A thermally resilient high-performing metal-free primary explosive

Abstract

Lead azide (LA), though discovered centuries ago, remains the most widely used primary explosive due to its reliable initiation performance. However, its toxicity and environmental persistence present serious health and ecological concerns. This has driven the pursuit of lead-free, environmentally benign, thermally stable, and intrinsically safe alternatives with high initiating capability. Herein, we report the design and synthesis of a novel organic metal free primary explosive 6-azido-8H-tetrazolo[1,5-b][1,2,3]triazolo[4,5-d]pyridazine (3) with a tricyclic fused-ring scaffold, prepared from commercially available reagents in high yield. Its planar structure having high nitrogen content and various noncovalent interactions imparts high density, controlled sensitivity, and excellent priming ability, while being free from metals and perchlorates. Compound 3 exhibits exceptional thermal stability with a decomposition temperature of 216 °C, the highest reported for any metal-free primary explosive. It also shows excellent environmental resistance, low cost, and scalability. Notably, in a detonation test, compound 3 initiates 500 mg of RDX with a minimum primary charge (MPC) of 10 mg, matching the performance of LA (10 mg) and outperforming DDNP (70 mg). These features position compound 3 as a leading candidate for next-generation, safer, thermally stable metal free primary explosives and a potential replacement of benchmark explosives such as DDNP, lead azide, and many recently reported primary explosives.