Elemental Phosphorus
Hazard to Others
Posts: 184
Registered: 11-11-2016
Location: Is everything
Member Is Offline
Mood: No Mood
|
|
Preparation of phosphorus halides from phosphorus pentoxide
I am new here and mostly talking without experience, but if dried HCl gas was passed over phosphorus pentoxide, would it produce phosphorus
pentachloride? This would provide an easier way to make useful phosphorus halides without actual phosphorus. It also seems thermodynamically
favorable, but would the produced water react with the remaining pentoxide to produce H3PO4? Also, if it would work, then to produce the trichloride,
could P4O6 be substituted?
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
Heat of formation of PCl5 = -399 kJ/Mol
". ". ". " P2O5 = - 3382 kJ/Mol
Why do you say the reaction is thermodynamically favorable?
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
PirateDocBrown
National Hazard
Posts: 570
Registered: 27-11-2016
Location: Minnesota
Member Is Offline
Mood: No Mood
|
|
You can reduce calcium phosphate in a crucible with carbon to calcium phosphide, which you can then chlorinate to PCl3.
|
|
|
Eddygp
National Hazard
Posts: 858
Registered: 31-3-2012
Location: University of York, UK
Member Is Offline
Mood: Organometallic
|
|
P=O bonds tend to be very strong, which makes many reactions, like the Wittig reaction, thermodynamically favourable.
In fact, the reason why you can use phosphorus chlorides to chlorinate alcohols is because you create these bonds to oxygen.
Therefore, unless you oxidise P directly forming P-Cl, making PCl3/5 will be very difficult. From phosphorus oxides, if we avoid reducing them, there
is no feasible method (most probably not, anyway).
EDIT: apparently, phosphoryl chloride can be formed by reaction of phosphorus pentoxide with sodium chloride at very high temperatures, so maybe there
IS a way to get the pentachloride.
[Edited on 30-12-2016 by Eddygp]
there may be bugs in gfind
[ˌɛdidʒiˈpiː] IPA pronunciation for my Username |
|
|
Melgar
Anti-Spam Agent
Posts: 2004
Registered: 23-2-2010
Location: Connecticut
Member Is Offline
Mood: Estrified
|
|
Quote: Originally posted by Eddygp  | P=O bonds tend to be very strong, which makes many reactions, like the Wittig reaction, thermodynamically favourable.
In fact, the reason why you can use phosphorus chlorides to chlorinate alcohols is because you create these bonds to oxygen.
Therefore, unless you oxidise P directly forming P-Cl, making PCl3/5 will be very difficult. From phosphorus oxides, if we avoid reducing them, there
is no feasible method (most probably not, anyway).
EDIT: apparently, phosphoryl chloride can be formed by reaction of phosphorus pentoxide with sodium chloride at very high temperatures, so maybe there
IS a way to get the pentachloride.
[Edited on 30-12-2016 by Eddygp] |
This is still the oxychloride, that is, POCl3. I believe the thermodynamics work because you're starting with P2O5, then getting a mixture of sodium
phosphates and phosphoryl chloride. Only the POCl3 would be volatile in that mixture. Temperatures aren't even that ridiculously high, if I remember
right.
I've heard that using aluminum powder to reduce P2O5 to phosphorus is fairly easy, although I haven't done it myself. Still, if you want a phosphorus
halide other than POCl3, you're going to need to start with either phosphorus, a phosphide, or a related phosphorus halide.
[Edited on 12/31/16 by Melgar]
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
This post has piqued my curiosity. I might try this when the weather warms up. Meanwhile I took a look at some real old-school chemistry here:
https://www.youtube.com/watch?v=ZvDppuCkoew
Phosphine anyone? Note how non-challant these old gals are. 
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
Elemental Phosphorus
Hazard to Others
Posts: 184
Registered: 11-11-2016
Location: Is everything
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by Magpie | Heat of formation of PCl5 = -399 kJ/Mol
". ". ". " P2O5 = - 3382 kJ/Mol
Why do you say the reaction is thermodynamically favorable? |
Guess I was an idiot and screwed up somewhere.
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
You are not an idiot when you take ownership and learn something. 
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
Elemental Phosphorus
Hazard to Others
Posts: 184
Registered: 11-11-2016
Location: Is everything
Member Is Offline
Mood: No Mood
|
|
Thank you for telling me. I will have to try this, as soon as my new furnace is built and maybe I can get a clay crucible (dont want to ruin my
graphite crucible). I assume this would also work to produce PBr3? Before anyone says " why don't you just make phosphorus?" I dread having to work
with white phosphorus, and the legality is questionable. It would suck to give the impression that we cook meth.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
