Synthesis of unsym.-heptachloropropane and hexachloropropene (updated)

In the book "Excuse me Sir, would you like to buy a kilo of isopropyl bromide?" which was recently uploaded to the Library by Polverone and which is very much worth reading, I read about how Mr. Gergel made heptachloropropane from perchloroethylene, chloroform and aluminum chloride.
I immediately thought "I'd like to do this!" and soon found the preparation on Orgsyn.
Moreover, the article about the discovery of the AlCl3-catalysed addition of chloroform to perchloroethylene by Prins and Boeseken turned out to be available for free.

I found that the exothermic nature of the reaction does not pose nearly as much of a problem as Mr. Gergel made it seem.
It probably only becomes potentially hazardous when working on a massive scale, like Mr. Gergel with his multiple runs in 12-litre-flasks.

Purification of the reagents

The chloroform was shaken twice with conc. sulfuric acid to remove the ethanol that was added as a stabilizer.
The first washing with H2SO4 produced a slight but noticeable exotherm as the alcohol was absorbed by the acid. No exotherm occured with the second acid washing.
It was then washed with water, Na2CO3 solution and water again, dried over CaCl2 and distilled over phosphorus pentoxide to render it perfectly dry and alcohol-free. It was stored in the freezer until use.

The technical perchloroethylene does not seem to require any purification, as a small test batch that I made with C2Cl4 straight from the bottle went fine and gave a high yield of good product.
Neverteless, I washed the C2Cl4 used for the depicted preparation with aqueous HCl to remove amine stabilizers, then with water, dried it over CaCl2 and distilled over P2O5.
I don't think that this made any difference.

The commercial AlCl3 was used straight from the bottle, a fine, somewhat yellow, free-flowing powder that gives off HCl fumes.

Preparation

I essentially followed the Orgsyn procedure, but used a little more C2Cl4 in order to better utilize the large CHCl3 excess.

180g Tetrachloroethylene and ca. 300g (200ml) chloroform were placed in a 1-litre round-bottom flask. 27g anhydrous aluminum chloride were added, and the flask was fitted with a reflux condenser which carried a drying tube filled with CaCl2.


The mixture was then heated with a bunsen burner. It assumed a red-brown color and continuously darkened as it it started to reflux.


After a few minutes of gentle refluxing, the boiling slowly grew more intense despite the heating not being increased.
The mixture soon reached a vigorous boil and continued boiling upon removal of the heat source:


A continuous stream of condensate was pouring down from the reflux condenser, but everything remained under control and the exothermic reaction gradually subsided over the next fifteen minutes.
The heating was now resumed and the mixture was refluxed overnight, for about 15 hours:


The next morning, its color had changed to dark green and it looked like this:


From below:


The mixture was cooled to room temperature, and the AlCl3 formed a precipitate on the bottom of the flask.
The supernatant was decanted from the sediment into a 500ml separatory funnel.

This is the sediment in the flask:


I added 100ml water to this black sediment. This turned out to be a mistake. It seems like the sediment consisted almost entirely of active AlCl3, and with the water it erupted into white smoke. The flask continued spewing acrid smoke for over a minute, and was extremely hot afterwards.
On the left side, you can see the black supernatant in the separatory funnel, covered with water:


Only a small amount of black lower phase remained in the flask where I hydrolyzed the AlCl3, and this was not further worked up.

The supernatant from the decantation of the AlCl3 (i.e. the main part of the reaction mixture) was thoroughly washed with three 100ml portions of water, which did not produce any noticeably exotherm.
After that, its color had changed from black to orange and it became almost clear:


It was dried over calcium chloride, with frequent shaking. This turned it clear:


A vacuum distillation apparatus with oil bath was set up.
You can see the frying fat in the oil bath/magnetic stirrer combo melting:


First the chloroform was distilled off at atmospheric pressure and up to 160°C oil bath temperature:


Then the mixture was cooled a bit, and very slowly and carefully, a vacuum was pulled.
This is the pump I used, a very old, obscure model from Vacuubrand that has 4 separate membrane pump heads on one motor shaft. Originally, those were connected in parallel, giving a useless 100 torr vacuum. After disassembly and cleaning of the pump heads, I connected three of them in series and added a gas ballast valve. Now it goes down to 18 torr- significantly better than my water aspirator, which I previously used for all my vacuum distillations. I checked the solvent resistance of the rubber diaphragms and they are resistant against chloroform.


Some residual chloroform and a small amount of perchloroethylene came over in the forerun.
Then the product started distilling at around 120°C vapor temperature (sorry, I can't give an exact boiling point, the vacuum varied somewhat, and the product even boiled over a slight bit at one time- this was my first time distilling with a diaphragm pump).

This is the distillate- essentially clear, only a few drops of the colored sump fell into it from the boiling over.


The distillate was a supercooled melt- it did not solidify despite the cooling water being colder than the 30°C melting point.
Upon adding a seed crystal of heptachloropropane from a previous batch, it rapidly started crystallizing, warming itself up to 30°C in the process:


It was remelted and poured into a wide-mouthed plastic dish with screw-on lid to solidify (the crystal cake is hard and difficult to remove from a glass dish).
The lid was screwed on tightly, as the solid has a significant vapor pressure, evident from the smell, and sublimates readily at room temperature, similar to iodine.
The plastic dish was hit with a hammer to break loose the crystal cake and coarsely crush it.
The crystal shards:


The final product: 280g from this batch, together with the previous batch, giving over 300g in total and filling a 250ml bottle to the edge:


Discussion

I obtained a yield of 280g (91%), which is almost exactly the literature yield from the Orgsyn procedure.
The product has a pronounced sweetish camphor-like smell which quickly fills the laboratory.

Dehydrochlorination to Hexachloropropene: Coming soon!
If you wonder why one would want to make hexachloropropene: look at patent US1320869.
Also, it can be used to make anhydrous metal chlorides from the oxides (e.g. Brauer: UCl4 from UO2) and from hydrated chlorides.
Look at this post from benzylchloride1 about the preparation of anhydrous chromium(III)chloride. This is the only previous mention of hexachloropropene on this forum.

[Edited on 12-10-2010 by garage chemist]

TCE is still available - I saw a gallon of it sitting on the shelf at the hardware store recently.

I see that route as being more useful just for acetyl chloride: TCE + acetic acid --(sulfuric acid)--> chloroacetyl chloride + acetyl chloride. Boiling acetyl chloride is 50.9C, chloroacetyl chloride is 107C. But other acyl chlorides it certainly won't separate nearly as cleanly as with your proposed method - didn't mean to discount the usefulness of what you're doing here!

Here is my synthesis of hexachloropropene.
I didn't use Mr. Gergels method with NaOH, but instead used the procedure from this patent, GB841358A, which uses an aqueous suspension of calcium hydroxide as the base.
There is no dangerous exotherm with this method, and the usage of the weaker base Ca(OH)2, with a pH of the suspension of 12, is supposed to reduce side reactions like hydrolysis that may occur when using the stronger base NaOH.
The use of Ca(OH)2 suspension for the dehydrochlorination of polychlorinated aliphatic hydrocarbons is a standard industrial procedure for the production of trichloroethylene and perchloroethylene from 1,1,2,2-tetrachloroethane and pentachloroethane, with practically quantitative conversion and yield.

Preparation

I an 500ml round-bottom flask, 65g technical calcium hydroxide (hydrated lime) were slurried into 250ml water by vigorous shaking, a stirbar was added, and the flask was clamped over a magnetic stirrer.


220g of heptachloropropane were added, and the flask fitted with a reflux condenser.


The mixture was heated with a bunsen burner, first carefully, until the heptachloropropane had all melted into a liquid lower phase.
Then the stirring was started, and the mixture brought to a reflux.
The stirrer was set to the highest possible speed that did not uncouple the stirbar. Since this is a two-phase reaction with the phases being almost insoluble in each other, the reaction can only occur at the phase interface. Powerful stirring which turns the two phases into a fine emulsion is therefore very important.


The mixture was refluxed with vigorous stirring for 6 hours (perhaps this was a mistake, as the patent specifies a temperature of 90°C, not 100°C).
After stopping the heating and stirring, a drop of phenolphthalein solution was added to see whether the aqueous phase was still alkaline.
This was done due to the questionable quality of the Ca(OH)2, which produced quite strong fizzing when a bit was added to HCl, showing considerable uptake of atmospheric CO2 during storage.
The pink color showed that some unreacted Ca(OH)2 was still present at the end of the reaction, as intended:


Now the mixture was acidified by careful addition of HCl to dissolve the residual Ca(OH)2.
As everything dissolved, the mixture cleanly split into two phases:


The lower phase was washed twice with water, then twice with Na2CO3 solution (there seemed to be some acidic impurity in the crude product that produced some CO2 in the first carbonate wash) and again with water.
It was dried with calcium chloride.
The product has such a high density that the calcium chloride floated on it:


There was some brown flocculent crud, probably from dirt in the lime, therefore the liquid was filtered.

It was then distilled in membrane pump vacuum. It went over practically completely at about 95°C. Only after nearly all of the product had distilled did the temperature start to rise, and the distillation was stopped at this point.


The product, ca. 160g of a clear, mobile heavy oil with pleasant sweetish smell:


The yield was ca. 83%, which is good, but not as high as the patent claims for this process (93%).
One possible cause could be the temperature being higher than the specified 90°C- perhaps this has caused some hydrolysis of the product to trichloroacrylic acid and its secondary products. This could be the source for the observed acidic impurity in the crude product after acidification of the aqueous layer.

If I do this synthesis again, I will try to keep the temperature at 90°C, and also use more water to slurry the Ca(OH)2- the mixture became somewhat harder to stir during the reaction, and thorough mixing could not be ensured throughout the whole reflux time.

Here is the patent that describes the preparation of acyl chlorides from the acid and hexachloropropene:
GB1320869.
If this actually works, it would be a great alternative to the usage of phosphorus chlorides- not only is hexachloropropene much easier to make, but it is also an amateur-friendly reagent because it is easy to store and handle (doesn't react with moisture, doesn't give off corrosive or choking fumes, and it even smells relatively pleasant).





[Edited on 12-10-2010 by garage chemist]

Quote: Originally posted by garage chemist

I can't find any information on octachloropropane, no physical properties, nothing. Yet it must be in the literature.

Quote: Originally posted by garage chemist

EDIT: I looked up Octachloropropane. mp: 160°C, bp: 268-269°C at 734 mmHg. Beilstein only lists the preparation from 1,2,3-trichloropropane and excess ICl3 at 200°C. It decomposes to C2Cl4 and CCl4 when its vapor is passed through a tube at 300°C. This might be of interest for those wishing to prepare some CCl4, but it would be a somewhat lengthy and work-intensive route.

Quote: Originally posted by garage chemist

aliced25: Do you have a source for that reaction of hypochlorite with citric acid? I've never heard of something like that.