Sciencemadness Discussion Board

Phosphorus pentachloride, easy AF preperation

theAngryLittleBunny - 6-5-2018 at 11:31

I always thought making phosphorus pentachloride is quite difficult, my first tries of suspending the phosphorus in DCM and bubbling chlorine into it kinda failed, turns out, it's much easier actually. Take a flask with 2 openings, put red phosphorus into it, hook up a chlorine generator on one neck, and the other is left open, you could also just put some plastic wrap with a tiny hole in it onto it, And now you just slowly pump chlorine into the flask and shake it occasionally. The flask will warm up and white smoke is produced in the flask, but no fireworks or anything, the reaction is suprisingly calm. The PCl5 starts to deposit on the wall, and the phosphorus in the bottom gets less and less. When you shake the flask, you will see some spaks as the red phosphorus reacts with the chlorine atmosphare and white smoke shoots out of the open neck. After the addition is done, the most difficult part begins actually, getting the PCl5 out of the flaks, because it's deposited all on the walls. You can try scraping it off, or just dissolve it off with DCM, as PCl5 is soluble in it, and then evapourate the solution to get the pure PCl5.

So no white phosphorus, or PCl3, or whatever other exotic thing other people say you need, making PCl5 is super easy.

If someone has some suggestions on how to do it better, feel free to comment.

unionised - 6-5-2018 at 11:33

Did you flush the air out of the flask first?

JJay - 6-5-2018 at 11:49

I think you can make crude calcium phosphide with a calcium phosphate thermite (warning: this will give off phosphine gas if it gets wet) and then react it with chlorine gas at high temperatures in a tube to distill off phosphorus pentachloride. I have not tried this, but it has the advantage of not requiring red phosphorus.

theAngryLittleBunny - 6-5-2018 at 12:04

Quote: Originally posted by unionised  
Did you flush the air out of the flask first?


No, just put the phosphorus in and started the flow of chlorine, I accepted the tiny amount of POCl3 that would be formed.
Quote: Originally posted by JJay  
I think you can make crude calcium phosphide with a calcium phosphate thermite (warning: this will give off phosphine gas if it gets wet) and then react it with chlorine gas at high temperatures in a tube to distill off phosphorus pentachloride. I have not tried this, but it has the advantage of not requiring red phosphorus.


I guess this is for the people who don't have phosphorus avaliable, but you need A LOT of calcium for that, and I don't think calcium is super easy to get either.

[Edited on 6-5-2018 by theAngryLittleBunny]

JJay - 6-5-2018 at 12:11

You don't need calcium metal... you need aluminum powder and calcium phosphate.

theAngryLittleBunny - 6-5-2018 at 12:51

Quote: Originally posted by JJay  
You don't need calcium metal... you need aluminum powder and calcium phosphate.


Well, that makes sense, but yeah, I mean it's a nice methode for all the american people who can't get phosphorus, but you need 60% more chlorine, and that would turn me kinda off, and the heating and all that stuff.

unionised - 6-5-2018 at 13:10

Heating phosphine will convert it to hydrogen and phosphorus so, if you really want to economise on chlorine...

Incidentally, does anyone have an OTC source of ferrophosphorus?

theAngryLittleBunny - 6-5-2018 at 13:45

Quote: Originally posted by unionised  
Heating phosphine will convert it to hydrogen and phosphorus so, if you really want to economise on chlorine...

Incidentally, does anyone have an OTC source of ferrophosphorus?


I didn't know that it would do that O.o
But I just realized, I fucking hate PCl5, worst stuff to work with ever, even bromine isn't that unpleasant as this stuff, so not gonna make it again lol.

And I dunno about OTC, but if you wanna order it, here ya go: http://onyxmet.com/?route=product/product&filter_name=fe...

Heptylene - 25-5-2018 at 09:36

theAngryLittleBunny, have you characterized the product you obtained? Tested it to see if it's really PCl5 and not something else?

If it is indeed PCl5, this method is promising.

unionised, what would you do with the ferrophosphorus? Is there a way to separate it from the iron or react it in some way? As suggested above, onyxmet has ferrophosphorus for very cheap.

symboom - 25-5-2018 at 11:21

If phosphine is decomposed into phosphourous and hydrogen then chlorine is introduced explosive formation of hydrogen chloride along with phosphourous pentachloride formationalthough the reaction of hydrogen and chlorine does produce heat to sustain the reaction of heating phosphourous with chlorine

[Edited on 25-5-2018 by symboom]

AJKOER - 26-5-2018 at 07:22

My recollection is that mixing hydrogen and chlorine is safe barring the presence of red light, at which point, a highly kinetic explosion does occurs. It proceeds, however, with only a pure H2/Cl2 mix as even small amounts of O2 will interrupt the chain reaction detonation.

I was recently reading about H2 and N2O which appears somewhat differently to be an unsafe experiment. Two reasons appear to be the uncertainty as to when an explosion may ensue and lastly, the very high temperature generated.

[Edited on 26-5-2018 by AJKOER]

unionised - 26-5-2018 at 07:49

Quote: Originally posted by AJKOER  
My recollection is that mixing hydrogen and chlorine is safe barring the presence of red light, at which point, a highly kinetic explosion does occurs. It proceeds, however, with only a pure H2/Cl2 mix as even small amounts of O2 will interrupt the chain reaction detonation.

I was recently reading about H2 and N2O which appears somewhat differently to be an unsafe experiment. Two reasons appear to be the uncertainty as to when an explosion may ensue and lastly, the very high temperature generated.

[Edited on 26-5-2018 by AJKOER]

Well, you are wrong about the light- it's blue/ UV light that triggers the reaction.
And it's likely that you are wrong about oxygen for two reasons.
First, it's a common classroom experiment done with balloons and balloons are permeable to oxygen so traces of it will always be present.
Second, by analogy with the reaction where there's plenty of O2 and no chlorine which explodes.

unionised - 26-5-2018 at 07:55

Quote: Originally posted by Heptylene  


unionised, what would you do with the ferrophosphorus? Is there a way to separate it from the iron or react it in some way? As suggested above, onyxmet has ferrophosphorus for very cheap.


I'd be interested in the reaction of ferrophosphorus with chlorine.
Chlorine is relatively cheap. Ferrrophosphorus is, at least, not substantially controlled . It may also be cheap.
The reaction would give FeCl3 and PCl3 which should be separable by distillation.

AJKOER - 26-5-2018 at 11:57

Quote: Originally posted by unionised  
.....

Well, you are wrong about the light- it's blue/ UV light that triggers the reaction.
And it's likely that you are wrong about oxygen for two reasons.
First, it's a common classroom experiment done with balloons and balloons are permeable to oxygen so traces of it will always be present.
Second, by analogy with the reaction where there's plenty of O2 and no chlorine which explodes.


Yes, my mind reversed the order of lights usually demonstrated as red being the weakest, green,...., blue, and finally UV which causes the H2/Cl2 mix to explode.

However, likely right on the oxygen poisoning of the chain reaction, to quote a source:

"It is well known that the reaction between hydrogen and chlorine is inhibited by oxygen at ordinary temperatures. "

Link: See page 335 at http://rspa.royalsocietypublishing.org/content/royprsa/135/8...

Another reference, but not my original source, which was another long lecture I found on the web: http://vallance.chem.ox.ac.uk/pdfs/KineticsLectureNotes.pdf . To quote:

"somewhat due to the extreme sensitivity of the reaction to inhibition by contaminants such as O2. Oxygen reacts with H and Cl radicals to form inert radicals, providing an alternative termination pathway and increasing the overall rate of termination. If O2 is present at a concentration of around 1% or greater, the following termination steps dominate to the point where the steady-state approximation becomes valid.

.H + O2 + M → .HO2 + M
.Cl + O2 + M → .ClO2 + M "
------------------------------------------

My research did also come across a comment that the hydrogen + chlorine reaction could be detonated by incidental catalyst like diffused light on an overcast day or dust, rubber contact,... Source: http://www1.chem.leeds.ac.uk/delights/texts/expt_28.html, to quote:

"The explosion of a hydrogen-chlorine mixture can be triggered not only by bright light but also by a catalyst. Dust, bits of rubber in a rubber tube, etc. can sometime act as such catalyst. In this case the explosion occurs unexpectedly during filling the vessel with chlorine. The authors have experienced the sudden explosion when they decided to fill the tubes (already half-full of hydrogen) with chlorine outdoor on a very dull and rainy day. Once the tube was filled and stoppered the mixture exploded."

The dust I understand as likely rich in transition metals and in the presence of moisture, some HOCl formed. The latter two reagents can act in a fenton-type reaction producing the hydroxyl radical. Then:

H2 + .OH --> H2O + .H

reforming the water vapor and commencing the hydrogen atom radical part of the chain reaction:

.H + Cl2 --> HCl + .Cl

So, the H2/Cl2/UV light experiment may be safer than H2/N2O, but perhaps not so clearly obvious. Note: N2O with H2O and UV is a known source of .OH as well.

N2O + H2O + UV --> N2 + .OH + OH-

And the presence of any photoactive metal oxides (like ZnO, MgO, TiO2,..) releasing electrons in sunlight may replace the need for UV light. Reaction:

e- (aq) + N2O --> N2 + .O-
.O- + H2O = .OH + OH-

[Edited on 27-5-2018 by AJKOER]

[Edited on 27-5-2018 by AJKOER]