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Sauron
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Inorganic Phosphorus Transformations
I am interested in some superficially simple but damnably hard to nail down reactions of simple P halides.
POCl3 -> PCl3
PSCl3 -> PCl3
Conventionally PCl3 is prepared from white P usually in CS2 solution. Although some lit. states that PCl3 can be prepared from red P our own garage
chemist reports otherwise. He says that all he gets from red P is PCl5 and that trying to correct the stoichiometry to PCl3 by adding more red P is a
mess and fundamentally fails. (See Inorg.Syn. for the contrary view.)
POCl3 is more readily prepared by a variety of means.
So can we get to PCl3 via POCl3?
I think metal hydrides are just going to make phosphine, diphosphine and HCl as they will cleave the P-Cl bonds.
P2O5 and NaCl react sans solvent above 250 C in an iron or steel vessel to produce mostly POCl3 with 10-25% PCl3, apparently by reduction of POCl3
from the Fe in vessel walls. So maybe Fe filings, or FeCl3, might reduce POCl3. I guess filings would form FeCl3 in situ so better to use FeCl3 and
not lose any POCl3. (See Tarbutton, JACS 1940).
H3PO3 (phosphorous acid) might be chlorinated by excess oxalyl chloride or other strong chlorinating reagents to PCl3 if the excess is large enough to
deal with the water formed.
P2O3 certainly forms PCl3 from oxalyl chloride (no excess needed) but the extreme toxicity of this compound mitigates against its preparation and use.
If PSCl3 can be obtained or made it might be dethiated, for example by PhPCl2. This works for RPSCl2 -> RPCl2.
Any ideas?
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gsd
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PCl3 is industrially manufactured by reaction of Chlorine with white P using PCi3 itself as a solvent.(I dont think CS2 is used as a solvent for large
scale preparation PCl3 is very mild solvent in comparison  )
There are several patents on this process. See e.g. US5260026A
gsd
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Sauron
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I have zero interest in chlorination of WP for the simple reason that I cannot get any. I can't even get RP in this country unless the tedious tweaker
way from matchbook strikers.
Obviously it is not the industrial route that interests me, it is bench scale and not from elemental phosphorus.
I have no trouble getting PBr3 but I am now after PCl3.
Just as clearly, throughout almost all of the history of such chemistry, union of the elements was the best and simplest and cheapest way to make
PCl3/PCl5 and still is industrially.
BUT for the last few years in most places these starting materials have been embargoed for most of us. So I have to use methods that previously would
have been absurd. We live in absurd times.
Preps that require you to use the target compound in the prep, are like trying to pick yourself up by your own bootstraps.
Great if you already have some to use as solvent. Otherwise, what do you do? If I could but the stuff I would but I can't. Period. End of story.
[Edited on 31-10-2008 by Sauron]
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chloric1
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Exactly what you said Sauron! You are after an absurd way to make PCl3. Since you have zero PCl3 then another solvent to slow the reaction must be
used. I would suspect a chlorinated hydrocarbon solvent would suffice. Preferrable one with a vastly different boiling point than PCl3. Making
calcium phosphide by reducing the tribasic phosphate may be an alternative to willie pete. This suspended in pentachloroethane would be chlorinated.
I am not sure what chlorinated hydrocarbons you can get but here in the US they are much more scarce than just a few years ago.
The pentachloroethane can be made from trichloroethylene by chlorination.
[Edited on 10/31/2008 by chloric1]
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Sauron
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No, you are still hung up on direct chlorination of elemental phosphorus which (a) will not work with red P, only white, and (b) neither is available
anyway.
So start thinking outside of the box. That is what this thread is about.
Dethiation is not such an exotic reaction, I have a largish bottle of PhPCl2 on hand. The two phosphorus atoms (one pentavalent, one tervalent) simply
exchange the sulfur (also works for oxygen.)
Look it up.
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Sauron
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Like you and the rest of us I am the victim, not the author, of the absurdities of our times.
Or are you going to tell me that you can get PCl3 at will, or red P, or white P? Can you?
If not and like me you wanted it, what would you do?
Probably something absurd.
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woelen
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Do you have the optoin of obtaining phosphides, such as Ca3P2 or Zn3P2 (used for killing rodents)? With this, you can make halogenated phosphorus
compounds, by passing Cl2 (or Br2) over the finely powdered solid, making the metal chloride and some phosphorus chloride. I'm not sure though whether
this will give the pentachloride or the trichloride.
These phosphides are dangerous and not easy to handle though. With water they hydrolyse to phosphine and the metal hydroxide. I am confident that you
can handle them.
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Sauron
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This has been mentioned before. I do not know if I can buy the phosphides, but can find out. Also I have never seen any lit. on this reaction and that
is where vagueries about the product and the stoichiometry would be answered.
Anyway thanks, woelen, for the first constructive comment in this thread.
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not_important
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I've wondered about this, too. In the past I've come across ferrophosphorus in 5 or 10 kg packages, although a quick search right now only showed 1
tonne sacks. It is used in steel and light metal alloy making, isn't too reactive with air and water, and generally is supplied as a powder.
Reaction with halogen could give PCl3 or PCl5, the attached patent states that a complex FeCl3.PCl5 is formed, but on hrating that with further
ferrophosphorus FeCl2 and PCl3 are formed, and they as easily separable.
Attachment: EDOTJABD_URBAUST.pdf (58kB)
This file has been downloaded 639 times
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Sauron
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The only supplier I have found in the past for Ca or Zn phosphides is Alfa. Acros zip, Aldrich zilch. I am quite sure that any US supplier is going to
mean deal-killing hazmat fees.
Ferrophosphorus I have never looked for, but it is certainly worth a try.
Thanks for the patent.
Ca3P2 tech grade lumps from Alfa about $400/Kg (packing 250 g) but it's TSCA listed and I'm sure hazmat due to moisture sensitivity and potential
phosphine release.
Ferrophosphorus not listed, irom phosphide Fe3P very expensive and half the P content by weight of Ca3P2.
Calcium phosphide is used in copper metalurgy.
[Edited on 1-11-2008 by Sauron]
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panziandi
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I have 2 x 500g of Zn3P2 from BDH but alas I tried looking it up on VWR.com and all I found was small packets by ALFA AESAR at a rediculous price.
Shop around the phosphides are technical chemicals and should be found.
You can find ferrophosphorus with a relatively high % of P I'm sure I have found web pages on it before.
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a_bab
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What about isolationg the WP out of Calgonit with Al? (last posts in http://www.sciencemadness.org/talk/viewthread.php?tid=65).
It really looks like the easiest method to get it at a labscale.
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Sauron
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Ca3P2 is prepared from red P and Ca metal and the % composition is about 1/3 P.
I will try BDH as I know they have an agent here.
Ajax is also a possibility.
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panziandi
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Something like BASF perhaps. It's more of an industrial chemical than a lab reagent, well apart form the high purity phosphides used in semiconductor
research etc. My BDH stuff is old perhaps 10/15 years? It's still a fine free flowing powder and is "technical" grade. Of course any phosphide is
suited most common ones are calcium, magnesium, aluminium and zinc.
Aldrich sells the following:
Calcium phosphide 400971 100g and 500g
Zinc phosphide is listed under rodenticides but I can't find a quantity or price etc.
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Sauron
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Are you looking at a print catalog? Because neither the name nor the number work on the S-A website, meaning they nolonger sell this.
The zinc phosphide is a former Reidel-Haas product now taken over by Aldrich, being rebranded. Reidel products are notoriously overpriced. And no
indication of availability from Fluka.
I will look at Merck, Panreac, Carlo Erba, BDH, Ajax, all non US and all with local agents. Industrial chemicals come in industrial packing like 20
Kg drums and up. I do not need 20 Kg of this stuff, in more ways than one!
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panziandi
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http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALD...
http://www.sigmaaldrich.com/catalog/search/ProductDetail/SIA...
Well sometimes industrial chemical suppliers can sell smaller quantities as samples especially if it's unusual. Perhaps say that you are looking for
suppliers in this field implying you will be making larger purchases then request samples and stick to the samples they supply. No need to actually
purchase 20kilos afterwards!
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Sauron
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I wonder why their SE was upgefucking?
Anyway it is clearly hazmat so they are out as a vendor for me. Hazmat is an annoyance within USA but a deal killer across an ocean.
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panziandi
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I see! Well yes it is water reactive, toxic gas releasing, dangerous to the environment chemicals LOL! Try some european vendours!
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Formatik
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| Quote: | | Originally posted by Sauron So can we get to PCl3 via POCl3? |
Yes, but the only thing Gmelin mentions about this are the following two: A) gaseous POCl3 is lead through a tube which is filled
with charcoal that is heated to glowing red heat (C.r. Acad. Sci [Paris] 95 [1882] 1160/3). B) Treating POCl3 with CO above 400ºC
in the presence of charcoal or active coal (DE 492061 [1928/30], C. 1930 I 2292).
Then the older Gmelin (7 Aufl., Bd. 1, p. 390) which mentions among other things that heating to very strong glow phosphoric acid glass with NaCl
seems to form some PCl3, citing author names Gay-Lussac and Thénard. The same if sodium phosphate is glowed with NH4Cl, citing H.Rose. These are
probably very low yield and seem to require high energy.
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panziandi
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I would expect most of what is formed to be hydrogen chloride and sodium phosphate :s.
Perhaps reduction of glowing charcoal is something to be looked at in more detail?! It's certainly easy to set up a system for doing this on a
semi-large scale.
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Formatik
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Note that the reference states it is the tube that is doing the glowing. May or may not be that important, until we find out further details.
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Sauron
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That's encouraging but vague, and the material ill defined. Even today activated charcoal is produced from a multitude of sources by a myriad of
methods and activity in a given reaction may depend on a specific sort of AC. Metals content is often high and needs to be lowered by acid washing. So
who knows what was the activated coal in this reference?
No yields stated.
I'd rather focus on Tarbutton's side reaction in which 10-25% of the POCl3 produced was reduced to PCl3 by the action of Fe from vessel walls (iron or
stainless.) Clearly this is suggestive that a large surface area of Fe ought to up that percentage.
Simple enough to design an experiment to pass POCl3 vapor over/through thoroughly dried Fe filings, or say FeCl3 on pumice or other support, at
250-350 C and see what the conversion is if any.
Meanwhile I will be happy to get 10-25% PCl3 out of the POCl3 made. It's just NaCl and P2O5 after all.
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panziandi
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Indeed activity of the AC depends on particle size, metal ion contamination, etc. Perhaps it would be worth a try by someone with a tube furnace and
POCl3. I don't have POCl3, I have PCl3 which can be oxidised to POCl3... but I don't fancy a forward-backward experiment to find out if and how well
it works LOL!
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Formatik
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This is from the DE 492061: if one leads dry CO gas through POCl3 which is in a gas washing bottle heated to 100º, and then this gas stream
containing POCl3 is lead over active coal which is at 650º (throughout the patent they say above 400º, and either wood charcoal instead of AC also
said to work, they aren't too specific about the carbon).
The velocity of the gas stream is advisable to gauge, so that the contact with the activated coal lasts for at least 30 seconds, the glowing coal also
converts a certain percentage of the phosphorus compounds to elemental P. The distillate obtained contains 90 to 100% PCl3. The reason for the CO gas
in this procedure is that it increases conversion by as much as 2 to 3 times.
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chloric1
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| Quote: | Originally posted by Sauron
Anyway thanks, woelen, for the first constructive comment in this thread. |
You always show this much gratitude when others are trying to help. But it is OK I have learned to expect this from you.
Anyways, I was thinking of your problem today and realized that pentavalent chlorides of phosphorus are reducable. In fact I remember there is an
equilibrium of PCl5 to PCl3 and Cl2 that is not too hard to push to the right. If iron only yields 15 to 20% PCl3, maybe a slightly more active metal
might improve yields. Some crude chromium from a thermite reduction might suffice. Both zinc oxide and chloride are quite volatile so that would not
be so good.
Do phosphorus chlorides form chloro complexes with metal chlorides or other adducts? If so it could be detrimental or favorable based on the
thermodynamic properties of said complexes or adducts.
[Edited on 11/1/2008 by chloric1]
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