Pyrazole bridges ensure highly stable and insensitive bistetrazoles

Abstract

• Insertion of a pyrazole-bridge between two tetrazole units increases the thermal stability. • Pyrazole-bridged bistetrazoles - high heats of formation, and nitrogen and insensitivity. • Mild, green halogenation at the 4-position was possible using Oxone® and halide salts. • Compounds 10 and 11 have good detonation properties relative to TATB and RDX. In the quest for efficient and thermally stable insensitive materials, the inclusion of a bridging molecule between symmetric or asymmetric azole units has recently emerged as a fruitful approach. However, the synthesis of new compounds with high density in combination with high thermal stability and insensitivity often occurs only with difficulty. Now a new class of pyrazole-bridged bistetrazole and bis(1-hydroxytetrazolyl) compounds was synthesized and fully characterized by NMR, IR spectroscopy, and elemental analysis. Thermal behavior was investigated by using differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). The solid-state structures of the diammonium salt ( 9 ) based on 4-nitro-1 H -pyrazole, and 5,5′-(4-chloro-1 H -pyrazole-3,5-diyl)bis(1 H -tetrazole) ( 18 ) were determined by single-crystal X-ray diffraction. These pyrazole-bridged bistetrazole compounds exhibit excellent thermal stabilities with high decomposition temperatures, moderate heats of formation, high nitrogen content, and insensitivities to impact and friction. Additionally, introduction of a halogen atom at the 4-position of the pyrazole ring gives rise to a new active heterocycle which holds considerable promise as a suitable substrate for further transformation.