Sauron
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Alkyl chlorides, Bromides and Iodides
A member asked me for a very efficient prep for alkyl chlorides from alcohols.
This is the most efficient that I know. With modifications it can be used to prepare bromides and iodides.
I have posted it previously in a zip folder but that file is now corrupt so I have no compunction about reposting.
Astute readuers will note that+ the TCT-DMF adduct fails with NaI to give the alkyl iodides, but, that conversion using TCT and NaI is described in
Chem. Ind., 1416 (1971).
a paper I do not yet have at hand.
[Edited on 7-3-2008 by Sauron]
Attachment: TCTDMF.pdf (54kB)
This file has been downloaded 813 times
Sic gorgeamus a los subjectatus nunc.
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chemrox
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Thank you Sauron- I was looking for this in my files too. I have an alcohol I wish to make into a chloride and I'm wondering how this compares with
HCl/ZnCl in terms of yield and cost? I suppose the good of the order motive would lead to trying both approaches and reporting back.
"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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PHILOU Zrealone
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| Quote: | Originally posted by chemrox
Thank you Sauron- I was looking for this in my files too. I have an alcohol I wish to make into a chloride and I'm wondering how this compares with
HCl/ZnCl in terms of yield and cost? I suppose the good of the order motive would lead to trying both approaches and reporting back.
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I had the same question in mind, it would be good to compare...HX and Lewis acids vs the TCT method; although TCT method is interesting solution.
HX and Lewis acid:
-Cheap starting reactants, easy especially in the case of sec and tert alcohols.
-Easy recovery of the halogenated compound (I don't know if for the TCT method DMF and hydroxy-DCT are easily separable from the target halide,
especially in the case of bifunctional compounds like the ones they mention in the attachement (amino alcohols, diols.) or carboxylic alcohols
(glycolic alcohol or tartric acid for example).
On a side note I find it frustrating  that only one halide equivalent is
apparently used while TCT contains 3 of them 
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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chemrox
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another method
Here's another mild conditions method that was cited by the authors of the paper Sauron gave us here. The yields range from a terrible 15% to a wow
100%. The TCT/DMF process is much more comsistent. I cite this for completeness and in case someone wants to use it for whatever reason.
Attachment: ionic liqs OH-X.pdf (24kB)
This file has been downloaded 926 times
"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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-jeffB
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| Quote: | Originally posted by chemrox
Here's another mild conditions method that was cited by the authors of the paper Sauron gave us here. The yields range from a terrible 15% to a wow
100%. The TCT/DMF process is much more comsistent. I cite this for completeness and in case someone wants to use it for whatever reason.
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Hmm! I've been wanting to tinker with ionic liquids, but they tend to be QUITE expensive. However, there are a bunch of "deep eutectic" mixes based
on choline chloride that act as ionic liquids -- including a 2:1 molar mix with urea. It would be interesting to see whether any of these reactions
could be done in this extremely cheap and green solvent system.
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vulture
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A modified Appel synthesis with PPh3 and NBS in DCM @ 0C is also a clean method with high yields. Only drawback is the PPh3=O you need to get rid of,
but that can be done by vacuum distillation if your product is volatile.
Diagonal reading of that paper reveals that optically active alcohols are inverted. The modified appel synthesis retains stereochemistry (through
double inversion).
[Edited on 15-3-2008 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Nicodem
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If distillation is not an option, there is also another efficient way of removing Ph3P=O and succinimide. You just triturate the evaporated reaction
mixture in diethyl ether, or better yet petroleum ether if the alkyl bromide happens to be well soluble in it, and filter trough a couple of cm of
silicagel a'la flash filtration/chromatography (but mind that if there is unreacted Ph3P present it will pass trough; only polar side products like
Ph3P=O and succinimide are retained which are also quite insoluble in Et2O and petroleum ether anyway).
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Sergei_Eisenstein
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They (= academically scholared chemists) told me that Ph3P=O can only be removed by column chromatography. I should have known about this
quick-and-easy short column trick 
I thought Ph3P is rather easily oxidized by oxygen, so maybe traces will easily oxidized if you let your product dry for, say, 2 weeks? 
damnant quod non intelligunt
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vulture
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| Quote: |
I thought Ph3P is rather easily oxidized by oxygen, so maybe traces will easily oxidized if you let your product dry for, say, 2 weeks?
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I don't think so. We have rather big jar of PPh3 which holds its own in air quite well. Zerovalent transition metal complexes of PPh3 tend to be very
air sensitive, however.
[Edited on 15-3-2008 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Sandmeyer
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| Quote: | Originally posted by Sergei_Eisenstein
They (= academically scholared chemists) told me that Ph3P=O can only be removed by column chromatography. I should have known about this
quick-and-easy short column trick
I thought Ph3P is rather easily oxidized by oxygen, so maybe traces will easily oxidized if you let your product dry for, say, 2 weeks? |
I use short silica plug (like a filter) on many occasions. Provided that you can develop a mobile phase system where the impurity is a non-moving spot
(post-Wittig or post-Lawesson* among other examples) and the goodies migrate relatively fast. Then you just rinse the goodies out.
*: http://www.organic-chemistry.org/namedreactions/lawessons-re...
[Edited on 27-3-2008 by Sandmeyer]
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