Sciencemadness Discussion Board

Separating chloroacetic acid and an sulfuric acid

Monoamine - 16-3-2024 at 11:52

I'm trying out the method from this patent for making chloroacetic acid from trichloroethylene by oxydizing it with sulfuric acid.

According to the patent this works very well. However, I'm having a lot of trouble separating the two later on.

To test their solubility, I tried DCM, dichloroethane, hexane and toluene. The thing is that the sulfuric acid does not seem to be soluble in any of these solvents - and neither does the chloroacetic acid!

So how am I supposed to separate them now, other than distillation (which I would like to avoid since that would likely damage the product or the sulfuric acid might react with the chloroacetic acid.

Does anybody know a likely solvent system that I can use to separate these two compounds?

Boffis - 16-3-2024 at 14:19

@Monoamine, the patent suggest extraction with ether so I presume you don't have access to this solvent. Maybe some other polar solvent like an alkyl acetate, or another ether say THF or dioxane (these might be too soluble in the aqueous medium) or diglyme (dimethylglycol / dimethoxyethane)

Alternatively could you add an alcohol and esterify it then distil the ester out of the sulphuric acid?

Alternatively could you treat with excess calcium carbonate, filter off the gypsum and isolate the calcium salt? Liberating it from the calcium salt may be tricky but it depends what you want to do with it. Quite a few operations with chloroacetic acid use the sodium salt anyway so you may be able to substitute the calcium salt. If not you could treat the calcium salt with sodium carbonate to get the sodium salt.

For me the methyl or ethyl ester would be most useful so I would probably go for the ester route.

DraconicAcid - 16-3-2024 at 15:36

Trying to extract with an ester will probably result in the acid hydrolyzing the solvent.

bnull - 16-3-2024 at 16:56

The same patent (US1304108) suggests:
  1. vacuum distillation (p.1, lines 58-62);
  2. use of a gas current (p.2, lines 1-5);
  3. solvent extraction (p. 2, lines 6-9);
  4. esterification (p.2, lines 10-17).

The way to go is either vacuum distillation or esterification. I'd go with vacuum distillation because the distillate wouldn't require more processing (apart from desiccation). The solvent extraction may work with solvents other than ether with varying degrees of success. Forget the gas current; it is more trouble than it is worth.

From Ullmann's (page 3 of attachment):
Quote:
2.3.1. Hydrolysis of Trichloroethylene[13–15]

Equal amounts of trichloroethylene and 75 % sulfuric acid are reacted at 130--140 °C in a continuous process so that with complete trichloroethylene conversion, the resultant reaction mixture contains about 50 % chloroacetic acid and 1--2 % water. This blend is vacuum distilled to give pure chloroacetic acid. During this process the vapors are washed with water, which is returned to the sulfuric acid as a diluent.


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clearly_not_atara - 16-3-2024 at 20:39

Depending on how much sulfuric acid you used, it might be possible to absorb it onto anhydrous sodium sulfate along with any water and then filter off chloroacetic acid.

Monoamine - 18-3-2024 at 15:55

Thanks for the replies. I will try it with ether then. But distillation also seems like a good option.

But keep in mind: the reaction calls for 4 times as much sulfuric acid as acetic acid, so there is quite a lot.

Also, Im slightly worried that the sulfuric acid will cleave the ether.

But it's certainly worth a go!

bnull - 18-3-2024 at 16:35

What did you do with all the hydrogen chloride generated?