Sulaiman
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Red phosphorus for phosphorus pentoxide ?
I want some P4O10/P2O5 to use as a dessicant, I can get 100g for £10.50.
but
Instead I ordered 25g of red P for £9.30 thinking it has more general use.
(not yet arrived so planning only)
P2O5 can be made by burning P in dry air (so says Wikipedia)
theoretically (if my math is correct) 25g of red P could produce 146g P2O5.
(and from there I can make a little phosphoric acid etc.)
I calculate approximately 2 dm3 of O2 required per 1g of red P
Since I have zero experience with P2O5 the main unknown for me is
how rapidly does P2O5 absorb moisture from the air?
Any suggestions for a physical setup?
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Magpie
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I would keep the red P and use it to make PCl5 (see my recent post in Prepublication), or other such energetic reagents.
I was using some P2O5 today. It is very useful as a high powered dessicant and that is what I would use it for, certainly not for making phosphoric
acid which you should be able to buy cheaply and easily. I would think that making it from P may be as difficult as making AlCl3 from Al.
P2O5 rapidly gums up (hydrates) in the atmosphere due to atmospheric water vapor.
P2O5 is so strong that it will make tar out of acetone by robbing it of H2O.
Your perspective may be different due to being in the UK vs the US. I can't even buy red P, or white P either for that matter.
[Edited on 1-9-2015 by Magpie]
[Edited on 1-9-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Sulaiman
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if I need phosphoric acid I will buy it since it is cheap and available,
the synthesis of a small amount would be purely for it's own sake
or to have a small quantity available.
any other uses for red P ? (a reason to keep the P and buy P2O5)
Also, I read how to convert white P to red or violet P,
how to go from red P to white?
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j_sum1
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Subliming red P will give you white. I have only done this on a small scale -- 50mg or so.
I think violet P is a bit of a trick to get to. Worth doing some research though. A sample of red, white and violet would be great in an element
collection.
As for P2O5 production. Let me state first of all that I have no actual experience in this. But if I was to take a stab at it, I would begin with
quarter gram quantities. I would burn it in (preferably dry) air in a large glass vessel with a lid or stopper. I would then scrape the P2O5 from
the sides of the jar. If this procedure worked you could probably replace the air and do several batches one after the other and scrape the product
off at the end.
Possible improvements -- use dry O2 rather than air if you have it. You might get autoignition which would be convenient.
You would want to check your mass of P against the volume of the jar to make sure you had enough oxygen to complete the reaction and limit the amount
of P as needed.
I believe that red P has multiple uses as a reagent. But as an element collector, I am more interested in it as is.
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Magpie
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P (red or white) is at the top of a reagent pyramid, in my opinion.
With it you can make PCl3, PCl5, POCl3, and HPO2. With these compounds you do many organic syntheses.
Pyro showed how to make white P from red P. I'm sure woelen knows how to do this too.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Sulaiman
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I looked at red P to white here by Chemistry Alchemist and by woelen at homescience,
I'll sleep on this one as I remember how reactive white P is 
(I used white P in CS2 for a special effect ('magically' smoking keris) for a film when I was living in Malaysia, the effect worked well and I was
left with 499 g of white (off-white) P, which I kept at home until after final edit, playing and demonstrating with a little. Due to paranoid
incendiary visions I eventually emptied the lot onto the ground and watched it burst into flames ... >400g of white P burning is scary !)
P.S. never dissolve white P in CS2 then pour it over sodium chlorate,
as when it dries (CS2 evaporates) the intimate mixture causes an incredibly powerful self-detonation 
A tea spoon full, unenclosed, shattered the concrete slab that it was sitting on.
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Magpie
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Quote: Originally posted by Sulaiman  | Due to paranoid incendiary visions I eventually emptied the lot onto the ground and watched it burst into flames ....
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Smart man.
I once wiped a little wet P residue off a spatula with a paper towel. Before I knew it that towel was on fire.
My paranoia is that somehow my P would lose its water cover and containment from the atmosphere and set my house on fire. I'm busy converting my
small supply of white P to less dangerous compounds like PCl5 and PCl3.
I recall the words of Rogermeryaw, who has made more white P than anyone else on the forum that I'm aware of:
"Phosphorus is a back stabbing bitch." Well put, IMO.
IIRC, he said that he had been burned by some of his white P.
The single most important condition for a successful synthesis is good mixing - Nicodem
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ave369
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Sulaiman, the solution you had was basically KS-Fluid, the World War 2 era Soviet military grade incendiary. Only KS-Fluid also contained sulfur.
Smells like ammonia....
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