Sciencemadness Discussion Board - Question: Red phosphorus purification

Question: Red phosphorus purification

SecretSquirrel - 28-7-2008 at 07:07

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]

not_important - 28-7-2008 at 07:43

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.

Klute - 28-7-2008 at 07:45

Out of curiosity, is there any solvent in which red phosphorus is soluble? CS2 maybe?

ScienceSquirrel - 28-7-2008 at 08:12

Insoluble in CS2, as it is a polymeric solid I would be very surprised if it dissolved in anything to an appreciable degree.

woelen - 28-7-2008 at 11:00

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.

SecretSquirrel - 28-7-2008 at 23:35

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.

not_important - 29-7-2008 at 00:45

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.

Picric-A - 29-7-2008 at 01:19

after about two bicarbonate wash with 3 distilled water washes to make it completly free from most impurities.

S.C. Wack - 29-7-2008 at 03:28

The NaOH should be dilute. Hot conc. NaOH + RP = fail. The phosphine will make itself obvious.

SecretSquirrel - 29-7-2008 at 04:51

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.

Endimion17 - 7-11-2011 at 06:14

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]

AndersHoveland - 7-11-2011 at 06:57

When white phosphorous is boiled with alkaline aqueous solution, hypophosphite and phosphine result.

P4 + (3)KOH + (3)H2O --> (3)KH2PO2 + PH3

Endimion17 - 7-11-2011 at 07:10

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.

symboom - 10-4-2016 at 00:54

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

woelen - 10-4-2016 at 06:46

Let it settle at the bottom, or use a filter. You should rinse again with distilled water and then allow the phosphorus to dry.

Sir M - 9-10-2017 at 09:14

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]

Melgar - 9-10-2017 at 14:28

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.

VSEPR_VOID - 9-10-2017 at 14:51

Is it legal to sell red P in the US?

Melgar - 9-10-2017 at 16:48

Quote: Originally posted by VSEPR_VOID

Is it legal to sell red P in the US?

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.

symboom - 9-10-2017 at 19:29

Does ammonium hydroxide work I heard it dissolves phosphorus without reaction

woelen - 9-10-2017 at 22:50

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.

Sir M - 10-10-2017 at 08:42

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.

VSEPR_VOID - 10-10-2017 at 09:50

Quote: Originally posted by Melgar

Quote: Originally posted by VSEPR_VOID

Is it legal to sell red P in the US?

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]

Melgar - 16-10-2017 at 06:09

Quote: Originally posted by VSEPR_VOID

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.

symboom - 16-10-2017 at 18:18

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]

Melgar - 16-10-2017 at 19:30

Quote: Originally posted by symboom

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]

I think rapid heating under pressure is all that's needed. I don't think the temperature necessary is even that high, and the pressure would just be to keep it from boiling. Obviously, an inert atmosphere would be required.

Chemateur80 - 3-2-2018 at 06:05

Greetings.

I decided to clean some of my red phosphorus a little.
It's been standing for a few years in a plastic jar inside a metal can with an airtight lid.
When I opened the metal can there was a faint, weird smell. Hard to describe, but kind of like onion and garlic.
The phosphorus was not clumped, but quite free flowing, like sand.
I put three scoops of P in some water. The pH was around 1-2, so I suppose there was some phosphoric acid present.
The heavier particles sank, but there was also a very fine, orange suspension of fine particles.
I then added a solution of Na₂CO₃ and let it simmer for a while with stirring. The pH was basic.
I then filtered the P through filter paper and rinsed until the pH was neutral. A lot of very fine particles made it through the filter, and the filtering was quite slow.
The P is now dried with gentle heat on the filter paper. There is a faint smell of garlic, though.
What could this be? Tiny amounts of phosphine? Seems weird.
Shouldn't clean phosphorus be odourless?

Is my red phosphorus reasonably pure after this cleaning?
Any improvements I could make, or anything I should do differently?
Has anyone else experienced that the phosphorus consists of a lot of very fine particles that are hard to recover?

I've seen here on SM that people suggest boiling the phosphorus with NaOH, but since my P seemed quite free flowing and pure, I just went with this method.

LearnedAmateur - 3-2-2018 at 06:20

Phosphorus is apparently described to have the odour of garlic, I’d put these down to impurities formed. Wikipedia says that pure phosphine is odourless, and substituted phosphines and/or P2H4 are responsible for the disagreeable odour, and are likely only present in trace quantities.

woelen - 3-2-2018 at 11:08

Red phosphorus is odorless, but in practice, samples of red phosphorus contain trace amounts of white phosphorus. Even the purest samples contain some. It is this contamination which gives it the particular smell. I never had red phosphorus, which is completely odorless. I purchased 20 grams of 99.99% red phosphorus for my element collection and even this had a faint smell.

If your red phosphorus is free flowing, then it is quite pure and contains hardly any white phosphorus. The white phosphorus makes it somewhat sticky.

[Edited on 3-2-18 by woelen]

Chemateur80 - 3-2-2018 at 11:16

Quote: Originally posted by LearnedAmateur

Phosphorus is apparently described to have the odour of garlic, I’d put these down to impurities formed. Wikipedia says that pure phosphine is odourless, and substituted phosphines and/or P2H4 are responsible for the disagreeable odour, and are likely only present in trace quantities.

Yes, it's probably traces of diphosphane and substituted phospines.
Can white phosphorus form spontaneously from red phosphorus, or why are there traces of the white allotrope?

It's strange that the wet phosphorus still smelled of garlic after cleaning.
It is now a dry, sand-like, free flowing powder, almost without any smell..
I've put it in a dry bottle with parafilm over and then a lid with a PTFE liner.
Will cleaned red phosphorus oxidize over time?

woelen - 3-2-2018 at 12:29

Clean and dry red phosphorus will remain so if stored tightly sealed. When it is not properly stored, then over the years it becomes wet and sticky.

Chemateur80 - 3-2-2018 at 14:23

Quote: Originally posted by woelen

Red phosphorus is odorless, but in practice, samples of red phosphorus contain trace amounts of white phosphorus. Even the purest samples contain some. It is this contamination which gives it the particular smell. I never had red phosphorus, which is completely odorless. I purchased 20 grams of 99.99% red phosphorus for my element collection and even this had a faint smell.

If your red phosphorus is free flowing, then it is quite pure and contains hardly any white phosphorus. The white phosphorus makes it somewhat sticky.

[Edited on 3-2-18 by woelen]

My red phosphorus is somewhat sticky, but not that much. After cleaning and drying it is free flowing and practically odourless.

I was under the impression that red phosphorus is very unreactive. When stored, what exactly does it react with? Or are small amounts spontaneously converted into white phosphorus, which then reacts to form the smelly phosphine-compunds?

Bert - 3-2-2018 at 15:28

It will oxidize slowly in air. For purposes such as match book covers or other ignition strips where it must remain reactive in long term, non sealed storage, it is available in microencapsulated forms.

BackyardScience2000 - 29-10-2020 at 07:10

Red phosphorus is not illegal to sell in the US as long as you can guarantee that it is not being used with the intentions to make methamphetamine. That's why companies like sigma have stopped selling it to average people. They can't guarantee that. Smaller companies that deal with far fewer customers can. I've been selling it for years and the feds have absolutely no problem with me selling it as long as I report any suspicious activity. Like large orders (I limit orders to no more than 100g per year per customer, any request for larger amounts gets reported), suspicious inquiries, when they ask if my product can be used for such things (making it obvious) and just any general suspicious activity. I normally only deal with people that I trust with it as well. New customers are few and far between. They have to be able to prove to me that they have no intentions whatsoever to use it in that manner. Which is hard for people to do. Every single purchase is recorded and kept on file forever as well. The feds want suppliers to keep detailed lists of the buyers name, address, how much they buy, what they want to use it for, etc. That stipulation usually drives away any wrong doers. I am required to tell customers of that fact and that the feds could show up anytime wanting to make a copy of said lists. So unless you want to put in all that work and have to deal with the federal government in a regular basis, I would stray away from attempts to sell it.