Practical Considerations for Phosgene Oxime

[MrSamosa]

This is according to the US Patent for the synthesis of Phosgene Oxime from Chloropicrin. Unfortunately, I don't remebmer the patent number and have too little time on this computer to look it up.

The general synthesis is as follows: Chloropicrin is dissolved in an Aprotic Solvent, treated with dry HCl, and reduced with powdered Tin. I may be a bit off, but please correct me where I'm wrong.

Anyhow, here are the sources I've found for the precursors:

Chloropicrin- most simply produced from the reaction between Nitromethane and Sodium Hypochlorite.

Aprotic Solvent- the most easily obtained will be Tetrahydrofuran, which is PVC solvent.

Dry HCl- efficiently and easily produced by adding concentrated sulfuric acid to Hydrochloric acid.

Tin- some Solder, especially the ones with reduced lead, contain even 90% Tin (some even more Tin, but i can't remember specific percentages). I suppose these could easily be powderized in a ball mill or by some other means...

The most difficult thing, it seems, would be storage. Not only is Phosgene Oxime extremely vicious towards the skin, but also towards anything that tries to contain it! It corrodes glass, metals, and rubber. So- that is the trick. What would be the easiest way to store Phosgene Oxime?

Also, what about ideas for weaponization? Would it best be dispersed as a fine powder, to slip through protective clothing? Or dissolved in some solvent, to be easily inhaled? One obvious idea would be to combine it with other chemical agents that are less violent towards the skin, thus increasing their potency. On skin contact, Phosgene Oxime causes vomiting- which prompts the person to remove the gas mask to prevent drowning. Therefore, on removal of the gas mask, they become susceptible to the other chemical agent.

Sorry for the fragmented post, but I really do not have much time. <img border="0" title="" alt="[Frown]" src="frown.gif" />

[Mr Cool]

Phosgene oxime is hideously nasty, but IIRC there's some reson why it was never used... polymerisation or something I think.
I don't know how you could store it etc (the first thing I'd try would be PTFE, PVC etc. Highly halogenated polymers), but I do have a hint on how to powder tin (the least difficult bit of the whole procedure..)!
It changes crystal form at a hundred and something degrees I think, commonly refered to as "tin pest". After this temperature, it becomes brittle and would therefore easily be powdered. I don't think you'd have much luck otherwise, it'd be like trying to powder lead.
Although I can't see why iron, zinc etc couldn't be used too.
H₂SO₄ and NaCl would be a better way to make dry HCl.
I haven't read the patent, but are you sure the HCl comes before the reduction? I can't think how it would react with chloropicrin.

[a_bab]

The tin pest occures at LOW temperatures, below 0 degrees C. Zn is a metal that could be powdered at 200 degress C as is becomes very brittle.
It is said that Napoleon lost a battle in Russia due to the tin pest !

[MrSamosa]

I know that one of the hazards with Chloropicrin is its reduction to Phosgene Oxime. This reductions works best in acid environments. Therefore, I think it would seem logical to add HCl first, to lower the pH of the solution. The tin, iron, or zinc would then be used to reduce the Chloropicrin to Phosgene Oxime.

This procedure is very simple, and I'm quite tempted to try it. I don't predict that the equipment used in the actual synthesis will be difficult to come by or particularly expensive. The only thing that is stopping me from testing this synthesis is trying to store it. Oh well- it's not something I'd want to be found with anyway, so if I ever do try it, I will most likely do some quick tests on it and then get rid of it...I don't feel like going to Guantanamo Bay <img border="0" title="" alt="[Wink]" src="wink.gif" /> .

The reaction to produce HCl could be carried out in a corked beer bottle with icemaker tubing through the cork. The other end of the tubing would go to the reaction vessel containing the Chloropicrin dissolved in THF.

Adding the metal will be very easy, and the finding the proper reaction times will also be rather simple. You would be looking out for a color change (I can't remember if it's blue or gray upon addition of the Tin, and then changes color to blue or gray during the reaction).

[Polverone]

THF is kind of a pain to obtain in pure form from pipe glue solvents, which typically contain a mixture of materials. But if you've found a particular source that you know is pure, by all means use it. In the U.S. I think the most easily obtained aprotic solvent is DMSO, which is often sold in smaller pharmacies, "alternative health" stores, and farm supply stores (for use on livestock). The stuff sold in pharmacies is very pure, though it will cost more than if you just buy it from a chemical company as lab or technical grade. I don't imagine you need much solvent in any case.

[Machiavelli]

Nitromethan to chloropicrin: US2365981
Chloropicrin to dichloroformoxime: US4558160
Chloropicrin to dichloroformoxime electrochemical: US2918418

They point out that everything should be anhydrous, so you should distill your solvent over a large amount of NaOH pellets and you should dry the HCl, too, maybe pass it through some silica gel or something.
The best yields were obtained using THF as the solvent. The reaction is bets carried out at -20°C-0°C.
In the example using THF they first cool down 400 ml of dried THF to 0°C, then bubble in 158.3 g of anhydrous HCl (measured by weighing the solution). 31.5 g of chloropicrin is added and then over a course of 2h15min 45.1 g of tin powder are added while maintaining 0°C.
Filtration and vacuum distillation yields 61.8% of the oxime.

FM 8-9 says:
"Phosgene oxime is a white crystalline powder. It melts between 39-40° C, and boils at 129° C.By the addition of certain compounds it is possible to liquify phosgene oxime at room temperature. It is fairly soluble in water and in organic solvents. In aqueous solution phosgene oxime is hydrolyses fairly rapidly, especially in the presence of alkali. It has a high vapour pressure, its odour is very unpleasant and irritating. Even as a dry solid, phosgene oxime decomposes spontaneously and has to be stored at low temperatures."

I think adsorbtion on silica would be good for weaponization, although I'm not sure, whether the free hydroxy groups in silica would promote hydrolysis.

[OUAGADOUGOU]

I know I'm a bit late but I just came across this thread.
I dont remember wether the optimal mesh size of the tin is mentioned in the patent, but I guess that the smaller the better. In my oppinion it is quite difficult to get the optimally small size with mechanical grinding. Oxide formation on the surface of the metal catalyst wuld also decrease efficeancy. When ground at high temperatures oxidation would be even more seveare. For such reduction metal catalysts it is quite essential for the metal to be in the reduced state (mostly this is accomplished by hidrogenation).
My suggestion for the prepn' of the substantially reduced tin catalyst would be to reduce it from a Sn salt solution (Sn2+)
Aluminium (foil) would be the optimal reducer. Prepare an aquaeous solution of SnCl2 or SnSO4, add Al foil in small peeces and drip a little HCl sol. to remove the oxide lyer of the Al. Metallyc Sn will form on the surface of the Al via methasthesis.

Sn salts can be obtained quite easily i guess. Or can be prepared by dissolving Sn in an acid. Tin reacts w/ HCl only wery slowly, so H2SO4 should be used (SO3 / SO2 are formed).