Advancing energy safety via stepwise nucleophilic substitution on tetrazine

Abstract

Historically hydrazine (N₂H₄) has served an essential function as a fuel in liquid rocket propellants; however, its intrinsic volatility and toxicity pose significant challenges in fulfilling the requirements for environmentally friendly and high-performance propellants. Introducing hydrazine onto a nitrogen-rich framework offers the possibility to use it as solid-rocket propellant. Now for the first time both hydrazine and nitroamine groups, energetic small groups, were introduced onto a tetrazine ring through stepwise functionalization. N-(6-(3,5-Dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazin-3-yl)nitramide (3) serves as an energetic intermediate, which upon reaction with hydrazine or ammonia results in the synthesis of unsymmetrically substituted tetrazine derivatives (4 and 8) via nucleophilic substitution and salt formation (a domino or cascade reaction). Compounds 5 and 9 (salts of 4 and 8, respectively) exhibit detonation properties on a par with RDX, providing the added benefits of high nitrogen content and reduced sensitivity, and 7 and 11 (neutral derivatives of 4 and 8, respectively) show promising propulsive properties, highlighting their potential as solid rocket propellants. This research will significantly advance the synthesis of unsymmetrically substituted tetrazines, enabling precise control over their energetic properties.