- and di-oxides with quantum modeling

Abstract

There is high prospect that derivatives of pentazole can lead to high energy density materials. However these molecules are potentially hazardous because of their high formation enthalpies and weak N–N bonds. In order to devise efficient protocols, possible schemes for the synthesis of nitro and azido derivatives of pentazole, and their mono- and di-oxides, have been explored using quantum chemical methods. Reaction pathways have been investigated in detail, with particular emphasis on locating transition states and on obtaining a reliable treatment of solvent effects. Oxidation by ozone is found to be a favorable process, leading to some regioselectivity in favor of β-mono-oxides. Nitration by NO₂⁺BF₄⁻ is also predicted to be favorable. In contrast the electrochemical azidation of N₅⁻ and its oxidized derivatives is found to be energetically inaccessible. Combination of the individual addition and oxidation steps leads to recommendations for future synthetic work. Finally the kinetic stability of products with respect to N₂ and N₂O elimination is assessed.