Towards Safer Rocket Fuels: Hypergolic Imidazolylidene‐Borane Compounds as Replacements for Hydrazine Derivatives

Abstract

Currently, toxic and volatile hydrazine derivatives are still the main fuel choices for liquid bipropellants, especially in some traditional rocket propulsion systems. Therefore, the search for safer hypergolic fuels as replacements for hydrazine derivatives has been one of the most challenging tasks. In this study, six imidazolylidene-borane compounds with zwitterionic structure have been synthesized and characterized, and their hypergolic reactivity has been studied. As expected, these compounds exhibited fast spontaneous combustion upon contact with white fuming nitric acid (WFNA). Among them, compound 5 showed excellent integrated properties including wide liquid operating range (-70-160 °C), superior loading density (0.99 g cm(-3) ), ultrafast ignition delay times with WFNA (15 ms), and high specific impulse (303.5 s), suggesting promising application potential as safer hypergolic fuels in liquid bipropellant formulations.

Stability of the zwitterionic liquid butyl-methyl-imidazol-2-ylidene borane

“…18,19 The resulting imidazol-2-ylidene borane compounds, so far as they are liquid, show comparatively low viscosities. 20 NHC-boranes combine good stability with reducing ability and have even been shown to participate in metal complexes. 21 This makes them interesting candidates for electrochemical applications.…”

Prospective Symbiosis of Green Chemistry and Energetic Materials

“…In particular,t hey have as ignificant potential in as pecific and very important area of research associated with the manufacture and processing of high-energym aterials (HEMs). In particular, useful application of these almost nonflammable neotericm ediai nn itration and some other reactions used for the manufacturing of HEMs that make these reactions less fire and explosion risky [49,50] (published after the excellent review by Zhang andS hreeve [51] ) in the field of energetic ionic liquids( EILs), [52][53][54] (in particular oxygen-balanced EILs [55][56][57] and hypergolic EILs capable of fast ignition upon contact with oxidizers [13,52] )a re thoroughly analyzed. Homogeneous [32] andh eterogeneous [33] catalytic or biocatalytic (enzymatic) reactions, [34][35][36] green polymerization processes, [15,16,37] and some other chemical reactions [38][39][40] were performed efficientlyi ns ub-and supercritical CO 2 .…”

“…[48] This Reviews ummarizes prospective approaches to address these concerns based on applications of ILs and sub-or supercritical fluids (CO 2 and freons) in the preparation and processing of HEMs. In particular, useful application of these almost nonflammable neotericm ediai nn itration and some other reactions used for the manufacturing of HEMs that make these reactions less fire and explosion risky [49,50] (published after the excellent review by Zhang andS hreeve [51] ) in the field of energetic ionic liquids( EILs), [52][53][54] (in particular oxygen-balanced EILs [55][56][57] and hypergolic EILs capable of fast ignition upon contact with oxidizers [13,52] )a re thoroughly analyzed. Significant attentioni sp aid to SCF-basedm icronization techniques that improvet he energetic performanceo fH EMs significantly through the efficient control of the morphology and particle size distribution of the HEM fine particles without degradation or contamination of products.…”

Green Imidazolium Ionics–From Truly Sustainable Reagents to Highly Functional Ionic Liquids

“…In addition, ionic liquids are prized for their large range of thermal and electrochemical stability as well as liquidity . By proper choice and design of the ions that constitute a given IL, tuning of their properties and introduction of further characteristics is possible, leading to, for example, electroactive or hypergolic ILs. The use of so called task‐specific ionic liquids allows for the creation of specialized and efficient media for a variety of applications such as the synthesis of organic and inorganic materials as well as nanostructures .…”