Sciencemadness Discussion Board

Can I expect good separation of haloform products?

Sulaiman - 13-7-2021 at 04:32

I intend to try making chloroform by a few methods;
- calcium hypochlorite + acetone
- calcium hypochlorite + ethanol
- TCCA + acetone
- TCCA + ethanol

I'm expecting mainly
CH2Cl2 (b.p. 39.6),
CHCl3 (b.p. 61.2)
CCl4 (b.p. 76.7),
acetone (b.p. 56)* or ethanol (b.p. 78. 2)*
and H2O

* plus higher b.p. due to water?

I have a still that has 5 to 6 theoretical plates.

Can I expect a good separation of products?

If not then any suggestions?

[Edited on 13-7-2021 by Sulaiman]

Amos - 13-7-2021 at 05:40

I don't think you should expect anything other than chloroform, to be honest, if you use excess hypochlorite. The reaction exhaustively chlorinates the terminal methyl group adjacent to a carbonyl carbon, and this then leaves as a trichloromethyl group to form chloroform. If it were to stop at only two chlorinations, you'd end up with something like dichloroacetone or dichloroacetaldehyde, which none of us have ever seen evidence of. Certainly not any carbon tetrachloride; it's not even a possible product.

karlos³ - 13-7-2021 at 08:13

If you react acetone with aqueous calcium hypochlorite... expect a very vigorous and exothermic reaction.
It can be used though, with appropriate cooling, while dropping the acetone into, to distill the (acetone contaminated) chloroform right off of the reaction mixture.
This way you still get a better yield than with the aqueous preparation where you separate it off in the end.
You need to wash and redistill though, but it works pretty well and much faster than the NaOCl methods, a few hours after you can already put the TCM to good use.

Oxy - 13-7-2021 at 09:25

I also don't think you would get anything other than chloroform.

You will not get DCM as HCCl2- anion will not leave the adjacent carbonyl group easily.

CCl3- anion will do that easily as it is an excellent leaving group and very quickly will undergo a protonation by taking a hydrogen from nearby water molecule. There is really low possibility that it would form CCl4 so I wouldn't expect any reasonable quantity.
Quote: Originally posted by Amos  
If it were to stop at only two chlorinations, you'd end up with something like dichloroacetone or dichloroacetaldehyde, which none of us have ever seen evidence of.

Each halogenation of alpha-carbon makes it more acidic and more reactive. So it's not really possible to stop it after one or two substitutions in basic conditions by using stoichiometric amount of chlorinating agent.



[Edited on 13-7-2021 by Oxy]

Mateo_swe - 14-7-2021 at 23:02

Is there no risk of phosgene if doing the acetone with aqueous calcium hypochlorite distillation preparation of chloroform?
I did a quick search on this method and found a rhodium preparation where they warn about phosgene.
A fumehood probably is good for this one, just chloroform vapours can make you pass out.
But i like the suggested preparation of chloroform, i might try it later if i need chloroform.

https://erowid.org/archive/rhodium/chemistry/chloroform.html

Oxy - 15-7-2021 at 01:04

No, there is no risk of phosgene formation during reaction. However, chloroform can itself decompose to phosgene so it should be stabilized before putting on the shelf for storage.

Fume hood is always a good to have. When reaction is performed in closed system with fumes absorber on the end (or just extractor) it is quite safe. The situation is totally different when using not air-tight system without any absorber or extraction. The fumes are toxic and should be avoided.

Sulaiman - 16-7-2021 at 19:38

This video shows chlorine bubbling through chloroform producing carbon tetrachloride.
https://www.youtube.com/watch?v=YdSoTBHEU0A

Should I not expect this as a side reaction ?

Oxy - 16-7-2021 at 21:40

I don't think so.
If you bubble chlorine gas through chloroform then the reaction conditions are definitely different than when you use water solutions of hypochlorite and acetone with continuos distillation.
Chlorination of chloroform you posted looks like a radical reaction which obviously will not happen when performing haloform.
When you perform the reaction in water remember that the concentration of water (which is about 55.56 moles/dm3) is a tough competitor. It is much more likely for a compound to react with water than other things (if is water -reactive).

SWIM - 16-7-2021 at 22:08

I'm skeptical about that reaction in the link.

I don't think that works without UV


Also, Len1 and Magpie both used UVC to do this reaction, and I'd be surprised if both of them went to the trouble of making UVC sources for this reaction if it was unnecessary.

And even more surprised that nobody pointed that out when Magpie posted that thread.

Sulaiman - 16-7-2021 at 22:28

OK... I think I get it... thanks.

I've got all required reactants, just cleaning and drying everything and looking for an affordable pressure-equalising addition funnel.
(I have some at home in UK, new ones seem to have significantly increased in price,
as has most glassware - and most other items.)
(The cost of food has risen significantly)

Oxy - 16-7-2021 at 22:33

Quote: Originally posted by SWIM  
I'm skeptical about that reaction in the link.

I don't think that works without UV


Also, Len1 and Magpie both used UVC to do this reaction, and I'd be surprised if both of them went to the trouble of making UVC sources for this reaction if it was unnecessary



Strong light is enough to initiate it. Not enough to keep it going at high rate but for simple demonstration can be just ok. For synthetic purposes the more energy, the better.