Sciencemadness Discussion Board

Phosphorus Pentachloride from Red Phosphorus

thechemMo - 7-10-2018 at 00:15

Hi,
I’ve seen a couple of threads here talking about various phosphorus chlorides and how they could be made.

My interest lies on the preparation of PCl5 by radical chlorination of red phosphorus.I‘ve heard many people talking about it but I’d like to know if it really works for an amateur chemist with normal lab equipment.Did some of you try it out by yourself or could you give me some advises?Would it work to put red phosphorus into a round bottom flask and attach a chlorine generator on to it.Then just pass a flow of chlorine into it and let it react?

Thankful for your answers!

Pumukli - 7-10-2018 at 02:06

I would not do that.
My understanding is the chlorine would ignite the phosphorus then the local hot spot (burning P) would crack and destroy your flask, releasing agressive P2O5 (and PxCly) smoke and top of that chlorine from the chlorine generator.

Yes, some of the members made PCl5 but it is more involved than your outlined plan.

Search the prepublication area, the synthesis is there.

mackolol - 7-10-2018 at 02:31

I have attempted the synthesis two times. My setup was chlorine generator tcca and hcl gas dryer with cacl2 and flask with stirrer. That was done outside. I performed the chlorination in choroform as chlorine is soluble in it to reduce chlorine loss and it isn't as exotermic.

I only had 100ml of CHCl3 so i put there 2g of red phosphorus. Further it turned out that the amount of CHCl3 was too small because at the end everything was thick white paste and stirrer couldn't turn. Also I took only slight molar excess of chlorine (which was bad idea because it's hard to react all of gas without losing much part of it).

Because of it, after reaction there was still noticeable amount of red phosphorus which reacted with pcl5 in removal of chloroform by distillation and formed more pcl3.

So i recommend using more chloroform (about 100ml per gram) and about 1,5 or 2 times more chlorine than required. Be carefull as pcl5 and pcl3 are very toxic and super corrosive (fumes smell like hcl mixed with horseradish and are very unpleasant ).

[Edited on 7-10-2018 by mackolol]

Sulaiman - 7-10-2018 at 03:23

how to search SM
e.g. https://www.google.co.uk/search?ei=sei5W6q5AY2D8gL3nL7wBA&am...

What scale/quantity are you considering ?

thechemMo - 7-10-2018 at 08:31

I would consider a very low scale prep at first to see how it behaves.I saw in the thread you sent(from Stefans prep) that he used 10 g of red phosphorus and the guy that followed Stefan’s synthesis used white phosphorus but just 2g.So does that mean that u can use the same amount of Solvent (Chloroform) like he did,100ml,and still use the 10g red phosphorus that Stefan used?Or did the other guy scale the prep down?And that would be why he used less phosphorus or is it because red and white phosphorus need a different amount?

fusso - 7-10-2018 at 08:36

Quote: Originally posted by thechemMo  
I would consider a very low scale prep at first to see how it behaves.I saw in the thread you sent(from Stefans prep) that he used 10 g of red phosphorus and the guy that followed Stefan’s synthesis used white phosphorus but just 2g.So does that mean that u can use the same amount of Solvent (Chloroform) like he did,100ml,and still use the 10g red phosphorus that Stefan used?Or did the other guy scale the prep down?And that would be why he used less phosphorus or is it because red and white phosphorus need a different amount?
No, same mass of red & white P will contain same # of P atoms. It's just different bonding between the atoms. He used only 2g WP probably due to higher reactivity & toxicity of WP.

[Edited on 07/10/18 by fusso]