Liquid Dinitromethanide Salts

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Abstract
The dinitromethanide (DNM) anion is a useful component of room temperature ionic liquids. Eight DNM ionic liquids with substituted imidazolium cations including 1-butyl-3-methylimidazolium (1), 1-allyl-3-methylimidazolium (2), 1-allyl-3-butylimidazolium (3), 1,3-diallylimidazolium (4), 1-(2′-methoxyl)ethyl-3-methylimidazolium (5), 1-(ethoxylmethyl)-3-methylimidazolium (6), 1-(hydroxyethyl)-3-methylimidazolium (7), and 1,3-dimethylimidazolium (8) were obtained. DNM ionic liquids 1−8 were synthesized by metathesis reactions from the corresponding imidazolium halides with potassium dinitromethanide or silver dinitromethanide. These DNM ionic liquids have been fully characterized by IR, NMR, elemental analysis, thermal stability, phase behavior, and viscosity. The molecular structure of 8 was determined by single-crystal X-ray diffraction. Compound 8 crystallizes in the triclinic space group P1̅, with a density of 1.453 g cm−3 (a = 7.1402(19) Å, b = 9.376(3) Å, c = 13.793(4) Å, α = 103.759(4)°, β = 90.757(4)°, γ = 96.874(4)°, V = 889.6(4) Å3, and Z = 4). Delocalization of both the DNM anion and dimethylimidazolium cation was found from the single-crystal structure data of 8. The heats of formation of 1−8 along with their detonation properties were investigated and analyzed. Their sensitivities toward impact were determined by BAM standards and found to be impact-insensitive (>40 J). The DNM-containing ionic liquids 1−7 are liquids at room temperature with desirable low viscosities. The temperature dependence of the viscosities for 1−7 was studied. These DNM ionic liquids were found to be a significant feature of glass-forming liquids. They also exhibit good liquid characteristics with desirable long liquidus ranges of more than 200 °C.

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