Picric-A
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Haloform reaction
Could a haloform reaction (eg. acetone + sodium hypochlorite --> chloroform) be used to chlorinang any neutral organic compound?
I was just thinking because this would be very usefull and save having to use elemental chlorine.
thanks,
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Nerro
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As far as I can remember there has to be a a methyl-group next to a CO group. The CO is converted to a COO- group.
#261501 +(11351)- [X]
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MagicJigPipe
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Apparently EtOH can be used, as well, so there need not be a Me-C=O group. Or did you mean a Me-C=O or a Me-CH2-OH group?
[Edited on 5-12-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
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JohnWW
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The usual industrial method of making chlorinated methanes is by direct reaction of CH4 with Cl2, in appropriate amounts with rapid mixing, with HCl
as byproduct, but even then the four chlorinated methanes need to be separated by distillation. I do not seem to be able to find a textbook reference
to it being prepared from CH3-C(=O)-CH3 + NaOCl, which is liable to produce chlorinated acetones, and possibly COCl2 (poisonous), as unwanted
byproducts, even if/when it works. Strangely enough, contrary to what the textbooks say, http://en.wikipedia.org/wiki/Chloroform and http://en.wikipedia.org/wiki/Haloform_reaction say that it can be produced by reaction of NaOCl or of "chloride of lime", Ca(OCl)2, with
CH3-C(=O)-CH3 or CH3-CH(OH)-CH3. The Haloform Reaction process is industrially obsolete for CHCl3, but is still used for CHBr3 and CHI3, and for
production of deuterated CHCl3.
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MagicJigPipe
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It does work. I've heard it was the main industrial method for producing chloroform. A long time ago...
Plus, I've done it before. It certainly produces chloroform. However, I don't know exactly what byproducts are formed and in what quantity.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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woelen
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This reaction almost exclusively produces chloroform if done under the right conditions. There is a lot info already about this reaction on
sciencemadness. It also is a very specific reaction and is not useful for general chlorination purposes.
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Klute
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I'm under the impression that by "haloform reaction", the poster simply means aq. hypochlorite to chlorinate a "neutral organic compound".
The conditions needed to chlorinate a compound vary enormously depending on the nature of the compound. In certain instance, aq. hypochlorite cna be
used at RT or lower (chlorination of thiols, disulfides and alkylthiosulfates to sulfonyl chlrides for example), but in other case gas Cl2 is needed
in anhydrous conditions and reflux temps (chlorination of toluene for example).
Most of the time, if elemental chlorine is used, it's for a good reason. It can be substitued by SO2Cl2 in certain case, like in certain
chlorinations of an activated phenyl ring.
I think the question is too vague to be answered correctly, I doubt the poster was simply asking if the haloform reaction can be sued to make
chloroform,a s this is a very well known fact, very documented here and elsewhere. Or did I get this wrong?
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chemrox
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@Klute - I got exactly the same sense of the question and indeed, "any neutral compound" could mean almost anything. I appreciate the desire to
learn. Please sharpen it up.
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smuv
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| Quote: |
Apparently EtOH can be used, as well, so there need not be a Me-C=O group |
Ethanol is oxidized under the reaction conditions to acetaldehyde, which has a methyl group attached to a carbonyl group, as well as alpha hydrogens
attached to the methyl group which can be abstracted under the reaction conditions; Everything which is necessary for the haloform. Only carbonyl
compounds can enter the haloform reaction; no alcohols.
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MagicJigPipe
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So, could 2-butanone be used to yield chloroform and sodium propionate? That would be a very useful salt!
Also, I was under the impression that EtOH could be used to make chloroform and sodium formate. I'm pretty sure I heard that on this very forum.
Perhaps ethanol is simply oxidized to acetone. But where would the carbon come from? I'm still a novice at reaction mechanisms.
[Edited on 5-15-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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BromicAcid
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Yes JigPipe, MEK can be used in a haloform reaction to give propionate. I think this was covered somewhere before somewhat exensively. Maybe in the
massive thread where people were trying to discern the byproducts of the haloform reaction.
Smuv above answers your other question.
[Edited on 5/15/2008 by BromicAcid]
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stygian
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Ethanol is oxidized to acetaldehyde, then chlorinated to trichloroacetaldehyde, which hydrolyses (is the the right word?) in base to give formate and
CHCl3
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MagicJigPipe
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Excellent, thanks! The only problem I can think of (in obtaining formic or propanoic acid) is that there will almost certainly still be some NaOH and
NaCl left in the solution. A mixture of HCl and formic or propanoic acid won't do me much good. I can't think of any way to thwart that...
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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woelen
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If you want the propionate pure (with the only impurity being water), then you can proceed as follows:
Mix the MEK with NaOH and bleach to get chloroform and propionate. Use excess bleach to be sure that all MEK is converted.
Next, add a pinch of a cobalt salt to the solution. This destroys any excess hypochlorite (conversion to chloride and oxygen, careful, solution may
froth over if the bleach is concentrated).
Then heat the liquid to drive off the chloroform. You could capture it if you are interested in this.
Now you have a solution with the propionate and a lot of other crap. To this, add an excess amount of sulphuric acid, such that the solution is fairly
acidic (pH = 2 or something like that). Now heat till almost dryness. What comes over is water with propionic acid. In this way you get a dilute
solution of propionic acid. This dilute solution then can be neutralized with NaOH and evaporated to dryness.
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MagicJigPipe
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Too bad the only cobalt "salt" I have is impure cobalt(?) oxide. Would this work? Is it simply the cobalt cation that does this?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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S.C. Wack
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| Quote: | Originally posted by MagicJigPipe
A mixture of HCl and formic or propanoic acid won't do me much good. I can't think of any way to thwart that... |
Propionic acid can be salted out. Some people use organic solvents to extract organics.
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not_important
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Combining several of the above posts - if you use Ca(OCl)2 as the hypochlorite source, distill off the CGCl3 and evaporate the remainder, and finally
liberate the carboxylic acid with concentrated hydrochloric acid, you should get an aqueous layer that is saturated with CaCl2 and may even contain
solid hydrate CaCl2, plus an organic layer that contains the carboxylic acid plus a little water. But you'll always need to distill the product.
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Formatik
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Just make sure to use wet reactants with the ethanol. Adding ethanol to dry Ca(OCl)2 gets a vigorous reaction, and distilling a yellow-green oil which
explodes when heated or put into light, most likley ethyl hypochlorite, as mentioned in Beilstein 1, p. 223. Distilling ethanol with water-containing
Ca(OCl)2 gets the chloroform.
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