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rocketman
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[*] posted on 15-11-2018 at 15:04
phosphorus trioxide


Anyone know how to change Phosphorus pentoxide to the trioxide? Can it be done? Phosphorus trioxide is the chemical compound with the molecular formula P₄O₆. Although it should properly be named tetraphosphorus hexoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, and its usage continues today. Wikipedia
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Melgar
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[*] posted on 15-11-2018 at 17:13


Phosphorus trioxide contains phosphorus in a lower oxidation state than phosphorus pentoxide. As far as I know, it's not possible reduce fully-oxidized phosphorus except at very high temperatures of the sort that are used to make elemental phosphorus.



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[*] posted on 15-11-2018 at 23:43


P4O6 cannot be made from P4O10, at least not with a lot of effort. Reducing phosphorus(V) to a lower oxidation state already is quite difficult. With wet chemistry it is nearly impossible, using red heat and carbon as reductor it is possible, but then you reduce all the way down to elemental P.

P4O6 is made by burning white phosporus in a gas mix, which has little oxygen in it. The resulting product, however, is not very pure. It usually contains lower oxides of phosphorus as well (so-called sub-oxides).

[Edited on 16-11-18 by woelen]




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chornedsnorkack
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[*] posted on 19-11-2018 at 13:24


If you do have pure white P and P4O10 as starting materials, can you have a reaction
3P4O10+2P4->5P4O10?
Under which conditions?
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[*] posted on 19-11-2018 at 18:56


I don't think anything short of high-temperature thermal reduction can reduce phosphorus in the +5 oxidation state. The whole reason lower oxides disproportionate the way they do is due to the extraordinarily high stability of +5 phosphorus oxides. Once they reach that state, they stick there.



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[*] posted on 20-11-2018 at 11:06


Quote: Originally posted by Melgar  
I don't think anything short of high-temperature thermal reduction can reduce phosphorus in the +5 oxidation state. The whole reason lower oxides disproportionate the way they do is due to the extraordinarily high stability of +5 phosphorus oxides.


How strong/irreversible is that disproportionation? I found reference to P4O6disproportionating at 440 degrees, in a sealed tube.

Boiling/sublimation points are quoted as follows:
P4O6 - 173 degrees
P4 - 280 degrees
P4O10 - 423 degrees
P (red) - 431 degrees (sublimation)
P2O5 - not easy to find, but above 600 degrees

How volatile are the other phosphorus suboxides? Because the volatility of P4O6 might be used to distil it off from reaction mixture even though P and P2O5 continue to prevail in the condensed phase.

There are other, stronger reducers available than carbon. Such as reactive metals. Sure, that introduces extra alternative reduced forms. But metal phosphides are also not volatile and therefore will not distil off in the temperature range of 170 to 400 degrees where P4O6 distils but (at least red) P and P2O5 do not. Nor do metals themselves, other than Hg which is not a good reducer anyway.
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[*] posted on 20-11-2018 at 13:17


Quote: Originally posted by chornedsnorkack  
How strong/irreversible is that disproportionation? I found reference to P4O6disproportionating at 440 degrees, in a sealed tube.

Boiling/sublimation points are quoted as follows:
P4O6 - 173 degrees
P4 - 280 degrees
P4O10 - 423 degrees
P (red) - 431 degrees (sublimation)
P2O5 - not easy to find, but above 600 degrees

How volatile are the other phosphorus suboxides? Because the volatility of P4O6 might be used to distil it off from reaction mixture even though P and P2O5 continue to prevail in the condensed phase.

There are other, stronger reducers available than carbon. Such as reactive metals. Sure, that introduces extra alternative reduced forms. But metal phosphides are also not volatile and therefore will not distil off in the temperature range of 170 to 400 degrees where P4O6 distils but (at least red) P and P2O5 do not. Nor do metals themselves, other than Hg which is not a good reducer anyway.

P4O6 isn't in the +5 oxidation state, so it would disproportionate into P2O5, among other things. Also, P2O5 and P4O10 are the same thing, and refer to the empirical formula, just because it's an amorphous partially-vitrified solid that isn't made of discrete units. I think the main difference is that P4O10 refers to the smallest possible discrete unit that a substance with that empirical formula can form.

I guess I'm curious why someone would be going for that particular compound, unless they had access to x-ray crystallography equipment that they could use to figure out its crystal structure or something.




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[*] posted on 20-11-2018 at 22:08


Quote: Originally posted by Melgar  
Quote: Originally posted by chornedsnorkack  

Boiling/sublimation points are quoted as follows:
P4O6 - 173 degrees
P4 - 280 degrees
P4O10 - 423 degrees
P (red) - 431 degrees (sublimation)
P2O5 - not easy to find, but above 600 degrees


P4O6 isn't in the +5 oxidation state, so it would disproportionate into P2O5, among other things. Also, P2O5 and P4O10 are the same thing, and refer to the empirical formula, just because it's an amorphous partially-vitrified solid that isn't made of discrete units. I think the main difference is that P4O10 refers to the smallest possible discrete unit that a substance with that empirical formula can form.

P4 forms crystals of discrete molecules that melt at 44 degrees to a liquid which boils at 280 degrees. On prolonged heating, white phosphorus polymerizes to red phosphorus, but the polymerization is slow enough even at the boiling point that the boiling point can be measured.
At polymerization, at first phosphorus forms amorphous red phosphorus, but after long annealing, it is possible to crystallize it to a form that sublimes at 431 degrees.

P4O10 forms crystals of discrete molecules that melt at 360 degrees to a liquid which boils at 423 degrees. On prolonged eating, these polymerize to a glass or to one metastable crystalline form, but eventually can be annealed to a stable crystalline form that is stable to over 550 degrees.
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