Magpie
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hydrochlorination of perc
I wish to hydrochlorinate perc (1,1,2,2 tetrachloroethylene) to 1,1,1,2,2 pentachloroethane using gaseous HCl. I've searched the internet and JACS at
the library but have not found anything useful.
A related synthesis is that for unsym.-heptachloropropane as found in Prepublication. In this synthesis AlCl3 is used as catalyst.
Does anyone have any experience doing this, or have any recommendations?
[Edited on 15-8-2015 by Magpie]
Attachment: perc eqn.doc (23kB)
This file has been downloaded 413 times
[Edited on 15-8-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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gdflp
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The closest article I could find was http://onlinelibrary.wiley.com/doi/10.1002/anie.200801760/ab... maybe that's of some use? I'm quite surprised that there isn't more literature on
this reaction, but it may be quite difficult due to the deactivated nature of that alkene.
On a different note, I remembered reading a patent a few weeks ago that mentioned pentachloroethane as a major byproduct. The procedure describes the production of chloral and it involves
reacting hypochlorous acid with trichloroethylene. A yield of slightly over 50% pentachloroethane based on trichloroethylene was obtained, as well as
chloral which is a precursor to isatin(I've been purifying some technical grade solvents recently and I want to ensure I've removed all of the thiophenes from the toluene, so
this is a planned future synthesis for myself). If you're only looking for the pentachloroethane, perhaps this method is worth considering.
[Edited on 8-15-2015 by gdflp]
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Magpie
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Thanks for the information. The link does not work for me.
What I'm after is a saturated chlorocarbon that has a bp in the range of 110-170°C. Perc would have been good but it is unsaturated (an alkene).
R-130 or R-130a refrigerants would work but R-130a doesn't seem to be in use anymore and R-130 has been banned by the Montreal protocol. R-140
doesn't seem to be available anymore either.
Halogenated hydrocarbon solvents are getting tough to find in the OTC market. It might pay to stock up on brake cleaner (Perc).
The single most important condition for a successful synthesis is good mixing - Nicodem
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gdflp
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Sorry, stray comma in the link. It should work now.
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Magpie
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Thanks, the link works now. I'm going to try to get it through References of the forum.
It is interesting that hydrohalogenation is invariably used to illustrate the Markovnikov rule in every organic text that I've seen. Some texts even
suggest that this reaction "readily occurs." But one text says that it is only practical when using HBr. HCl is a reluctant participant because of
the chlorine's strong affinity for H. H+ is the necessary reactant for the 1st step in the reaction.
There is another reference that may prove useful by Kropp et al. It is in JACS so I can get it Monday when the library opens.
[Edited on 15-8-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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Here's the article by Kropp et al:
Attachment: Hydrohalogenation of Alkenes and Alkynes.pdf (273kB)
This file has been downloaded 516 times
It looks promising.
[Edited on 17-8-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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This reference by Kropp et al indicates that the hydrochlorination of alkenes can be greatly facilitated by the addition of alumina or silica gel:
Attachment: Hydrochlorination of Perc.doc (27kB)
This file has been downloaded 352 times
I just finished trying this:
CCl2=CCl2 + HCl ----> CHCl2-CCl3
125mL of perchloroethylene was sparged with one equivalent of dry HCl gas over a period of 100 minutes, at room temperature. 25g of neutral alumina
[ICN, chromatographic grade, activity I (0% water)] had been added. The reaction vessel was continously stirred. The HCl was admitted using an 8mm
fritted end glass tube. There was no uptake of HCl.
The similar reaction of ethylene reacting with HCl to form ethyl chloride is highly endothermic, ie, I calculate the heat of reaction to be 249.9 kJ
/mole.
CH2=CH2 + HCl ---> CHCl2-Cl3
Presumably the perc hydrochlorination would be similarly endothermic.
Does anyone have any suggestions for facilitating the hydrochlorination of perc?
[Edited on 23-8-2015 by Magpie]
[Edited on 23-8-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Oscilllator
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I was walking along yesterday and something fell off the back of a truck. I'll post it here as I think you might like it Magpie.
Attachment: Gaspar_et_al-2008-Angewandte_Chemie_International_Edition.pdf (326kB)
This file has been downloaded 359 times
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Magpie
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Thank you for that Oscillator. But I'm afraid that the catalysts "PhSiH3, Co-(BF4)2·6H2O, as well as ligand 6 (from Aldrich under the name of
SALDIPAC)" are too exotic for me.
I have high hopes that use of a Lewis acid catalyst like AlCl3 or ZnCl2 will do.
I'm keeping the gasification train set up in my hood in anticipation of making another try:
 
The single most important condition for a successful synthesis is good mixing - Nicodem
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Nicodem
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As far as I know, it is not possible at all and there are no literature examples that I could find. I could not find hydrobromination either. The
inductive effect of the chlorines is simply too deactivating and there is no mesomeric effect to allow for a conjugate nucleophilic addition.
Nevertheless, strong electrophiles do attack it. You can make hexachloroethane by chlorination with Cl2. There are a few examples in the
literature. Similarly, it reacts with Br2 to give 1,2-dibromo-1,1,2,2-tetrachoroethane (DOI:10.1016/0040-4020(81)85057-0).
You could also try to prepare trichloroacetic acid by oxidation with trichloroisocyanuric acid in water, but a cosolvent like acetonitrile or acetic
acid would most likely be needed. I'm not sure this would work as the double bond is pretty deactivated, but might be worth trying.
Acetoxychlorination with TCCA in acetic acid might be a home chemist friendly route to acetyl chloride, it it worked (may require some
ZnCl2 as a catalyst), giving trichloroacetic acid as a bonus byproduct.
Trichloroacetylchloride or alkyl trichloroacetates can be made by UV photooxidation of tetrachloroethylene with oxygen (DOI:
10.1080/00222337708061286).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Magpie
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unsym.-heptachloropropane can be made from perc and chloroform using AlCl3 as catalyst. This is shown in OrgSyn (search: unsym.-heptachloropropane).
garage chemist tells how he did this in Prepublication.
I'm presuming this employs an electrophilic attack of H+ on the perc double bond. Is there a reason why this couldn't work using gaseous HCl in place
of the chloroform?
The single most important condition for a successful synthesis is good mixing - Nicodem
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Nicodem
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Quote: Originally posted by Magpie  | | I'm presuming this employs an electrophilic attack of H+ on the perc double bond. Is there a reason why this couldn't work using gaseous HCl in place
of the chloroform? |
No, the reaction between CHCl3 and Cl2C=CCl2 is most likely an electrophilic addition of CHCl3 activated
with AlCl3, thus formally with CHCl2+ as the attacking electrophile. It is only due to the symmetry of
Cl2C=CCl2 that you get the same product by imagining the electrophilic addition of a proton.
Is there a particular reason you want this hydrochlorination to work? Do you need the product? Because pentachloroethane can be made by chlorinating
trichloroethylene (which used to be quite easy to acquire last time I chacked, maybe it still is).
You can also obtain pentachloroethane from perchloroethylene, by first preparing hexachloroethane via Cl2 and then hydrodechlorinate it.
Unfortunately, I could only find photochemical hydrodechlorinations of hexachloroethane using either triethylamine (CA99:194170) or diethyl ether
(CA108:221256). There are few other methods, but suitable only for industrial processes (DOI: 10.1016/j.apcata.2011.02.035) or require expensive
reagents (DOI: 10.1016/j.tetlet.2009.05.087). The reduction with diethyl ether only gives a ≤20% yield, while the yield using triehtylamine is not
reported in the abstract. This later reaction is particularly interesting as the byproduct is diethylvinylamine, a quite useful reagent. Toluene,
2-propanol or other compounds with easily abstractable hydrogens might also work as a reducing reagent, toluene yielding benzyl chloride and
2-propanol yielding acetone as byproducts. I guess it could be an interesting experiment to let a flask of hexachloroethane in toluene stand on
sunlight for a month or so (you can check if the reaction worked by looking for BnCl with TLC; with 2-propanol you can monitor the pH increase from
the released HCl).
| Quote: | Chem. Abstr. 99: 194170
Photochemical oxidation of triethylamine by hexachloroethane
Zhurnal Organicheskoi Khimii, 1983, 19(7), 1553-1554.
By: Markaryan, Sh. A.
The title reaction gave Et2NCH:CH2 and C2Cl5H. Initially an ion radical pair was formed, and this lost HCl to give a neutral radical pair.
Chem. Abstr. 108: 221256
The photochemical reaction of dialkyl ethers with perchloroalkanes
Armyanskii Khimicheskii Zhurnal, 1987, 40(5), 334-335.
Markaryan, Sh. A.
RCCl3 (R = Cl, Cl3C) reacted with (R1CH2)2O (I; R1 = Me, Pr) in a 1:10 ratio under UV irradn. to give HCl and the corresponding R1CH2OCHClR1 and
RCHCl2 in ≤20% yield via initial C-Cl bond cleavage and radical-chain abstraction of an α-H from I. |
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Magpie
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| Quote: Originally posted by Nicodem |
No, the reaction between CHCl3 and Cl2C=CCl2 is most likely an electrophilic addition of CHCl3 activated
with AlCl3, thus formally with CHCl2+ as the attacking electrophile. It is only due to the symmetry of
Cl2C=CCl2 that you get the same product by imagining the electrophilic addition of a proton.
|
Yes, thanks for this. You just saved me a wasted experiment.
| Quote: Originally posted by Nicodem |
Is there a particular reason you want this hydrochlorination to work? Do you need the product? Because pentachloroethane can be made by chlorinating
trichloroethylene (which used to be quite easy to acquire last time I chacked, maybe it still is).
|
I see that trichloroethylene is available on eBay. This would be an option.
The single most important condition for a successful synthesis is good mixing - Nicodem
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organicchemist25
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| Quote: Originally posted by Magpie | Thank you for that Oscillator. But I'm afraid that the catalysts "PhSiH3, Co-(BF4)2·6H2O, as well as ligand 6 (from Aldrich under the name of
SALDIPAC)" are too exotic for me.
I have high hopes that use of a Lewis acid catalyst like AlCl3 or ZnCl2 will do.
I'm keeping the gasification train set up in my hood in anticipation of making another try:
|
Magpie, are you generating the Cl gas from table salt, using a trap to collect any condensed liquid then scrubbing the gas through water?
I ask because I am looking to make a Cl gas generator and your setup seems its doable with stuff I have laying around.
Thanks.
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Magpie
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What you see in the above photos is an HCl generator. It uses NaCl and NaHSO4.
I use pool TCCA and dilute HCl to generate Cl2. The apparatus, however, is very similar. Len1 in Prepublication tells how to do this.
I use a trap before and after the H2SO4 water vapor absorber. This is to protect from suckbacks and foamovers, which I learned about the hard way.
The single most important condition for a successful synthesis is good mixing - Nicodem
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