night429
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Hexachlorocyclopropane
I found a procedure in the Journal of the American Chemical Society after looking into uses for perchloroethylene. The procedure I did is on a 1/5 scale.
I synthesized the chloroform from bleach and acetone, followed by reflux and distillation over sulfuric acid. Because I didn't have the stirring setup
called for by the paper, I opted to double the amount of chloroform to account for decomposition.
100mL of perchloroethylene, 60g of potassium hydroxide flakes, and 10mL of chloroform were mixed with stirring. A condenser was attached and heating
started. 2mL of additional chloroform was added while it was below reflux. At this point, the stirring had seized, so the flask was manually stirred
every so often.
The remaining 8mL of chloroform was added in 0.5mL spurts, the flask was swirled after every addition, which took about 12 minutes. Over this time,
the potassium hydroxide had gone to a brown color. The reaction mixture was refluxed for an additional 10 minutes, with swirling every 2 minutes. The
flask was then placed in a water bath to bring the temperature down, and then allowed cool to room temperature.
The solids were filtered off and eventually discarded. The remaining supernatent was about 90mL, and was a yellowish color. The flask was then covered
loosely. I then forgot about this reaction for several months, over which time the solvent conveniently evaporated.
The slightly-yellow, damp crystalline mass was weighed, and came out to be roughly 2g. 14mL of methanol was measured out and added to the crystalline
mass. Solution was heated to boiling, and an additional 10mL of methanol was added due to the crystals not dissolving fully. Once everything had
dissolved, the solution was slowly cooled to freezer temperature. Large crystals had formed, and these were filtered off, washed with a small amount
of cold methanol, and dried.
This came out to 1.68g of slightly-damp, off-white crystals. The smell was obvious when working with this compound: piney, camphorous, and
reminiscent of chlorobutanol. This is consistent with the paper. The melting point was 102°–104°C, which is slightly broader than reported
(103°–104°C), but consistent with hexachlorocyclopropane. Thus, I believe this is the compound isolated. The yield was about 2.7%, which is a bit
far off from the paper (4.5%). But, the paper used better stirring, and the percent is slightly skewed lower because of the doubled chloroform. Also,
I used a bit more methanol than the paper did in the recrystallization.
Some notes on safety:
Due to the low yield, it can be inferred that most of the dichlorocarbene decomposes in the basic solution, either to carbon
monoxide or potassium formate (I presume via a formyl chloride intermediate). Just in case it was mostly the former, I performed the reaction outside,
and severely limited my exposure to the reaction by only being around it if needed.
The toxicity of the hexachlorocyclopropane has also not been established. It doesn't seem far off to think that it would be a liver toxin based
on similar molecules. I tried to limit my exposure to it.
The solution was evaporating for 10 months or so in my garage, so the stability of the product is, as the paper describes, quite high. I probably
won't revisit the synthesis due to the low yield, but I'm extremely happy that the reaction was successful.
[Edited on 4-4-2025 by night429]
And the boat sails on...
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Fery
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Good job and thx for sharing. I have about 10 L of tetrachloroethylene and did not yet find any usage for it.
I remember times like 30 years ago when it was possible to buy OTC trichlorethylene in every chemist shop which had much more usage for chemistry like
this one: https://www.sciencemadness.org/talk/viewthread.php?tid=62148
But today only OTC tetrachloroethylene available.
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Boffis
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Interesting chemistry! When I read your account I notice that you let it stand for "10 months" over which time the excess solvent evaporated. This
makes me wonder if you didn't loose some product too as I am pretty certain it will be fairly volatile.
My other question is what can you do with hexachlorocyclopropane? Conc sulphuric acid hydrolyses some of the linear polychlorohydrocarbons to various
poly chlorofatty acids etc. so I wonder if this compound might undergo such a reaction? and what would it make? I presume that if it will withstand
refluxing with caustic alkali it is fairly stable under alkaline conditions.
Have you seen the write-up here on SM on the preparation of heptachloropropane and its dehydrohalogenation to hexachloropropene by Garage Chemist? -
unsym-Heptachloropropane synthesis
I wonder if its possible to reduce tetrachlorethylene to trichloroethylene? I am sure this has been discussed too on SM.
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Texium
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Nice! I really love carbene chemistry.
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Boffis
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Agh.. Having now read the paper you referenced above, I see that it answers most of my question about hexachlorocyclopropane.
An interesting compound all the same, well done!
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night429
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Thanks for the replies!
Fery: I wish trichloroethylene was more accessible. It seems to have far more uses than tetrachloroethylene.
Boffis: Yep, I did let it sit for a while. It did remain loosely covered with aluminum foil, so it can't be super volatile. I most likely did lose a
small amount of product over this time, though, since I have no idea when the solvent was gone.
Texium: Carbene chemistry is definitely really cool. I learned to appreciate it during this reaction, and figure out exactly how it reacts. I just
wish the intermediate wasn't so short-lived. I should try some more reactions with the dichlorocarbene in the future.
And the boat sails on...
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chempyre235
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I've been reading about some carbene chemistry as of late, and I found that the synthesis of isocyanides from amine and chloroform works through a
carbene intermediate. Apparently, salicylaldehyde (with CHCl3) and salicylic acid (with CCl4) can be made from phenol this way
as well.
Following this same logic, can salicylic alcohol (from DCM) and o-cresol (from MeCl) be made in this manner as well? Likewise, can other products be
made from amines by utilizing different chlorinated methanes?
@night429, do you know of any uses for the perchlorocyclopropane? Maybe hydrolysis to deltate salts by reaction with strong base?
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DraconicAcid
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I'm not an expert on the Reimer-Tiemann rxn, but I suspect DCM wouldn't be acidic enough to form the carbene. I don't know the mechanism for the
reaction of CCl4 to give carboxylic acids, so I wouldn't guess if, say, CH3CCl3 would react to give a ketone.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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