Host-Guest Technique for Designing Highly Energetic Compounds with the Nitroamino Group

A new energetic material, 2-azido-4,7-nitroamino-1H-imidazo[4,5-d]pyridazine (ANIP) with a highly sensitive azido group and its host-guest compounds (ANIP/H2O and ANIP/H2O2), and energetic salts were obtained. With the guest and protons in host molecules, an abundant hydrogen bond system can be formed. This results in high crystal density and good sensitivity, which suggests that the host-guest strategy is a promising way to balance the contradiction between energy and sensitivity and provides a new path to obtain a new generation of high energetic materials.

Highly Selective Nitroamino Isomerization Guided by Proton Transport Dynamics: Full-Nitroamino Imidazole[4,5-d]pyridazine Fused-Ring System

Due to the advantage of the hydrogen bond system formed by nitroamino isomerization, by the calculations of hydrogen transfer in reported nitroamino explosives, the proton transport dynamics was first proposed to predict the nitroamino isomerization of energetic materials. With the calculated results of zero-point energy, the full-nitroamino fused energetic materials, 2,4-nitroamino-7-nitroimino-1,5-dihydro-4H-imidazolo[4,5-d]pyridazine (FNPI-1) and 2,2',7,7'-tetranitromino-4,4'-azo-imidazolo[4,5-d]pyridazine (FNPI-2) were designed and successfully synthesized. The highly selective nitroamino isomerization of neutral compound FNPI-1 is shown by X-ray diffraction. After the hydrogen transfer occurs, the intermolecular hydrogen bonds will greatly promote tight stacking, which enhances the density and thus a series of comprehensive properties of energetic materials. The theoretical calculations of zero-point energy explain perfectly the selectivity of hydrogen transfer between the nitroamino groups and the fused-ring skeleton for FNPI-1. The hydrogen atom transfer and selective isomerization of nitroamino energetic materials can be accurately predicted following proton transport dynamics, which provides computational bases and new ideas for the efficient design of fully nitroamino-based explosives.

Imidazole-Based Energetic Materials: A Promising Family of N-Heterocyclic Framework

Imidazole represents a fascinating class of explosophoric units with exciting structures and unique properties. As compared to other nitrogen-rich heterocycles, imidazole demonstrates great potential applications due to economic effectiveness and superior energetic performances. The field of traditional chemistry has been extensively explored for imidazole, and thus established bond-building methods and functionalization strategies promote further development as high-energy density materials (HEDMs). This review addresses the development of energetic imidazole compounds in the past decade, summarizes their physiochemical properties, and is divided into three parts (explosives, propellants, and energetic biocides) according to application requirements. Various synthetic strategies for these energetic molecules are highlighted, including the construction of heterocyclic frameworks and following functionalization. The selected and discussed reactions illustrate the versatility of imidazole in energetic applications as building blocks for the future design of new HEDMs.

Synthesis of Energetic 7-Nitro-3,5-dihydro-4H-pyrazolo[4,3-d][1,2,3]triazin-4-one Based on a Novel Hofmann-Type Rearrangement

Rearrangement reactions are efficient strategies in organic synthesis and contribute enormously to the development of energetic materials. Here, we report on the preparation of a fused energetic structure of 7-nitro-3,5-dihydro-4H-pyrazolo[4,3-d][1,2,3]triazin-4-one (NPTO) based on a novel Hofmann-type rearrangement. The 1,2,3-triazine unit was introduced into the fused bicyclic skeleton from a pyrazole unit for the first time. The new compound of NPTO was fully characterized using multinuclear NMR and IR spectroscopy, elemental analysis as well as X-ray diffraction studies. The thermal behaviors and detonation properties of NPTO were investigated through a differential scanning calorimetry (DSC-TG) approach and EXPLO5 program-based calculations, respectively. The calculation results showed similar detonation performances between NPTO and the energetic materials of DNPP and ANPP, indicating that NPTO has a good application perspective in insensitive explosives and propellants.

Multisubstituted Imidazolo[4,5-d]pyridazine Fused Ring System Resulting from Nitroamine-Nitroimine Tautomerism

A series of multisubstituted imidazolo[4,5-d]pyridazine fused ring compounds was synthesized in which nitroamine-nitroimine tautomerism is exhibited. The electrostatic potential indicates that the nitroimino group has the lowest negative value, second only to the nitro group, culminating in the nitroamino area, which has the highest positive value. In addition, a strong hydrogen bond system which arises from the newly formed nitroimino tautomer suggests that the nitroimino is more stable than its nitroamino analogue.