HMTD synth.

[Helos]

I have some thought about HMTD that I will share.
First I begin with experiments I have done.

I did two batches with HMTD.

The first one used 50 ml of 20% H2O2 and 10g of Hexamine that was dissolved in the H2O2.
10ml of HCl 35 % was added.

After some hours the pH had raised from around pH 1 to pH 5! I added 5 more ml of HCl
35 %, after that the pH raised somewhat again (around pH 2) but as this value was lower than the one in the method with citric acid I didnt add more HCl.

After 24 hours the white crystals were washed well with water and after that mixed with acetone (to remove impurities) and filtered and washed.

Yield was surprisingly low, 6,1g. This means 41% of theoretical yield One mole of HMTA is converted in one mole of HMTD. (Calculate molar masses)

This should be the total reaction
3 H2O + 3 H2O2 + HMTA ====> HMTD + 2 NH3

The second synth. used 50 ml of 20% H2O2 and 10g of Hexamine that was dissolved in the H2O2.
18g of citric acid was also dissolved in the reaction vessel and the pH was checked.
I dont remember exactly but I think when I first cheked the pH was 2-3 and 24 hour later it was higher, maybe 3-4.

After 24 hours the white crystals were washed with water and after that mixed with acetone (to remove impurities) and filtered and washed.

Yield was 8,4g. This means 56% of theoretical yield.

With HCl the reaction seemed to be faster, in only minutes the first crystals formed and gave the solution a milky colour.

All liquid reactants was chilled in a fridge to around 5C, after that no more cooling was needed.

The reaction of HMTD is somewhat complicated.

[URL=http://www.roguesci.org/cgi-bin/ewforum/ultimatebb.cgi?ubb=get_topic;f=2;t=000441#000]http://www.roguesci.org/cgi-bin/ewforum/ultimatebb.cgi?ubb=get_topic;f=2;t=000441#000[/UR L]

In this thread I think an important misunderstanding is repeated over and over again. (Dont read this as critic)
This is that the HCl just acts as a catalyst but that it just affects the rate. This can also be understood like it doesnt matters which acid is used. This is not true, and reports of too much acid killing the reaction can also be read in the above thread.

Acid
C6H12N4 + 6 H2O ======> 4NH3 + 6CH2O

The acid is needed to catalyse the reaction, after that is done the acid becomes a problem. Ammonia is created and if there is to many H+ ions they will react with to much ammonia. In fact only half of the created ammonia is needed to create HMTD.

This is the next reaction (may be catalysed by acid)

6 HCHO + 3 H2O2 ==> 3 HO-CH2-O-O-CH2-OH

The third reaction is this:

3 HO-CH2-O-O-CH2-OH + 2 NH3 ==> HMTD + 3 H2O

Here the ammonia is needed to create HMTD. To little, and it will not be created.
Its important to understand that ammonia is created in the first step this synth, and needed in the last step.

In my experiments I showed that the pH raised very much when HCl was used(in fact almost all of the HCl must have been reacted with ammonia due to the change from pH 1 to pH 5)

Looking at the last reaction it seems very understandably that acid breaks down HMTD (therefore washing is very important, maybe the best is to even store HMTD with a pH higher than 7)

On the other side there is nothing that says that AP is more stable when it isnt in an acid environment. Here acid is needed for the reaction that creates AP in the last step and maybe acid even makes it more stable, just like the case is with H2O2.

The complicated thing with HMTD is that the reaction needs acid, but to much H+ ions will kill the ammonia. Therefore an organic acid that gives away their ions slowly (as they are reacted may be preferable. But as I see, a acid like HCl may also be used.

An organic acid a little bit stronger than citric is probably preferable.

But based on availability and cost many acids can be used.

I will not apologize for opening a new thread :)

Any comments!?

<small>[ March 23, 2003, 05:02 PM: Message edited by: Helos ]</small>

[rooster]

When using the HCl method, at pH 1 why not add some NH3 to make the reaction a bit less acidic? The ammonia would form an equilibrium with the ammonia: HCl + NH3 <==> NH4Cl, if I am not wrong, and the HMTA will have more NH3 to react with.

[Al Koholic]

I'd also be willing to bet that citric acid is desirable in the procudre because it is a tricarboxylic acid. The 3 pKa's are
pK1 = 3.128
pK2 = 4.716
pK3 = 6.396

The average of these...ie: the isoelectric point where the zwitterion is at its highest concentration is the average of the 3 = pI = 4.746
Interestingly, the pKa of good old acetic acid is 4.76. This acid would also likely be a good substitute for tricarboxylic acid due to the similar pKa and therefore similar affinity for protons.

Al

[simply RED]

According to you a mix of amonia, CH2O and H2O2 will give HMTD.
Try it to see if it really does!

[Helos]

No a mix of the mentioned chemicals will give HMTA!

NH3+CH2O-->HMTA.

But if you also add H202 (and probably an acid) you will theoretically come up with HMTD.

I think acid may be needed, but you will not need that much acid, the first step is done aldready.

It may be worth trying if someone has the chemichals available.

<small>[ March 28, 2003, 05:08 PM: Message edited by: Helos ]</small>

[metafractal]

SWIM just got back from producing a batch of HMTD, and thought of another minor benifit of using citric acid over HCl- citric acid reacts endothermically with water, whilst HCl reacts exothermically, so it is much easier to keep the temperature down. Using 20% H2O2, 18g citric acid, and 10g hexamine, there was no significant change in temperature throughout the reaction.

[rooster]

The word you were looking for is plastic foil.

Why not just follow mega's recipe? It always worked for me. Are you sure no ice or snow got in your beaker while tanding in the fridge? In mega's recipe, he says keep it AT 0 degrees after adding the acid.

Normally i would believe a slight difference in temperature, volume of reactants, and so on woldnt matter too much. Are you sure the tablet contains hexamine/methenamine?

I would try raising the temp some degrees and see if anything happens. Reactions tend to go faster at higher temps...

[Mr Cool]

Just leave it in a fridge, at about 5*C, for 24 hours. Cover the reaction to keep dust out. If nothing has formed after an extra 24 hours in the fridge, then throw it away.

[DBSP]

Just thought I'd remind you of a nother HMTD method that gives you a lot better yields. I posted a topic about this last summer, might still be arround.

Dissolve 10g HMTA in 50ml of glacial acetic acid, then add 25ml of 35% H2O2, let it stand for 5h at room temperature then filter the HMTD and neutralize it. Dry as usual.

I made a batch using this metod last saturday. I got 14g of dry HMTD +/-1g (inacurate scale). this means a yield of a minimum of 87% and max 100% and if scale would prove to give the right weight a 94% yield , theoretical yield from 10g HMTA is ~14,85g.

[Arthis]

Need the acetic acid really be glacial, or 75% would be alright ? What's the advantage of pure acid since your H2O2 is diluted anyway ?

[rooster]

Is there any specific reason you want to dissolve the HMTA in the (acetic) acid,m and not in the H2O2, as usual?

[DBSP]

I don't know very much about the rection itself nor why hex is added to acetic acid and not H2O2.

The swedish infomania files this prodedure comes from states that lower conc acid might cause the reaction to overheat and start to boil. I don't know if this is correct though.

What I do now is that this is the far best method of making HMTD I've tried, the yields are 90+% which must be concidered very good for HMTD. The text states yields of 70-80% of theoretical, I don't know why my yields are so good. The yield isn't increased by wax content that might be the case with ESBIT hexamine, my hex is >99,5% pure.

I would like to get a better scale with a 0,1g resolution instead of the 1g res. I have now. Would make things a bit easier when meassuring yields etc.

Has anyone else got the chems needed?, could you try it and see if you get the same result as I do?

[Anthony]

Icecool, my first guess would be that your 10 year old hexamine might be to blame!

[frogfot]

Can't the problem be that he never lets it react at room temp?
For me HMTD starts to form only when reaction mix is taken out from ice bath into room temp (after about 20 minutes soln becomes turbid). I then usually immerce it in water bath with room temp water since without it temp can rise to 30*C.
I use megas synth, though i let it sit in room temp for 24h (insted of 2h).

[IPN]

Something weird just happened..

I took 28g of HMTA, 100ml of 35% H2O2 and 40g of citric acid, first I added the HMTA to the H2O2 then I added the citric acid and left.
When I came back to check if anything had happened I noticed that the beaker where the reaction was going on was covered in some sticky yellow goo...

Does anyone know what happened?

EDIT: Ok, now I now what happened, this thread explained everything:
http://www.roguesci.org/theforum/showthread.php?s=&threadid=2227

[rp3o8]

I had a bad dream a while ago; I prepared HMTD using,

20g Hexamine
50ml 27% H2O2
20ml 30% HCl (IIRC the synthesis I followed called for 30ml)

I had the reaction vessel sitting in an ice bath for two hours with no problems. At this time the ice was getting low but I figured the water was enough to keep it cool for the rest of the reaction. I came back an hour latter to find a cloud of gas (HCl, and probably formaldehyde and ammonia) hovering around the ceiling from where the contents in the reaction vessel had boiled off.

I’m certain the cause was too much acid and improper temperature control; 10ml would have been plenty. The only impurities that I know of were the binder from the hexamine tablets.

Luckily, the small amount of HMTD that had formed did not detonate from the heat!

[Macgyver]

Originally posted by rp3o8
I had a bad dream a while ago; I prepared HMTD using,

20g Hexamine
50ml 27% H2O2
20ml 30% HCl (IIRC the synthesis I followed called for 30ml)

I had the reaction vessel sitting in an ice bath for two hours with no problems. At this time the ice was getting low but I figured the water was enough to keep it cool for the rest of the reaction. I came back an hour latter to find a cloud of gas (HCl, and probably formaldehyde and ammonia) hovering around the ceiling from where the contents in the reaction vessel had boiled off.

I’m certain the cause was too much acid and improper temperature control; 10ml would have been plenty. The only impurities that I know of were the binder from the hexamine tablets.

Luckily, the small amount of HMTD that had formed did not detonate from the heat!

I think that it's not just the amount of acid, you also used too strong acid....

I'd say that about 15% HCl solution should be okay.

But then again, for HMTD I really prefer 60-99% acetic acid, for HMTD production. I find it has much less potential for runaway reactions a few hours into the synthesis.

But beware of citric acid, using citric for HMTD *will* cause a runaway reaction unless proper temperature control is used throught the whole process. It's not a question about if, rather about when it's about to happen.

Also try to make HMTD in batches using around 10g of hexamine (HMTA), making bigger batches also increases the risk of runaway reactions.

[IPN]

But beware of citric acid, using citric for HMTD *will* cause a runaway reaction unless proper temperature control is used thought the whole process.

If you didn't know the reaction of citric acid with water is endothermic witch LOWERS temperature...
Also the strength of the HCL is not the problem IMO.

[nitriees]

I have make HMTD more than 20 times, used citric acid or HCL (30%) as catalyse.
The H2O2 i used is 50% in concentration.
By using HCL, the HMTD do not precipitate immediately, i need to wait for a while for it to form and once it start precipate out from the solution, the reaction is vigorous and difficult to control even in 0 degree celcius salted ice bath.
By using citric acid, it is more controlable, i add citric acid slowly until the reaction start, the HMTD start to precipitate from solution, wait for 2 hours for HMTD crystal to finish precipitate.
For my self, i prefer citric acid as catalyse because it is more controlable to reduce runaway reaction and no need to measure the quantity, just add until reaction start.

[Macgyver]

Originally posted by IPN
If you didn't know the reaction of citric acid with water is endothermic witch LOWERS temperature...
Also the strength of the HCL is not the problem IMO.

Yes, that is correct.

With water that is.

But I happen to have a friend who researched many different acids for HMTD synth, and he found out that citric acid was one of the ones most likely to cause runaway reactions when used for HMTD synth.

If you use acetic acid with a conc of 60% or above, you can simply mix everything and don't worry about runaway reactions.

If you use concentrated acid and also use too much, that is a surefire way to make sure things go wrong.

I usually use the following mix for HMTD:

10g HMTA
82 ml 60% Acetic Acid (50 ml if you have the 98-99% acid).
25 ml 35% H2O2

There are many ways to make it that work good, and I am not saying this is absolutely the best way. But it has worked reliable for me many times without any accidents or problems.