Question: polychlorination of acetone with CuCl2

[former_chemist]

Haven't been here in a while - (A year)

Does anyone know if chlorination of acetone with CuCl₂ actually forms 1,1-dichloroacetone or 1,3-dichloroacetone?  I know that more traditional chlorination greatly favors the 1,1 product while the 1,3 is not as favored.  Is the stearic hinderance sufficient to prevent the 1,1 product from being formed.  Prior experience seems to indicate the 1,1 product doesn't form in large quantities however that could be due to the small quantity of chloroacetone formed (1.5% of the final solution).

Yes, I am familiar with the safety hazards of this chemical.

[xxxxx]

somewhere in journal of american chemistry is an article where they used cubr2 to make bromoacetone with no polyhalogenation. also in organic chemistry somewhere there is an addition of bromoacetone to a phenyl substrate with a much higher yield (78%) than chloroacetone (30%).

[former_chemist]

Would you happen to have any better references?

That isn't quite what I was looking for but I can see how the bromination would stearically hinder the 1 carbon to the point that no new addition could occur there.  Does chlorine do the same thing?

Was this the triphenyl borane method?

Post 453831

(Rhodium: "Synthesis of ketones (P2P) via alkylboranes", Novel Discourse)

[WizardX]

1,1-dichloroacetone will predominate as chlorination of acetone is much less selective.


BROMOACETONE 

http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0088

C3H5BrO
CAS Registry Number: 598-31-2
ACX Registry Number: X1003696-9
Synonyms for Bromoacetone :
 a-bromoacetone
 2-Propanone, 1-bromo-
 Bromoacetone

[former_chemist]

> 1,1-dichloroacetone will predominate as chlorination of
> acetone is much less selective.

With traditional chlorination methods this is definitely true but the CuCl₂ method has a low rate of dichloro formation (<20%).  My question was specific to this method.  The mixture formed includes a bunch of side products but 1,1 seems to be much less than expected.  I believe 1,3 and 1,1 can both rearrange and form polymers etc.  Does stearic hinderance prevent the complex from forming that would directly lead to 1,1 with the CuCl₂ method or is it strictly a function of the low concentration of monochloroacetone in the final solution?

> BROMOACETONE 

http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0088

>
> C3H5BrO
> CAS Registry Number: 598-31-2
> ACX Registry Number: X1003696-9
> Synonyms for Bromoacetone :
>  a-bromoacetone
>  2-Propanone, 1-bromo-
>  Bromoacetone

Good link for bromoacetone.  This however is not the CuBr₂ method that might have an answer to my question.

[Organikum]

former_chemist, if you might provide us with some more detailed information on the reaction and conditions you talk about? Do you intend to add an second salt like LiCl or KCl? What temperatures? References? Or where does your idea come from? I did a search on this lately and found not much except that the chlorination of acetone by CuCl2 is well known (haha) and that LiCl will speed the process up. Volumetrically the process is bad - immense amounts of CuCl2 are needed for a small amount of chloroacetone. But perhaps its possible to refresh the CuCl to CuCl2 in situ by HCl? This would of course change things dramatically.
My knowledge onj other acetone chlorination methods tells me:
- low temperatures will favor the monochlorinated compound
- a big excess of acetone too
- monochloroacetone is not very very soluble in a acetone/water/HCl mixture and will drop out. So stirring might be a bad idea if the monochlorinated compound is wanted.

The thread should be moved btw. - it belongs IMHO into "Chemistry" or "Methods", it relates strongly to the FC thread lately. (FC = Friedel-Crafts)

[former_chemist]

I have a reference on two different reactions from the same article

The Reduction of Cupric Chloride by Carbonyl Compounds, Kochi, Jay K. (1955), JACS vol 77. pgs 5274-5278.

The first is 150ml Acetone, 50ml Water, 12g CuCl₂, 6g LiCl with a yield of about 2g (60%).

The second is 5g CuCl₂, 4ml Water, 1L Acetone with a yield not given.

Another reaction mentioned is 3g CuCl, 2.98g LiCl, and 45ml anhydrous acetone, which absorbes oxygen from the air and forms 2CuO-2CuCl₂ complex.  This reaction has a half life of 25 minutes.  Somewhere or other (rhodium or here) this is incorrectly stated as being the chlorination reaction.

I am looking for ways to carry out this reaction without huge excesses of Acetone without compromising yield too badly.

My current theory is that a two layer reaction might be possible.  With one layer being water saturated with CuCl₂ and LiCl and the second layer being acetone.  Since adding excess salts to the mix causes these two to separate this seems feasible.  And since chloroacetone will prefer the acetone layer and be lighter than the salt saturated layer it will be removed from the primary reaction zone.  By very slowly bubbling oxygen through the mixture it should be possible to cause the reacted copper salt complex to precipitate where it should react with the HCl present to regenerate CuCl₂.  Since the original reactions were done at a reflux temperature this should probably be done just below refluxing to avoid emulsifying the two layers.  If the CuO won't react under these condition then it could still be separated and reacted with boiling HCL and added back to the reaction mixture.

I am not sure if this would work but it certainly seems like an avenue to explore.  The primary drawback would be if the dichloro compounds were formed in much larger quantities,  which is the root of my question about the stearic hinderance.  This does nothing to solve the problem with the heavy molar weight of CuCl₂ but it may reduce the number of moles needed below 2 as well as the quantity of acetone needed.

I also agree that this thread should probably be moved to general chemistry if one of the moderators would be so kind.

FC

[Organikum]

A frankly admit that it is way over my head what positive role the CuO-CuCl complex named shall play in this reaction - I cannot see it. I can see well the the role of the LiCl which will work as a halogen-carrier for it is soluble in acetone. This of course excludes the use of KCl instead of LiCl what would have been nice so possible .

The addition of HCl will - of course - diminish the amount of CuCl2 which will go into solution - a drawback. The presence of HCl will though - after my best of knowledge - speed up the reaction.

The problem is:
- higher temperatures and stirring will favor polychlorination.

Maybe its best to do as Vogel says: Chlorinate acetone in the cold. Patents named in the FC thread hint that HCl will make the reaction more smooth (at 20°C) and the exclusion of water may avoid polychlorination. The first is sure the second - not. It may apply for gasphase reactions but not for liquidphase.

I am rather sure that ANY reactionscheme which allows the chlorinated ketone to drop out is favorable to monochlorination. If there is a way to be found which accomplishes this with CuCl2 and refreshing this in situ - this would be great of course. Two phase - yes, but the second phase is the monochlorinated compound on the bottom - withdraw, neutralize with chalk and store. Hopefully  

Thanks for the references.
ORG

[WizardX]

I am looking for ways to carry out this reaction without huge excesses of Acetone without compromising yield too badly.

My current theory is that a two layer reaction might be possible. With one layer being water saturated with CuCl2 and LiCl and the second layer being acetone. 

Why??? Are you trying to avoid distillation?

[former_chemist]

A frankly admit that it is way over my head what positive role the CuO-CuCl complex named shall play in this reaction - I cannot see it. I can see well the the role of the LiCl which will work as a halogen-carrier for it is soluble in acetone. This of course excludes the use of KCl instead of LiCl what would have been nice so possible.

The addition of HCl will - of course - diminish the amount of CuCl2 which will go into solution - a drawback. The presence of HCl will though - after my best of knowledge - speed up the reaction.

The problem is:
- higher temperatures and stirring will favor polychlorination.

Maybe its best to do as Vogel says: Chlorinate acetone in the cold. Patents named in the FC thread hint that HCl will make the reaction more smooth (at 20°C) and the exclusion of water may avoid polychlorination. The first is sure the second - not. It may apply for gasphase reactions but not for liquidphase.

I am rather sure that ANY reactionscheme which allows the chlorinated ketone to drop out is favorable to monochlorination. If there is a way to be found which accomplishes this with CuCl2 and refreshing this in situ - this would be great of course. Two phase - yes, but the second phase is the monochlorinated compound on the bottom - withdraw, neutralize with chalk and store. Hopefully

Thanks for the references.
ORG

HCl inhibits the reaction.  In the gas phase this is very important to reduce the reaction rate (make it smoother).  The hope is that the CuO component will scavenge some of the HCl allowing the reaction to proceed and providing some additional CuCl₂

I have to agree that faster reactions tend to favor dichloro products.  In this case the reaction is fairly slow to begin with.  Stirring will definitely be a bad thing in a two phase reaction.  Unfortunately, I have yet to think of a way that puts the monochloroacetone on the bottom.  Saturated salt solutions are unfortunately very heavy   .

[former_chemist]

wizardx wrote:

Why??? Are you trying to avoid distillation?

The primary goal is to avoid using a lot of acetone.
The current method uses a huge amount of acetone for the monochloroacetone produced (75:1 volumetric).  This of course yields a dichloroacetone free product (or close to it).  If a two phase scheme could be made to work without reducing the yield below, say, 30% and not produce an overwhelming amount of dichloro with only a small excess of acetone (5:1?) this would be a distinct advantage in distillation.  I only wish there really was a way to avoid distillation, noone likes distilling teargas.  

[Organikum]

HCl inhibits the reaction

This is in direct contradiction to

Patent US2204135

which calls for 1% HCl to get the reaction smoothly going at 20°C. My personal experiences back the information up - it is exactly as described in the patent, without HCl the reaction wont take place for some time and then all of a sudden it will spew the contents of the flask all over - not nice at all. With HCl it will take place smoothly and without problems.

former_chemist, please avoid such statements without backing them up.
thanks
ORG

[former_chemist]

directly from the JACS article I quoted:

The rate of this reaction is increased by increasing the acetone concentration (in aqueous solutions) and by chloride ion, decreased by neutral salt and is inhibited by the products, hydrogen chloride (or acid) and cuprous chloride.

There isn't anything contradictory about a chemical being a useful initiator (Cl-) as well as an inhibitor (H+).  In the specific case of the reaction under discussion CuCl₂ chlorination of acetone, HCl is definitely an inhibitor in large quanitities.  In the gas phase if some initiator isn't present the reaction explodes but HCl still acts as inhibitor in large quantities.  I would expect the liquid/gas reaction to be similar.  From the patent it looks like the discovery is primarily for the initiator.  The patent also seems to claim that HCl inhibits side reactions.  I think there are some gas phase patents making the same claim.  Since in the solution HCl forms two ion species, it should be entirely possible for one to act as a catalyst and the other as an inhibitor.

Side note: HCl can also form radical species.

[lugh]

The article, JACS 77, 5274-8 (1955)

and the referenced article, Ber 37 1153-71 (1904)

[Organikum]

Thanks lugh!

I will try to excerpt and translate the important parts of the german reference the next days - the whole article is too big, sorry.

ORG

[former_chemist]

I needed a copy of that whole article.
Just wish I could read german