Sciencemadness Discussion Board

Separation of CHCl=CCl2 and CCl4

woelen - 21-8-2012 at 09:48

Some time ago, I received two very old and dirty bottles of chlorinated solvents. One of these bottles contains impure CCl4 and the other contains CHCl=CCl2. The CCl4 was yellow and had a sweet smell, but also an unpleasant sharp smell was associated with it. The CHCl=CCl2 was colorless, but contained a lot of flocculent solid matter, suspended in the liquid. I decided to clean up these chemicals and use distillation. The yellow color must be some non-volatile organic contamination and the sharp smell could be some sulphurous compound (CCl4 in the past was made from CS2). I have no idea what the flocculent solid is, it might be some stabilizer, which has deteriorated after so many years of storage in a dirty warm and dusty place.

I distilled both liquids, discarding the first 5% or so and left appr. 5% of the final volume, which has a deep yellow/brown color. This process gave me a nice colorless and sweet smelling liquid, but I made a really stupid mistake :mad:, I mixed up distilled CCl4 with distilled CHCl=CCl2. I poured the distilled CHCl=CCl2 in the bottle which already contained the distilled CCl4 :(. I now have around 400 ml of clear colorless liquid with a sweet smell and this liquid is a mix of CCl4 and CHCl=CCl2. Their boiling points are really close and I see no way of separating them.

Any ideas what to do with this? I was really angry with myself, this is sooo stupid.
If no separation is possible, what interesting things can be done with the mix of these two chemicals? Is it still useful for anything chemistry related, or is its only use reduced to degreasing and maybe as a non-selective general chlorinated solvent?

Magpie - 21-8-2012 at 10:46

Sorry to hear that you made such a mistake. This is easily done and I did the same when separating some coconut oil derived esters by distillation.

It seems the bp's are about 10C apart. A highly efficient fractionating column and a lot of patience should be able to separate them, assuming they don't form an azeotrope, which is not likely I think.

Whether you want to do this or not depends on how badly you want to - CCl4 being rather rare and all.

Nicodem - 21-8-2012 at 11:03

Quote: Originally posted by woelen  
If no separation is possible, what interesting things can be done with the mix of these two chemicals? Is it still useful for anything chemistry related, or is its only use reduced to degreasing and maybe as a non-selective general chlorinated solvent?

I should check the literature, but perhaps it might be possible to use it for an acid catalysed alkylation analogously to what garage chemist describes in his Synthesis of unsym.-heptachloropropane and hexachloropropene. Do you have any aluminium chloride?

Magpie - 21-8-2012 at 11:35

A more drastic approach might be to brominate or oxidize the alkene sacrificially, thereby allowing a more facile recovery of the CCl4.

woelen - 21-8-2012 at 11:58

I have AlCl3 anhydrous, but does that help in making heptachloropropane. The synth of Garage chemist is based on CCl2=CCl2 and CHCl3. I have a mix of CHCl=CCl2 and CCl4. Indeed quite similar (an hydrogen atom is exchanged between the molecules), so I could give it a try, but I do not really expect any results, because CCl4 is much less reactive than any of the other chemicals mentioned here.

Brominating the CHCl=CCl2 to make its boiling point much higher indeed is an option, but I doubt whether I am willing to sacrifice my precious bromine for this. A lot of bromine is needed to do this bromination and from experience I know that bromination of CHCl=CCl2 is not that easy. It is a slow reaction and may be hard to bring to completion.

Most likely I take my loss and try to find an application for this mix of chemicals.

unionised - 21-8-2012 at 12:01

Just a thought: Carbon tet will freeze in dry ice ( by quite a margin). Trike won't.

Nicodem - 21-8-2012 at 14:05

Quote: Originally posted by woelen  
I have AlCl3 anhydrous, but does that help in making heptachloropropane. The synth of Garage chemist is based on CCl2=CCl2 and CHCl3. I have a mix of CHCl=CCl2 and CCl4. Indeed quite similar (an hydrogen atom is exchanged between the molecules), so I could give it a try, but I do not really expect any results, because CCl4 is much less reactive than any of the other chemicals mentioned here.

Friedel-Crafts alkylations with CCl4 are known. I did a cursory literature search on the analogous reaction between CCl4 and trichloroethene and found no conclusive evidence of what the major product would be. US3268603 describes the electrophilic addition to occur from the less substituted side:
Cl2C=CHCl + CCl4 <=> Cl3C-CHCl-CCl3
It explicitly lists CCl4 as a suitable electrophile for this addition reaction on polyhaloethenes, but gives no example. Similarly, some Japonese patents also claim the possibility of this reaction, but from the little I could understand from the schemes, the examples do not mention this specific reaction (see JP4193841, JP4305542, JP4253928). In the examples, however, there are described the related reactions of CFCl3 on chlorofluoroethenes.

Edit: Nevermind. I found a reference where the reaction is described to give sym-heptachloropropane:
Journal fuer Praktische Chemie 1914, 89, 414-424; DOI: 10.1002/prac.19140890126
I believe you probably understand German enough to understand the article. I would have to struggle trough it to comprehend. Quoting from its CA:
Quote:
The following syntheses were carried out: CHCl3 + CHCl:CCl2 = CHCl2CHClCCl3; CCl4 + CHCl:CCl2 = CCl3CHClCCl3; CHCl3 + CHCl:CHCl = CHCl2CHClCHCl3; CCl4 + CHCl:CHCl = CHCl2CHCl2CC; CHCl3 + CHCl:CH2 = C3Cl4H4; CHBr3 + CHBr:CHBr = CHBr2CHBrCHBr2.


And here is another one:
J. Am. Chem. Soc. 1938, 60, 2491–2495; DOI: 10.1021/ja01277a059
Quoting from its CA:
Quote:
Cl2C:CHCl and CCl4 with AlCl3 at 20-30° for 48 h. give 49% of Cl3CCHClCCl3, b20 126-32°.

A ratio of 520 g trichloroethene vs. 1220 g CCl4 was used (with 50 g aluminium chloride). After the workup, distillation at 20 torr is used for the isolation of the product, so you can use an aspirator.

[Edited on 21/8/2012 by Nicodem]

woelen - 21-8-2012 at 23:23

Thanks for these references. This looks very promising and I am willing to try this. I read the thread from Garage chemist and this heptachloro compound would be a nice addition to my lab.

I can read German without any problems, but I cannot access the article. Is it possible for you to access them and make them available in the references section?
This is a general problem for me. In the past (e.g. before the year 2000) many interesting articles were available from university websites as postscript document, but nowadays you have to pay outrageous amounts of money for just a single article (e.g. EUR 30 or so) and sometimes the access only is for two days or even one day. This is really bad.

Nicodem - 22-8-2012 at 08:31

Quote: Originally posted by woelen  
I can read German without any problems, but I cannot access the article. Is it possible for you to access them and make them available in the references section?

Get them here.

woelen - 22-8-2012 at 22:37

Thanks very much!

Formatik - 23-8-2012 at 00:09

Quote: Originally posted by woelen  
I can read German without any problems, but I cannot access the article. Is it possible for you to access them and make them available in the references section?
This is a general problem for me. In the past (e.g. before the year 2000) many interesting articles were available from university websites as postscript document, but nowadays you have to pay outrageous amounts of money for just a single article (e.g. EUR 30 or so) and sometimes the access only is for two days or even one day. This is really bad.


Many volumes including that reference of Praktische Chemie is available at Gallica bnf for free. Check also hathitrust and archive.org, sometimes you can find what you need there when it comes to old references.