Preparation of sulfur monochloride S2Cl2

Initially I wanted to post this the thread Garage Chemist started a few years ago, but considering the rather large screen size needed to visualize the whole thread, i prefered starting a new one.

A note concerning the cleaning of sulfur deposit on glassware: having heard of how annoying sulfur is to remove of glassware, i aprehended the cleaning. I've found out that a base bath (KOH/NaOH in EtOH/IPA) is terribly efficient at removing it. A single night soak removed a black, burnt sulfur deposit entirely. All the glassware came out as new, though i thought i was going to have to use pirhana (sp?) on this. Once more, I can only recommend preparing such a base bath for people willing to stop spending hours removing organic residu off glassware. No more scrapping of the glass surface from scrubbing with soap. Be sure to use adequate protection though (full facial protection, thick propylene gloves, lab coat and tight lid).

Preparation of Sulfur Monochloride by chlorination of Sulfur

S2Cl2 is said to be produced in high yield by bubbling dry Cl2 in hot, melted sulfur, with direct distillation of the formed S2Cl2.

The sulfur was obtained by purifying 80% gardening sulfur, by hot xylene extraction, a task I wouldn't give to my worst enemy. it smells bad, clogs up any filter fine enough to prevent the small black particules to pass, and spoils alot of glassware for little product. Next time (if ever), i will buy sublimed sulfur. I finally isolated over 50g of pur-ish sulfur.

The chlorine was produced by dripping 15% HCl over a TCCA slurry, as per Len's excellent document (original work by Organikum, sorry for typo!). Indeed, it produced a constant, easily monitered flow of chlorine, which was dried over CaCl2.

I made two attempts, the first one not producing a workable amount of distillate, the second being much more succesfull.
In the first attempt, stoechiometric amount of chlorine was passed, and in the second 1.5 excess was used. Although the success of the second didn't only depend on the use of excess chlorine, using at least 2x excess would give rise to higher yields, any formed SCl2 being reduced to S2Cl2 upon vac distn of the crude distillate over sulfur.

First attempt


The setup was composed of:
- A pressure-equalized addition funnel attached to a erlenmeyer, connected to a wash bottle full of granulated CaCl2, itself connected to a gas admission tube.



- A 100mL RBF, fitted with gas admission tube, a thermometer, magnetic stirring, and a adaptator in the central 29/32 neck.



-A simple distn setup, connected to the top of the adaptator
-A anti-suck back wash bottle, with a bed a CaCl2 (avoid admission of moist air), connected to a inverted full immersed in 30% NaOH solution to neutralize unreacted chlorine.

Complete setup:



15g (~<0.5 mol) of sulfur where introduced in the RBF, 17g (~>70 mmol) of 92% TCCA powder were introduced in the erlenmeyer and slurried with a little dH2O, and 48mL of 15% w/v HCL introduced in the addition funnel.



The RBF was heated with a mantle to 150°C. The sulfur started to melted above 110°C. The gas admission tube was then lowered as far as possible under the melted sulfur.



The HCl was then slowly dripped over the TCCA slurry, causing some bubbling and evolution of green Cl2 gas, until a flow of 1-2 bubbles/sec were passing through the sulfur.




There was some bubbling at the NaOH trap. After 5 min, some yellow droplets were seen refluxing on the sides of the flask.



Gassing was continued, and heating increased to above 180°C, and, even with strong insulation with aluminium foil, hardly any distillate was seen passing over, even though there was some reflux on the central neck of the flask. The gassing took a little less than 2 hours, and only a few drops of red distillate had been collected. During the gassing, there was constantly a little bubbling in the trap, apparently there was quite some unreacted Cl2. Heating was increased again. When HCl addition was finished and the Cl2 generator produced only a very faint flow of gas, it was disconnected from the flask, and the Cl2 trap was replaced by an aspirator. Vacuum was applied, but only a few mL of dark red distillate were obtained. The pot temp increased over 230°C, the take off came to a halt, so heating and vacuum were cut. A total of 4mL of red distillate was obtained.



The major problem was that the S2Cl2 vapors couldn't travel through the 5cm long adaptator, even with the insulation. I guess it finally turned to crap, as only a high boiling residu was left in the flask. Upon cooling, it turned to a very thick black tar, and i was scared i would never get my favorite RBF clean. Hopefully, scrapping under boiling xylene, and 24h soak in the base bath got it as new.



Second attempt


This time, a single neck 100mL RBF was used, and the gas inlet tube was fitted in the distn head, at the place of the thermometer. I had no means of reading the internal temperature though. The same, cleaned Cl2 generator was used, but the distn setup was used directly, without any cleaning. A fine layer of sulfur had appeared on the inside, from the hydrolysis of the sulfur chlorides by the moist atmosphere overnight. The same Cl2 trap was used (added some fresh 30% NaOH).



Again, 15g of sulfur was heated until it melted, the gas inlet tube immersed as deep as possible, and gassing started when the sulfur turned a little more brownish. The same amount of TCCA/HCl as in the first attempt was used. The setting on the mantle was roughly the same as when a temperature of 200°C was attained in the first attempt. The gassing was done a little more quickly this time. Pretty soon, a yellow liquid was seen refluxing on the sides of the flask.



Hopefully, a orange/red distillate started passing after 30min of gassing (heating had been slightly increased), some white smoke was seen in the condenser too. This time, there was hardly any bubbling in the trap. The distillate cleared up to a more golden yellow/orange color.



When all the HCl had been dripped in, the erlenmeyer was shaken for a while to get most of the Cl2 out. It was obvious that the take-off increased with the gas flow, surely by "pushing" the vapors up to the distn head. A second erlenmeyer was charged with 8g of TCCA, slurried with a little water, and with adequate precautions, the first erlenmeyer was disconnected and replaced by the second. 25mL of 15%HCl were added the the addition funnel, and gassing started again. The take off increased noticeably. Once the second gassing was complete, take off came to a near halt, even with increased heating. The Cl2 generator was disconnected, and vacuum applied, but only a few drops of distillate were recovered.




Heating and vaccum was stopped, the flask was left to cool a bit. A dark red/orange residu was left, much more fluid than the first one.



50mL of xylene were added, and brough to a boil for 5min. Upon emptying the flask, only a few "burnt" stains were left. A base bath soak removed them.

The red distillate was placed in a 50mL RBF, and a few grams of sulfur were added. It was connect to the simple distn setup, full aspirator vacuum applied (~25 Torr), and heating started.



At first, a red/orange distillate passed, so vacuum was cut, the distillate replaced in the still, and a little more sulfur added. Distn was started again, and this time a clear yellow distillate passed. It was collected between 51-56°C, giving 22.5g of pur S2Cl2:



The very slight orange tone must be du to the trace amounts of SCl2 present in the distn setup during the second vac distn. The product fumes slightly in moist air, and smells badly of rotten eggs/ sewers. Hopefully, the smell doesn't last long.


Comments

Although the second attempt was much more succesfull, more Cl2 would surely have produced a better yield. Any produced SCl2 isn't a problem, as it is reduced to S2Cl2 when distilling over sulfur. Next time, a short coluum will be used.
The yield wasn't calculated, as some of the S2Cl2 comes from the reduced S2Cl2, and it isn't possible to count the amount of SCl2 in the distillate, or the amount of sulfur remaining after distillation.

So for best yields, this reaction should be done at high temperatures (>200°C, no unreated chlorine), and with healthy (can i use that word for chlorine?! ) excess of Cl2. Also, the distillate should have the shortest path to the condenser, as it is hard to seperate from the unreacted sulfur in the pot, as Garage Chemist explained to me.

Many thanks to him for his advice, and for sharing his results in his thread, which was very helpfull.

Details on the use of the S2Cl2 are to come shortly.

[Edited on 16-4-2008 by Klute]

Nice work Klute and thanks for the detailed write-up. And BTW that is Len's Cl2 generation procedure (original work by Organikum), not Leu's.

May I ask what is in that lecture bottle with the green label? I am always on the lookout for possible new sources of reagents.

Sorry for the typo! I evidently meant Len's document

The lecture bottle is a disposable argon cartridge, with a inline CaCl2 dryer. I'm thinking of buying a rechargeable one, as these come expensive after a while...

Sauron, I have no interest whatsoever in sulfur moustard gas, or in any chemical weapons.
I'm using this reagent to form hydroxydisulfides (see my post in orgchem shortly). Not having CS2, I prefer this route. Apparently it gives a less complex mixture of substance. And i wouldn't know what to do with CCl4, i have no use for it that i can think of at the moment.

Thanks for the advice regarding the sulfur purification. But I realized my local supplier can sell me 500g of sublimed sulfur for 16E, while i paid 8euro for 750g of dirty 80% gardening sulfur, and 7E for a liter of xylene-containing solvant :S...

Sauron has a good point. Its like the meth situation, you may well own iodine or red phosphorus (or both :O) and have no intention of making any illegal substance, but thats not how the authorities will see it. As Sauron also said, the restricrions on chemicals vary from country to country (e.g. In the US both Iodine and Phosphorus are prohibited, whereas in the UK, there is no such legislation). Better to be safe than sorry right?

Other than that, this is an intersting synthesis. And a very well written up one at that

[Edited on 16-4-2008 by DJF90]

Yes, good point actually, I hadn't considered things that way. So thank you for the warning.
But i check the legislation, i have to file a declaration if i start handling more than 100kg per year for 3 consecutive years , which is not going to happen .
In any case, the S2Cl2 was used up like... 15min after having been isolated

When i distilled my crude product with excess sulfur to reduce the SCl2, there was sulfur left only in the still flask. As i distilled some xylene in the setup after distillation, it cleaned the droplets of product in the setup before it had time to hydrolyze to sulfur. I obtained a yellow solution of S2Cl2 in the receiver (which smells as bad!), and most of the tarry sulfur residu was dissolved in the hot xylene in the still. The "burnt" stains left in the flask were removed by a simple soak in the base bath, the rest of the setup came out perfectly clean too.
So after all cleaning sulfur out of glassware isn't that much of a hassle, when you've got a base bath .

EDIT: BTW, i didn't even know what the structure of mustard gas was before checking the textes. I was also surprised to see things like tiethanolamine or dimethylaminoethanol been restricted as weapons precursors.

[Edited on 17-4-2008 by Klute]

Lovely to see someone else doing experimental work! The first part is similar to what ive just been doing - its the third time thats happened with my posts - must be some form of collective ESP. I didnt have any S cleaning problems, the reaction vessel had no S in it at all. I believe NaOH marks the glassware - especially the quickfit? Even a 2% boiling solution has once left a mark on my glassware.

In chloroform? Whatever for? The yield is great in just liquid S, why complicate things.

"Thanks for the advice regarding the sulfur purification. But I realized my local supplier can sell me 500g of sublimed sulfur for 16E, while i paid 8euro for 750g of dirty 80% gardening sulfur, and 7E for a liter of xylene-containing solvant :S... "

I think Klute would have used the pure sulphur if he knew it was available at the time

[Edited on 19-4-2008 by DJF90]

Exactly
I spent nearly as much money for 500g sublimed sulfur, to get some crap from a gardening store and a bottle of paint remover, out of which i obtained 50g, emptying nearly the whole bottle in the process.. Needless to say, if i will try this again, i will buy the sulfur. I prefer having 450g pur sulfur lying on a shelf, than 600g of dirty garden sulfur

Might be worth a shot? Klute, once again, nice...

Attachment: SulfurChloridesfromBrauer.pdf (1.4MB)
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Thanks for adding this, but i think the temperature would be too low to distill the product as it is formed, with the setup i used, considering i had to heat somewhere between 200-300°C to get it going..

I think i would follow Len's direction if i try this again, he managed to do the reaction in better yields and shorter time, and has kindly provided a very detailed report on it.
But considering the tough work with the product disulfide made with phenols, until i get some commercial silical gel to purify those damn viscous disulfides, i working on TEMPO synth (yes, i am pissed off )