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Help with synthesis of a tetrazole salt


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Edit: I hit "Post Topic" instead of "Preview Post" on accident. Please PM any typos you find and I will update them the first chance I get.The Schemes/diagrams can be found here: http://imgur.com/a/bVzcY Images inline.


Hello all,


First off, this is not HE nor HE related, I have no reason or interest in poking around with that stuff. The final product burns, is chemically, thermally, and physically stable (as far as pyro goes that is) as well as almost smokeless and environmentally clean; it is a Strontium salt, a red colorant. To quote, "Salt 3a-6 burned with an intense bright red flame and its color purity exceeded the control value."


The chemical I want to try to make is called: Strontium bis(1-methyl-5-nitiminotetrazolate) monohydrate


I discovered it in the survey paper called "Azole-Based Energetic Salts" by Haixiang Gao and Jean'ne M. Shreeve, published by Chemical Reviews on pubs.acs.org/CR

Based upon the references in the paper I believe this salt was originally discovered by Klapötke in "Propellants, Explosives, and Pyrotechnics".


Because the paper does not give explicit step-by-step instructions I have been working on making sense of it. The problem is I am not a chemist. I need a chemist, or a chemist's help. Could someone please read through what I have here and review the both the theoretical and practical chemistry? I would be indebted to you.






(n) - An id number for a compound, in this case 2

(n"a") or (n"b") - A derivative of n, where the bond structure of the ring is changing

(n-m) - A some compound related to n

(n"a"/"b"-m) - A derivative of n


Strontium bis(1-methyl-5-nitiminotetrazolate) monohydrate is 3a-6


I will begin with a little information from the paper:



5-Nitrimino-tetrazoles (3), which are five-membered aromatic heterocycles with a nitoimine functional group, are one interesting approach in the development of new energetic materials. Because they are inexpensive and easy to manufacture via various routes, nitrominotetrazoles have been long known...Physical properties of the nitrominotetrazole derivatives and their salts are given in Table 3. They are highly endothermic compounds. The enthalpies of all compounds are positive ranging between 22 (3a · H2O)and 694 (3-11) kJ/mol. However, their thermal stabilities are marginal. Differential Scanning Caliometry (DSC) studies show that decomposition of the nitrominotetrazolates occurs between 69.0 (3-11) and 243.6 (3-5) °C with the majority decomposing ~120 °C (3, 3-1, 3a, 3b, and 3d). Impact sensitivities range from those of the 3a-1, 3d-1, and 3d-2 (>40 J) to the very sensitive compounds 3-2 and 3e (<2 J).


The color performance of copper complexes 3c-1, 3d-3, and 3e-1 was tested for application as coloring agents in "green" (read: environmentally friendly) pyrotechnics. Complexes 3c-1 and 3e-1 show a brilliant green flame, and complex 3d-3 gives a bright blue flame. The combustion of these complexes is almost smokeless, which makes them promising coloring agents in modern pyrotechnic compositions. Salt 3a-6 burned with an intense bright red flame and its color purity exceeded the control value. [sensitivities vary] depending on the amount of coordinated water or ammonia.


Energetic ionic materials based on aminotetrazoles are also known to form strong hydrogen-bonding networks and thus show remarkable stability and considerable insensitivity to physical stimuli, while providing good performance. In addition, known aminotetrazole salts are mainly composed of nitrogen and thus have large positive heats of formation as well as high densities comparable to or greater than those of widely used neutral, covalent, organic molecular explosives. The salts only have slight negative oxygen balances when an oxygen-rich counteranion (nitrate, dinitramide, and perchlorate) is used. Furthermore, energetic ionic materials tend to exhibit lower vapor pressures than similar neutral nonionic analogues, essentially eliminating the risk of exposure through inhalation. Given these properties, aminotetrazole-based compounds have long been of interest as potential energetic materials.




Now onto the synthesis. I will explain this in the same manner as I figured it out, hopefully by doing so you can catch any errors. Knowing the final product that I want I began with that and worked my way back piece by piece until I hit OTC/available materials, I then worked forwards to double check myself.


Step 1) Strontium bis(1-methyl-5-nitiminotetrazolate) monohydrate 3a-6



Nitration of the amino group in aminotetrazole leads to enhanced energetic character as well as higher sensitivity compared to aminotetrazole and improves the oxygen balance. The methyl group lowers the sensitivity compared to the nonmethylated 5-nitroiminotetrazole.


The strontium 5-nitriminotetrazolate dihydrate (3-12), strontium bis(1-hydro-5-nitriminotetrazolate) tetrahydrate (3-13), Strontium bis(1-methyl-5-nitiminotetrazolate) monohydrate (3a-6), and strontium bis(2-methyl-5-itraminotetrazolate) * xH2O (x = 2--4) (3b-1) were synthesized by the reactions of strontium hydroxide octahydrate and 3, 3a, and 3b, respectively.


So let's keep a running summary of what we have at each step:


Reactants: Strontium hydroxide octahydrate (commercially available), and 3a

Products: Strontium bis(1-methyl-5-nitiminotetrazolate) monohydrate 3a-6



Step 2) 1-methyl-5-nitroiminotetrazole 3a



The most recent method of syntheses for 5-nitroiminotetrazole (3), 3), 1-methyl-5-nitroiminotetrazole (3a), 2-methyl-5-nitroaminotetrazole (3b), 1-(2-hydroxyethyl)-5-nitroiminotetrazole (3c) and 1-(2-chloroethyl)-5-nitroiminotetrazole (3d) based on one-step nitration of functional derivatives of 5-amino-1H-tetrazole (2) with HNO3 (100%) (Schemes 17 and 18).


Reactants: Nitric Acid (100%) and 2a-2

Reaction: Single step nitration of a functional derivative of 5-amino-1H-tetrazole, in this case 2a which is 5-Amino-1-methyltetrazole which is the methylated derivative of 2

Products: 1-methyl-5-nitroiminotetrazole (3a)



Step 3) 1-Methyl-5-aminotetrazolium Salt 2a-2



The introduction of methyl groups helps to reduce the sensitivity of the compounds while concomitantly increasing their thermal stability at the cost of performance and makes interesting compounds accessible. Compound 2a or 2b react with strong acids (either perchloric or nitric acid) to generate the corresponding energetic salts 2a-1, 2a-2, 2a-3 and 2b-12b-3 (Scheme 11).


Reactants: Nitric Acid and 2a

Products: 2a-2



Step 4) 5-Amino-1-methyltetrazole 2a



5-Aminotetrazole (2) is an especially valuable intermediate in the synthesis of tetrazole compounds because of its varied reactions and its ease of preparation. 5-Amino-1-methyltetrazole (major isomer, 2a) and 5-amino-2-methyltetrazole (minor isomer, 2b) can be obtained by methylation of the sodium salt of 5-aminotetrazole with dimethyl sulfate or MeI (Scheme 10, method 1).


Reactants: The sodium salt of 5-aminotetrazole 2 with dimethyl sulfate or MeI (former is cheaper and more effective though toxic)

Products: 2a and 2b (the production of 2b is a problem I will explain later)



Step 5) Sodium salt of 5-Amino-1-methyltetrazole 2-12



Compound 2 also behaves as a weak acid and can be used to obtain nitrogen-rich energetic salts and ionic liquids. The AT anionic salts and ionic liquids were prepared by using three different methodologies (Scheme 9). Compound 2 can be easily deprotonated in aqueous solution using strong bases (hydrazine, biguanidine, LiOH, and NaOH, method 1).150Salts 2-11, 2-12, 2-16, 2-19, and 2-20 were synthesized by using this methodology.


Reactants: Sodium Hydroxide and 2

Products: 2-12




Compound 2 is "5-Aminotetrazole (5-AT, 2), a simple, commercially available, nitrogen-rich (82%) compound."


So in summary:


2 + NaOH --> 2-12 + (Me)2SO4 --> 2a + 2b + HNO3 --> 2a-2 + HNO3 (100%) --> 3a + Sr(OH)*8H20 --> 3a-6


Now when I went to check the reaction moving forwards I noticed that step 2 produces both 2a and 2b, 2b then reacts with the Nitric acid in step 3 to form 2b-2 which then reacts the Nitric acid (100%) to form 3b which then reacts with the SrOH to form strontium bis(2-methyl-5-itraminotetrazolate) * 4H2O 3b-1

I do not know if this avoidable or even undesirable in the first place, they should behave similarly.


Reactants: 5-Aminotetrazole, Sodium Hydroxide, Nitric acid, Dimethyl Sulfate or Methyl Iodide, and Strontium Hydroxide Octahydrate.




My questions for you are:


1) Does this all add up? As in, does this make sense? Is it even theoretically possible? I have read and reread and rereread this article however it doesn't make the connection between each step clear, and is in fact in some places contradictory to the text and other diagrams.


1b) Is there any reason why the methyl functional group would not be drawn? At times it is shown as N-R (where R = Me) and sometimes simply as N--. The latter implies a simple single nitrogen-carbon bond to me, am I wrong?


2) Is there any way to avoid the generation of 3b-1?


3) Do the nitric acid reactions need to be done in the presence of sulfuric acid and/or washed with a base/water after? (I have never performed an esterfication (such as making Nitrocellulose) and do not know the role of the Sulfuric acid in such, please forgive my ignorance). Should it be done in an ice bath?


4) The paper makes no mention of the byproducts, however I believe it will generate water and sodium sulfate at the very least. What else? Do I need to purify during each step and remove these?


5) What is going on with the methylation of 5-AT? Despite the text the provided diagram (Scheme 10 method 1) shows the reaction as: 5-AT + i) NaOH + ii) MeI or (Me)2SO4 --> 2a + 2b. Can I skip step 2 by reacting 5-AT with both NaOH and Me2SO4 at the same time? Won't that cause NaOH and Me2SO4 to react, at least partially, without touching 5-AT?


6) Why does it react with the nitric acid twice? Why isn't the reaction carried out fully during the first reaction? During the first reaction it shows the molecule gaining a Hydrogen cation and an -NO3 anion, during the second reaction it shows NH2 bond becoming N-NO2. My guess is that the concentration of Nitric acid in the first reaction (although not specified) is too low, however, if this is the case then why not raise it to 100% to complete the reaction then?


Edit: I hit "Post Topic" instead of "Preview Post" on accident. Please PM any typos you find and I will update them the first chance I get.The Schemes/diagrams can be found here: http://imgur.com/a/bVzcY Images inline.

Edited by AzoMittle
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