4-amino,5-nitro-1,2,3-triazole Preparation

[Anders Hoveland]

This topic is about preparation of 4-amino,5-nitro-1,2,3-triazole,
which, while being itself a very stable and powerful explosive, may be of greater value as a precursor to several other advanced explosives. 4-amino,5-nitro-1,2,3-triazole (decomp 297C) is also more thermally stable than 3-amino,5-nitro-1,2,4-triazole.

Bubbling nitrogen dioxide into a mixture of glacial acetic acid and acetic anhydride should form some 2-nitroacetic acid. To add a second nitro group, a modification of the procedure below may be employed.

This procedure is for oxidizing nitroethane into 1,1-dinitroethane, but could no doubt be used on nitroacetic acid instead:

To a stirred solution of 2.66 g (66.5 mmoles) of sodium hydroxide in 15 ml of water at 20° was added 5.0 g (66.5 mmoles) of nitroethane. When all the nitroethane dissolved, the solution was cooled to 5°-7° in an ice-water bath.

The sodium salt of nitroethane was prepared as above. To the stirred solution was added a solution of 20 g (288 mmoles) of sodium nitrite in 50 ml of water, followed by a solution of 4.4 g (13.4 mmole) of potassium ferricyanide in 25 ml of water. Finally, 16.0 g of solid sodium persulfate (67 mmoles) was added all at once. The reaction temperature, moderated by an ice-water cooling bath, increased to 50°. The orange mixture was stirred at 25° for 1 hour and then cooled to 10°. Urea, 20 g (0.33 mole), was added, followed by 10 ml of glacial acetic acid. The mixture was extracted with three 25 ml portions of ether and the combined extracts were washed with brine and dried. The crude product was distilled to give 4.2 g (52% yield) of 1,1-dinitroethane, b.p. 87°-89° (16 mm), identified by its nmr spectrum. Patent 4910322

With the dinitroacetic acid thus obtained, the ethyl ester can be formed. This is somewhat complicated by the fact that any concentrated strong acid could risk hydrolyzing the nitro groups away. It may be better to react with ethyl bromide instead, using propylene carbonate (or some other such solvent) to ensure the HBr formed stays very dilute.

Here is the main procedutre:

4-amino, 5-nitro, 1,2,3-triazole was synthesized by condensing acetaldehyde with ethyl 2,2-dinitro-acetate in the presence of sodium azide, to form 3-methyl, 5-nitro, 1,2,3-triazole.

The cyclization reaction with the azide ion is very comlex. To get some idea of the intermediate steps, see the attachment at the bottom of the page. For step #3, a nitrous acid is pulled out under the alkaline conditions, leaving a double bond between carbons. (cyclize is the American spelling)

CH3CH=O (NO2)2CHC(=O)OCH2CH3. I think that (NO2)2CHC(=O)O(-) converts to (-)NO2=C(NO2)H and CO2.
The (-)NO2=C(NO2)H would then condense with CH3CH=O, in a Michael-type addition, and the aldehyde would disproportionate, being reduced while oxidizing another free CH3CH=O under the alakine conditions. Then an azide ion would displace one of the nitro groups. So now the intermediate is CH3CH*C(=NO2(-))(--N=N=N). Where the * signifies a radical. This then spontaneously cyclizes, the electron moves toward a nitrogen in the ring, and then a hydrogen ion stick on. This is all just my own conjecture. So the methyl group on the resulting ring almost certainly comes from the methyl on the acetaldehyde. The carboxyl groups comes off as CO2. The original ester gets hydrolyzed by the NaN3, and in so doing acts as a dehydrating agent.

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[Anders Hoveland]

There is probably a much better route. Starting with ethyl acetate, dissolving in acetic anhydride should cause conversion of the ethyl acetate to its unsaturated tautomer, which can readily react with bromine. The mixture, which contains bromine, should be kept out of direct sunlight, and should not be allowed to stand for too long, otherwise undesirable radical cacade reactions may proceed, in which the ethyl group would also become brominated to varying degrees.

As can be seen in the picture below, in the final step simple dilution with water (probably would want to use only a limited ammount, just enought to react with the acetic anhydride Ac2O, as additional water could slowly cause the ethyl bromoacetate to hydrolyze since esters hydrolyze under acidic conditions and there will still be excess acetic acid from all the Ac2O that reacted with the water) will give the final ethyl bromoacetate. It may be desirable, however, to rather simply store or directly use the solution as is, in the next step, in which the bromine will be substituted for a nitro group.

Bromoalkanes slowly hydrolyze with water. (the hydrolysis isusually made even slower by the fact that bromoalkanes are nearly insoluble, but of course not in the case of ethyl bromoacetate) Refluxing bromoalkanes with a solution of sodium hydroxide in water more rapidly forms the associated alcohols.

Another quick note: bromine readily forms by reacting NaBr with acidified H2O2, but then one would want to isolate the pure Br2 from this, as the excess H2O would dilute the valuable Ac2O.

Here is a relevant procedure to substitute the bromine atom with a nitro group (to form ethyl nitroacetate) :

32.5 grams of ethyl bromide (0.3 moles) was poured into a stirred solution of 600ml dimethylformamide and 36 grams dry NaNO2 (0.52 mole) in a beaker standing in a water bath keeping the solution at room temperature as the reaction is slightly exothermic. Always keep the solution out of direct sunlight. The stirring was continued for six hours. After that, the reaction mixture was poured into a 2500 ml beaker or flask, containing 1500 ml ice-water and 100 ml of petroleum ether. The petroleum ether layer was poured off and saved, and the aqueous phase was extracted four more times with 100 ml of petroleum ether each, whereafter the organic extracts were pooled, and in turn was washed with 4x75ml of water. The remaining organic phase was dried over magnesium sulfate, filtered, and the petroleum ether was removed by distillation under reduced pressure on a water bath, which temperature was allowed to slowly rise to about 65°C. The residue, consisting of crude nitroethane was distilled under ordinary pressure (preferably with a small distillation column) to give 60% of product, boiling at 114-116°C. Ethylene glycol also works as solvent, but the reaction proceeds pretty sluggishly in this medium, allowing for side reactions, such as
CH3CH2-NO2 + CH3CH2-ONO -> CH3CH(NO)NO2 + EtOH. KNO2 can also be used instead of NaNO2. If NaNO2 is used in DMF, 30g of urea can also be added as nitrite scavenger to minimize side reactions, as well as simultaneously increasing the solubility of the NaNO2 and thereby significantly speeding up the reaction.

If the ethyl bromide is substituted with ethyl iodide, the required reaction time is decreased to only 2.5 h instead of 6 h. In case ethyl iodide is employed, a slight change in the above procedure needs to be done. The pooled pet ether extracts should be washed with 2x75ml 10% sodium thiosulfate, followed by 2 additions of 75ml water, instead of four of 75ml water as above, to remove trace leftover I2.



For the next step, the solution is made alkaline (with dilute NaOH), and a solution of Br2 is added. This puts a bromine atom
on the carbon atom with the nitro group. The structure of the resulting ethyl 2-bromo,2-nitro-acetate is
CH3CH2OC(=O)CHBr(NO2)

The procedure described above is again used to substitute the new bromine atom with another nitro group to obtain ethyl-2,2-dinitro-acetate. It will be this compound that can later react with sodium azide NaN3 to form the triazole.

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