Sciencemadness Discussion Board

Preparation of ionic phosphide from red P

woelen - 14-3-2019 at 08:18

I want to perform some experiments with PH3 in a somewhat easier way than I can do now. I need to heat white P in concentrated alkali solutions. This is dangerous and white P is not something which one can easily obtain in decent quantities (nor do I want that, given the high risk of storing much of it).

So, I thought about getting some metal phosphides, like Ca3P3, Mg3P2, or AlP. Adding these to cold dilute HCl conveniently gives a nice and steady flow of PH3 (possibly mixed in with some H2 and P2H4). I have been looking for these phosphides, but they are amazingly hard to find. I do not know any company who sells one of these chemicals to a private person.

Next thing I was thinking about is making it myself. Red P is no problem. I also have powdered Mg and powdered Zn. I tried mixing stoichiometric amounts of finely powdered red P with finely powdered Mg or Zn, but such a mix is not suitable for making the metal phosphide. The reaction is very fast, like burning black powder and all phosphide escapes as smoke and burns up in the air because it is very hot. I only tried with small amounts, unconfined. I didn't have the guts to try this in a test tube. The reaction is so violent that it may explode or at least be ejected from the tube, giving a big flame.

How would you proceed in making the phosphide? I have seen descriptions of processes, where vapor of phosphorus is led over finely divided metal in a red hot quartz tube, but that is not the kind of things I can do in my lab. Does one of you know of any other way of making ionic phosphides? If you know of a company in the EU which sells Ca3P2, Mg3P2, Zn3P2 or AlP to private individuals then that also is an option for me.

DavidJR - 14-3-2019 at 08:26

Maybe the problem is white phosphorus vapour and fine metal particles reacting with oxygen at high temp. It might be worth trying it in a test tube with a blanket of argon gas to see if it's less violent that way.

SWIM - 14-3-2019 at 08:42

Moletox mole and gopher killer is 2% zinc phosphide.
And $13 US per pound on ebay.

Bet you could get some fairly pure PH3 from that.

Ubya - 14-3-2019 at 09:57

Quote: Originally posted by SWIM  
Moletox mole and gopher killer is 2% zinc phosphide.
And $13 US per pound on ebay.

Bet you could get some fairly pure PH3 from that.

So $13 for 13 grams of zinc phosphide
PS i read on wikipedia
Quote:

AlP is used as a rodenticide, insecticide, and fumigant for stored cereal grains. It is used to kill small verminous mammals such as moles and rodents. The tablets or pellets, known as "wheat pills", typically also contain other chemicals that evolve ammonia which helps to reduce the potential for spontaneous ignition or explosion of the phosphine gas.

So maybe it's not a viable source

[Edited on 14-3-2019 by Ubya]

Metacelsus - 15-3-2019 at 00:28

Maybe you could try reacting excess magnesium or aluminum with a phosphate salt (for example, sodium metaphosphate) at high temperature?

Sulaiman - 15-3-2019 at 04:37

According to Wikipedia the laboratory preparation method is the thermal decomposition of phosphorous acid at about 200oC
https://en.wikipedia.org/wiki/Phosphine#Laboratory_routes

Apparently Weevil-cide pellets are 60% Aluminium phosphide (if available in NL)
http://www.upi-usa.com/fumigants/weevil-cide-fumigant
Attachment: mp2RS012.pdf (89kB)
This file has been downloaded 313 times

[Edited on 15-3-2019 by Sulaiman]

12thealchemist - 15-3-2019 at 05:44

Is it possible to use some sort of inert heat dissipant, like sand for Zn3P2 or calcium fluoride (fluorite, fluorspar) for Mg3P2? These heat dissipants would be unreactive and insoluble, so shouldn't affect your generation of PH3.

Cezium - 15-3-2019 at 08:30

From wiki:
2 NaH2PO2 → PH3 + Na2HPO4

I can obtain this locally at photographist store.

arkoma - 15-3-2019 at 11:05

Them phosphides are not real healthy......we used them on the farm as poison in grain bins.

fusso - 15-3-2019 at 15:12

Do you also want to make substituted phosphines?

kmno4 - 15-3-2019 at 16:08

Very similar topic was created in 2011 by the same user:
http://www.sciencemadness.org/talk/viewthread.php?tid=16106#...

woelen - 17-3-2019 at 14:21

Yes, indeed, but in 8 years things may change, new people may give new insights.

Making the stuff in a small scale home chemistry setting is very hard when you don't have the high-temperature equipment to safely perform this kind of experiments. Small scale experiments don't work, I tried several. In air, a small amount of mix of red P and metal simply burns. Somewhat larger amounts react very violently.

In the meantime I do have phosphorous acid and also sodium phosphite. Of course I also tried the decomposition of these by heating, but that reaction has no synthetic value at all. You get a yellow/brown or yellow/reddish mix of compounds and indeed I smell some PH3, but it definitely is not a clean reaction, giving nice amounts of PH3. I think that you get sub-oxides of phosphorus, or mixed sub-oxides/hydrides. Phosphorus at lower oxidation states is notorious at producing all kinds of lower oxides/hydrides. If you want to see yourself, just ignite a little amount of red P and watch till it stops burning. What remains behind is some yellow/brown stuff, which is some ill-defined lower oxide mix of phosphorus. A similar thing is what you get by heating phosphorous acid.

I also read about aluminothermic reactions (which was mentioned in the old 2011 thread), but these are beyond what I can do safely. You use very finely divided Al-metal as a reductor to get other chemicals, but performing that kind of reactions in a controlled and safe way requires quite some high-temperature engineering. I do not have a place where I can do that kind of things. I am confined to wet chemistry and low (less than appr. 200 C) chemistry.

With MgO mixed in, I did not have success. The reaction indeed can be made slower, but then I get all kinds of brown and yellow stuff (probably mixed oxide/phosphide or maybe even very impure white P, mixed with unreacted metal). In literature I read about passing vapor of phosphorus over metals, again not feasible for me.

@Sulaiman: In NL a private person cannot buy phosphides for the use of killing rodents, moles or other animals. There are companies who do this for you, but you may not handle the phosphide yourself. Only people with certain certificates may use phosphide compounds for this purpose. This does not mean I cannot buy phosphides, but up to now I did not find any suitable source of decent quantities of ionic phosphides.

Probably this section of chemistry remains inaccessible for me :(
Safety, however, comes first, doing high temperature chemistry is out of the question where I live.

DavidJR - 18-3-2019 at 08:29

Apparently magnesium phosphide is, in itself, flammable. So I think I was right about needing to do the reaction in an oxygen-free environment, like a test tube with the headspace purged with argon