Melgar
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Maximizing chloroform from the haloform reaction
The output of the haloform reaction has always varied so much, in my experience, that output always seemed to be more a matter of luck than skill.
However, I think I finally figured out a few rules of thumb that can help get the most yield out of a hypochlorite solution of unknown concentration.
First of all, if you're buying it, get the highest concentration of sodium hypochlorite solution available. Usually, that's the 10% stuff for
swimming pools, although that's seasonal. There's also 8% "germicidal" concentration, although how 5% isn't germicidal is beyond me.
Chloroform is slightly soluble in water, and when you have this much water relative to your chloroform, the amount in your aqueous solution is
significant.
Do the reaction in glass. It doesn't have to be borosilicate. "Carlo Rossi" one-gallon wine jugs work well for this reaction. It's best to take
your time with this reaction, and chloroform diffuses through plastic. It should also be done in a sealable vessel.
Add sodium hydroxide to the solution beforehand. About 0.5 g/L for each percent hypochlorite you expect the solution to be. The haloform reaction is
a net acidifier, and if you have greenish-yellow neutral solution at the end of it, that's because pH got too low. You might be tempted to use sodium
carbonate because it's not as strong of a base, but the CO2 bubbles released take a lot of chloroform with them.
Limit the reaction by acetone addition. The sodium hydroxide will accelerate the reaction, so you need to use low temperature, time, and acetone
concentration to keep it from going into thermal runaway. Add 1 mL to a cold solution, for example, and stir immediately. Wait a few minutes. Add
another mL, etc. This is best to do while you're doing something else so you don't get impatient.
Don't add anything solid after starting the acetone addition, and make sure there are no precipitates. Any solids added or precipitates present will
mix with the chloroform, and possibly react with it.
Carefully acidify once your're sure acetone is no longer reacting with the hypochlorite solution, assuming the solution is still basic. If you see a
greenish color when you add acid, and smell chlorine, then that's an indication that your hypochlorite isn't spent. Acetic acid and hydrochloric acid
are preferred, because their ions will already be in solution, so you're not complicating the reaction unnecessarily. The last part of the reaction
requires acid hydrolysis, and if your solution is basic, that won't happen.
Keep everything cold the whole time. Virtually all the complications of this reaction can be reduced with low temperatures, including chloroform
evaporation.
[Edited on 3/28/17 by Melgar]
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Amos
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Just out of curiosity, what are your yields like based on this method? It sounds like a whole lot of extra work when perfectly respectable yields can
be obtained in a few hours by using bleach as it is and using the jug as the reaction vessel.
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Melgar
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It's not really extra work, just extra time, which is minimal if you're doing several things at once. And doing it in glass lets you see what you're
doing, which is something I wouldn't ever forego even if I was trying to do it quick and dirty. I never worked out the yields the last time I did it
because like I said, solution was of unknown concentration. Basically, a half full jug of bleach that was at least a year old. I don't use chloroform
regularly enough to justify making another batch for a while either.
It also minimizes contamination with other halogenated species that form at neutral pH, which seems to be a definite advantage.
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MrHomeScientist
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I judged a cool science fair project a while back where he measured the concentration of hypochlorite in bleach of various ages and from various
manufacturers. 100% of the time it was less (sometimes far less) than what was stated on the bottle. Even if you use it immediately after you buy it,
who knows how long it's been sitting in a warehouse since it's been manufactured. For reproducible results, you definitely want to measure the
concentration every time before you use it.
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clearly_not_atara
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Are you sure that yields are better with acetone than with ethanol? Is bleaching powder any more reliable than liquid bleach?
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Cryolite.
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Bleaching powder works, but I found that the massive quantities of insoluble calcium hydroxide produced makes workup extremely difficult. In addition,
the extreme exotherm means that one must add acetone slowly or dunk the reaction container in cold water. (I didn't do this at first, and got a hot
geyser of calcium hydroxide and chloroform.) I ended up distilling chloroform and water directly out of the mixture, but this bumps like crazy and
several times the lime overflowed into the condenser, meaning I had to re distill the product. I got a ~45% yield of chloroform in the end, but this
can probably be improved with better temperature control and a better workup. However, I have a suspicion that the calcium hydroxide breaks down the
chloroform into chloride and formate, meaning final yields are a bit limited.
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XeonTheMGPony
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https://erowid.org/archive/rhodium/chemistry/chloroform.html
I've used that synth several times now and by far my preferred method, it is clean, efficient, very smooth running.
Very easy clean up after wards as well using pool shock, I am going to modify it and use MEK via NerdRages pyrimethamine synth to all so try and
extract propionic acid for my next run.
Like any thing if your impatient or sloppy you get bad results, going so and keeping temps in check = success
I usually distill my acetone over anhydrous Magnesium sulfate to clean it up
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Melgar
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Propionic acid is easily available via calcium propionate (a mold inhibitor used by bakeries, about $2/lb) and virtually any cheap acid that has a
high boiling point. That's a lot easier than extracting it from haloform residuals, which typically contain a lot of other crap too. Also, MEK
doesn't mix well with water, but DOES mix well with chloroform, so it can be sort of a bitch to separate the two.
Adding some NaOH at the beginning, keeping the solution in the refrigerator in a gallon-sized glass jug, and adding the acetone in small portions, to
keep the solution from getting warm, all seem to help the haloform reaction proceed with minimal contamination. It definitely reduces the appearance
of whatever that green stuff is that always seems to contaminate chloroform made this way.
| Quote: | | I usually distill my acetone over anhydrous Magnesium sulfate to clean it up |
You mean chloroform? Distilling your acetone for the haloform reaction seems a bit excessive.
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XeonTheMGPony
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not when it is hard ware grade, and the point of it isn't because it is expensive or cheap, the point is for the experience doing it! That's the whole
point of the forum and science! to try new things and record what happens! I will forward my findings to Nerd Rage as well if it turns out good as it
should be much less work and hassle then he had to go through!
Here in Canada it isn't as easy to get things that in all logic should be easy as it is ells where FYI
I've never had green gunk in my chloroform interesting to know it is a possibility
There is a very easy way to ensure there is no left over MEK, same one I use to ensure no left over Acetone!
I have run plenty of the bleach ones and prefer pool shock as it is much more reliable yield Vs the unknown bleach issue
[Edited on 29-3-2017 by XeonTheMGPony]
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Melgar
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Quote: Originally posted by XeonTheMGPony  | | not when it is hard ware grade, and the point of it isn't because it is expensive or cheap, the point is for the experience doing it! That's the whole
point of the forum and science! to try new things and record what happens! I will forward my findings to Nerd Rage as well if it turns out good as it
should be much less work and hassle then he had to go through! |
The main reason I'd think that someone would distill acetone is to get it anhydrous, which makes no sense if you have to add it to an aqueous
solution. It also makes no sense in the context of the haloform reaction, which can use a huge variety of different substances, and is one of the
least contamination-sensitive reactions there is. I mean, if you haven't distilled solvents hundreds of times already and it's still fun for you,
then more power to you...
| Quote: | | Here in Canada it isn't as easy to get things that in all logic should be easy as it is ells where FYI |
Propionic acid, sodium propionate, and calcium propionate are all commonly-used food additives in Canada too:
http://www.hc-sc.gc.ca/fn-an/securit/addit/list/11-preserv-c...
| Quote: | | I've never had green gunk in my chloroform interesting to know it is a possibility |
I'm not really sure what it is, but it's soluble in chloroform. It wouldn't look like gunk, rather it'd give your chloroform a yellowish color.
| Quote: | | There is a very easy way to ensure there is no left over MEK, same one I use to ensure no left over Acetone! |
Distill your chloroform? I guess as long as there's no azeotrope. Their boiling points are about 19C different.
| Quote: | | I have run plenty of the bleach ones and prefer pool shock as it is much more reliable yield Vs the unknown bleach issue |
The appeal of sodium hypochlorite is that you DON'T have to do any distillation to separate the chloroform from the crap on the bottom, but you seem
to enjoy distilling acetone for fun, so I guess that doesn't apply to you?
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macckone
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Chloroacetone tends to yellowish green.
chlorine is greenish.
metal chlorides could be green.
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JJay
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I've made chloroform with Wally World concentrated bleach a couple of times. I tried once with some el cheapo brand that was hard to titrate and
didn't get any product, but it was definitely greenish. I'm not sure what the issue was... perhaps there were surfactants in the cheap bleach or
something.
Bleach typically contains some sodium hydroxide anyway, so I'm not sure why you would add it.
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Melgar
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| Quote: Originally posted by JJay | I've made chloroform with Wally World concentrated bleach a couple of times. I tried once with some el cheapo brand that was hard to titrate and
didn't get any product, but it was definitely greenish. I'm not sure what the issue was... perhaps there were surfactants in the cheap bleach or
something.
Bleach typically contains some sodium hydroxide anyway, so I'm not sure why you would add it. |
The haloform reaction is a net acidifier, since it uses up OH- ions, and turns a ketone into an acid. Thus, adding a small amount of NaOH ahead of
time helps ensure you don't run out of OH- ions during the course of the reaction.
Mostly, I'm just sharing what I found from doing this reaction with various concentrations of sodium hypochlorite. Another factor is that the NaOH
can absorb CO2 over time, lowering the pH, which creates bubbles during the reaction, which can carry away CHCl3.
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XeonTheMGPony
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Hard ware grade acetone where I get it has contaminants, some sort of oil, distilling it gets all this crap out, the MgSO4 helps to glue all the gunk
in a ball enabling for smoother distillation! Since I do mass batches Some goes to work as dry solvent, some goes for chloroform or what ever task
needs doing (Doing large batches is more efficient and economical energy/time usage)
Despite living here I never knew they where available and where used!!! :0 here!!
Yes they are but allot of places won't sell to an individual, so yes they are every where but less you are a bakery or a business you're told to go F
your self for the most part (Varries by region, in mine I can't even get a fcking 100A breaker with out jumping through hoops) Welcome to the nanny
state! yet I can buy 35 H2O2 from a hippy shop! and 10L metal pails of Toluene
Using a slight excess of my chlorination compound Vs Acetone ensures full chlorination, You should be drying and distilling your Chloroform after
making it IMO!
If you like dirty solvents?! My policy is to clean, dry and distill any solvent I use, I dislike unknown variables and for a few cents of energy and a
bit of time I can remove allot of wild cards! Probably why I never ended up with mystery green gunk in my chloroform 
Next run I'll do it with normal (clean distilled acetone ) run and try adding a
bit of NaOH and see what it does.
[Edited on 29-3-2017 by XeonTheMGPony]
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