Furoxan-Tetrazole

 
It is well known that 3,4-diaminofurazan will form 3,3'-diamino-4,4'-azo{xy}furazan on oxidation with specific reagents. What seems to be common knowledge (e.g. http://www.sciencemadness.org/talk/viewthread.php?tid=5813) is that the azoxyfurazan will form in cold aqueous H2O2/H2SO4. What is problematic with this synthesis is its low yield (57%), the use of concentrated sulfuric acid and careful temperature control.

another route exists, much simpler to perform and much higher yielding.

The best yielding variation of this synthesis
An aqueous solution of DAF (150 g, 1.5 mol) and sodium bicarbonate (378.2 g, 4.5 mol) in water (about 9 liters) was prepared at room temperature (about 22 deg C) in a 22-liter non-jacketed flask. Oxone (922.5 g, 1.5 mol) was added in three portions of about 300 g each to the solution. After stirring for about 2 h the pH was measured at 6.32. Additional sodium bicarbonate (378 g, 4.5 mol) was added resulting in a pH of 7.36. Additional Oxone (922.6 g, 1.5 mol) was added, resulting in a pH of 6.98. Stirring was continued for about another 2 h, after which the pH was measured at 6.78. The solid product that precipitated from the solution was filtered and washed with water, yielding 134.3 g (89.55%) of essentially pure DAAF. The mean particle size of DAAF was determined to be 41 um.

As can be seen, the relatively very high yielding synth uses a very simple protocol, requiring 2 mols oxone per 1 mol DAF and only rudimentary pH control with sodium bicarbonate. I have a feeling it might be minimally improved, at least to eliminate the second addition of bicarbonate, by employing a buffer solution. Oxone (potassium peroxomonosulfate, 2KHSO5.KHSO4.K2SO4) is relatively cheap and unwatched, non-toxic, non corrosive and easy to use.

A second interesting synth in this application can be seen:

DAF (0.5 g, 5 mmol) was added to an aqueous solution of sodium bicarbonate (0.84 g, 10 mmol) and 10 ml of water at room temperatur (about 23 deg C). A solution of 5% NaOCl (i.e. household bleach, 15 ml) was then added slowly over 15 minutes to the DAF/sodium bicarb mixture. The reaction was then stirred an additional 15 minutes. The orange solid was filtered from the solution and washed with cold water and dried. Analysis of the solid showed that the product was not DAAF, but instead was 3,3'-diamino-4,4'-azofurazan. The yield was 90%

Another super-simple and high yielding protocol, this time only utilizing easily improvised regents.

Interesting question that these two methods raise is: can these be used on 5-aminotetrazole to form, respectively, azotetrazole with NaOCl (instead of the usual inelegant and pricey oxidation with KMnO4) and - perhaps! - azoxytetrazole with oxone? Is azoxytetrazole even known in the literature? My search turned exactly zero results. If it can be prepared this way and is stable (it should be!), it should be quite a powerful explosive that easily forms salts, just as the azotetrazole forms them.

My reason for expecting these methods to carry over to aminotetrazole is that the tetrazole ring is chemically similar to the furazan ring - both are very electron deficient and generally very stable to chemical transformations. If someone has some aminotetrazole on hand, these two ideas might be very much worth trying!
 
The above compound would be expected to be moderately insensitive and extremely powerful, more so than HMX. The amino group would need to be protected before the oxidation that would add three of the oxygen atoms. The regent for the oxidation could be Oxone (which is currently known to be capable of oxidizing nitrotetrazole).
 
 

Nitrous acid (HONO) oxidizes aminoguanidine nitrate H2NC(=NH)NH2 into guanyl azide N=N=NC(=NH)NH2, which cyclizes into aminotetrazole {HN4C}NH2 when boiled under alkaline conditions. This takes several hours and gives 70-85% yield.

included is the tested procedure for oxidizing a tetrazole compound 
12.5g of the sodium salt of 5-nitrotetrazole is dissolved in 50mL water, then reacted with 45g of potassium peroxy-monosulfate ("Oxone") and 20g of potassium acetate, which acts as a buffer. The solution is stirred for 24 hours at 50 degC. A solution containing 0.09 moles of tertiary amine sulfate, such as Et3NH(+), Na(+), SO4(-2), dissolved in 200mL of water, is added. Then the 5-nitro tetrazole-2N-oxide is extracted using 300mL of ethyl acetate. The yellow product moves into the ethyl acetate layer. The 5-nitro tetrazole-2N-oxide product may be purified by crystallization from EtOAc or toluene, resulting in thin yellow crystals. The yield is 70%.
Several salts of the nitrotetrazole oxide anion decomposed at between 153 and 211 degC.


 
 
Č
ċ
ď
Anders Hoveland,
Feb 9, 2011, 3:44 PM
Comments