aromaticfanatic
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Chloroform from calcium hypochlorite
Has anyone had success with this? I have found a few SM threads on it but they tend to just say to go for bleach.
I need 250mL of chloroform and while I have made it plenty of times before, this go around my reaction got too hot and lots of the chloroform
evaporated (thankfully didn't boil). I want to use more concentrated solutions with an addition funnel and more precise control in return for a higher
yield and faaar less waste. The waste from that run which produced a shitty 40-50mL of chloroform made about 4 liters of waste. While I do like the
ease of the synthesis I'd prefer to just spend some more time and effort into high yields and low waste. This is what I'm hoping to achieve via the
calcium hypochlorite.
The issues are as follows:
Using calcium hypochlorite on its own seems to not work too well. From what I've seen the yields aren't the greatest and the cleanup is a mess.
Adding a sodium cation base to make sodium hypochlorite in situ is great and all for making very concentrated bleach, but a pain to filter/clean off
the insoluble precipitate.
Something that I though might work is setting up a 1L flask and filling it with calcium hypochlorite, water, and sodium bicarbonate. This should make
my very concentrated bleach. I'll set that aside with a stopper on top to prevent nasty smelling hypochlorite smells. I could take a sample and do a
quick and rough titration using hydrogen peroxide of known concentration. Then I set up a 3 necked RBF onto a magnetic stirrer hot plate and add an
ice bath. I add a thermometer to one neck, an addition funnel for the acetone on the other, and a fractional distillation set up to the other last
neck.
I add the hypochlorite solution before adding the thermometer and drop in a stir bar. Begin stirring and letting it get as cold as possible. Then I
begin slow and careful addition of acetone. The acetone will then react and produce chloroform. I'll keep the temp below 30C.
After additions are done the temp is raised to fractionally distill the chloroform.
One done, the flask is emptied and another shot of hypochlorite solution is added until all of the reactants have been used up. Then I can dry the
chloroform using CaCl2 and redistill over CaCl2 to get dry and pure chloroform. I'll stabilize it for storage of course.
The remaining remaining water can then just be added to the chloroform waste and the flask washed with water and HCl to get rid of Ca(OH)2 deposits.
Are there any flaws I don't see yet with this method? Would the yields be worth it? The remaining waste water would be much much less and so the waste
is less of a PITA. Although the bleach method is very easy, I'm tempted to go back to it. I may have found some pool bleach at 10% concentration. I'll
add the acetone dropwise next time and use good stirring/shaking in between additions. I assume yields will be good enough. So far I can store a max
of 500mL of chloroform but I think I will keep one storage container for another very strong solvent.
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JJay
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I've done it. It works. It's a lot easier to just use bleach. I don't remember which was cheaper, but the prices certainly didn't favor calcium
hypochlorite to the point where all of the extra work involved was worth it.
If you have a lot of extra calcium hypochlorite for some reason (as did I), it's worth doing, but otherwise I wouldn't bother.
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Pumukli
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Ca-hypochlorite seems interesting - until you actually start to work with it :-)
Last year I tried to use it in the Hoffman -rearrangement reaction of phthalimide but I quickly abandoned the idea.
Main reason was: the reaction produced a lot of crap this way. I know, this is unrelevant to you (different reaction) but here comes my second reason:
Ca-hypochlorite produces a thick suspension which you definitely want to filter before pouring into any addition funnel. :-) I filtered it through a
wad of rock-wool. Not the nicest procedure I know... Then I checked the hypochlorite content of the filtrate - it was somewhat stronger than store
bought sodium-hypochlorite solution but the difference was not that serious that it would outweigh the problems associated with its use...
I can only second JJay's advice: use it only if you have a big supply, otherwise use bleach, the stronger the better.
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aromaticfanatic
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Okay thank you for the response. I'll see if my local store has any pool bleach. So far I was unable to get any due to Covid. If I find it I'll try to
buy as much as I can and do a higher yield chloroform synthesis.
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aromaticfanatic
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Does anyone have good advice on how to get rid of the waste water from the reaction? Doug's Lab says to pour it down the drain. I think letting it sit
in the basic solution for a few week is pretty good to destroy remaining chloroform, right? If all else fails I'll reflux with sodium hydroxide bit by
bit and then get rid of it properly.
Or I may just bring it to a local disposal site during one of the hazardous waste days. I'd prefer not to though.
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macckone
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Letting it sit as a basic solution will eventually remove all of the chlorinated product but leave it outside protected from light as phosgene is a
by-product of neutralizing chloroform with a base, it doesn't produce much at room temp but it doesn't take much. If you have done a good separation
there should not be significant chloroform in the water solution and phosgene should not be a concern. If it is highly basic, which it should be,
letting it sit 24 hours should be sufficient. Pouring it down the drain is acceptable since the main components will be hydroxide, acetate and water.
You can bring the ph down with sodium bicarbonate or acetic acid but sodium hydroxide is drain cleaner so the waste water system is designed to handle
it.
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aromaticfanatic
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Awesome, thank you.
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monolithic
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Quote: Originally posted by JJay  | I've done it. It works. It's a lot easier to just use bleach. I don't remember which was cheaper, but the prices certainly didn't favor calcium
hypochlorite to the point where all of the extra work involved was worth it.
If you have a lot of extra calcium hypochlorite for some reason (as did I), it's worth doing, but otherwise I wouldn't bother. |
I also considered it and did some calculations on cost. Bleach was cheaper per unit of chloroform produced, and it's easier because you can do the
reaction in the bleach jug.
[Edited on 8-22-2020 by monolithic]
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BromicAcid
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Water containing chloroform >6.0 mg/L (note that RT solubility is close to 8 g/L) is considered hazardous waste (code D022). Disposal of this
material untreated can be a felony and result in prison time / outrageous fines. Of course most people don't care and just dump it down the drain.
Using sodium hypochlorite generates large quantities of this waste, that is why the calcium hypochlorite route was appealing to me, much smaller
liquid waste stream for treatment.
Before chloroform was made commercially from hydrocarbons/chlorine reaction it was actually made via the haloform route using calcium hypochlorite. I
found some good literature references and posted them to this forum at one time. If you dig (or I dig after I post this) I can probably find them
with ease.
Edit: Here we go, from From 'Thorpe's Dictionary of Applied Chemistry'
| Quote: | Manufacture of Chloroform from Acetone and Bleaching-powder.
-This is the process most generally employed. The method differs in minor detail with the various manufactures, but the following may be taken as
representatives. The reaction is carried out in a cast-iron still of about 800 gallons capacity, which is provided with stirring gear, steam-coils,
and cooling-coils, and is connected with a condenser; 300 gallons of water are run into the still, and 800 lbs of bleaching powder are added through a
manhole, which is then securely bolted down. During addition of the bleaching powder the mixture is very thoroughly stirred. (In some processes the
mixing is carried out in a separate vessel, and the suspension is strained from the larger unbroken lumps of bleaching powder before being allowed to
run into the still.) The container (A in the diagram shown on p. 78) is charged with 70 lb of acetone, which is then slowly run into the bottom of the
still by means of a valve B. The introduction of the acetone is accompanied by a rise in the temperature which is not allowed to exceed 110 F.,
cooling being effected if necessary by stopping the flow of acetone and circulating cold water though the cooling coil in the still. When all the
acetone has been introduced the contents of the still are raised to 134 F. At this temperature chloroform begins to distill over. The temperature is
then very gradually raised to 150 F., so as to keep the chloroform readily distilling. Towards the end of the reaction the mixture is stirred and the
temperature raised until no more chloroform distills over.
The crude chloroform obtained is separated and purified first by agitation with concentrated sulfuric acid. This operation is carried out in the
vessel shown in the diagram ; 1,500 lb. of crude chloroform are introduced into the vessel and thoroughly stirred, by means of the agitation gear
shown, with 600 lb. of sulfuric acid. The stirring is continued until a sample of the chloroform when thoroughly shaken with pure concentrated
sulfuric acid does not impart the slightest color on the latter. The time required for complete purification is usually about 3 hours. The chloroform
is next separated from the sulfuric acid and finally distilled over lime. The yield obtained from the above quantities averaged from over 2,000
batches was 124 lb., the highest yield in any one case being 131 lb. Variation in yield is attributed to the varying composition of bleaching powder,
though doubtless other factors influence the result. Bleaching powder containing less then 33% of available chlorine gives unsatisfactory results,
while samples containing more then 35% of chlorine are also unsatisfactory. The best results appear to be obtained with bleaching powder containing
34% of available chlorine. |
[Edited on 8/22/2020 by BromicAcid]
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JJay
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The part about purification with sulfuric acid seems to have been glossed over in many modern descriptions of the process. I have usually attempted
purification with sodium bisulfite, but it's hard to know how effective the purification was.
I suggest distilling the chloroform out of the bleach jugs by pushing a distillation adapter or copper tube through a cap and immersing them in
boiling water. Yields are not improved that way by all of 8g/liter, likely due to decomposition, but they are improved.
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S.C. Wack
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| Quote: Originally posted by JJay | | The part about purification with sulfuric acid seems to have been glossed over in many modern descriptions of the process. |
There's probably a good reason for that. Cumming and Mann e.g. use NaOH.
I'm not sure that adding bicarbonate to bleaching powder would go in the desired way...some have been known to use a mixture of carbonate and
hydroxide. The problem with HTH is foam IME and there may be other ways of dealing with it than precipitating the Ca.
[Edited on 22-8-2020 by S.C. Wack]
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macckone
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A couple of points.
Although the solubility of chloroform in water is 8g/L, the solubility of chloroform in a saturated salt solution is much much lower.
Letting the extracted liquid sit will decompose the remaining chloroform.
Also the minimum reportable release quantity is 10 lbs according to the EPA.
So you have to be making a lot chloroform to release 10lbs at 8g/L.
That is 153 gallons of waste water.
Specific states may have lower reporting thresholds but that is going to pretty much be California.
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aromaticfanatic
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Interesting points have been made here. Yea I agree that the calcium route makes a lot less waste which is mainly why I'm after it. But looking at the
low solubility of chloroform (not negligible) in water, and seeing how easily it is destroyed by the leftover strongly basic solution, I think it's
fair to say that the disposal can be done properly. I'm not sure about just pouring it out into the environment (as chloroform is naturally made but
still hazardous to the environment) but I think letting traces of chloroform into treated water systems who should be dealing with potential
chlorinated organic contamination anyway is something negligible and not illegal. I'm sure if you let it sit for a week in the basic solution in the
dark, there'd only be extremely minor traces of chloroform left. So you really only need enough waste containers for holding one jug worth of bleach
since you can pour the remaining waste water back into the bleach jug for decomposition and subsequent disposal. I'd have to check on proper laws
though. I'm sure you can't legally or safely just dump pure liquid even in <100mL amounts down the drain. Traces are different and I'm sure there
are plenty of traces of chloroform in water that goes to treatment centers. Algae produces it naturally and I think some other aquatic plants make it
as well.
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macckone
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Chloroform is also a byproduct of chlorinating water.
That is why they try to reduce organics to a minimum before chlorination.
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