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Author: Subject: Improving chloroform yield with acid.
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[*] posted on 21-11-2020 at 01:21
Improving chloroform yield with acid.


Hi, mostly new to the forum. I did loads of (in hindsight quite dangerous) chemistry as a kid. I recently got back into it with a goal of synthesising as many elements as I can that I can't purchase locally. Fireworks too. I've spent far too much money on glassware.

One of the first things I did was make chloroform. I don't immediately have a use for it but it's probably the easiest/cheapest to obtain strong solvent here in Australia (DCM paint stripper is expensive).

I tried the calcium hypochlorite method first but moved on to NaClO because of the annoying CaOH precipitation. I purchased 12.5L of 125g/L chlorine NaClO for pools from Bunnings, cooled the whole thing in an ice bath and slowly added acetone. Seeing how easily the reaction can run away, I only added more acetone once it got below 20C and tried to avoid going over 30C. It took about 4 hours to add the acetone and by that point it was late enough that I left it until the next morning. Once I separated it the next morning I ended up with only ~750g of chloroform instead of the calculated 1470g.

I suspect some migrated though the HDPE container given the cooling water smelt like chloroform but I'm sure much more was lost to hydroxide decomposition. I was thinking of adding an acid next time to keep the pH lower.

Weirdly, while looking for info on improving the yield I an across a relatively recent post on this forum from a long time member saying that the haloform reaction is a net acidifier and they suggested adding sodium hydroxide before hand... This defies what i know about acetone haloform reactions as I'm pretty certain a hydroxide salt is a reaction product.

Now, I know hydroxide ions are needed for the reaction to take place so it does need to remain basic, but given the reaction produces hydroxide I think getting very close to 7 pH is probably a good idea in terms of reducing decomposition.

Interesting I found this paper on chloroform decomposition in potassium hydroxide. While they don't explore alkaline decomposition too much, it does show that the decomposition rates are very high at 7.1*10^-1 mol/L.min at ~12 pH, 2.2*10^-2 mol/L.min at ~10pH and 1.8*10^-4 mol/L.min at ~8 pH. The rates drop to basically nothing in acidic conditions.

I have to wonder if the net acidifier belief came from the fact that chloroform breaking down consumes hydroxide ions. I'm not sure if posting a link to the thread is appropriate so I won't.

So has anyone tried improving yield by adding small mounts of acid to control pH? Or maybe I've got this all wrong and it really is a net acidifier.
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Tsjerk
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[*] posted on 21-11-2020 at 05:05


Welcome to the forum! Always nice to see new people, especially when they think about their experiments.

More references are more better, so I would post a link to the thread.

It would be interesting for a starter to determine the pH of the bleach you have. It is probably a good idea to make a dilution series and measure the different dilutions. Good chance measurements of highly concentrated solutions not to be too accurate.

The decomposition of chloroform by hydroxides you talk about is described at 100 degrees, does it really happen at low temperatures?
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[*] posted on 21-11-2020 at 05:36


Quote: Originally posted by Tsjerk  

The decomposition of chloroform by hydroxides you talk about is described at 100 degrees, does it really happen at low temperatures?


It definitely happens, that's why we leave the leftover reaction mixture in the bleach bottle for a couple days after the synthesis before dumping it down the drain (as an environmental measure). A short time afterward no smell of chloroform can be noticed. In my experience yield also greatly suffers if I come back to separate the layers more than 12 hours after the preparation.
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[*] posted on 21-11-2020 at 05:51


Quote: Originally posted by Amos  

It definitely happens, that's why we leave the leftover reaction mixture in the bleach bottle for a couple days after the synthesis before dumping it down the drain (as an environmental measure). A short time afterward no smell of chloroform can be noticed. In my experience yield also greatly suffers if I come back to separate the layers more than 12 hours after the preparation.


Then maybe add acid while adding the acetone? I thought about using a buffer salt like HPO42-, but the concentrations are way too high to be buffered. Adding acid to acetone will probably make the acetone polymerize. Then possibly adding acid to react with the hydroxide could improve yield.
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[*] posted on 21-11-2020 at 12:39


Quote: Originally posted by Tsjerk  
Quote: Originally posted by Amos  

It definitely happens, that's why we leave the leftover reaction mixture in the bleach bottle for a couple days after the synthesis before dumping it down the drain (as an environmental measure). A short time afterward no smell of chloroform can be noticed. In my experience yield also greatly suffers if I come back to separate the layers more than 12 hours after the preparation.


Then maybe add acid while adding the acetone? I thought about using a buffer salt like HPO42-, but the concentrations are way too high to be buffered. Adding acid to acetone will probably make the acetone polymerize. Then possibly adding acid to react with the hydroxide could improve yield.


My approach has always been "chloroform is already expensive to make as a solvent, I'm not spending more on additives to increase yield by another 5%". As long as you carefully control heat (freezing your bleach is a must) and process the chloroform in about 8-12 hours you'll consistently get 70-80%.
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[*] posted on 21-11-2020 at 14:36


If you look at the first step of the haloform reaction mechanism, you’ll see that base is required to deprotonate the ketone to form its enolate. This will not happen to an appreciable extent at pH 7... otherwise we’d see mixtures of acetone and water spontaneously polymerize. Yes, the base will degrade the chloroform, but it’s also necessary for its formation. As Amos said, the key to success with the haloform reaction is temperature control and proper timing.



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[*] posted on 21-11-2020 at 18:29


It still sounds like an opportunity to increase yield by a bit more than 5%. Once the reaction is done you could neutralise the base with HCl and then distil the remaining product dissolved in the water with minimal degredation. Assuming the numbers on Wikipedia are correct, chloroform's solubility is 10g/L at 0C. In my case of 12.5L NaClO that's immediately 125g more chloroform or a yield increase of ~15%. HCl isn't expensive.
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[*] posted on 22-11-2020 at 13:58


Quote: Originally posted by Download  
It still sounds like an opportunity to increase yield by a bit more than 5%. Once the reaction is done you could neutralise the base with HCl and then distil the remaining product dissolved in the water with minimal degredation. Assuming the numbers on Wikipedia are correct, chloroform's solubility is 10g/L at 0C. In my case of 12.5L NaClO that's immediately 125g more chloroform or a yield increase of ~15%. HCl isn't expensive.


I am sure the trapped CHCl3 can be pushed out from the water phase (aka salting out) with saturated NaCl solution as well.
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[*] posted on 31-1-2021 at 22:13


Or distilled off.
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[*] posted on 1-2-2021 at 01:17


https://www.youtube.com/watch?v=heqMdYqqMGs

They appear to be getting high yield from this process?

They make a slurry from calcium hypochlorite and water, mix in acetone and distill off chloroform, add dilute NaOH (to neutralize?) and CaCl2 (to dry? no layer separation showed) and then redistill the chloroform.

Considering that calcium hypochlorite is a lot cheaper per unit than solution of bleach, this should be better method by all means.
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[*] posted on 13-2-2021 at 06:03


Quote: Originally posted by Fyndium  
https://www.youtube.com/watch?v=heqMdYqqMGs

They appear to be getting high yield from this process?

They make a slurry from calcium hypochlorite and water, mix in acetone and distill off chloroform, add dilute NaOH (to neutralize?) and CaCl2 (to dry? no layer separation showed) and then redistill the chloroform.

Considering that calcium hypochlorite is a lot cheaper per unit than solution of bleach, this should be better method by all means.


That's the method I prefer, clean simple and effective.
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[*] posted on 13-2-2021 at 06:26


Since the topic of using calcium hypochlorite is fresh in the thread, are there any US members that know of a consumer product that is nearly pure calcium hypochlorite? I've seen EU and Australian members claim that they find it as a single chemical, but all of the pool shock products I've seen here have a maximum of around 57%, with impurities of calcium chloride and calcium hydroxide.
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[*] posted on 13-2-2021 at 06:51


Dry tec shock claims 68%
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[*] posted on 21-2-2021 at 04:19


Quote: Originally posted by XeonTheMGPony  
Quote: Originally posted by Fyndium  
https://www.youtube.com/watch?v=heqMdYqqMGs

They appear to be getting high yield from this process?

They make a slurry from calcium hypochlorite and water, mix in acetone and distill off chloroform, add dilute NaOH (to neutralize?) and CaCl2 (to dry? no layer separation showed) and then redistill the chloroform.

Considering that calcium hypochlorite is a lot cheaper per unit than solution of bleach, this should be better method by all means.


That's the method I prefer, clean simple and effective.



Yeah...thats one weird video, love the piano.
Pharmacists certainly ain't chemists
Xeon if you use this method have you abbreviated it in any way. What i find odd is that they begin distilling off chloroform immediately, however wouldn't acetone come over initially, without at least sometime to reflux/react??
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[*] posted on 21-2-2021 at 12:51


Quote: Originally posted by Amos  
Since the topic of using calcium hypochlorite is fresh in the thread, are there any US members that know of a consumer product that is nearly pure calcium hypochlorite? I've seen EU and Australian members claim that they find it as a single chemical, but all of the pool shock products I've seen here have a maximum of around 57%, with impurities of calcium chloride and calcium hydroxide.

I titrated my "pool shock" in northern europe to 82%
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