1-Amino-3-nitroguanidine (ANQ, 1 ) was synthesized by hydrazinolysis of nitroguanidine (NQ) with hydrazine hydrate.
1-Amino-3-nitroguanidine (ANQ) can be described as the aminated sister compound of the famous 1-nitroguanidine (NQ). The next step in the preparation
of mixed aminonitroguanidines would be the synthesis of 1,3-diamino-5-nitroguanidine (DANQ), which is completely unknown yet.
Interestingly, only very little correspondence on aminonitroguanidine is found in the literature.
We recently investigated the use of ANQ in energetic materials in its neutral as well as protonated form. For example, highly energetic
1-amino-3-nitroguanidinium dinitramide has been described. Because dinitraminic acid (HN(NO2)2) and concentrated aqueous solutions can explode
spontaneously, the reaction pathway using a metathesis reaction of amino-nitroguanidinium chloride with silver dinitramide was chosen. This example
shows the utility of the herein described compounds as precursor materials for the synthesis of ionic energetic materials containing the
1-amino-3-nitro-guanidinium cation when using metathesis reaction protocols to precipitate low soluble silver halides in case of reacting the ANQ
halides with the corresponding silver salts of the used acids or to precipitate BaSO4> in case the corresponding Ba-salts are reacted with the
herein described sulfate salt of ANQ. Here we present the synthesis and characterization of three amino-nitroguanidinium halides and
bis(amino-nitroguanidinium) sulfate.
Synthesis
The synthesis of 1-amino-3-nitroguanidine ( ANQ) was achieved starting from commercially available nitroguanidine (NQ) by treatment with hydrazine
hydrate. In a hydrazinolysis reaction, the aminated nitroguanidine is formed after the elimination of ammonia. Unprotonated ANQ shows rather poor
solubility in water, so that it can be isolated from the reaction mixture after neutralization by suction filtration. Unlike in water or buffered
neutral solutions, in acidic media ANQ is dissolved comparatively easily upon the formation of the protonated ANQ species. Therefore, the halides as
well as the sulfate salt can be prepared by dissolving ANQ in dilute aqueous solutions of the respective mineral acids HCl, HBr, HI and H2SO4. To
fully synthesize and characterize all halides (F−, Cl−, Br−, I−) of ANQ, it was
also dissolved in 40% aqueous HF. Unfortunately it was only possible to isolate unprotonated ANQ from this reaction mixture. The reason for this
behavior is easily found in the pK values of the used mineral acids. ANQ, due to the presence of the electron withdrawing character of the nitro
group, is a comparatively weak base and requires strong mineral acids for protonation in aqueous media. Since the acidic strength of the hydrohalides
in aqueous solution decreases in the order HI > HBr > HCl > HF, the latter one is not able to protonate ANQ in aqueous solution any more.
However, 40% aqueous HF proved to be an excellent solvent for the recrystallization of the poorly water soluble ANQ, especially if single crystals,
e.g., for single crystal X-ray diffraction, are needed. The storage stability of the halides decreases with increasing molecular weight of the anion.
Whereas the hydrochloride remains a colorless crystalline material even after several months, the hydrobromide discolors slightly and the hydroiodide
turns completely dark after the release of I2 indicating a decomposition of the material.
Sensitivity Testing
Since 1-amino-3-nitroguanidinium salts show enhanced sensitivity towards outer stimuli such as impact and friction, the impact and friction
sensitivities were determined and carried out...
Regarding the sensitivities of the salts, a large difference between the halides and the sulfate salt is also observed. Whereas the halides reveal
sensitivities of 25 J (impact sensitivity) and 288 N (friction sensitivity), the sulfate salt is much more sensitive, having 6 J (impact sensitivity)
and 120 N (friction sensitivity). This can primarily be explained by the formation of monohydrates, which is true for all halides, whereas the sulfate
salt crystallizes water-free. The determined values imply a classification of the tested materials as “sensitive” towards both impact and
friction. The higher sensitivities of the protonated species discussed herein compared to the neutral compound ANQ can be correlated to a lowered
C–N bond order of the hydrazine moiety of the molecule, which appears upon protonation of the molecule as it was found during the structural
investigation of neutral ANQ and its protonated species in reference 4. The same argumentation can also be applied to the thermal stabilities of the
compounds, whereas a weaker C–N bond of the hydrazine moiety facilitates the loss of the hydrazine moiety and thus, decomposition of the material.
"Inorganic Amino-Nitro-Guanidinium Derivatives", Niko Fischer, Thomas Klapötke, Karin Lux, Franz Martin, Jörg Stierstorfer, University of
Munich, (2012)
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