SuperOxide
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Smelly red phosphorus - Best way to clean it?
I purchased some relatively pure red phosphorus a bit ago which didn't smell like anything. I used some in a synthesis to make iodomethane, and was
able to recover a decent amount of it after the reaction. However how the recovered red phosphorus smells absolutely horrendous. I tried washing it
with alcohol, acetone, water and a few other things but it seems to still smell pretty terrible. It's also very free flowing which is pretty odd. The
new stuff (which doesn't smell at all, even though it's been sitting there for some time) is kinda clumpy, but the recovered redP is a fluffy powder.
I also purchased some new red phosphorus which has the same smell as the stuff I recovered from the iodomethane synthesis (though not nearly as bad).
Is there an easy way to clean this up a bit with some magical solvent?
Thanks.
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Rainwater
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http://library.sciencemadness.org/library/books/brauer_ocr.p...
Page 519 of this cool library book. Be sure to check it back in before its due. They got steep late fees there.
"You can't do that" - challenge accepted
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SuperOxide
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Oh wow. Very useful. Thanks!
| Quote: |
I. Red Phosphorus. Commercial red phosphorus is purified as follows: Portions of 100 g. are boiled for 24 hours with a 7% NaOH solution. After removal
of the hydroxide, the phosphorus is boiled for 24 hours with water, washed with cold water until the alkaline reaction disappears (a centrifuge may be
used here to advantage) and dried in vacuum on clay plates over P3O5 . Phosphorus which has stood for some time must be freshly washed before use
because of its oxidation on exposure to air.
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I couldn't find much on how to do it when I looked. I was actually told to convert it to white phosphorus, distill the white phosphorus, then convert
the white phosphorus to red phosphorus.... lol. So glad I asked here.
[Edited on 22-1-2022 by SuperOxide]
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SuperOxide
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I started working on this yesterday, put all of my RP into a 1L flask, and filled the flask half way with 7% NaOH solution. It wasn't a violent
reaction when I added the NaOH solution, but the smell was immediately evident. It smelled pretty terrible.
I put a reflux condenser on and put a hose adapter on the top, which I passed through some activated carbon to try to capture any of the smell (since
I'm not entirely sure what it is). While the activated carbon did trap most of the smell I hadn't even refluxed it for 4 hours and there was a very
weird looking yellow solid that started to collect in the tube. It smelled pretty terrible (same smell as what I smelled earlier).
Here are some other photos: https://imgur.com/a/XM0vy3P
Anyone have any idea what this could be? The RP i'm purifying isn't recycled at all, so its not from any previous reactions or anything. I wasn't
expecting the purification process to left off anything that would settle in the tube like that. Im not sure how much of this will get released
considering it's supposed to be refluxed for 24 hours.
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SuperOxide
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I gave this another shot, but on a much smaller scale and with better preparation/research beforehand.
I took 7g of red phosphorus that was previously used to make iodomethane. After the iodomethane synth, it was washed very well then dried in a vacuum
desiccator over some P2O5, but it still smelled a bit (which is kinda how I was gauging its purity, along with it's appearance):
I poured the 7g of rP into a 250mL erlenmeyer flask along with 100mL of 7% NaOH solution (using distilled water) and a stir bar, and setup for a 24
hour reflux:
Because of the release of phosphine, I also setup a gas washing bottle with some boric acid, this seemed to work much better than the bottle packed
with activated carbon from my first attempt, lol. But the output was still leading to outside, along with the window being open just in case.
I couldn't do 24 hours straight, so I did 12 hours on two separate days.
After about ~10 hours or so, the color started to change to a darker kinda purple color, which I wasn't at all expecting:
After the first 12 hours, I turned off stirring/heating and let it settle. It was then apparent that the discoloration wasn't really due to the red
phosphorus changing color, but the water which had turned slightly yellow/green (but still somewhat transparent):
But this may not be entirely correct, since you can see some of the phosphorus up on the sides still has the purple color:
The heating/stirring was resumed the next day, and the mixture got even more purple in color:
After another 12 hours, I turned off the hotplate and let the phosphorus settle to the bottom of the flask. The solution was decanted off, then the rP
was washed several times with distilled water until it was no longer basic. Now with the yellow water removed, it's evident that the rP has darkened
over the 24 hours:
100mL of distilled water was added to the erlenmeyer flask, and it was setup for another 24 hours of boiling. The only real difference I noticed now
that I didn't see when I boiled it in 7% NaOH solution was that the red phosphorus seemed to whick up the sides of the flask, which didn't at all
happen before. The heat/stirring was at the exact same settings as well so I doubt it splashed up on the sides any more than it could have in the
NaOH:
After 12 hours of boiling in distilled water, the heat/stirring was turned off. To my surprise, once the rP had settled down to the bottom I could see
that the water was a very nasty dark brown color:
The next day I decided that before I boiled it for another 12 hours, I would decant the nasty solution from the red phosphorus. It didn't say to do
this in the literature, but I can't see what harm it would do.
After 100mL of fresh distilled water was added, the solution was setup for another 12 hours of boiling:
Once it had cooled down, I poured off the brown solution and washed the phosphorus several times with cold distilled water. Then decanted all the
water and put the wet rP into a vacuum desiccator over some P2O5. When the rP had dried out, I could see that it had darkened considerably:
Also, not only had it darkened a lot, but it doesn't smell any better.
The "purified" red phosphorus now weighs in at 3.75g:
While I may have lost almost half of the red phosphorus, I wouldn't blame this on the procedure. Instead of vacuum filtering I decided to decant
everything through the whole process, and sometimes the phosphorus would float on the water due to the surface tension, and I would just pour it off.
So that's my fault (but I was going for purity here, not yield).
Here's one last picture of the red phosphorus next to the vial of which I pulled the P from for this purification procedure. You can tell the color
has changed a great deal:
In summary - I don't think this procedure is very effective. I guess it could be user error, but it's such a basic procedure that I don't know what I
could have possibly messed up. But I'm open to any constructive criticism :-)
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Rainwater
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Sorry for the bad referral. I've never dealt with phosphorus but have performed about 30 procedures from that book with great results.
"You can't do that" - challenge accepted
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clearly_not_atara
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Turn it into black phosphorus by autoclaving in ethylenediamine:
https://dlisv03.media.osaka-cu.ac.jp/contents/osakacu/journa...
https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10....
Yes, you read that right. 
[Edited on 04-20-1969 by clearly_not_atara]
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woelen
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If I look at your original red P, then it looks quite pure to me. Red P always has a certain typical smell. Adding it to NaOH-solutions leads to
reactions, in which you lose quite some phosphoprus and in which smelly compounds can be formed (PH3, and from that some ill-defined oxygen/hydrogen
compounds of phosphorus can be formed. Red P is much less reactive than white P, but it is far from inert and reacts with quite some compouns,
especially when oxygen from the air is allowed in as well. So, I would not hassle with the red P at all, unless it looks sticky and wet. In the latter
case, I just would treat it with 0.5% NaOH for a few tens of minutes and then with distilled water.
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SuperOxide
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Quote: Originally posted by Rainwater  | | Sorry for the bad referral. I've never dealt with phosphorus but have performed about 30 procedures from that book with great results.
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Im inclined to say it was user error as well, but it's such a simple procedure I just don't know how I could have messed it up. It doesn't get any
simpler than boiling it in 7% NaOH for 24 hours, washing it, boiling it in H2O for 24 hours, washing it then drying it. lol.
Holy crap, I've been wanting to make black phosphorus for some time.... That almost seems too simple, lol.
| Quote: Originally posted by woelen | | If I look at your original red P, then it looks quite pure to me. Red P always has a certain typical smell. Adding it to NaOH-solutions leads to
reactions, in which you lose quite some phosphoprus and in which smelly compounds can be formed (PH3, and from that some ill-defined oxygen/hydrogen
compounds of phosphorus can be formed. Red P is much less reactive than white P, but it is far from inert and reacts with quite some compouns,
especially when oxygen from the air is allowed in as well. So, I would not hassle with the red P at all, unless it looks sticky and wet. In the latter
case, I just would treat it with 0.5% NaOH for a few tens of minutes and then with distilled water. |
I have several different bottles of red phosphorus from different suppliers, and some of them (the ones that are apparently more pure) have absolutely
no smell at all.
And almost all of them seem somewhat wet to some degree. But I just put them in a vacuum desiccator with some P2O5 to dry them out, and that seems to
work very well.
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PirateDocBrown
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When you say it "smells absolutely horrendous", exactly how does it smell? Is it a phosphine smell? Some other smell?
Phlogiston manufacturer/supplier.
For all your phlogiston needs.
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SuperOxide
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Definitely phosphine smell ("a disagreeable garliclike odour").
I have several different bottles of rP, one smells like nothing, and the recycled bottle is the one I said smells terrible and tried to purify.
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