Sciencemadness Discussion Board

Violet Phosphorus

APO - 13-4-2013 at 18:49

Is there a way to make Violet Phosphorus by recrystallizing from Gallium instead of Lead?

Adas - 14-4-2013 at 00:42

Probably not. And if yes, you would still to use high temperature. It is a waste of Gallium, IMO.

And still, the lead with phosphorus has to be heated to 550°C for 18 hours. Do you really want to do it?

Finnnicus - 14-4-2013 at 01:16

How about zinc? MP=~210C IIRC. Or am I missing some science here? :)

[Edited on 14-4-2013 by Finnnicus]

kristofvagyok - 14-4-2013 at 05:43

According to Gmelin Handbook: P: MVol.B, 3.4.1.5, page 276 - 281

Heating white phosphorous in a sealed tube with water to 248°C and 48 atm. purple P is formed, at 360-380°C >89 atm black P formed; byproducts: H3PO4, PH3.

Plese do not try this at home :D

Adas - 14-4-2013 at 06:26

Quote: Originally posted by kristofvagyok  
According to Gmelin Handbook: P: MVol.B, 3.4.1.5, page 276 - 281

Heating white phosphorous in a sealed tube with water to 248°C and 48 atm. purple P is formed, at 360-380°C >89 atm black P formed; byproducts: H3PO4, PH3.

Plese do not try this at home :D


Black P is formed when white P is heated under 12000 atm. No need for any water, even in the purple P route and you would not get the PH3. (Wikipedia)

12AX7 - 14-4-2013 at 17:10

Gallium phosphide will form readily -- which is handy if your reagents are >6n purity, since can make green LEDs.

Solubility of GaP in Ga or P is likely quite small at any ordinary temperature.

Tim

BromicAcid - 14-4-2013 at 18:04

Somewhat unrelated but you can see a table of allotropes of phosphorus along with their preparation here:

http://www.sciencemadness.org/talk/viewthread.php?tid=3563#p...

The table is a bit dated. This thread made me at least go to Wiki and I was surprised to see an article on the allotropes of phosphorus (though I shouldn't have been surprised to see it). I used to consider myself an expert in the field but no longer. At one time it was my understanding that the different varieties of red phosphorous (i.e., violet, scarlet, sanguine, etc.) were all just different polymer lengths or in the case of scarlet phosphorus, mercury contamination from manufacturing. However there is a structure for Hittrof's phosphorus there that is intriguing.

Anyway, I am with the above posters, gallium seems like it would not work, I think the phosphide is too stable. Lead forms a phosphide too but at the temperatures employed it is unstable. I think that it allows the material to go into 'solution' and precipitate out by building these polymer chains during the decomp similar to the mercury acting on PBr3 to form the scarlet form. In any case, you heat up phosphorus too much and it will break down into P2 molecules but if you hold it at just the right temp you will get the thermodynamically favorable phosphorus at that temp which is why most of these involve heating and holding.

woelen - 14-4-2013 at 23:11

I more and more have the impression that red P is not a nice well-defined entity. I have seen so many differences!

I myself have three samples of red P. My first sample (100 grams) was sold to me as better than 99.8% phosphorus content. It is a fairly light brick red powder, which is very dry and free-flowing. I tested this in 12% sodium hypochlorite. All of the red P dissolves, leaving a clear and colorless solution. So, indeed (nearly) all of this must be phosphorus. Still I have severe doubts on its purity. The seller only tells it's better than 99.8% phosphorus, but how much white P is in the material? I think a lot, it has a strong smell and its color is remarkably light.
My second sample (few tens of grams) is from an official chemical warehouse (Merck) and that bottle states that it is 98% red P. This material is much darker (dark violet/red) and it also is a much coarser powder which is slightly damp and nearly odourless. When this is added to 12% sodium hypochlorite, then quite some black material remains left, which does not dissolve. What is this black material? Is this some darker allotrope of phosphorus?
My third sample is from a German supplier (250 grams from Lippert Lehrmittel, which was raided a few years ago) and this is very similar to the Merck-sample. Also slightly damp, but having a more brown color and having a somewhat stronger smell than the Merck-sample. No purity is specified on the bottle. When this is added to strong bleach, then also quite some dark material remains.

All three samples burn well and make very sensitive mixes with KClO3.

Adas - 15-4-2013 at 07:48

Quote: Originally posted by woelen  
I more and more have the impression that red P is not a nice well-defined entity. I have seen so many differences!

I myself have three samples of red P. My first sample (100 grams) was sold to me as better than 99.8% phosphorus content. It is a fairly light brick red powder, which is very dry and free-flowing. I tested this in 12% sodium hypochlorite. All of the red P dissolves, leaving a clear and colorless solution. So, indeed (nearly) all of this must be phosphorus. Still I have severe doubts on its purity. The seller only tells it's better than 99.8% phosphorus, but how much white P is in the material? I think a lot, it has a strong smell and its color is remarkably light.
My second sample (few tens of grams) is from an official chemical warehouse (Merck) and that bottle states that it is 98% red P. This material is much darker (dark violet/red) and it also is a much coarser powder which is slightly damp and nearly odourless. When this is added to 12% sodium hypochlorite, then quite some black material remains left, which does not dissolve. What is this black material? Is this some darker allotrope of phosphorus?
My third sample is from a German supplier (250 grams from Lippert Lehrmittel, which was raided a few years ago) and this is very similar to the Merck-sample. Also slightly damp, but having a more brown color and having a somewhat stronger smell than the Merck-sample. No purity is specified on the bottle. When this is added to strong bleach, then also quite some dark material remains.

All three samples burn well and make very sensitive mixes with KClO3.


The black thing could be traces of violet P which may not dissolve in bleach so readily. Have you got any idea how to test it? Is there enough of it to collect the black powder and light it up?

[Edited on 15-4-2013 by Adas]

APO - 15-4-2013 at 10:11

Hold, on, is there a way I can crystallize Red Phosphorus from 12% Sodium Hypochlorite?

Adas - 15-4-2013 at 10:25

Quote: Originally posted by APO  
Hold, on, is there a way I can crystallize Red Phosphorus from 12% Sodium Hypochlorite?


NO, lol. The hypochlorite oxidizes it. Red P doesn't dissolve in anything. You can get rid of any white P impurities using a proper solvent, though.

woelen - 15-4-2013 at 12:26

@APO: I did the test of dissolving red P to see whether non-oxidizable matter is in the red P which does not dissolve in bleach. Red P (and white P) both react with bleach to phosphate ion and the bleach is converted to chloride. The phosphate and chloride give a colorless and clear solution. Some of the material in some samples of the red P, however, do not dissolve and remain present as (nearly) black particles. What I wanted to test is how much black stuff remains. The black stuff is not red P, nor white P and if a lot of this stuff remains, then it may be that there is a higher non-phosphorus content, or a high other (e.g. black or violet) allotrope phosphorus content.

@Adas: I only have a very small amount of the black material. I'll repeat the experiment with a gram or so of red P and see if I can isolate a small pile of dark stuff, enough to put it on a small spatula and keep it in a flame.

vmelkon - 17-4-2013 at 16:40

So, how do you make violet phosphorus? Just heat together lead and phosphorus in a closed chamber? Do you get some violet crystals floating on the lead?

SM2 - 17-4-2013 at 18:48

So many allotropes, and sub allotropes. No, purple (violet) phosphorus is the usual, cheap $5/Lb of commerce. It has always been this way, where red phosphorus appears purple. At least on this planet.

woelen - 20-4-2013 at 10:49

I did an experiment with red phosphorus and it shows how different it can appear.

http://woelen.homescience.net/science/chem/exps/redP/index.h...

Please comment on this. Is this another allotrope or just red phosphorus?

elementcollector1 - 20-4-2013 at 11:04

Looks violet to me, but why didn't it react when the other allotrope did?

Adas - 20-4-2013 at 11:05

Quote: Originally posted by woelen  
I did an experiment with red phosphorus and it shows how different it can appear.

http://woelen.homescience.net/science/chem/exps/redP/index.h...

Please comment on this. Is this another allotrope or just red phosphorus?


I think it is just some violet P "impurity". It is definitely the violet P, IMO. The more violet P in the sample, the higher the quality (because violet allotrope is less reactive = safer). I believe that this has something to do with reaction temperature, pressure and time.

[Edited on 20-4-2013 by Adas]

woelen - 21-4-2013 at 12:15

I have a collection of elements and I keep white P and red P as separate entities, because they are really different. What about this grey material? Would you add that as another allotrope of the element phosphorus, or isn't it interesting to keep this as an additional sample. For now, I put this material aside, besides my other samples, just because it looks so different, but I wonder whether this really is useful to do.

Adas - 21-4-2013 at 12:22

Quote: Originally posted by woelen  
I have a collection of elements and I keep white P and red P as separate entities, because they are really different. What about this grey material? Would you add that as another allotrope of the element phosphorus, or isn't it interesting to keep this as an additional sample. For now, I put this material aside, besides my other samples, just because it looks so different, but I wonder whether this really is useful to do.


You said that red and violet P behave the same when mixed with KClO3, just their reactivity towards bleach is different. It is a different allotrope, but there is not as much difference as between white and red P.