innervision
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Stabilizing trichloromethane
I hear repeatedly that 1 percent methanol or ethanol added to trichloromethane is used to stabilize it. Can isopropanol also be used because that is
all I have that is pure?
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BromicAcid
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The mechanism behind the stabilization is the formation of the alkyl carbonate from the alcohol and the phosgene formed instead of allowing the free
phosgene to accumulate. I don't see any problem using isopropyl alcohol instead of methanol or ethanol off the top of my head.
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innervision
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Yep, you're right.
Interestingly, I ran into a source that said isopropanol and phosgene creates the isopropyl chloroformate and HCl like you said (before reacting to
form CO3), and that at temperatures slightly above ambient isopropyl chloroformate can decompose explosively in
the presence of iron salts.
Even more interesting... a chemical safety card for isopropyl chloroformate said that "The substance decomposes on heating or on contact with acids
producing toxic and corrosive fumes including chlorine and phosgene."
Now if phosgene converts IPA into isopropyl chloroformate and HCl, and isopropyl chloroformate decomposes on contact with acids to Cl and phosgene,
then doesn't that defeat the purpose of the stabilizer just a little?
[Edited on 9-2-2006 by innervision]
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garage chemist
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An MSDS is the worst source of reaction data that you can get.
An MSDS lists the reaction products that MIGHT be produced in EXTREME CASES, like in accidents and fires and when very large amounts of product are
involved.
I hate MSDSs, or "chemical safety cards", like they are also called. Most people interpret them entirely wrong. There was a case when someone who read
a MSDS for ethyl bromide thought that ethyl bromide and water vapor would react violently, which is bullshit, of course.
Again: Do not take reactivity information out of MSDSs.
Isopropanol is a good stabilizer for chloroform, and it will react with produced phosgene to form diisopropyl carbonate and HCl.
[Edited on 9-2-2006 by garage chemist]
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Magpie
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The only pure alcohol that I have is likely methanol from the OTC products (HEET) used to prevent automobile fuel line freezeups.
What ratio of methanol to cholorform (v/v) is recommended for stabilization? What happens if I don't add anything? Is there enough phosgene formed
to be a problem?
[Edited on 9-2-2006 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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garage chemist
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Most likely not, if the chloroform is stored in a brown glass bottle.
With a clear glas bottle phosgene accumulation can actually become an acute health hazard if the chloroform is handled outside a fume hood.
I have 500ml of ca. two year old chloroform, to which I added 1% (vol.) of ethanol as I received it.
I recently tested for presence of phosgene by shaking with AgNO3 solution, and the test was absolutely negative. Not the slightest hint of cloudiness
in the AgNO3 (phosgene would produce an AgCl precipitate because of hydrolysis and HCl formation).
This also means that no HCl was present in the chloroform, which is very remarkable. It seems that ethanol does not only react with already formed
phosgene, but also prevents its formation efficiently.
1% ethanol and brown glass bottle are fine for long storage of chloroform.
Methanol should work equally well, although I don't recommend it since if you want to chlorinate your chloroform to CCl4 the methanol will be
partially converted to the extremely carcinogenic bis(chloromethyl)ether.
Anyway, for CCl4 production, why don't you start from your dichloromethane, from which you have plenty? No need to waste your chloroform on this.
Oh, I see, it's because of its methanol content. That's a problem, of course.
Maybe adding a quantity of anhydrous CaCl2 will remove it, it forms alcoholates as well as hydrates.
[Edited on 9-2-2006 by garage chemist]
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innervision
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Thanks for the heads up. I'll keep an eye out for those MSDSs then 
I have mine stored in a clear glass vial that is tightly wrapped in brown gummed packaging tape. I slide it out when I need it. I'm assuming that is
ok, but eventually i'll get some amber bottles.
Maybe that non-phosgenation, CO3ination, HClination (?!) was due to fantastic storage? Maybe you should try an experiment with the stabilized
chloroform in a clear bottle out in the open and then test again after a few days...
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Magpie
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GC, you are right about I shouldn't waste chloroform as I can only make it at about 10 mL at a time  (you have to love organic chemistry).
The reason I was going to start with chloroform vs DCM as I thought that this was the most direct way to end up with CCl4. I'm not sure how logical
this is.
I keep my chloroform in an amber glass bottle in a dark closet. I will do a test with my newly made AgNO3 to see if any has been converted to HCl.
Thanks for sharing that test with us. 
[Edited on 10-2-2006 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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mycotheologist
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Sorry to resurrect this thread, I just didn't want to start a new thread for this question. I like the idea of using EtOH or IPA as a stabilizer
because I have both those solvents but will adding 1% alcohol will significantly alter chloroforms solubility properties?
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AndersHoveland
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Also to mention, chloroform, although it is almost insoluble, nevertheless very slowly reacts with water. The half-life for the hydrolysis of
chloroform with water is 15 months at room temperature and a pH of 7.
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