dome13 - 11-6-2023 at 05:10
Hello!
I found an interesting route to make new sulfur bonds between Bunte salts and Grignard reagents. I gave it a try, but I am not sure in the resulted
product. Theoritically it could be an oil, but mine is a solid. Anyway, here is what I did:
The Bunte salt was prepared as follows: equal mol n-propyl bromide and soudium thiosulfate pentahydrate was stirred under gentle reflux in 50:50
ethanol-water mixture for 50 minutes, after it becames homogenous. The solvent was removed under vacuum. The resulted white solids were extracted with
boiling ethanol. After evaporating the ethanol, white, crystalline solids remain with a faint cabbage smell, resembling to propylthiol. Yield almost
quantitative.
The Gringard reagent was prepared as follows: 19 mmol magnesium turnings were placed in a flask. 19 mmol bromobenzene was diluted with 10ml THF
(sodium dried, freshly distilled) and poured into an addition funnel. About 3ml of the solution was added at once. After 5 mins, I added a tiny amount
of iodine to initiate the reaction. It didn't started, so I turned on the heat for a short time. It did the trick, I turned off the heating and
started adding dropwise the remaining bromobenzene. After the addition, I stirred and gently heated the mixture for 30 minutes.
The reaction mixture was cooled with ice for the next step. Some salts precipitated. I gravity filtered from the salt and a few pieces of unreacted
magnesium.
The main reaction: 5,6 mmol sodium propyl thiosulfate was suspended in 10ml THF and cooled with an ice bath. From an addition funnel, there was added
the Grignard reagent dropwise. (The paper claims a 2-3 molar excess) The temperature was at around 2-4°C during the addition (instead of 0°C). After
the addition it was stirred for 30 minutes and let come to room temperature. I vacuum filtered from the white solids, the filtrate is yellow. After
concentrating in vacuum, a white-yellow crystalline solid remains which I powdered. It was 0,7g corresponding to a 82% yield, what is expected.
After a day, it became waxy. I tried to measure a melting point but it didn't melt even at 200°C. It has a strong smell, I would describe as somehow
similar to p-dimethoxybenzene.
The paper doesn't describe a detailed work-up, so I'm honestly not sure that I missed something, but I feel it.
I'm looking for any suggestion, comment, recommendation.
I attach the paper:
Attachment: bunte salt sulfides.pdf (606kB)
This file has been downloaded 133 times
Fery - 11-6-2023 at 21:29
Thanks for sharing the synthesis. It is interesting route suitable for home labs as it avoids malodorous thiols. Did you try to determine m.p. of your
product when it was freshly synthesized or the next day after it become waxy ?
dome13 - 12-6-2023 at 11:37
On the next day, because I was tired and it was late when I finished the reaction. I also tried to see the solubility but it was insoluble/hardly
soluble in DCM, ether and THF. It was soluble in dilute sulfuric acid. I extracted the sulfuric acid with ether for curiosity and some yellow-brown
spots remained after evaporation of the ether. There is no progress.
Fery - 12-6-2023 at 19:59
I found only this one info with its melting point:
http://www.chemspider.com/Chemical-Structure.12833.html
click on properties -> experimental melting point
-45 °C Jean-Claude Bradley Open Melting Point Dataset 18793
http://dx.doi.org/10.6084/m9.figshare.1031637
dome13 - 13-6-2023 at 07:31
Fery, this is what I exactly found too. And this is why I suppose it should be an oil instead of solid.
UC235 - 13-6-2023 at 13:51
Supplemental info is available for free from the publisher and has detailed procedure and workup. You are missing several workup steps including a
quench. https://pubs.acs.org/doi/abs/10.1021/ol500067f
dome13 - 14-6-2023 at 06:04
UC235 thank you very much! It seems I didn't notice at the and of the paper the supporting information reference. Now I see what did I miss. Luckily,
I have enough starting material to repeat the procedure. I'll come back with the results.
dome13 - 15-6-2023 at 10:09
Bad news 
I repeated the reaction, now with the quenching and the descripted
workup. I ended up with the same solid material with the same odor. Maybe it could be really a solid? I don't know... Unfortunatelly I don't have
acces to any analytical equipment for further analysis.