Synthesis of DPT (Dinitropentamethylenetetetramine) for HMX
I would like to share with you an interesting way of synthesizing DPT that apparently has not been described on this forum.
This method was invented by the participant "TNT Turtle" on the, unfortunately, already dead (closed) forum of high energy density materials
"exploders.info".
I have nothing to do with the authorship of this article, and just thought I'd post a translation. I don't want valuable information to be forgotten
in the depths of the web archives, and moreover, I think I will show some respect to the forum, the members and the author by sharing this. The
author, by the way, did not prohibit distribution (if there is a link to the original (already only archived)).
For those not in the know. DPT is useful as a precursor for HMX, since it can be nitrolyzed with 10% ammonium nitrate solution in fuming nitric acid
at 10-12°C without using acetic anhydride. The yield is 48%, if ammonium nitrate is not used, the yield is half as much. Variations of this method
used in industry are essentially waste-free, as the DPT is partially returned and the spent nitric acid is used for the production of ammonium
nitrate. The disadvantage of this method is the reduced quality of HMX crystals (intracrystalline defects and chips), compared to the acetic anhydride
method (DPT can be nitrated and with acetic anhydride with a yield of 75-80%), but in any case, obtaining through DPT gives relatively pure HMX
(melting point 272-276°C and 278-280°C after recrystallization from acetone) in contrast to the modified Bachmann-Ross scheme (melting point
265°C).
The article itself:
«Dinitro-pentamethylenetetramine or DPT. This substance is one of the intermediate products in the nitrolysis of urotropine and can be a precursor
for both HMX and RDX. The use of pre-prepared DPT for the synthesis of these nitramines allows to reduce the consumption of nitric acid, but the
existing methods of obtaining DPT also require a significant consumption of strong nitric and sulfuric acid.... All these methods, in one way or
another, are based on condensation of methyl nitramide derivatives with ammonia or methylolamines at pH from 3 to 5.5. Let us briefly review the known
methods:
1) The classical method is based on neutralization with ammonia of spent nitric acid after RDX production by nitrolysis of urotropine. Such acid
contains dissolved methyl derivatives of nitramide, but they are relatively few, so the yield of DPT is small. By changing the concentration of the
initial nitric acid and the modulus towards reduction, it is possible to increase the yield of DPT (up to 60%) by several times at the expense of
reducing the yield of RDX.
2) The source of methyl derivatives of nitramide can be the solution obtained by dilution of the reaction mixture after treatment of DNU (urotropine
dinitrate) with concentrated sulfuric acid. Subsequent neutralization of such solutions gives DPT yields up to 30-33%.
3) As a source of nitramide for subsequent methylolysis and condensation in DPT it was proposed to use nitrourea. The method consists in dissolution
of nitrourea in formalin under heating, methylolysis and hydrolysis of carbamate group of urea occurs, further addition of ammonia solution leads to
the formation of DPT. The yield of the product by this method reaches 50-60%
4) Also as a source of nitramide can be used N,N'-dinitromourea, obtained by excess nitration of urea strong sulfur-nitrogen mixtures at temperatures
of about -20 ° C. Dinitromurea is much easier to hydrolyze than mono-nitromurea - heating is not required, nitramide is better preserved and
subsequent manipulations similar to item 3 give a yield of DPT up to 70%.
The disadvantages of these methods for home chemists:
Method 1 - requires nitric acid of concentration 85% and above, and it is not sold in chemical stores, obtaining it only by distillation ... in terms
of consumption of this component is obtained no more than 250g DPT with 1 liter of nitric acid (concentration >85%).
Method 2 - not high enough yield in relation to DNU, in addition, requires concentrated sulfuric acid, the consumption of reagents - 1 liter of
sulfuric acid (90%) and 720g DNU, the yield of DPT no more than 130g.
Method 3 - it is still required to prepare nitrourea, which is already a ready-made explosive, add to this the need to work with a large volume of
formalin, which although it can be replaced by urotropin, but even the calculation does not want to carry out ...
Method 4 - anhydrous nitric acid, oleum and low temperature are required to drive two nitro groups into urea.... no comment...
As can be seen from the above, synthesis of DPT by known methods for its use as a precursor for RDX and HMX is a luxury that few people can afford.
However, when studying this topic, a thought arose - why the possibility of using sulfamic acid (sold as descaler - Translator's note) as a source of
nitramide has not been investigated! The sulfogroup as an electrophile strongly enough knocks down the basicity of ammonia, so much so that it becomes
possible to put not one but two nitro groups on nitrogen (recall the synthesis of dinitramide). The sulfogroup can also be directly substituted on the
nitro group, for example, if there are substituents on the nitrogen instead of hydrogen - this is a fairly common technique for obtaining nitramines
(the same RDX by the method of "W" or some frame nitramines). In addition, in the literature there are references to a method of obtaining nitramide
from sulfamic acid directly, but the source is a very rare and old foreign journal and it is not possible to get it to know the details of the
process. Another, extremely interesting reference to the reaction of nitric and sulfamic acids was found in the literature: "nitrous oxide can be
obtained by heating a mixture of 65% nitric acid with sulfamic acid". What does the last quote mean!!! It means that nitramide is formed in this
reaction, since nitrous oxide is a direct product of its decomposition:
HNO3 + H2N-SO3H --> H2N-NO2 + H2SO4
H2N-NO2 --> N2O? + H2O
All this prompted me to start experiments in this direction. The first experiment gave a positive result - when adding sulfamic acid to a mixture of
56% nitric acid and DNU, it was possible to obtain DPT with a yield of 8% - not bad considering the concentration of nitric acid.... In further
experiments, nitric acid of higher concentrations was used, and the addition of concentrated sulfuric acid was used, resulting in more than 90% yield
of DPT. So, I will describe in more detail my experiments. First, it was necessary to choose approximate conditions for the transformation under
study. Here are the considerations that guided me:
1) temperature - it obviously should not exceed 45-50°C, so that the formed nitramide does not have time to decompose.... Plus about a year ago I
studied the reaction of sulfamic acid with urotropine in order to obtain the sulfo-analog of DPT (so-called DSPT, it was planned to nitrate it to HMX
instead of DPT), it was found that the reaction of sulfamic acid with urotropine is exothermic in nature and to let the temperature rise above 38-40
° C is highly undesirable, so this point will be the limit in further experiments.
2) Obviously, the higher the concentration of nitric acid, the higher the yield of nitramide.
3) The most convenient reagent for the formation of methyl derivatives of nitramide is urotropine, and in the light of point 2 it is more appropriate
to use its dinitrate (DNU).
4) the addition of concentrated sulfuric acid can be very useful, since the method of preparation of DPT via DNU and sulfuric acid is known (see
above).
5) neutralization of diluted reaction mixtures to pH 5-6 can be carried out by any alkaline agents, but the use of pure alkalis or their concentrated
solutions leads to a strong heating of the mixture, which may lead to decomposition of the formed product, so cooling is required.... It is much more
convenient to use ammonium/potassium/sodium carbonates or hydrogen carbonates, because when they are added to the acid, on the contrary, there is a
noticeable decrease in temperature, probably due to energy consumption for evaporation of carbon dioxide, plus there is a strong increase in the
evaporation surface of the liquid when foaming...
6) If sodium or potassium carbonates/hydrocarbonates/hydroxides have been chosen for neutralization, care must be taken to ensure that sufficient
ammonium ions are present in the system for successful DPT formation. Ammonium can be introduced in the form of sulfate/nitrate after diluting the
nitromass or, even better, when diluting the nitromass with an ice slurry prepared by freezing the ammonium sulfate/nitrate solutions.
Following is a report on the experiments performed.
Experiment #1. Confirmation of the possibility of formation of nitramide from sulfamic acid and dilute nitric acid and subsequent condensation of
products in DPT.
To 100ml of HNO3 (p.1.353g/mL or 53%) cooled to +10°, 50g of H2N-SO3H was added, no temperature rise was observed. After holding the mixture at
stirring and 10° for 30 minutes, 53g of DNU was added, and the temperature was held at 20° or less. After holding for 20 minutes, the reaction
mixture was heated to 30°, then external heating was stopped, but the temperature rise continued. After reaching 35-36°, a slight cooling to 30°
under running tap water was carried out. The temperature still slowly but surely continued to rise, and after the 35-37° point the mixture was again
cooled to 30-33° and so on until the temperature rise ceased. The reaction mixture was cooled to 15°, at which time it became more viscous. After
dilution with 300ml of cold water, neutralization with sodium hydrogen carbonate was carried out to pH=6, by the end of neutralization the solution
became cloudy and some fine precipitate was formed. After standing for 1 hour, the solution was filtered, the precipitate was washed first with water
and finally with isopropyl alcohol to facilitate drying. The mass of the dry product amounted to 3.5 g or ~8% of the theoretical one (assuming
formation of 1mol DPT from 1mol DNU). The character of combustion of the obtained sample did not differ from the reference DPT (obtained by the
classical method, has melting point = 200-201°C), the measured melting point was about 195-198°С.
Experiments #2 through #7. Increase the concentration of nitric acid, each experiment +5%.
In this series of experiments, I followed the methodology of experiment No. 1, the amount of nitric acid was taken 100ml, the amounts of sulfamic acid
and urotropin dinitrate are the same - 50g and 53g, respectively. The yield of DPT in this series of experiments increased: 6g (13%), 8.7g (20%),
13.5g (31%), 14.2g (32.5%), 15.6g (35.8%) and 16.4g (37%) for nitric acid concentrations of 60, 65, 70, 75, 80 and 85%, respectively. The quality of
DPT at the same rather high level – melting point of the obtained samples is in the range of 193-200°C.
As can be seen from experiments 2-7, there is no significant increase in the yield of DPT after increasing the concentration of nitric acid to 70-75%.
In this regard, it was decided to introduce the addition of sulfuric acid, and the amount of nitric acid to reduce by a factor of 2, because it was
taken a clear excess to avoid working with too thick mixtures, and sulfuric acid with its volume could compensate for this. It was also decided to
reduce by 2 times the amounts of DNU and sulfamic acid due to the obvious prediction of an increase in the yield of DPT. I will describe the most
significant experiments with sulfur-nitrogen nitrating mixtures.
Experiment #8. Concentration of nitric acid ~63% (pl.1.386g/mL).
In a mixture of 50ml of nitric acid and 35ml of sulfuric acid (92.5%, pl.1.825g/mL) cooled to 0°C, 25g of sulfamic acid was added with stirring, the
temperature rose to 5°C. After holding for 20 minutes at 0°C, 27g of DNU was started to be added in small portions with stirring and temperature not
exceeding 15°C. Next, the reaction mixture was allowed to stand for 40 minutes at 5-10°C without stopping stirring. Then the mixture was gently
heated to 30°C, then the heating was stopped, but the temperature continued to rise as in the previous experiments. Just as before, the temperature
was allowed several times to reach 38-42°C, periodically knocking it down to 35°C. When heat generation ceased (about an hour after heating to
30°C), the reaction mixture was cooled to 15°C, at which time it thickened and became similar to the reaction mixture when cooking PETN.... It was
then diluted 1 to 2 with ice-cold gruel prepared in advance by freezing a 10% solution of ammonium nitrate. This was followed by neutralization with
sodium hydrogen carbonate to pH~6, which produced quite a lot of precipitate, it was filtered, washed with water and isopropanol. After drying, the
mass of the precipitate was 14.2g or 65.1% of the theoretical mass (1mol DPT from 1mol DNU), and the melting point of this product was 194-198°C.
Experiment No. 9. Concentration of nitric acid 70% (pl.1.411g/mL). All manipulations are identical to experiment No. 8, but there are differences: the
amount of sulfuric acid reduced to 20ml; the reaction mixture after the stage of cessation of heat generation thickens to a state of porridge much
faster and when the temperature is reduced to 25-30°C. The yield of DPT in this experiment amounted to 21g or 96.3% of the theoretical (assuming the
formation of 1mol DPT from 1mol DNU). When reproducing this experiment two more times, the yield was 20 and 20.5g, i.e., consistently above 90%.
Melting point of the products obtained by this methodology in the range of 198°C.
Experiment No. 10. Concentration of nitric acid 99.5% (pl.1.511g/mL). In this experiment there is no stage of heating up to 35-40°C, due to the great
difficulty of temperature control after passing the 20-25°C mark - the first attempt ended with a fountain  . Quantities of reagents are also changed. To the mixture of 20ml of nitric acid and 50ml of sulfuric acid (92.5%)
cooled to -5°C, sulfamic acid in the amount of 35g was added with stirring. After holding for 20 minutes at -5°C, 53g of DNU was started in small
portions with stirring. The temperature increased by 5-8° after each portion (4g), each subsequent portion was introduced only after the mixture
cooled to 0-5°C. After the introduction of 2/3 of the amount of DNU, the temperature did not rise as fast, which allowed to accelerate the
introduction of DNU. Further the reaction mixture was kept for 1 hour at 8-10°C. The consistency of the reaction mass already a few minutes after the
introduction of DNU became a rather steep mush, so stirring was only intensified to avoid local overheating. Then the ice porridge (frozen AC
solution) was diluted 1 to 3 by volume. When the ice residue had melted, some mud remained in the mixture. To avoid clogging of the DPT with this
turbidity, the solution was filtered, the precipitate was washed and dried (precipitate No. 1). The mother liquor was neutralized with sodium
bicarbonate and the precipitate was filtered, washed and dried (precipitate #2). After drying it turned out that precipitate #1 (the obscure mud) is a
dirty RDX (!!!) and its mass is 3g - a nice bonus, however  ). The mass of
sludge #2 was 25g or 55.5% in terms of spent DNU. The purity of the obtained DPT was somewhat worse than in the experiments with lower concentrations
of HNO3 - this sample melted already at 188°C. The reason for the latter was probably excess DNU - it should have been taken less by a factor of 2. I
do not know what induced me to take as much as 53g, but I see no point in repeating the experiment and clarifying, since it uses 99.5% nitric acid.
Now a little bit about purification of DPT for those who previously managed to work up its appreciable amounts by the method with nitrourea. One of
the serious disadvantages of this method is the low quality of the product, it usually has a melting point no higher than 185°C and contains about
85% of DPT, the rest is tar-like condensation products of nitrourea that has not had time to hydrolyze. DPT can be cleaned up by recrystallization.
Since we could not find accurate data on the solubility of DPT in various solvents, we had to work by guesswork. In ethanol, isopropanol and acetone
solubility of DPT both at room temperature and when heated is very low and these solvents can be used when washing the raw product to facilitate its
further drying. In glacial acetic acid solubility at 25 ° C is about 3-5g per 100ml CH3COOH, at 50 ° C is already up to 10-12g per 100ml, further
heating is not recommended due to the decomposition of DPT (to the already wonderful vinegar odor begins to mix formaldehyde). The most suitable
solvent was DMSO (you can also try with DMFA, but I ran out of it). At room temperature in 100ml DMSO dissolves up to 6-7g DPT, when heated to
60-80°C can dissolve up to 15-18g DPT in 100ml DMSO, but at such temperatures there is a smell of formaldehyde, so 60-65°C - optimal. I carried out
recrystallization as follows: on 300ml DMSO took 70g DPT, gradually heated with stirring to 65 ° C, kept 5-10 minutes and sent to be filtered on
Buechner; undissolved DPT raked from the filter and threw back into the flask, and the filtrate cooled in a separate flask to room temperature,
crystallized in the form of the smallest (~0. 1-0.2mm) shiny crystals of DPT filtered on a separate filter; the filtrate was sent to the flask where
the original undissolved DPT was, again heated to 65°, filtered.... and such cycles in one day recrystallized 200 g of raw DPT. The crystalline DPT
collected on a separate filter was additionally washed with acetone to remove DMSO residues and facilitate further drying. The melting temperature of
the obtained product was set at 208-210°C.... In case of purification of the product obtained on nitrourea it is necessary to add crushed activated
carbon for adsorption of resinous impurities in the ratio of 1 mass parts of carbon per 10 mass parts of DPT. DPT, otherwise the polymer swollen in
DMSO will block the filter.
So, what do we have at the end of these experiments?! We have a simple and accessible for many of us method of preparation of DPT of good quality,
following which you can safely get up to 1kg of the desired substrate from 1L of sulfuric acid (see experience #9) and 2.5L of nitric acid 65-70%.
Immediately make a correction about 70% nitric acid - you need a concentration of 70%, because if you take 63% (it would seem a very small
difference), then the yield of the product becomes noticeably less, and the consumption of sulfuric acid is 1.65 times more (Experience № 8). At the
same time, I have only 92.5% sulfuric acid at my disposal, which means that if it is possible to use 98.2% sulfuric acid, it is possible to take
nitric acid of 65% concentration, i.e. the usual azeotrope from the chem-store, and not to dilute nitric acid of higher concentrations.
Notes: I admired my article and found a couple of missed points, important for practitioners - 1) DNU when introduced is very fond of clumping, so
throw it in small portions and stir very thoroughly, but in principle this is not a problem, because all the clumps of DNU, even the largest will
easily dissolve at 25-30 ° C, ie before the stage of heating. 2) thickening of the reaction mixture after the heating stage does not mean that it is
released DPT , it is a consequence of hydrolysis of urotropine, and DPT will be
formed only at the stage of neutralization. 3) neutralization is very convenient to carry out in an ordinary PET bottle, optimally, if the bottle is
filled with no more than 1/4 of the neutralized acid bourda - we pour a couple of spoonfuls of soda through a funnel, close the lid, shake it, drain
the gas, pour soda again. 4) DPT turns out to be very fine, so it is better to filter with vacuum, without the latter the process can take a very long
time... filter paper "yellow strip" was able to hold all the sediment well, no turbidity in the filtrate did not leak...»
Link to original article (Archived): http://web.archive.org/web/20160327092856/http://www.explode...
[Edited on 4-9-2023 by DennyDevHE77]
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
