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SecretSquirrel
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Question: Red phosphorus purification
I recently acquired a bottle of red phosphorus that is over 25 years old. The problem is that it has formed a paste that reacts acidic to litmus. My
guess is some of it got oxidized over the years to form phosphorus oxides that absorbed moisture from the air, hence acidic reaction. I tried to
purify it by dumping the whole amount in water, but after 3 washes it is still acidic.
I was wondering if I can wash it with sodium bicarbonate solution to neutralize the acid, following with few washes of water and finally washing it
with distilled water.
[Edited on 28-7-2008 by SecretSquirrel]
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not_important
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As red phosphorus is purified by boiling with NaOH solution to remove yellow phosphorous, and alkali wash should do well. Might be able to use
aqueous ammonia, several washes with prolonged stirring, followed by several DW washes.
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Klute
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Out of curiosity, is there any solvent in which red phosphorus is soluble? CS2 maybe?
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ScienceSquirrel
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Insoluble in CS2, as it is a polymeric solid I would be very surprised if it dissolved in anything to an appreciable degree.
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woelen
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There is no solvent in which red P dissolves (without reacting and getting converted to something else). Red P does dissolve in some liquids, such as
chlorine-water, or concentrated hot nitric acid, but in those liquids it is oxidized and no free phosphorus is present in solution.
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SecretSquirrel
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| Quote: | Originally posted by not_important
As red phosphorus is purified by boiling with NaOH solution to remove yellow phosphorous, and alkali wash should do well. Might be able to use
aqueous ammonia, several washes with prolonged stirring, followed by several DW washes. |
Won't boiling it with NaOH solution produce phosphine? My phosphorus does smell a bit like garlic/rotting fish.
Thanks for the advice on purification. I think I will use sodium bicarbonate instead of ammonia, because I would like to avoid nasty vapours.
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not_important
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Any remaining yellow phosphorous will produce phosphine, that's why it is used to purified red phosphorous.
Make sure you mix the wash solutions and the phosphorous very well, breaking up any lumps and stirring for several minutes.
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Picric-A
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after about two bicarbonate wash with 3 distilled water washes to make it completly free from most impurities.
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S.C. Wack
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The NaOH should be dilute. Hot conc. NaOH + RP = fail. The phosphine will make itself obvious.
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SecretSquirrel
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Of course I will use dilute solution of NaOH, but thanks for the warning anyway. However, I didn't know red P also reacts with hydroxides (doesn't say
so in the literature I checked). But just to be safe, I'll use dilute solution of NaOH.
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Endimion17
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Great, an existing thread.
I had a small sample of 6.7 g of red phosphorus which was beggining to cake, so I went by the manual for purification (Armarego, Chai).
My opinion is that sodium hydroxide should not be used, as we all know it's mighty difficult to get rid of its ions (flame test), and samples of red P
rarely contain WP, unless they were heated in a fire accident in a closed vessel.
I used boiling water only and let it boil for more than 15 minutes. After that, I decanted the water few times, and transfered the element on a filter
paper in a Büchner funnel, washing it with almost boiling water. The wastewater stopped to be acidic after few washings, so I rolled the paper and
put it in a flask immersed sideways in a boiling water bath. After almost half and hour of heating at 100 °C, it was dry.
It looks pristine at the moment, like a fine, dry sand. I got 5.4 g, therefore 80.5 %. Pretty much most of the 1.3 g lost was phosphoric acid.
Now my sintered glass Büchner funnel is dirty and requires a chlorine water bath. Does anyone have experience with this kind of cleaning? How long
would this take?
[Edited on 7-11-2011 by Endimion17]
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AndersHoveland
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When white phosphorous is boiled with alkaline aqueous solution, hypophosphite and phosphine result.
P4 + (3)KOH + (3)H2O --> (3)KH2PO2 + PH3
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Endimion17
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Yeah, I know that. It's phosphorus basics.
But there's no WP in red P samples in appreciable concentrations that are easily removed. 100-200 mg/kg is a usual trace contamination. It's not
neccessary because as soon as you make the sample it will start to deteriorate, unless you use vacuum and need it for sophisticated analysis which we
don't.
Boiling it with sodium hydroxide will introduce obnoxious sodium ions. Traces of WP are better than traces of sodium.
Red P is usually analytical grade and therefore low on WP. Phosphoric acid is the problem, and it can be dealt with using distilled water.
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symboom
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How can I get the red phosphorous out of solution with the ammonium hydroxide I boiled ammonia hydroxide with red phosphorus now its yellowish color
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woelen
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Let it settle at the bottom, or use a filter. You should rinse again with distilled water and then allow the phosphorus to dry.
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Sir M
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Hi there,
so I got my hands on an old sample of red P as well. I already washed with water and cleaned it. I wanted to wash it with ethanol or acetone in the
end, but i had seen a text, where they didn't recommend it and said the last wash must be with water. This made me curious - do you think, that the
red P could react with the traces of organic solvent or is it a nonsense?
thanks
[Edited on 10-10-2017 by Sir M]
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Melgar
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Phosphorus is actually not very reactive to much besides halogens and a few other strong oxidizers at room temperature. I think the concern would be
that organics could get absorbed, which could certainly interfere with any reactions done with it in the future. Considering organophosphorus
compounds can be especially dangerous, it's probably a good idea to avoid any surprise reactions from solvent contaminants.
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VSEPR_VOID
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Is it legal to sell red P in the US?
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Melgar
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If you call it "red P", it's probably safe to assume you'd be breaking the law by selling it. 
I believe you need to be registered with the DEA in order to legally sell it. Either that, or you could be in another country with different laws,
and thus not under the jurisdiction of the DEA.
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symboom
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Does ammonium hydroxide work I heard it dissolves phosphorus without reaction
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woelen
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Ammonium hydroxide is nearly non-existent  call it aqueous ammonia
As you can read higher up in the threrad, people used ammonia to clean phosphorus. But I would use very low concentrations, and probably using plain
hot distilled water is good enough.
Anyway, ammonia does not react with red phosphorus, it probably does react very slowly with white phosphorus, due to its alkalinity, but as it is only
weakly alkaline, I expect that reaction to be very very slow.
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Sir M
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Thanks for answer and by the way, I also think the ammonia solution is really not needed. For my phosphorus/phosphoric acid paste, few washes with hot
distilled water were enough.
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VSEPR_VOID
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Quote: Originally posted by Melgar  |
If you call it "red P", it's probably safe to assume you'd be breaking the law by selling it.
I believe you need to be registered with the DEA in order to legally sell it. Either that, or you could be in another country with different laws,
and thus not under the jurisdiction of the DEA. |
Is it difficult to register with the DEA and gain their approval? If it is legal to do so it would be a boon to make my hobby a small source of
income. It might help put a reasonable dent in the over head.
[Edited on 10-10-2017 by VSEPR_VOID]
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Melgar
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| Quote: Originally posted by VSEPR_VOID | | Is it difficult to register with the DEA and gain their approval? If it is legal to do so it would be a boon to make my hobby a small source of
income. It might help put a reasonable dent in the over head. |
You're welcome to try. Of course, that'd mean keeping detailed records on every sale you make, and submitting those records to the DEA. You
generally have to state the nature of your business though, and saying you supply amateur chemists would probably not gain their favor.
The first step in the process of learning something is admitting that you don't know it already.
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symboom
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Now the question if you have white phosphorous homemade from phosphate how can that be converted to red phosphorus
To make it safer to handle
[Edited on 17-10-2017 by symboom]
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