Difference between revisions of "Phosgene"

Revision as of 17:34, 26 May 2016

Phosgene, or carbonyl chloride, is a very toxic gas with a formula of COCl₂.

Properties

Physical

Phosgene is an easily liquefied colorless gas with a smell that is often described as either freshly mown or stale hay.

Chemical

Phosgene is not very stable. It reacts with water, forming carbon dioxide and hydrochloric acid. However, one must remember that this reaction is slow, which makes water a very ineffective phosgene scrubber! It is also quite reactive with various organic substances, which makes phosgene an important industrial chemical and precursor to things like plastics. Heat causes phosgene to decompose into carbon monoxide and chlorine.

Availability

Phosgene is sold in cylinders. However, given its extreme toxicity, organizations do not sell it to home chemists.

Phosgene is listed on schedule 3 of the Chemical Weapons Convention and all production sites manufacturing more than 30 tonnes per year are to be declared to the OPCW.

Preparation

Seriously, if you want to prepare phosgene, reconsider. It is an extremely potent choking agent. Death from phosgene is slow, messy and not pretty at all.

But if you absolutely want to know, it can be made by reacting carbon tetrachloride with sulfur trioxide or oleum.

Industrially it is produced by reacting carbon monoxide with chlorine gas in a bed of porous activated carbon, between 50-150 °C. If the temperature is over 200 °C, phosgene reverts to carbon monoxide and chlorine. Needless to say, this process is too dangerous for the amateur chemist.

Phosgene is accidentally produced when chloroform is left unprotected in contact with air, more vigorously under UV light. This is undesired when storing and using chloroform, so a stabilizer, such as ethanol, is usually added to prevent the formation of phosgene. This is actually the source of phosgene's name: it means "generated by light" in Greek. It has nothing to do with phosphorus except being derived from the same root.

If you're crazy enough to synthesize phosgene, you must do it in a glovebox, to prevent any phosgene from leaking in the room and poison you. Keep a neutralizing agent, such as base in the glovebox to neutralize the vapors and later wash or scrub the inner atmosphere. Try to use it immediately after synthesis, as it's too risky to avoid storing it for long time.

Projects

Do something else! But if you're crazy enough:

• Make polycarbonates
• Make carbonate esters (propylene carbonate e.g.)

Handling

Safety

Phosgene is an extremely powerful choking agent, powerful enough to be used as a chemical weapon. The lethal dose is 0.01-0.03 g/l. There is no known antidote.

It is believed that one Sciencemadness member might have died from pulmonary edema that might of been caused by phosgene, as in his last post he expressed his desire to try and make the said compound. However, this hasn't been officially confirmed.

If you're a smoker, it's a very good lab practice to chain-smoke when experimenting with phosgene. Even very small, otherwise undetectable amounts of phosgene in the air react with smoldering tobacco and change the taste of the smoke to something revoltingly bad. This should give you an early warning in case of a phosgene leak.

Storage

Don't store it! EVER! Even in industry it's generally consumed by the same plant it produces.

Disposal

A base, such as calcium oxide or hydroxide, sodium bicarbonate or even ammonia can be used to safely neutralize phosgene. The products are non-toxic and can be safely disposed of.

References

Relevant Sciencemadness threads

• Toxicity of phosgene