Sciencemadness Discussion Board

Mix of iodoform and hexamethylenetetramine

woelen - 30-9-2005 at 04:04

I just made some CHI3 (see thread on preparation of this compound) and while looking up some of its properties I found this:

1:1 mixtures with hexamethylenetetramine explode at 178 C.

Hexamethylenetetramine is another easy to obtain chem (and it can be prepared also easily from NH3 and CH2O as far as I remember).

Does anyone know of this explosive nature or even tried this? What would be the mechanism behind that? Formation of NI3 from the two different compounds, while they decompose?

I'm just posting this out of curiousity. Sometimes I stumble on remarkable reactions and this may be one of them.

Axt - 30-9-2005 at 21:13

Where'd you source that from? Bretherick words it a slightly, but significantly different.
Quote:
The 1:1 addition complex exploded at 178°C.

Ref: Giftige und Explosive Substanzen, Sorbe, G., Frankfurt, Umschau Verlag, 1968


It seems that its not a simple physical mixture, rather forming a complex. "Exploded" is quite a general term, whether it exploded unconfined with violence, or simply popped a sealed container upon heating can't be determined by the reference. It is an odd one though.

From PATR2700
Quote:
There is considerable confusion in the literature whether iodoform is an explosive. Beilstein (Ref 1), Sax (Ref 2), and CA 1947– 1971 do not mention any explosive properties. Ref 3 states that iodoform decomps violently at 400°F. Friction makes a mixt of CHI3+AgNO3 decomp explosively (Ref 1)

Refs: 1) Beil , 73, (18), (19), [38], {102} & <97>
2) Sax (1968), 840-R
3) CondChemDict (1971), 473-L


And on topic,
Quote:
Solutions containing hexamethylenetetramine and iodoform or bromo-form do not show any tendency to deposit mixed crystals when the solvent is evaporated. This may be due to the attraction of the "active" hydrogen atom towards amino nitrogen. A solid 1:1 hexamethylenetetramine-iodoform adduct has been prepared and its crystal structure determined. In this crystal (Fig.4) every acceptor molecule is tetrahedrally linked to four neighbouring donor nitrogen atoms by three I-N bonds (2.94 Å long) and to a fourth nitrogen atom via the CH hydrogen atom. <b>The C(H)-N distance is only 3.21 A and the bond appears therefore to be energetically of some importance</b>.

Ref: Hassel, O. "Structural aspects of interatomic charge-transfer bonding", Nobel Lecture, June 9, 1970 <a href="http://nobelprize.org/chemistry/laureates/1969/hassel-lecture.pdf">[online]</a>


[Edited on 1-10-2005 by Axt]

chemoleo - 1-10-2005 at 06:31

That's fascinating.
I had no idea that for instance Br2 can also form a crystallisable complex with 1,4 dioxane, or that iodoform can do the same with dioxane. THe writer even points out that such stable complex formation could help in chemical separations...

Anyway, Woelen, since you recently made iodoform, did you test it yet?

woelen - 7-10-2005 at 05:47

No, I did not yet test it. I first need to make a setup, such that the (possible) explosion does no harm. I don't want glass or ceramics flying around my ears :D .

What, if I try with 100 mg of each, very finely grounded and mixed thoroughly AFTER grinding? How violent would such an explosion be?

garage chemist - 7-10-2005 at 06:35

I ground approximately equal amounts of iodoform and hexamine together (a pinhead sized amount each) until it were a homogenous fine powder.

On heating on a spatula over a bunsen flame, it partially melted, became black and released a noxious smell. There was absolutely no observable exothermic reaction.
On touching a new portion with a flame, the same thing happened.

The mixture is as energetic as a dead dog.
I have no idea how the stated energetic properties have been observed.

If energetic properties exist, then only for the adduct and not for the mixture.

woelen - 8-10-2005 at 09:14

I also did the experiment with 50 mg of each of the chems. I first did the test by heating over a flame, without direct flame contact, and that resulted in formation of purple iodine vapor, some brown vapors and a kind of black crap remained.

I also did the experiment by blowing the flame of a propane torch directly onto a finely ground and carefully mixed mixture of both chems, again 50 mg each. Now, I obtained some smouldering, but no energetic reaction.

So, the mix indeed cannot be regarded as energetic.

Joeychemist - 8-10-2005 at 11:39

Quote:
Originally posted by woelen
So, the mix indeed cannot be regarded as energetic.


I have never seen anyone give up so quick as you just have. :P

Try warming the sample to its melting point and allowing it to then cool to room temperature, then place the sample on an anvil or similar piece of steel and strike it very hard with a hammer. If the sample is explosive a good heavy blow should detonate it.

Axt - 8-10-2005 at 12:51

Umm, yuh. How about someone read the second post down. The adduct having a stressed bond seems to be the source of the instability, this you wont get from simply mixing/melting. So find a solvent which isnt stated in the article but possibly DCM, methanol or better chloroform if it remains inert. Dissolve iodoform & hexamine, evaporate out then try igniting or heating on a spoon.

[Edited on 8-10-2005 by Axt]

woelen - 11-10-2005 at 01:51

Quote:
Try warming the sample to its melting point and allowing it to then cool to room temperature, then place the sample on an anvil or similar piece of steel and strike it very hard with a hammer. If the sample is explosive a good heavy blow should detonate it.

I have actually thought of this, but this does not work. Both iodoform and hexamine decompose when heated. Even well below the iodoform melts, it becomes brown/red and it looses iodine already. I did an experiment with heating iodoform (look at my website).

I tried the suggestion of Axt. I proceeded as follows:

1) Dissolve 1 small spatula of CHI3 in appr. 1 ml of chloroform. This gives a clear and bright yellow solution.
2) Dissolve 1 spatula of hexamine in appr. 1 ml of chloroform. This gives a colorless solution. The hexamine dissolves in it quite well, better than I expected.
3) Mix both solutions. A very fine white crystalline solid is formed, the solution remains light yellow. It looks as if the hexamine precipitates out of solution again and the iodoform remains in solution. Of course, the precipitate may also be the adduct.
4) Evaporate all to dryness (liquid + precipitate). Result is a pale yellow solid with some brighter yellow rims in the test tube.
5) When all CHCl3 has evaporated, heat carefully, but stronger, over a flame. This results in decomposition. A thick yellow/brown smoke is formed, I think it is a dirty mix of decomposition products of hexamine, hydrogen iodide and iodine, which has a brown smoky appearance. No energetic reaction could be observed, just a (fairly quick) decomposition with brown smoke and black stuff (impure carbon?) left behind. The decomposition was not self-sustaining and only, where the test tube was in the flame, the decomposition could be observed.

I did just a quick experiment. The experiment gives evidence for my first conclusion that no energetic compound is formed, but it might be that the conditions were not completely right, amounts were not in the correct ratio, etc. But I'm inclined to believe that indeed CHI3/hexamine is as energetic as a dead dog as garage chemist suggested.

[Edited on 11-10-2005 by woelen]

Axt - 16-11-2005 at 19:38

For what its worth, heres the Sorbe reference, the wording does seem to imply some vehemence to the explosion, I guess if your keen enough you could try iodopicrin:

<img src="http://scimadpic.webtop100.net/images/sorbe-hexamine-iodoform.jpg">

And another related complex, from Bretherick:

<img src="http://scimadpic.webtop100.net/images/hexamine-iodine.jpg">

[Edited on 17-11-2005 by Axt]