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Author: Subject: How fast does chloroform decompose into phosgene
mycotheologist
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[*] posted on 22-5-2012 at 08:36
How fast does chloroform decompose into phosgene


I've been making chloroform in 20mL batches and after decanting the water, I add the crude chloroform/water mixture to an Erlenmeyer flask. I intend on distilling the CCl3 but I got lazy and have left this mixture there for about 3 weeks in total now. The flask is wrapped in tin foil to keep out the light but I'm guessing water makes the decomposition more likely. What is the probability that dangerous amounts of phosgene will form in a matter of weeks like this?

Also, is the smell of phosgene easy to tell apart from chloroform? In other words, will I know if there is phosgene present before it kills me? I read that its an insidious gas but don't know if its quite as insidious as CO. If it has an odour, then at least you can get some form of warning before its too late.

[Edited on 22-5-2012 by mycotheologist]
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DDTea
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[*] posted on 22-5-2012 at 12:35


Phosgene has a distinct smell that is very different from chloroform. "Musty hay" versus the sweet paint thinner smell of chloroform. A single whiff is unlikely to seriously injure you.

Water probably doesn't affect the decomposition. It's a radical reaction between chloroform and atmospheric oxygen. Take this statement with a grain of salt because I'm having a hard time finding the mechanism for this reaction. I'll probably put my foot right in my mouth.




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mycotheologist
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[*] posted on 22-5-2012 at 15:03


Yeah I suppose dissolved oxygen in the water would be far less of a threat than atmospheric oxygen.
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[*] posted on 23-5-2012 at 06:13


As I recall you need both light and oxygen to get phosgene this way. Also, water will decompose phosgene rather more rapidly than you could produce it this way. I wouldn't worry about it. If you carefully dry your chloroform and then leave it exposed to both sun and air while keeping it cold, then it might be time to take some precautions.

[Edited on 23-5-2012 by bbartlog]




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mycotheologist
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[*] posted on 23-5-2012 at 09:00


Quote: Originally posted by bbartlog  
As I recall you need both light and oxygen to get phosgene this way. Also, water will decompose phosgene rather more rapidly than you could produce it this way. I wouldn't worry about it. If you carefully dry your chloroform and then leave it exposed to both sun and air while keeping it cold, then it might be time to take some precautions.


Thanks. That puts my mind to rest. I couldn't find the mechanism of the reaction myself either, all I know is its a autooxidation involving a free radical intermediate. I doubt homolysis can occur with the C-Cl bond, so I'm guessing O2 homolyses.
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BromicAcid
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[*] posted on 23-5-2012 at 14:11


Even in amber glass bottles where you would expect exposure to light to be minimal significant quantities of phosgene can be generated over time with repeated opening of the bottle. Water I would expect could expedite the process as postulated above by acting as reserve of dissolved oxygen. One might expect phosgene formed then to react with the water forming CO2/HCl however hydrolysis is markedly slow, much slower than most expect and is made even slower (or perhaps non-existant) by acidic water.

I remember recently reading the article below, I thought to find it again after reading that your mind was put at ease:

http://www.bnl.gov/esh/shsd/programs/Program_Area_Chemicals_...

Additionally, a mixture of phosgene/chloroform is not as easy to distinguish as DDTea suspects, although the smell of phosgene is often described as musty hay it has a certain sweet quality to it that I suspect would blend quite well with the chloroform.




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