angelhair
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Cleaning DCM/Chloroform
Can you use HCl to purify DCM and chloroform instead of H2SO4. Any disadvantages other than volume needed?
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Klute
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I don't think it will work as well. The conc H2SO4 is much more agressive towards organics than is HCL: it has a strong deshydration potential. Try
conc. phosphoric acid instead; I guess you will be able remove some impurities with HCl, depends what you've got in there. I would sugest washing with
a ice cold conc NaOH solution, then water and brine, drying and carefully fractionnating over CaCl2.
Or reflux and distill over P2O5 after having washed and pre-dried.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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vulture
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| Quote: |
I would sugest washing with a ice cold conc NaOH solution, then water and brine, drying and carefully fractionnating over CaCl2.
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Chloroform and strong bases are not compatible.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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chemrox
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What part of the world are you in? In the US you can buy technical H2SO4 cheap at the hardware store. Plumbing section - called drain cleaner. It's
usually a little off color but works fine for most things. Acid catalyzed biodiesel for example. Chromic acid solutions... "and many many more.."
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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grind
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| Quote: | Originally posted by vulture
Chloroform and strong bases are not compatible. |
This is only partially true. Pure CHCl3 is not attacked by bases such as conc. NaOH solution. Only in the presence of special substances like alkenes
a reaction can occur.
It is absolutely no problem to wash CHCl3 with a warm conc. NaOH-solution.
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BromicAcid
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I would think that conc NaOH is going to give some carbenes with chloroform whether or not there are alkenes/ketones/etc around to tie them up. I was
under the impression that it was when chloform comes into contact with solid NaOH that you get large amounts of carbene formation but some would form
from contact with just a NaOH solution, there is no need for a substrate to be there. With ammonia and sodium hydroxide you'd create some cyanides,
another case where strong bases and chloroform are incompatible.
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Klute
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I have already washed some "dirty" chloroform with cold 30% NaOH solution, and even if there was some carbene generated, it didn't cause any
problems.. That's why I used ice-cold NaOH, and washed with water just after. I mean, in most reactions generating carbene from CHCl3 and NaOH, solid
or concentrated NaOH is used at reflux for several hours.. or at least extended periods of time. I think the amount produced by washing for 10-15secs
at 10°C wouldn't be very problematic.
If one is really concerned about that, washing with conc. H3PO4, water, drying over CaCl2 and carefull fractionnation should do the trick.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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smuv
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This was recently posted somewhere in these forums; it is a nice overview of the hydrolysis of the various chloromethanes.
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grind
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| Quote: | Originally posted by Klute
I have already washed some "dirty" chloroform with cold 30% NaOH solution, and even if there was some carbene generated, it didn't cause any problems.
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I did the same without problems.
| Quote: | Originally posted by Klute
I mean, in most reactions generating carbene from CHCl3 and NaOH, solid or concentrated NaOH is used at reflux for several hours
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Such reactions were often accelerated by use of a phase transfer catalyst, absence of such a PTC is a further barrier for extensive decomposition of
CHCl3 with bases.
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vulture
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Conc. NaOH solution is not the same as 30%, be specific. Distilling chloroform over NaOH or leaving it in contact with it for prolonged periods will
get you into trouble. It's not because carbenes didn't cause any problems with your specific application that it's good practice.
[Edited on 10-5-2008 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Klute
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Yes, I should have specified. I guess 50% NaOH would have a more marked effect. On the other hand, I never mentionned distilling over NaOH, nor that
the two are generally compatible. just that a short ice-cold wash isn't a problem, in my opinion, and would be much more effective than a conc. HCl
wash.
You are right to insist on the possible degradation though, I understand someone can take it for granted that ChCl3 won't react with NaOH after
reading that it can be washed with a such a solution.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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angelhair
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I used a techical H2SO4, slightly brown to clean some Pet ether that I distilled from petrol and it left the ether coloured yellow as apposed to AR
H2SO4. So I'm not sure I want to use the brown stuff on DCM.
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The_Davster
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Carbenes? I was under the impression that NaOH solutions and chloroform would give sodium formate, which was an experiment I read about in an old
experimental chemistry manual at one point. I got as far as dissolving the chloroform in conc. NaOH, but I never worked it up.
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Klute
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Angelhair, as long as your fractionnate your washed DCM afterwards, those dyes won't be problematic. In any case fractionnation is the minium to
purify IMHO. Conc. H2SO4 removes any traces of alcohols,formaldehyde, amines and volatil other compounds that could get through distn, I'm refering
to recycling DCM used in extractions and such more specifically.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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vulture
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| Quote: |
On the other hand, I never mentionned distilling over NaOH, nor that the two are generally compatible. |
You didn't mention that indeed, I'm just mentioning it because someone might have the idea to distill it over NaOH to clean and dry it in one go.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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