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Author: Subject: Selenium polycations
Bedlasky
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[*] posted on 11-7-2023 at 08:52
Selenium polycations


Hi.

I tried to make polycations of selenium in 96% H2SO4. Procedure is simple.

Add small amount of selenium in to the test tube and add H2SO4. Heat the mixture carefully above a flame. After some time Se start slowly dissolving to form green solution containing Se8(2+) cations.

I made few inovations to this experiment based on this paper:

https://macsphere.mcmaster.ca/bitstream/11375/18737/1/Kapoor...

I added some Na2SeO3 to the green solution. Not much happend and I wonder why this reaction refuse to work. So I try to decant solution in to the clean test tube, leaving undissolved Se behind. Then I added Na2SeO3 again. Yellow solution containing Se4(2+) was formed. Se(IV) is ideal oxidant, because it won't overoxidize yellow solution.

Oxidation of elemental selenium by selenite works well even at room temperature or in hot water bath, no strong heating needed.

I tried reduction of Na2SeO3 by hydrazine sulfate, but reduction was incomplete because hydrazine probably reacted with conc. H2SO4, but at least partiall reduction to Se4(2+) was succsesful. Next time I will try different reducing agent.

I also plan experiments with Se and other oxidizing agents.

Both polycations hydrolyze in water to red selenium and SeO2.

IMG_20230711_185031.jpg - 1MBIMG_20230711_185106.jpg - 1MBIMG_20230711_185129.jpg - 1.9MB
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Fery
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[*] posted on 11-7-2023 at 12:28


Bedlasky well done! Beautiful colors!
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teodor
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[*] posted on 11-7-2023 at 16:42


Thank you for the article. I found some information about behaviour of CrO3 in concentrated sulfuric acid which could explain some peculiarities I have observed.

As for selenium chemistry - it is interesting. I have some interest in SeOCl2 but its high toxicity stopped me to explore the world of this element yet.
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woelen
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[*] posted on 11-7-2023 at 23:58


I have done similar experiments, with Te, Se and S. This indeed is very interesting chemistry: https://woelen.homescience.net/science/chem/exps/SSeTe_H2SO4...

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The next link can be used to view a textual description of an experiment with Te, Se and S in chlorosulfonic acid: https://woelen.homescience.net/expviewer

On the webpage, click "experiment by ID" in the blue bar at the top of the page. Next, in the text field, give the number 652. Then you can read about the experiment.






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Bedlasky
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[*] posted on 12-7-2023 at 05:42


Quote: Originally posted by Fery  
Bedlasky well done! Beautiful colors!


Thanks, Fery!

Quote: Originally posted by teodor  
Thank you for the article. I found some information about behaviour of CrO3 in concentrated sulfuric acid which could explain some peculiarities I have observed.

As for selenium chemistry - it is interesting. I have some interest in SeOCl2 but its high toxicity stopped me to explore the world of this element yet.


Solutions of SeOCl2 in HCl:

https://sci-hub.se/https://pubs.acs.org/doi/pdf/10.1021/ic50...

You can find this usefull.

Quote: Originally posted by woelen  
I have done similar experiments, with Te, Se and S. This indeed is very interesting chemistry: https://woelen.homescience.net/science/chem/exps/SSeTe_H2SO4...


I was inspired by your article when doing this experiment. Nice work as always Woelen!

[Edited on 12-7-2023 by Bedlasky]
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Bedlasky
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[*] posted on 15-7-2023 at 18:47


Here is another set of experiments.

Dissolve small amount of NaNO3, K2S2O8 and NaClO3 in 96% sulfuric acid (in the case of chlorate it's important to add chlorate in to the acid, not the other way around). Chlorate form red-orange solution containing ClO2+ ions, other solutions are colourless. Add some elemental selenium in to these solutions. Heating in hot water bath speed things up. Reactions with nitrate and chlorate are rapid - in the case of nitrate you can see gradual change from colourless to green to yellow solution. In the case of chlorate you can see change from red-orange to yellow. Further addition of oxidant doesn't change the colour, it seems that Se4(2+) is final oxidation product, but oxidation in reality proceed further to Se(IV) (yellow colour is from NO2/ClO2). If you add these solutions in to the water, little to no red Se precipitates out. Oxidation by persulfate is slugish, you can observe green colour relatively quickly, but change from green to yellow is painfully slow.

I tested if nitrite and sulfite can reduce selenite in 96% H2SO4 in to coloured polycations, but they didn't react (which is surprising with sulfite, because normaly sulfite in acidified solution reduce selenite to red Se). Hydroxylamine hydrochloride react quicker with H2SO4 than with selenite, so this didn't work also. Only think that worked is thiosulfate, which produce orange mixture of red Se and sulfur.

However, nitrite fairly quickly oxidize elemental selenium in to the green Se8(2+) and then in to yellow Se4(2+).

IMG_20230716_044758.jpg - 916kB

Nitrate on the left, persulfate on the righ.

IMG_20230716_044829.jpg - 2MB

Chlorate.

IMG_20230716_044859.jpg - 1.5MB

Thiosulfate on the left, on the right and in the middle nitrite.

IMG_20230716_044915.jpg - 1.4MB

Chloryl cations in 96% H2SO4.

[Edited on 16-7-2023 by Bedlasky]
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chornedsnorkack
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[*] posted on 16-7-2023 at 13:10


Are you sure that chlorate or persulfate do not oxidize selenite to selenate?
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Bedlasky
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[*] posted on 16-7-2023 at 15:02


It's possible, I didn't check if oxidation proceed to IV or VI oxidation state.
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[*] posted on 17-7-2023 at 02:16


Quote: Originally posted by Bedlasky  
Only think that worked is thiosulfate, which produce orange mixture of red Se and sulfur.

How did you test the product for being a pure mixture, and rule out selenium sulphides? Chromatography?
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Bedlasky
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[*] posted on 18-7-2023 at 06:24


Selenite reacts with thiosulfate to form selenopentathionate:

https://cdnsciencepub.com/doi/pdf/10.1139/v96-082

Sulfur in reaction mixture is from decomposition of thiosulfate.

Selenium disulfide is prepared by decomposition of selenosulfides in acidic solution:

https://patents.google.com/patent/CN102060277A/en
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[*] posted on 19-7-2023 at 10:08


Quote: Originally posted by Bedlasky  

Selenium disulfide is prepared by decomposition of selenosulfides in acidic solution:

https://patents.google.com/patent/CN102060277A/en


It´s called SeS2 (with the given molecular mass), as is common. Which actually is an unlikely compound, at low temperatures!
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[*] posted on 27-7-2023 at 10:18


I have some so-called "SeS2". It is a nice orange powder, with a slight brownish hue. I do not believe it really is SeS2. Most likely it is like sulfur (S8) in the form of rings, with some S-atoms, replaced by Se-atoms, approximately, averaged over many many molecules, one out of every three sulfur atoms is replaced by Se-atoms.

In an experiment I did, however, I was not capable of making "SeS2" from pure Se and pure S. I took a little S, melted this until I obtained a yellow liquid (which still is mobile) and I added a small amount of pure Se. This Se dissolves (slowly), and it makes the liquid very dark, almost black. On cooling down, I obtained an olive-green solid. This solid only contained a tiny amount of Se, compared to S, but this smnall quantity of Se has a very strong influence on the color of the S. In my experiment, probably no rings were broken en simply very dark Se dissolved in the sulfur, giving a very dark solution, which also remains dark when it solidifies again.




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[*] posted on 28-7-2023 at 01:53


Quote: Originally posted by woelen  
I have some so-called "SeS2". It is a nice orange powder, with a slight brownish hue. I do not believe it really is SeS2. Most likely it is like sulfur (S8) in the form of rings, with some S-atoms, replaced by Se-atoms, approximately, averaged over many many molecules, one out of every three sulfur atoms is replaced by Se-atoms.

Indeed. Both S and Se alone minimize ring strain at 8-membered ring... but you cannot get SeS2 of 8 atoms. The neighbouring 8 membered compositions would be Se2S6 (3 isomers) and Se3S5 (5 isomers). But there are some different sized molecules in S certainly.
Quote: Originally posted by woelen  

In an experiment I did, however, I was not capable of making "SeS2" from pure Se and pure S. I took a little S, melted this until I obtained a yellow liquid (which still is mobile) and I added a small amount of pure Se. This Se dissolves (slowly), and it makes the liquid very dark, almost black. On cooling down, I obtained an olive-green solid. This solid only contained a tiny amount of Se, compared to S, but this smnall quantity of Se has a very strong influence on the color of the S. In my experiment, probably no rings were broken en simply very dark Se dissolved in the sulfur, giving a very dark solution, which also remains dark when it solidifies again.

Well, S8 rings do break already at melting point of 120 degrees, because while S8 remains the main component of molten S, it equilibrates with S6 and S7 admixture. And Se8 rings break well below 100 degrees because while red Se is stable at 20 degrees, in hot water (that is below 100 degrees) it promptly converts into black Se.
Both S and red Se dissolve in carbon disulphide. Do S8 and Se8 form solid solutions when they are crystallized out of solutions of both?
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