Phosgene

Phosgene

Names
IUPAC name Carbonyl dichloride
Preferred IUPAC name Carbonyl dichloride
Other names Carbon dichloride oxide Carbon oxychloride CG Chloroformyl chloride Dichloroformaldehyde Dichloromethanal Dichloromethanone
Properties
Chemical formula	COCl2
Molar mass	98.92 g/mol
Appearance	Colorless gas
Odor	Suffocating, stale or fresh cut hay-like
Density	1.432 g/cm3 (0 °C, liquid) 4.248 g/L (15 °C, gas)
Melting point	−118 °C (−180 °F; 155 K)
Boiling point	8.3 °C (46.9 °F; 281.4 K)
Solubility in water	Reacts
Solubility	Reacts with alcohols, amines, carboxylic acids Soluble in glacial acetic acid, benzene, carbon tetrachloride, chloroform, dichloromethane, toluene
Vapor pressure	1.6 atm (20 °C)
Hazards
Safety data sheet	MathesonGas
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LC50 (Median concentration)	500 ppm (human, 1 min) 340 ppm (rat, 30 min) 438 ppm (mouse, 30 min) 243 ppm (rabbit, 30 min) 316 ppm (guinea pig, 30 min) 1022 ppm (dog, 20 min) 145 ppm (monkey, 1 min)
Related compounds
Related compounds	Formaldehyde Urea
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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 gas 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, there are several ways it can be made:

A simple and quick method is reacting carbon tetrachloride with sulfur trioxide or oleum, at temperatures between 100-120°C. Sulfuryl chloride is produced as side product.

CCl₄ + SO₃ → COCl₂ + SO₂Cl₂

Sulfur dioxide can also be used instead of sulfur trioxide, at 150 °C, under pressure. In this case, thionyl chloride will also be produced as side product.

CCl₄ + SO₂ → COCl₂ + SOCl₂

If an excess of sulfur dioxide is used, the resulting phosgene will react with it, and produce more thionyl chloride, with carbon dioxide as side product.

Industrially, phosgene is produced by reacting carbon monoxide with chlorine gas in a bed of porous activated carbon, at temperatures between 50-150 °C.

CO₂ + Cl₂ → COCl₂

If the temperature is over 200 °C, phosgene reverts to carbon monoxide and chlorine, so god temperature control is necessary for this reaction. 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.

CHCl₃ + ½ O₂ → COCl₂ + HCl

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 storing it for long time, which should be avoided.

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 that produces it.

Disposal

A base, such as calcium oxide or hydroxide, sodium bicarbonate or even ammonia, best mixed with water as solution or suspension 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
• Theoretical Synthesis of Phosgene
• Taming Phosgene