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Author: Subject: Synthesis of thioacetone?
macckone
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[*] posted on 4-3-2022 at 11:39


Fery,
Interesting paper on the working conditions.
glove box and destroying any vapors in situ.
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Fery
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[*] posted on 5-3-2022 at 00:28


Hi macckone, I'm not so brave to crack the trimer to monomer, but maybe I will try to synthesize the trimer. Cracking requires quite strong conditions. I found in literature that during the synthesis of trimer, there is a lot of side product propane-2,2-dithiol "with an intensely powerful, disagreeable odor" (60-70% trithioacetone and 30-40% propane-2,2-dithiol, see the experiment in the attached pdf, they had to perform vacuum distillation to separate them). This side product (geminal dithiol) worries me more than the trithioacetone itself which is quite stable and hard to crack to monomer. My friend who already does organic chemistry business (still studying PhD) told me, that the trimer is in equilibrium with monomer so traces of monomer are always present. He also told me that he is specialized in organosulfur chemistry and performed a lot experiments in organosulfur syntesis. In university lab they finally always washed equipment with methanol or isopropanol, but once his schoolfellow mistakenly used acetone to wash a glass with remainders of P2S5 so the thioacetone "was cooked". It happened inside fume hood but the whole building was full of very bad odor. My friend also pointed me out, that using P2S5 is best with pyridine complex, otherwise P2S5 is very strong dehydrating agent because P2O5 is formed.
Yet I still did not succeed with preparation of thioformaldehyde trimer (I tried Na2S2O3 to avoid H2S but it did not work in my case). My first step would be trimer of thioformaldehyde = 1,3,5 trithiane and I will have to bubble the nasty H2S into the reaction (or drip solution of Na2S but that will introduce sulfur contamination as my Na2S is not colorless but yellow so with impurities of disulfide/polysulfides which would decompose to sulfur in solution with excess of HCl). Maybe only then I'll try the trimer of thioacetone somewhere in wood few kilometers away from civilization, maybe not (distillation of propane-2,2-dithiol is quite distractive for me, but maybe it could be separated by creating its Na salt by reaction with NaHCO3 or Na2CO3? which should be soluble in water unlike trithioacetone which is almost insoluble).

https://sci-hub.ee/10.1002/pol.1970.150080826

Attachment: pol.1970.150080826.pdf (728kB)
This file has been downloaded 215 times




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Lionel Spanner
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[*] posted on 10-3-2022 at 04:13


Quote: Originally posted by Keras  
What’s funny about thioacetone is that it seems to stink more in a diluted form (so far away from the source). I suspect, like H₂S, some sort of overload of the olfactory nerves when the concentration is too high.

Good target for a microscale experiment :p


Could also be down to its vapour pressure, i.e. it evaporates more quickly when diluted.




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Tsjerk
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[*] posted on 10-3-2022 at 04:50


No, because it is already evaporated when diluted. Also vapour pressure only starts playing a role in high relative concentrations, which I really hope no one is experiencing with thioacetone.
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[*] posted on 27-12-2022 at 02:14


I suppose it was inevitable that someone like NileRed would try to make it and post a video on it:

https://www.youtube.com/watch?v=LmAG8-V_WQY

Apparently not the first youtuber. LabCoatz beat him to it:

https://www.youtube.com/watch?v=E_wboFJZBTU&t=0s

PS:Happy new year everyone

[Edited on 12/27/2022 by wg48temp9]




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[*] posted on 27-12-2022 at 02:42


The famous NileRed that rents an island to make the stuff but later admits the nearest houses are only a couple hundred meters away...
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[*] posted on 27-12-2022 at 22:06


It should be possible, but please don't. You'll stink up your entire neighborhood.
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[*] posted on 28-12-2022 at 02:05


i like this topic.
i really want to make it
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[*] posted on 16-1-2023 at 20:34


Both NileRed and LabCoatz did not follow the original procedure that produced the infamous odor. In both the Freiburg incident [1] and Whitehall Soap Works [2] the procedure was to bubble H2S into a mixture of Acetone and HCl. It is likely the next step was taken immediately after which is to steam distill the trithioacetone. This is important because free thioacetone is not stable [3] and will likely polymerize shortly in storage.

Another error is smelling it up close. It is reported to smell worse in more dilution so it would be better to have a person far away walk towards where it is being produced to have a true sense of the odor.

I will attempt the synthesis when I can with both of these in mind and report the result.

An alternate method to produce monomeric thioacetone that does not involve cracking is bubbling H2S into an acidic solution of acetone ketal [3] [4]. Produces more monomer than cracking and seems easier.

Quote:

For each mole of the corresponding ketal or enol ether, double the amount by weight of glacial acetic acid and about 1 g of hydroquinone are added, 3 drops of concentrated sulfuric acid are added and a trickle of hydrogen sulfide is introduced until the theoretical amount is absorbed. As a rule, the reaction is completed after 15-20 min. Final temperature about 35 deg. The mixture is then poured into ice water, the insoluble organic phase is rapidly taken up in petroleum ether, purified and distilled in a column. The following aliphatic thioketones are extremely unpleasant and pervasive smelling, indeterminate, deep red oils. We report separately on thioacetone and on the chemistry and spectroscopic properties of the thiones.
[4]


[1] https://www.sci-hub.se/10.1002/cber.188902202151
[2] https://books.google.com/books?id=MSDOAAAAMAAJ&pg=RA3-PA... pg. 219
[3] https://www.sci-hub.se/10.1002/anie.196402771
[4] https://sci-hub.se/10.1002/cber.19630961139
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[*] posted on 16-1-2023 at 22:27


Hi zero, very useful information! Starting from acetone + HCl + H2S there is a side reaction producing 2,2 propanedithiol (30-40% dithiol while trimer of thioacetone 60-70%). As you wrote - it is necessary to column distil, otherwise you could smell this dithiol with a false hope that it is monomer of thioacetone. One of the mentioned youtubers whose knowledge as well practical skills in chemistry were inversely proportional to his courage even did not distill either did not apply vacuum to crack the trimer. The other who was more careful and has years of practical chemistry skills, at least used steam distillation in lab, but I do not know whether his vacuum pump running on electrical battery on the island produced sufficient vacuum level to crack the trimer (if the steam distillation was not sufficient to get rid of gem dithiol and vacuum level too weak then he could again smell the propane-2,2-dithiol instead of monomer of thioacetone). Anyway I appreciate that both were brave enough to try this experiment! One PhD student who is focused on organosulfur chemistry discouraged me to do such experiments if I would like to avoid contact with a team of professionals dressed in spacesuits arriving in big red truck with loud siren horn. He also told me a story how his university schoolmate mistakenly used acetone to clean a glass with remainders of P4S10-pyridine complex, the washings were poured into a waste container with acetone so an undesired product was cooked spontaneously. Acetone is the most commonly used solvent to clean a glass but in organosulfur chemistry I should use methanol.
If the reaction from acetone ketal you mentioned produces more monomer, that could be very interesting route.
Personally I would be more happy for the trimer of thioacetone which should have scent of some tropical fruit and is used in some candy. So far I was brave to synthesize only trimer of thioformaldehyde which I did outside of my house during night when there were no passersby on street and neighbors were inside their houses. The scent of H2S produced at 0,5 mol scale during few hours from which circa one half did not react and was vented into atmosphere, was terrible. I did not bother to trap the H2S into an alkaline / hypochlorite / permanganate solution and just did the trithioformaldehyde synthesis outside.
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Keras
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[*] posted on 17-1-2023 at 02:14


I suppose thioacetone acts on the smell receptors the same way hydrogen sulphide does: at too high a concentration, the receptors become saturated and ‘pass out’. That would explain why the smell is worse at low concentrations, where the receptors are still fully functional.
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[*] posted on 17-1-2023 at 07:49


Fery: Saw your synthesis of thioformaldehyde, very nice! Do you know how far you could smell the H2S from?
You are correct that the gem-dithiol is formed but it is only mentioned with the ZnCl2 modification, not with the original HCl. Not saying it wouldn't be formed, but the references I have only mention it when using ZnCl2. [1]
Another reason I doubt both Nilered and Labcoatz succeeded is also in [1]:
Quote:

Thioacetone was prepared by pyrolyzing hexamethyl-s-trithiane on hot quartz rings under reduced pressure with subsequent quenching of the product as quickly as possible to -78°C. The pyrolysis temperature was fairly critical. Within the pressure range of 5-20 mm, a temperature below about 500°C permitted much of the trimer to survive. Above 650°C, decomposition to simpler compounds became excessive, and allene and hydrogen sulfide became important products. Under favorable conditions, 80% yield of red-orange, clear liquid monomer could be obtained, which could be redistilled quantitatively in a vacuum system.

The odor they describe is more like H2S, a thiol, or even the trimer evaporating unchanged. I don't think a blowtorch without argon or a vaccuum will produce much monomeric thioacetone.
According to the Esso researchers:
Quote:

Two of our chemists who had done no more than investigate the cracking of minute amounts of trithioacetone found themselves the object of hostile stares in a restaurant and suffered the humiliation of having a waitress spray the area around them with a deodorant.

Surely if either Nilered or Labcoatz made thioacetone, they would have a similar experience with family or friends? To be clear these researchers were working in a fumehood so imagine how tiny the amount of thioacetone got on them. In both the Freiburg incident and the Esso researchers mention the smell travelled about 0.5 km. Nilered was much closer than that to houses which likely would have complained and Labcoatz reported the smell only travelled 200 ft. Again, more consistent with H2S or a thiol.

Keras: Agreed, it does seem to overpower much like H2S.

I will be focusing on producing monomeric thioacetone from the ketal method since it should bypass the temperature control issues and the hydroquinone will prevent polymerization.

[1] https://sci-hub.se/10.1002/pol.1970.150080826

[Edited on 17-1-2023 by zero]

[Edited on 17-1-2023 by zero]
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Fery
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[*] posted on 17-1-2023 at 09:33


zero - my trithiane was not completely odorless, I smelled something a little sulfurous, but definintelly only veeeeery weak... that could also be some impurity... traces of organosulfur compounds have strong enough scent...
you can scent H2S from distance, it just depends on its concentration (amount and how fast are you releasing it into air) and the direction of wind... there is some threshold of H2S which could be found in some literature, below this threshold you do not scent it (in my synthesis I scented it from few meters already and circa 0,25 mol was released into air during few hours)... you can avoid that by trapping gas into alkaline solution / hypochlorite / permanganate etc... the last 2 trap and oxidize also escaping organosulfur compounds which have worse scents than H2S but I was just lazy to trap H2S because I did the reaction outside
you are right, cracking thioacetone trimer into monomer is not so easy... strong enough vacuum, narrow window of temperature, quickly cooling into very low temperature - otherwise polymerization occurs quickly:
https://sci-hub.ee/10.1016/0032-3861(67)90069-9
Attachment: 0032-3861(67)90069-9.pdf (1002kB)
This file has been downloaded 9 times

anyway if any of the 2 youtubers yield of monomer was something like 0,00000001% they would be able to notice its scent at this very low but sufficient concentration



[Edited on 17-1-2023 by Fery]
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