Sauron
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Chlorination of CS2 Revisited
The hassle with making CCl4 from CS2 and Cl2 is that the product is a mixture of CCl4 and the two sulfur chlorides SCl2 and S2Cl2. The above assumes
Fe or Fe chloride as catalyst.
The difficulty arises because CCl4 boils at 71 C while SCl2 boils at 59.6 C and thus it is difficult to seperate them by fractionation (for difficult
read: slow, energy intensive and therefore costly.)
S2Cl2 is high boiling.
On the other hand if a small mol% of I2 is used as catalyst, diffuse light is maintained and temperatures kept below 30 C, the high boiling
intermediate CSCl4 (CCl3SCl) if formed, and now the problem is that its boiling point is too close to S2Cl2 for a clean fractionation.
There is a third fortuitous alternative. Rather than I2, granulated activated charcoal, which needs to be metals free, will catalyze this reaction and
by manipulating the temperature, the sulfur dichloride can be produced almost exclusively.
This allows a clean fractionation of SCl2 from CCl3SCl
SCl2 bp 59.6 C
CCl3SCl bp 149 C
The CCl3SCl is then treated with iron filings (dry) to obtain CCl4 quantitatively
The stoichiometries are:
CS2 + 3 Cl2 -> CCl3SCl + SCl2
2 CS2 + 5 Cl2 -> 2 CCl3SCl + S2Cl2
2 SCl2 <--> S2Cl2 + Cl2
On a bench scale, this is done in a vertical jacketed column like a chromatography column or a Hempel fractionating column with a water jacket. The
reactants are introduced in a countercurrent fashion, Cl2 from bottom and CS2 from top at a ration of 3-4 equiv Cl2 to 1 equiv CS2 and the coolant
maintained (preferably by a refrigerated recirculating chiller) at 0-40 C. The column dimensions are 1.5 m high by 25 mm ID.
This is a slow trickle reactor. The CCl3SCl and SCl2 collects in a receiving flask.
SCl2 is not very stable, Brauer says it can be stored for a few days in glass over a drop or two of PCl3. So obviousl;y the mixture should be
seperated as soon as possible. The CCl3SCl is obnoxiously lachrymatory and toxic. Treat it immediately with Fe filings and it converts to CCl4, filter
off the solids. You can refractionate the CCl4 but it will be quite pure, you can verify by TLC or HPLC or IR.
I have not found any better way to make CCl4.
Though I have found a number of routes to CHCl3.
Chlorination of MeSCN produces TCT, and a complex mixture of intermediates that if exhaustively chlorinated end up as CCl4 and sulfur chlorides. But
MeSCN is too expensive to use unless you really need to make your own TCT.
MeSCN is about $70/100 g while CS2 is $170/liter.
I have previously posted on preps of MeSCN, some of which can achieve economy.
But on balance chlorination of CS2 seems to be the most direct route to CCl4.
Vapor phase chlorination starting from DCM at 500 C in a tube fornace with or without catalysis will produce a mix of CHCl3, CCl4, C2Cl6, chlorinated
ethylenes and ethanes and is a bit of a muddle. Same goes for photochemical chlorination, again usually in vapor phase but lower temperature.
SO2Cl2/peroxide initiated radical chlorination will stop at CHCl3 if it even gets that far.
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Panache
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Perhaps you have already considered the possibility of firstly separating the SCl2 and carbon tet from the S2Cl2 via a simple distillation and
thereafter using a reverse distillation on the mixture of SCl2 and carbon tet using dry ice and patience. If this is the case i would be interested to
know why it has been discounted.
I attempted to find a phase diagram for either system but was unsuccessful, this is not surprising however there would have to be some extra-ordinary
features of the diagrams to preclude this separation method from being successful, especially if you do it twice, given the massive difference in
melting points.
When i have done it (not on this system rather ethanol/water systems, wine basically) i typically use a vessel say for instance a 1L reagent bottle,
connected to an inverted 1L reagent bottle by means of a glass frit in a small section of glass tube. The solution is left to crystallise, after which
the arrangement is simply inverted and left at temperature again for a few more days so as to filter most of liquid slowly. I find the atmosphere
escaping the lower bottle to the upper bottle slowly produces enough agitation through the slurry. However each system is unique. If you have an
ultra-low freezer or access to plentiful dry ice then perhaps its worth a shot.
If it works it would be a very straightforward and innocuous solution to the shitty problem. Given the nature of the sulphur chlorides i would be
happiest having them at cryo temperatures anyway.
[Edited on 30-10-2008 by Panache]
[Edited on 30-10-2008 by Panache]
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Sauron
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I should have posted the AKSO patents by Rupp and Meyer.
Here's how this works:
1. Forget the iodine catalyst.
2. Use a trickle feed, countercurrent column of Cl2 from bottom, CS2 from top. The column is packed with GAC. Temperature is held to <40 C with
cooling water via a jacket.
Ratio of CS2 to Chlorine is held between 1:3 and 1:4
Under these conditions you get only SCl2 and CCl3CSCl and these boil almost 100 C apart.
So now you have pure CCl3SCl and can treat with dry Fe filings and get CCl4.
CCl3SCl is a fascinating compound with versatile chemistry and you can make many things from it besides CCl4. There a paper in Chem Rev on it, very
illuminating.
The SCl2 will revert to a mixture or better can be forced to S2Cl2 cna that can be used to make Ac2O.
The stench is what hoods and scrubbers are for.
Here are the patents. I like the trickle column better than the flooded clumn because refluxing CS2 is not my idea of fun.
I combined both patent docs into one pdf.
[Edited on 31-10-2008 by Sauron]
Attachment: 3673246.pdf (902kB)
This file has been downloaded 401 times
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Sauron
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What I like about this approach is that it is basically the same setup as for making SOcCl2 (colmn packed with GAC and jacketed for removing reaction
heat with a recirculaying chiller.) Only one reactant is different.
I have several peristaltic pumps, both fixed and variable speed, and even with the fixed speed pump drives you can vary the tubing size so to control
flow rate. So a slow steady feed of CS2 is easy to achieve. Getting in the right range of Cl2 feed is also pretty simple.
Here's an article in German from Synthesis by same authors detailing the bench scale process. They show their column with thermometer wells all along
the length which I regard as an extravagance. A little experimentation with an unjacketed column and you will know where the reaction zone is.
[Edited on 31-10-2008 by Sauron]
Attachment: s-1971-21761.pdf (187kB)
This file has been downloaded 511 times
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panziandi
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I hate to say it but all the time spent trying to find a high yielding "easy" and "economical" method to produce CHCl3 and CCl4 utilizing or
generating noxious by-products such as CS2 (neurotoxic, rediculously flammable (in a hot climate like yours I'd hate to be using it really especially
as it can even ignite from just a hot surface!)) sulphur chloride and what not. And all of these methods seem to involve distillations and
fractionations etc. Not something I'd be keen on to isolate large quantities of chloromethanes. What size/scale are you proposing running a batch on?
I would be tempted to revisit chlorination of DCM. Ok so chlorination of CH4 will yield a higher degree of various by-products but when your starting
material is already partially chlorinated the number of possible by-products and the % of them in the final composition should be lower I would have
expected. Perhaps radical chlorination of DCM would be viable. It would yield CHCl3 CCl4 (and CCl3-CCl3) as the main compounds all 3 should be easily
fractionated. Perhaps chlorination of a surface or using different ratios may give a prefered ratio of products. I'm sure this pathway may be worth
looking into in more detail if you are prepared to look at what I consider riskier options.
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Jor
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Is it maybe possible, to chlorinate DCM, in te presence of a little phosphorus, iodine or sulfur. This would form respectively PCl5, ICl or sulfur
chlorides, wich are all good chlorinating agents as far as I know. The elements are regenerated. Maybe this is easier than the radical chlorination.
What do you think?
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panziandi
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Well I PCl5 will not chlorinate DCM AFAIK. ICl will halogenate DCM via radical reaction to form iodo and chloro products I would imagine. Even if you
get by products via free radicals, on a large lab or pilot scale (as I have th efeeling Sauron wishes to make CCl4 and CHCl3 on), the mixture would be
easily fractionated to yield quite sizble fractions of the tri and tetra chloromethanes and even the polychlorinated ethanes are good solvents /
useful.
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Jor
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So ICl might then be a solution? I think the easiest and cheapest method would be trying to develop one wich exclusively uses DCM and chlorine, with a
catalyst (wich will form a strong chlorinating agent with chlorine in situ, and being regenerated, thus being a catalyst).
ICl can work you say, but will give iodo-by products. That is a problem as iodine will then not be catalytic and the stuff is expensive. Will there be
much iodo-byproduct? How about sulfur chlorides? And how are selenium or even tellurium chlorides as chlorinating agents? Are they stronger than the
sulfur chlorides?
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panziandi
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Well, I suggest UV &/or peroxide induced free radical chlorination of CH2Cl2 using Cl2. For example by passing a stream of Cl2 through chilled DCM
irradiated by UV. Using ICl you will generate I* and Cl* radicals which will both react so you will form in theory 50% chloro and 50% iodo containing
products. Chlorinating agents capable maybe hypochlorite ClO- which MAY chlorinate CHCl3 to CCl4 (not too sure I know BrO- will brominate CHBr3 to
CBr4). Ofcourse hypochlorite + acid = chlorine which can chlorinate.
As to sulphur, selenium and tellurium chlorides as chlorinating agents:
1) sulphur chlorides do chlorinate some C-H groups but not the C-H groups in methane or DCM
2) selenium chlorides probably will be similar to sulphur chlorides but much MUCH nastier to work with
3) tellurium chlorides may possibly work,but would be rediculously costly
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Sauron
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Peroxide initiated FR chlorination (w/SO2Cl2) stops at 2 chlorines per C stage, so you can't get past DCM.
UV initiated FR chlorination is a good way to get from DCM to CHCl3 but beyond that point you get not only CCl4 but C2H6 and a variety of
chloroethylenes and chloroethanes as byproducts.
It's a mess.
I prefer a cleaner process that produces a purer product. I am set up for photochemical work on a medium to large bench scale with 400 W medium
pressure Hg Hanovia lamp in immersion well.
I have lots of routes to CHCl3, best is from CCl3Br.
But this one from CS2 is best for CCl4.
Two interrelated alternatives I have posted about before are exploitation of chloral as feed stock, from chlorination of ethanol; and exploitation of
trichloroacetic acid by photolytic chlorination of acetic acid.
The chlorination of ethanol to trichloroacetaldehyde is not a UV reaction. But if you introduce UV photolysis late in the process, as if trying to
overchlorinate chloral, you get trichloroacetyl chloride and that promptly falls apart to CCl4.
Same thing happens with acetic acid, or more properly trichloroacetic acid.
In fact if you take preformed trichloroacetic acid and try to prepare the acyl chloride you get low yield and CHCl3/CCl4 byproduct. And that is
without UV.
Ethanol and GAA are cheaper feedstocks than CS2 but the process requires UV.
CS2 chlorination requires no UV and you get lots S2Cl2 for making Ac2O.
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Sauron
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panziandi, I know how to handle CS2. I first acquired some about 45 years ago and in a climate much like this.
As to all that blather about noxious intermediates and byproducts, are you writing a paper for Green Chemistry? Because chlorination of CS2 is the
standard method of making CCl4 industrially and that is why sulfur chlorides are cheap and plentiful. That is why CS2 plants and CCl4 plants are
always sited together. Most CS2 in fact is used to make CCl4. All of this will be done in a huge (2 x 1x 1 m) hood with a scrubber scaled to match.
All CCl3SCl will be destroyed (with Fe filings to make CCl4) while SCl2 will be stored for conversion to S2Cl2 and use in making Ac2O. Scale? A few
liters at a time.
So much wringing of hands! For what? The author of the celebrated Illustrated Practical Guides made noxious sulfur chlorides and noxious SO3 and
reacted them to produce noxious SOCl2. For that he was practically canonized. You'd think he could heal incurables with his touch.
I propose something arguendo less hazardous than making your own SO3 and we get all this gnashing of teeth and rending of garments as if the
antichrist had just sent clouds of SO2 out of his orifices in all directions.
Go figure!
Furthermore, I did not say anything about easy or cheap except in relative terms. There's only one bottom line, and that is I need CCl4 and I cannot
buy it. I have no choice but to make it. The same goes for CHCl3, and an unfortunately long list of other "common" solvents. I must make them or do
without.
[Edited on 1-11-2008 by Sauron]
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panziandi
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Good I expected you to know how to handle CS2!
I have no problem really getting hold of CHCl3 and I have enough CCl4 to last a while I expect. And CS2 I can get relatively easily too.
I am merely saying that I personally would not want to manipulate the chlorination of CS2 on a large scale in a hot country! Mainly because I see
potential for an accident. I personally could probably get sulphur chlorides if I needed them and have Ac2O.
If I had your photoreactor and had a ready supply of Cl2 and DCM I would run a photochemical chlorination... why?
because:
1) I'd do it just to find out what % of the products is CHCl3 and CCl4
2) Why the hell not? It's called experimenting! And for people without CS2 perhaps DCM chlorination with UV may be practical on a largish scale?
It seems like the work up may be just as intensive as separating S chlorides from C chlorides.
It was only a suggestion, CS2 has so many uses itself and DCM is cheaper.
I was also under the impression that industrially CH4 chlorination was used to a range of chloro compounds from CH3Cl to C2Cl6 etc. They do not form
azeotropes with each other so should be relatively easy to isolate by fractionating and azeotropic distillation with H2O etc
(Edit)
Why not do both reactions? Just to get an idea of ease and yields and also just to write it up so that anyone interested in that pathway could perhaps
repeat it?
[Edited on 1-11-2008 by panziandi]
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Sauron
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I envy your ability to get chloroform and CCl4. Both are prohibited here, the former as an anti-meth measure and the latter for Montreal Treaty
reasons. Both absurd. Reducing industrial use is one thing, but prohibiting lab use is ridiculous.
Those industrial chlorinations are vapor phase generally. Just not my cup of cha. I intend to do the CS2 route, the chloral route and possibly the GAA
route at which point I ought to have all the CCl4 I need.
CHCl3 is easier.
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Jor
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It's quite strange chloroform is prohibited in your country due to meth reasons, but iodine is not. I really wonder why to ban all the precursors wich
are used in the lab very frequently. If I was the government, I would instead take a tighter grip on epredine en loosen the grip on CHCl3, I2, red P,
and so on. I can understand the banning of red P, wich is a key in the production of meth and also a key to making the phosphorus chlorides, wich can
be used for Chemical Weapons. So I can understand the red P, although we ofcourse suffer from it. But I2? Chloroform? I think these should be removed.
Have you though of decarboxylating trichloroacetic acid for chloroform? Not the cheapest method, but seems to be easy, and in my impression money is
not the greatest issue (all the equipment and expensive chemicals you buy , eg oleum  , you payed like 2000US for that right?).
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panziandi
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I'm jealous of some of your equipment and chemicals Sauron... it woirks both ways :p!
Ah ok! I suppose vapour phase is a little trickier. The GAA may be a useful way to go since full chlorination to TCAA is easily achieved and from
there to CCl4 shouldn't be an issue! And I personally feel it would be better (safety & ease wise) for other people on this forum to follow.
Perhaps someone could look into CCl4 from GAA and see if how viable it is?
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Klute
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This question might be a little off topic, but what's the fuss with CCl4? What applications absolutely require it and cannot work with another
solvent?
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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Sauron
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A myriad of them.
And I am stubborn, obstinate and dislike being told I can't have something like this.
It's easy to test the final stage of the GAA -> CCl4 process. Buy some trichloroacetic acid. Try to chlorinate it under UV (if I recall, in
benzene.) It should fall apart quantitatively to CCl4. I posted a review on chloral that contains the refs on this. Trichloroacetyl chloride is
unstable. See also the H.C.Brown JACS paper on volatile acyl chlorides from carboxylic acids and benzoyl chloride. He observed the same thing (without
UV) while trying to prepare trichloroacetyl chloride.
[Edited on 2-11-2008 by Sauron]
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Klute
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| Quote: |
And I am stubborn, obstinate and dislike being told I can't have something like this.
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He he
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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Sauron
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A new use for CCl4 just fell into my lap.
3 CCl4 + 2 P2O5 -> 4 POCl3 + 3 CO2
200-210 C, 48 hrs, 80% from Ber., 1872]]The second cheapest way of making POCl3 I have ever heard of.
[Edited on 3-11-2008 by Sauron]
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panziandi
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POCl3 doncha mean Sauron? :p ...
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Sauron
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Of course. It was correct in the equation. Other was a typo. Now corrected.
Thanks
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