Sciencemadness Discussion Board

Phosphorus Oxidation Problems

BromicAcid - 5-6-2004 at 16:16

The topic itself really doesn't make much sense until you think about it. At least to me it doesn't. "Problem oxidizing phosphorus? Don't you have air where you come from?" That would be my witty reply. However I am having a problem with oxidizing it on two fronts and I'm hopping for a nifty solution from my comrades at sciencemadness.

First problem, a while ago I tried to more readily store my phosphorus by attempting to make saturated solutions of phosphorus in numerous solvents and dispensing them in that fashion. CS2 was never one of my solvents but benzene was. Benzene does not dissolve much phosphorus, but it does dissolve enough to make it spontaneously flammable when exposed to air. I only have about 25 ml of saturated solution but it is a problem not only due to its spontaneous flammability but the toxicity of phosphorus and benzene on their own. I attempted to just leave some of it out and burn it but the fire was unmanageable and the fumes coming up looked none to happy.

So I was wondering about a way to oxidize away the phosphorus easily to at least solve spontaneous flammability. I could add a halogen then add water to try and turn it to phosphoric acid. But beyond that I really don't know, I might just end up with bromo benzene and burn my eyes. Phosphorus in solution is actually quite resilient to oxidation, for example, phosphorus is purified by stirring under acidified dichromate. So any ideas on this other then setting the whole mess on fire?

My other pondering. On previous occasions when I tried to clean my phosphorus producing apparatus after my runs I had the terrible problem of cleaning impure phosphorus out of the crevices in my metal pipes. If left to burn out on their own they make phosphoric acid or other compounds, react with the iron, or are just impure enough themselves, to make a protective surface layer that easily gets scraped away and catches on fire again. My only luck has been with either
a) A blow torch heating each joint individually and allowing it to melt out the phosphorus and burn it out.
b) Using a baby bottle brush and olive oil then manually scrubbing each area clean.

Both are unsatisfactory considering the toxicity of phosphorus. Therefore aside from a solvent like CS2 anyone know a good idea for cleaning out the phosphorus?

S.C. Wack - 5-6-2004 at 18:21

S is also somewhat soluble in benzene.
The pentasulfide is useful, if that can be the product here.
Merck says that chloroform dissolves almost as much P as benzene.
So many refs say that P and light gives red P eventually. Does it in solution? Perhaps more speedily with mercury-vapor if so?

EDIT: Merck says S dissolves in hot benzene much more than at room temp.

[Edited on 6-6-2004 by S.C. Wack]

BromicAcid - 5-6-2004 at 18:27

Yes, red phosphorus will form and precipiate from the solution. The best example is the specific grade of red phosphorus obtained from a CS2 solution being exposed to light. Well, I guess I could transfer it to a different container and leave in the sun for a bit. As for the pentasulfide and sesquisulfide, etc. Do they form spontaneously at STP? Or would additional heating be involved. They are somewhat less reactive and would be helpful in disposing of phosphorus solutions if readily prepared.

vulture - 6-6-2004 at 01:08

70% HNO3 readily oxidizes phosphorus to phosphoric acid.

BromicAcid - 6-6-2004 at 17:24

I tried adding sulfur to my benzene/P mixture and there was no visible reaction. So I cautiously heated the reagent bottle capped for several minutes till the benzene began to condense on the top of the bottle and run down continuously. Still there was no visible color change. Upon dumping out the contents the mixture was still just as flammable as before if the phosphorus had been consumed as sulfides then this reaction with air would have been slowed or not occurred at all. Regardless of their apparent ease of reaction (my chemistry book says gentle heating is necessary between P and S) the reaction appeared not to take place in benzene.

As for Vulture's method, I knew of that but I have not practiced it because I really don't have any 70% HNO3 to spare. In addition I remember reading a story about phosphorus wastes from a production plant being discharged into a lake and that the water discharged was aerated for three days prior to discharge and it still contained enough elemental phosphorus to kill many of the fish in the area, however on a small scale bubbling air though a mixture of phosphorus at a slow rate sealed from outside air entry might be a good controlled oxidation of phosphorus and under an inert solvent it might even lead to a P2O5 precipiate.

vulture - 7-6-2004 at 11:35

Well, it certainly works with 70% HNO3, but lower concentrations should do too with a little heating.

EDIT: By my knowledge, phosphorussulfide is very flammable itself, too. Not as flammable as white P, but IIRC it ignites at 30C.

[Edited on 7-6-2004 by vulture]

BromicAcid - 7-6-2004 at 13:39

Phosphorus forms many different sulfides, P4S7(Flamable), P2S5(Odor of H2S, decomposes in moist air, hygroscopic), P4S3(Auto ignition temperature 100C, the component of match heads), P2S3(Flamable, Mp 290) and I believe there is a poly sulfide. Are all listed under different sections in my chemistry dictionary, each has different properties. None of them appear to have as low an auto ignition temperature as 30C though. Possibly a mix of sulfides is formed that could have a lower flamability point then any of the pure substances.

BromicAcid - 15-12-2004 at 16:43

I'd read in several places about treating phosphorus on the skin with solutions of copper sulfate and picking off the phosphorus manually so this destruction procedure came as no surprise.

From "Destruction of Hazardous Chemicals in the Laboratory" 1990 Lunn, George
John Wiley & Sons
Quote:
White Phosphorus
Cut 5 g of white phosphorus under H2O into pellets that are no more then 5 mm across and add these pellets to 800 ml of 1 M cupric sulfate solutions. Allow the reaction mixture to stand in a 2-L beaker in a hood for about a week. Stir occasionally. If one of the larger black pellets is cut under H2O and no waxy white phosphorus is observed. the reaction is complete. Filter off the precipitate and, while keeping the mixture wet, add to 500 ml of 5.25% sodium hypochlorite solution. Stir this mixture for 1 h to oxidize any copper phosphide to copper phosphate. Dispose of the final reaction mixture in the appropriate fashion.

alchemie - 16-12-2004 at 09:36

You are trying to oxidize white phosphorus right?

In that case be wary. Ihave an old chem book that advizes not to use concentrated HNO3 beucause there is danger of explosion

The book says that even red P shouldn´t be oxidized with too strong HNO3.

On the other hand, the reaction is very slow if you use too dilute acid.

JohnWW - 16-12-2004 at 16:48

Oxidizing elemental P to P2O5 or phosphate is rather a waste of good P, (a) because it is a fairly highly exothermic reaction, (b) elemental P (whether red or white) is a valuable reagent in organic syntheses and has other uses e.g. as a vermin poison and in matches, and (c) soluble phosphate and P2O5 can be obtained cheaply in any case in industry by treating rock phosphate (apatite) with an excess of sulfuric acid.

chemoleo - 16-12-2004 at 17:22

JohnWW, did you actually read the thread?

HNO3 - 16-12-2004 at 17:37

One simple solution! (pun unintended)
Ship it to me.:D
Somewhere I read that if you expose WP to UV rays, you will get RP. UV lamps are rather easy to get.http://www.unitednuclear.com/lights.htm;)

BromicAcid - 16-12-2004 at 17:47

I really don't think you want a bunch of rusted metal pipes full of iron phosphide with dirty phosphorus in the grooves, or a benzene solution of unknown composition containing an unknown amount of phosphorus dissolved in it. This thread was about the destruction of things that contained phosphorus that could not be salvaged or used in a useful way and only presented a safety hazard by their further existence. All the matters have already been taken care of however and I would have been happy to learn that little copper sulfate / white phosphorus thing that I just posted, although the action of light on a solution of phosphorus does readily convert it to red phosphorus. I used to have my phosphorus under water until I tried the benzene thing, when it was under water it turned a little yellow and orange over the course of several months. When I tried to dissolve it in benzene that was a mistake so I added water and took off the bottom layer containing the water and phosphorus and a little benzene to store. The tiny amount of benzene solvated in the water must act catalytically because since this attempt much of the phosphorus has converted to red phosphorus despite the fact that its almost always kept out of the light.

HNO3 - 16-12-2004 at 18:50

I love Phosphorus.:D

runlabrun - 22-12-2004 at 17:43

"soluble phosphate and P2O5 can be obtained cheaply in any case in industry by treating rock phosphate (apatite) with an excess of sulfuric acid." -JohnWW

Apatite is Ca5(PO4)3(OH, F or Cl) wouldnt the reaction with sulphuric acid go soemthing like this:
Ca5(PO4)3OH + 5H2SO4 --> 5CaSO4 + H2O + 3H3PO4 ??
or for F and Cl as the alternate instead of water being produced HF and HCl are produced...

All circumstances leads to the production of phosphoric acid not P2O5.
Or more than likely the reaction doesnt go like that.... can someone clear this up? Apatite is easy to get so would be good for a cheap and easy source of P2O5...

-rlr

JohnWW - 23-12-2004 at 02:16

In the industrial production of "superphosphate" fertilizer, ground phosphate rock is usually only partly acidulated with concentrated H2SO4, resulting in soluble CaHPO4 and Ca(H2PO4)2, along with sparingly soluble CaSO4. Only an excess of H2SO4 would result in H3PO4.

runlabrun - 23-12-2004 at 03:50

Well in the quote of yours i originally sighted you said an excess of H2SO4 will produce P2O5.....

But yeah less than excess will produce the mixed phosphates... how would you get from the mixed phosphates to P2O5 though?

-rlr

JohnWW - 23-12-2004 at 11:45

Dehydration of the H3PO4 obtained using excess H2SO4. I am not sure, offhand, what would be the best method.

S.C. Wack - 23-12-2004 at 12:34

There is no method to the oxide, other than reducing to P and going from there, or using one of the P halides - though the latter doesn't involve the acid. Wish one of the usual US sellers would sell some of the oxide, UPS allows 500g.

AFAIK, P2O5 dehydrates H2SO4 to SO3, not the other way around.

BTW, just uploaded Vogels Qualitative Inorganic Analysis 5th ed (1979). Even if you aren't particularly interested in analysis, it's a good book, wouldn't have scanned it if it wasn't worth reading.

JohnWW - 23-12-2004 at 15:00

It may look that way, although it is energetically expensive to do, to get P2O5 by reduction and re-oxidation. I wonder if there is anything, or a method, which could be used to dehydrate H3PO4.

Thanks for uploading Vogels Qualitative Inorganic Analysis 5th ed (1979). It should be observed, though, that the current version is the 7th, published in 1996 by Prentice-Hall. ( http://vig.prenhall.com:8081/catalog/academic/product/0,4096... )

However, what I am really looking for is Vogel's Quantitative Inorganic Analysis, latest edition which is the 5th, of 1989. ( http://www.campusi.com/isbn_0582446937.htm , http://www.open.mis.surrey.ac.uk/misweb/modules/4462.htm ). I have only the print version of the 3rd edition, from 1961 or 1962, published by Longmans, which is not strong on recently-developed instrumental methods. The 4th edition appeared in 1978.

S.C. Wack - 23-12-2004 at 16:26

As I mentioned in an weeks ago post, I scanned Quantitative Chemical Analysis as well. I'm taking a break from straightening pages (my OCR program will only straighten to within .4 degree) right now. It is rather longer than the other - 906 pages. I did the QIA one because its a good book, even though much is duplicated in QCA, and because I made up my mind to scan all three 5th eds (what the library had) when I decided to do the Pract. Org. Chem. one. I thought that a matching set - all made the same way - should be made. Don't forget to upload them elsewhere. This last of the Vogel 5 trilogy should be up by New Years.

You, me, and every meth cook in the country is looking for a method to reduce or dehydrate phosphoric acid to something other than the pyro acids or P - there just isn't one that I've ever heard of. Supposedly HI will reduce it to a measurable extent - AFAIK that's it. If anyone knows of a reference - let me know, because I look up refs that match my interests.

HNO3 - 27-12-2004 at 14:09

BromicAcid: Could you distill the benzene off under an inert atmosphere?

BromicAcid - 27-12-2004 at 19:28

Could have, but it really would have been more of a hassel then I'd want, phosphorus might have carried over to at least the stillhead and opening up that distillation apparatus would not be what I would call a fun day.

ordenblitz - 6-8-2005 at 13:06

On my way toward SO2, I decided to make some P2O5 today by direct oxidation of elemental P.

I tested the possibility in glass, of heating a small amount of P and adding O slowly to form the pentoxide which worked quite well and was controllable. I therefore decided to scale up.

In a 500ml three neck flask I put a cobbled together hotwire igniter, a narrowed pipette and a cooled condenser to catch any escapees.
http://img286.imageshack.us/img286/2792/flasksetup8nu.jpg

Into the flask I placed ~20 grams of red P.
http://img38.imageshack.us/img38/9805/pstart9gm.jpg

The plan is to add Oxygen, in a slow and controlled manner to avoid unpleasantness.
http://img38.imageshack.us/img38/9038/o24dn.jpg

A few volts to the nichrome, crack the regulator and we were busy oxidizing.
http://img79.imageshack.us/img79/3202/glow5uc.jpg

The trick I surmised was to keep the reaction proceeding slowly enough so that I could dissipate the heat and not have a meltdown. I placed a fingercot (I know what it looks like) over the condenser for a visual indication of the addition requirement of oxygen.
http://img142.imageshack.us/img142/4952/regulate13rz.jpg

Incidentally in this event.. The deed is over when it’s engorged, not the reverse. J
http://img38.imageshack.us/img38/2403/regulate4xr.jpg

A couple of times I was not paying enough attention and thus getting a bit behind the curve and adding way to much O2. This as it turned out was a big mistake.
http://img142.imageshack.us/img142/2230/slowo6ai.jpg

Unfortunately this days work was ruined and resulted in a TLOG.
(tragic loss of glassware)

tlog.JPG - 89kB

BromicAcid - 6-8-2005 at 16:45

Incidentally, I had a small amount of benzene and water under which my phosphorus was stored, the container fell over and the benzene and water came out leaving a tube with phosphorus in it, luckily the benzene did not catch on fire as it would smoke when exposed to the air normally.

Since then I have been messing with burning phosphorus, attached is the stereotypical picture of phosphorus burning.

BTW, ordenblitz, I don't know if this is such a problem with red phosphorus, but as we know white phosphorus forms the other oxide when exposed to limited oxygen, do you know if the same thing happens with red phosphorus? My condolences on your flask. Oh, and that watch glass I have the phosphorus burning on cracked in half when it was done burning, I could have sworn it was pyrex.

[Edited on 8/7/2005 by BromicAcid]

phossyburn4.jpg - 64kB

Glassware issue

chloric1 - 6-8-2005 at 18:10

ordenblitz, you protect the flask with glass wool or other silicated insulator. Maybe infusorial earth? diatameous earth may also work.

ordenblitz - 7-8-2005 at 09:37

I had the flask immersed in a bath of circulating cool water. I didn't think that insulating it was the best idea with all the heat that was being generated.

I think I am going to try building a metal reaction chamber out of stainless steel pipe for the next attempt.

Bromic:
I would imagine that redP would act the same as white when burning and also form P4O6 in a limited O atmosphere. I should try to combust under pressure in my next design.