Carbon Disulfide from sulfur and charcoal

Introduction

Four years ago, BromicAcid was the one who did several experiments on the amateur production of carbon disulfide. Although he once obtained a very small amount of product, he was not able to devise a working method to produce useful amounts of this chemical.
Neither was I. We both heated sulfur and charcoal together in flasks and retorts, in hope to get a distillate of CS2. The only thing I ever managed to do was foul up my glassware.
Paraffin and polyethylene did not give any CS2 with sulfur either, only large amounts of H2S.

We all knew from the beginning what the problem was: the reaction between charcoal and sulfur requires a temperature far above the boiling point of sulfur, so that heating a charcoal- sulfur mixture in a retort always only results in the sulfur boiling off, without any noticeable reaction.
Our problem was firstly the lack of a suitable apparatus to react superheated sulfur vapor with charcoal, and secondly the inability to heat the charcoal to the temperature of 900°C that is required for a sufficiently fast reaction between the two elements.

The first thing I realized was that a bunsen burner is unsuitable as a heat source to bring useful amounts of reactant to 900°C.
Placing several burners in a row under a quartz pipe results in a temperature of just about 650°C, as the synthesis of ketene on orgsyn shows.

One also has to abandon the "retort" apparatus design in favor of a hot-tube design.
This is a perfect application for a tube furnace.

In cooperation with Len1, I was able to, for the first time, produce a useful amount of carbon disulfide in an amateur laboratory and document the process on the internet.

The uses of CS2 to the amateur chemist are many- apart from its very good solvent properties, it can also be chlorinated to carbon tetrachloride, a substance that is very hard to get today.

Warnings
This is an unusually dangerous procedure. Carbon disulfide is very volatile, extremely flammable and has a self-ignition point of 100°C. Having to make it at 900°C means that there WILL be a fire if there is a leak in a hot part of the apparatus!
An even greater danger is the toxicity of the hydrogen sulfide byproduct that the offgas contains. The condensation apparatus must be located under an efficient fumehood!
Carbon disulfide is rather toxic as well.

As H2S and raw CS2 have very offensive odors, one surely understands that this is a very smelly procedure. Consider the neighbors.

Apparatus and Operation

The reaction vessel is a fused quartz tube, 26mm outer diameter and 1 meter from end to end, with two NS 29/32 male joints on both ends.

Note: If quartz joints are to be connected to borosilicate joints, the inner joint must be the one made of quartz, otherwise the larger thermal expansion coefficient of borosilicate would break the outer joint upon heating.

The tube was filled with crushed (not powdered) beechwood charcoal on a length of 50cm, the charcoal was held in place at both sides via ceramic wool plugs. The charcoal bed must not have too high an airflow resistance.



A closeup of some larger charcoal pieces- most of the rest was of much smaller size.


The tube was then placed in the tube furnace, and a 250ml borosilicate round-bottom flask filled with 120g sulfur attached to the left side.


Before the flask was attached, the charcoal bed was briefly heated to 800°C in the tube furnace to drive off any volatile matter it contains. This is extremely important!
The charcoal contained a fair amount of adsorbed moisture- quite some water condensed to the left and right side of the charcoal bed. The condensed water was driven off by heating both ends of the pipe with a bunsen burner until it was completely dry on the inside.
Failure to do this will result in large amounts of hydrogen sulfide being generated, by the reaction:
CS2 + 2 H2O ---> CO2 + 2 H2S
This reaction already takes place at 150°C and the equilibrium completely lies on the H2S side.
So precalcination of the charcoal bed and driving the moisture out of the system is very important both from a safety and yield perspective.
Some H2S will still be generated though.

On the right side, a 250ml three-neck round bottom flask was attached via a 45 degrees bent adapter. A Dimroth condenser was attached to the middle neck, the third neck was stoppered.
From the top of the dimroth condenser, a hose led into the fume hood in order to dispose of the toxic offgas (contains H2S). The joints were later greased. The black bucket was then filled with ice water for cooling, and ice-cold water circulated through the condenser.


With everything in place, the charcoal bed was then heated to 900°C and the sulfur heated with a bunsen burner in order to distill it into the pipe.


As the sulfur vapor reached the charcoal bed, a yellowish white fog soon appeared on the right side. Unreacted sulfur condensed directly after the furnace and soaked into the ceramic wool. The electronic thermometer is also visible here.


The whole apparatus running:




We were delighted when we saw that drops of nearly colorless liquid were condensing on the inside of the flask- this was our product! The white fog prevented us from seeing how much was accumulating until the end, when the ice bath was removed.
The Dimroth condenser contributed very little to the condensation- only very small amounts were condensing in it, almost all of the product was condensing in the flask before.


We stopped after most of the sulfur had distilled into the pipe.


Upon removing the ice bath, we saw that a generous amount of yellowish liquid had accumulated in the flask. Success!


This was then transferred into a 100ml flask and distilled in a small distillation setup in order to remove the dissolved sulfur. Ice water was used in the condenser.


The liquid passed over almost completely at a constant temperature of 46°C, confirming its identity.


A small amount of sulfur remained in the distillation flask.


The product: 44g of crystal clear carbon disulfide!


A few drops burning, it burns with a blue flame and deposits sulfur on the glass dish due to incomplete combustion:


Results and discussion
We weighed the unreacted sulfur in the sulfur boiler flask and in the tube back and determined a CS2 yield of about 50% in regard to the reacted sulfur. I do not have my lab notes here at the moment- more exact values will be added later.
This leaves the question: where did the other half of the reacted sulfur go?
During the process, we briefly attached a washing bottle filled with water to the offgas hose, and almost no bubbling was observed. However, this was during a period of low flux through the tube- at the beginning of the synthesis, we had a very large flux, and it is possible that during this time a considerable amount of CS2 escaped uncondensed.
Another theory would be that the sulfur was lost to H2S.
There certainly was a strong smell of H2S in our garden, at the exhaust of the fume hood!
This would mean that there still were some hydrogen-containing compounds in the charcoal after calcination.
Ullmanns Encyclopedia says that the offgas contains H2S, so this seems to be the case to an extent.

Problems and possible improvements

At the entry side of the tube, a large amount of highly viscous liquid sulfur accumulated in the portion of the tube not inside the furnace. The next time, I will certainly completely insert the entry side of the tube into the furnace to prevent this.

Ice water does not seem to be cold enough to completely condense all of the CS2, as seen by the only 50% yield.
The next time, I will lead the offgas through a cold trap cooled with ice and salt in order to try and condense some additional CS2.
The dimroth consenser also seemed quite useless, as it wasn't contributing to condensation- maybe I will leave it away the next time.

The sulfur boiler could be improved by connecting the flask to the pipe via a 45° bent adapter so that it is inclined in such a way that it can hold more sulfur- I would then be able to use ca. 200g sulfur per run. The adapter would have to be insulated with glass wool.

I will soon do the preparation a second time and make pictures of the improved procedure.

[Edited on 22-5-2008 by garage chemist]

Bravo Stephan! Very impressive!

You just keep on knocking barriers down! Would you have been born 100 years ago, your name would be all over scholar chemistry books

Any plans with the CS2 at the moment? Chlorination? IIRC it it's an excellent solvent for Friedel-Krafts alkylations also.

Be carefull with that bloody H2S by the way...

I agree, Klute. Stefan's lab always has the look of a seriously productive workspace. It reminds me of some those pictures of Wohler's laboratory.

Yes, Fleaker, I was also wondering if Len was there in person. If so, I'm doubly jealous!

[Edited on 22-5-2008 by Magpie]

Great job!

Well done garage chemist, you must be thoroughly pleased with your progress and the amount of crystal clear carbon disulphide you have produced (44g is about 34ml yes?). So whats next? First SO3, now CS2, perhaps the next obstacle for you is white phosphorus? Keep up the good work; your write ups are always a pleasure to read and also well written

Quote:

Originally posted by DJF90 Well done garage chemist, you must be thoroughly pleased with your progress and the amount of crystal clear carbon disulphide you have produced (44g is about 34ml yes?). So whats next? First SO3, now CS2, perhaps the next obstacle for you is white phosphorus? Keep up the good work; your write ups are always a pleasure to read and also well written

Garage chemist already made White P
I think the writeup is on versuchschemie.

Good luck in your adventures garage chemist... Unfortunately I myself am in no position to be doing any serious experimenting yet, still building up a collection of glassware Nearly there though .

Using a larger flask (and probably some sort of support for it) do you think it would be possible to scale up and make about 100ml (abbout 120g IRC) of CS2 at a time? This would probably make the whole process more efficient in terms of energy used to heat the charcoal bed. The only major problems I can forsee are:

1) There will be not enough thermal energy provided to the larger amount of sulphur to allow sufficient vaporisation (although your burner should be able to handle it )

2)There may not be enough capacity in the furnace tube for the quantities of charcoal needed to make this much CS2 in one batch. If this is the case then the only real solution I can see is to work in smaller batches, unless you have the facilities to make a longer tube furnace (and have a longer tube).

However the amount of CS2 you make in one batch is of a reasonable size. What I would like to ask is how long the whole procedure takes, from setting up the apparatus, allowing the tube furnace to reach temperature, do the reaction, let everything cool down, and then clean up? Are the sulphur "deposits" easy to clean away?

[Edited on 27-5-2008 by DJF90]