Sciencemadness Discussion Board

Phosphine and white P from sodium hypophosphite?

woelen - 22-3-2007 at 01:06

I was able to get some NaH2PO2, the salt of the monobasic hypophosphorous acid (a.k.a. phosphinic acid). I expected this to be a very strong reductor, but it is acting very slowly, much slower than I expected. E.g. it makes CuH from copper (II) salts, when allowed to stand for several hours. I expected a nice energetic reductor, but unfortunately that is not the case.

I also read that it can decompose to form PH3, but no reaction conditions were specified. Is this really true? And if so, how could I make the PH3, such that it nicely can be bubbled through water and collected in an inverted bottle?

Is it also possible to make white P from PH3 in an easy way?

I know of the dangers of PH3 and white P, so no need to emphasize on that.

garage chemist - 22-3-2007 at 10:01

I do not have any sodium hypophosphite myself, but a member on the german forum wrote that he obtained PH3 and white P by simply heating the salt dry in a test tube.
Maybe the initial product is only PH3 and if the glass above the salt is hotter than 350°C, it decomposes partially into white P and H2.

If you want white P, use the sublimation of red P, you wont be bothered by PH3 then. Another chemist has designed an apparatus for this that allows it to be done under vacuum, I just need the 25ml quartz flask, its the only part thats missing.

garryb - 23-3-2007 at 02:13

I hope I'm not wandering too far from the topic here, but I am intrigued by the reminder from garage chemist that white P is made by subliming red P. I had always considered this to be a little too complex and dangerous as an "amateur" procedure, but given that white P is now virtually unobtainable to ordinary mortals, I am wondering if/how this can be done. My first thoughts are as follows.

Set up a supply of an inert gas (CO2 is probably easiest, perhaps from a Kipps apparatus) and lead this into a 100ml RB flask containing, say, 5g of red P. Heat this, and lead vapour into a cooled receiver (perhaps another RB flask sitting in water) then vent surplus CO2 (with traces of white P) to atmosphere. After a few g of white P have appeared in the second flask, then add water and we have a small sample of this interesting (and dangerous!) allotrope.

Does anyone have any experience of this sort of thing? Any major problems forseen? Any improvements suggested? (By the way, I am a medical doctor, so am fully aware of the exceedingly poisonous nature of white P).

YT2095 - 23-3-2007 at 03:06

5g is a little ambitious for my tastes, but I have done a 1/4 gram in a test tube also under CO2 gas with an air lock.
white P is very simple to obtain although the results Look a little disappointing, it`s not actually Pure white at all, more an off yellow with little orange bits in it.

the condensate on the side of the tube will sparkle and make a little noise when you fill it up with water in a darkened room also :)

edit: and Don`t use Butane as the inert gas, I know someone that did that and had to dispose of the test tube later, the Stench could Not be removed from it, isn`t that Right Woelen :P

[Edited on 23-3-2007 by YT2095]

garryb - 23-3-2007 at 03:15

Thanks YT2095. That's the sort of practical advice I was looking for. Yes, perhaps 5g is a little optimistic for a first go. Maybe 0.5 or 1g in 25ml flasks would be safer. I would like to collect the white P in a separate container from the red P to save scraping it away.

woelen - 23-3-2007 at 05:51

Yes, I was the one, who used butane as a non-reactive gas, but that was combined with sulphur also. Later testing revealed that it is the sulphur which reacts, not the P.

I also did the test with red P alone, and then the P sublimes, and an orange coating appeared on the inside of the test tube. In the dark, I observed a mysterious glow. The white P obtained in this way, however, is very impure, I think that the orange color is due to the formation of red P as well, which strongly contaminates the white P.

garage chemist - 23-3-2007 at 06:51

1g? 5g? I have made white P in 20g-amounts by sublimation of red P, by the bent test-tube method:,5774,-Wei%DFer+Phosphor.h...

The material obtained by this procedure is indeed orange to reddish, but can be used like that for any synthesis involving white P (e.g. PCl3).
It can be cleaned up by filtering it molten (dangerous, the liquid immediately catches fire upon air contact) or less dangerous, melting and stirring it under an acidified solution of dichromate.
Contrary to what one might expect, only a very small amount of the P4 is lost by oxidation this way, and the reddish impurities are oxidised preferentially.
Ideally, the P will be yellow afterwards.

Making P that is really white is too much work and not necessary, since the yellow purified material is already very pure and useable for every application.
Any "white" phosphorus that you can buy is yellow anyway, it only slowly becomes white on the outside of the sticks due to formation of a mixed polymerisate that contains water. The P itself in the core is yellow.
Making "white" P involves special purification procedures like steam distillation (takes very long, due to the high boiling point of P4). It will become yellow again upon storage anyway.

[Edited on 23-3-2007 by garage chemist]

garryb - 23-3-2007 at 07:34

Vielen Dank garage chemist! I liked your link - my German is only very basic, so I could only get the gist of it, but I have printed it off and will ask a German friend to translate it for me. I am ashamed to say that, like most British people, my foreign language skills are not good. I am interested in getting "white P" in the "chemical" sense, rather than the colour descriptive sense, so orange or yellow colouration does not bother me.


S.C. Wack - 24-3-2007 at 10:15

Décomposition thermique de l'hypophosphite de sodium
Bulletin de la Société chimique de France
927-30 (1955)

Attachment: bull_soc_chim_927_1955.djvu (211kB)
This file has been downloaded 470 times

BromicAcid - 24-3-2007 at 11:08

Once upon a time I was pondering electroless nickel plating. The secret ingredient or at least the hard to find ingredient in these mixes being the hypophosphite. The thing I was contemplating was that the alloys produced are high phosphorous alloys, some up to 10% and higher. The thing is, in purification of some metals, such as copper, an anode of the impure metal dissolves leaving behind the impurities to plate on the cathode. As I mentioned in the phosphorus thread, would this leave behind phosphorus as some kind of paste as waste from the anode?

Wow, that was a very round about away of getting to my point.

Mumbles - 24-3-2007 at 23:23

I do believe sodium hypophosphite is the secret ingredient to super black, supposedly the blackest black known to man. I always wanted to make it, but always lacked the sodium hypophosphite, or white P to make it.