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Author: Subject: Question about h2s and phosphine
draculic acid69
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[*] posted on 21-12-2018 at 00:00
Question about h2s and phosphine


I read somewhere that hydrogen sulphide bubbled thru h2o2 results in elemental sulphur but upon googling this it seems this isn't right but so2 turns it into elemental sulphur so would phosphine bubbled thru so2 solution make elemental p4 or would the peroxide turn ph3 into p4. Also is the peroxide thing wrong or not?
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Ubya
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[*] posted on 21-12-2018 at 01:47


SO2 in water makes H2SO3, H2O2 oxidises it to sulphuric acid, no elemental sulphur. on the other hand H2S+SO2 makes elemental sulphur, so maybe phosphine with phosphorus pentoxide?




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woelen
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[*] posted on 21-12-2018 at 02:00


Quote: Originally posted by draculic acid69  
I read somewhere that hydrogen sulphide bubbled thru h2o2 results in elemental sulphur but upon googling this it seems this isn't right but so2 turns it into elemental sulphur so would phosphine bubbled thru so2 solution make elemental p4 or would the peroxide turn ph3 into p4. Also is the peroxide thing wrong or not?

When writing posts, please use capital letters where appropriate. Especially in formulas, so use PH3 instead of ph3 and so on.

PH3 is not as easily oxidized to elemental phosphorus as H2S is to elemental sulphur.
If PH3 is oxidized, then it easily is oxidized to phosphorus in oxidation state +3 or phosphorus in oxidation state +5. Bubbling it through a solution of phosphoric acid will not lead to a reaction. Phosphoric acid only is acidic, it has no oxidizing properties. I also do not expect any reaction between dissolved SO2 and PH3.

I have done quite a few experiments with PH3 and I saw, that if I burn PH3 and there is insufficient oxygen, then you get brown and yellow stuff, which settles on the vessel in which the PH3 is. This most likely is a complicated mix of phosphorus-compounds in lower than +3 oxidation state, but it certainly is not pure phosphorus.
I noticed that phosphorus in low oxidation state (<=0) does not tend to react cleanly when there is shortage of oxidizer. You get all kinds of brown, red/brown or yellowish compounds, which do not dissolve in water, but which can fairly easily be dissolved in bleach or chlorine-water. Probably phosphorus forms sub-oxides of indeterminate composition.




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unionised
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[*] posted on 21-12-2018 at 02:59


If I had phosphine and I wanted phosphorus, I'd just heat it.
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Herr Haber
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[*] posted on 21-12-2018 at 05:32


If I had phosphorus and I wanted phosphine I'd just heat it (with dilute acid) :cool:

Or: How I inadvertantly discovered the smell of phosphine...
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chornedsnorkack
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[*] posted on 22-12-2018 at 11:50


Quote: Originally posted by unionised  
If I had phosphine and I wanted phosphorus, I'd just heat it.

Phosphine is not arsine.
I am not sure PH3 would be unreactive with SO2

From Pourbaix diagram of sulphur, SO2 has no stability field. It is always unstable to dismutation to sulphates and S (in acid conditions) or HS- (in base). However, sulphites and sulphurous acid are reasonably long-lived. Meaning they are also stronger oxidants than sulphates and dilute sulphuric acid.

I see that Pourbaix diagrams of phosphorus diverge from each other. The species proposed for strongly reducing conditions include H3PO3, H3PO2, P4 and PH3.
P4 is known to dismute in both acidic conditions (as reported by Herr Haber and others) and basic conditions. Of course, since P4 exists outside its stability field, it can also be produced outside its stability field.
A weak oxidant reacting with excess of PH3 might be selective for reasons of mechanism, and produce mainly P4, not H3PO4, H3PO3, H3PO2 or suboxides. But I do not know which oxidants might have such selectivity.
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morganbw
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[*] posted on 22-12-2018 at 12:11


wow @chorenedsnorkack
I may need to back up and read all of your posts.
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clearly_not_atara
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[*] posted on 22-12-2018 at 22:25


Quote:
A weak oxidant reacting with excess of PH3 might be selective for reasons of mechanism, and produce mainly P4, not H3PO4, H3PO3, H3PO2 or suboxides. But I do not know which oxidants might have such selectivity.


Mechanism schmechanism. If you want to avoid forming phosphoric acids, just don't let there be any oxygen present. Actually the first thing that comes to mind is PBr3. Perhaps you can oxidize some phosphine with bromine, and then comproportionate PBr3 and PH3 in the presence of a catalytic amine? Eg:

2 PBr3 + 2 PH3 + 6 NEt3 >> 6 NEt3HBr + 3 P4

However, to me the main problem is I just don't want to deal with any phosphine whatsoever ;D

EDIT: With careful stoichiometry:

4 PH3 + 6 Br2 + 12 NEt3 >> P4 + 12 NEt3HBr???

[Edited on 23-12-2018 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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