mycotheologist
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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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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.
"In the end the proud scientist or philosopher who cannot be bothered to make his thought accessible has no choice but to retire to the heights in
which dwell the Great Misunderstood and the Great Ignored, there to rail in Olympic superiority at the folly of mankind." - Reginald Kapp.
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mycotheologist
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Yeah I suppose dissolved oxygen in the water would be far less of a threat than atmospheric oxygen.
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bbartlog
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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]
The less you bet, the more you lose when you win.
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mycotheologist
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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.
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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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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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