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?gsd - 30-10-2008 at 20:19
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
gsdSauron - 30-10-2008 at 20:52
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]chloric1 - 31-10-2008 at 16:03
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]Sauron - 1-11-2008 at 02:53
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.Sauron - 1-11-2008 at 03:03
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.woelen - 1-11-2008 at 04:00
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.Sauron - 1-11-2008 at 06:45
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.not_important - 1-11-2008 at 07:03
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.
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]panziandi - 1-11-2008 at 08:03
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.a_bab - 1-11-2008 at 08:10
It really looks like the easiest method to get it at a labscale.Sauron - 1-11-2008 at 09:00
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.panziandi - 1-11-2008 at 09:53
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.Sauron - 1-11-2008 at 10:21
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!panziandi - 1-11-2008 at 10:30
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!Sauron - 1-11-2008 at 10:37
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.panziandi - 1-11-2008 at 10:51
I see! Well yes it is water reactive, toxic gas releasing, dangerous to the environment chemicals LOL! Try some european vendours!Formatik - 1-11-2008 at 13:03
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.panziandi - 1-11-2008 at 13:08
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.Formatik - 1-11-2008 at 13:14
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.Sauron - 1-11-2008 at 14:06
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.panziandi - 1-11-2008 at 15:13
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!Formatik - 1-11-2008 at 17:11
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.chloric1 - 1-11-2008 at 17:36
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]Sauron - 1-11-2008 at 19:22
Reliable other members with experience in this area report no success at trying to convert PCl5 to PCl3 or at obtaining PCl3 from chlorination of red
P.
Like, garage chemist. I believe him.
Anyway we are not concerned with PCl5 but with POCl3.
The reaction of PCl5 with water or alcohols produces POCl3 and HCl or RCl
If HCl on POCl3 reverses that reaction under any conditions I am unaware of it.
If that were so then
POCl3 + 2 HCl <--> PCl5 + H20
The problem being to segregate the products at the right before they can react I do not believe this is preparatively useful.
---------------
H3PO3 = P(OH)3 and PCl3 is its acid chloride.
P2O3 (P4O6) is the anhydride, produced by burning P in limited air or O2. VERY toxic. So it's a good thing we can't get P so we are not tempted to
make it!
P2O3 reacts with oxalyl chloride to produce PCl2, CO and CO2. In short, since the carbon oxides are gases, PCl3 is the only liquid product.
Can we start with H3PO3 and use excess oxalyl chloride to dehydrate the acid to P2O3 in situ? Maybe.
2 H3PO3 + 6 (COCl)2 -> 2PCl3 + 6HCl + 6 CO + 6 CO2
which is the combined form of the following two equations:
2 H3PO3 + 3 (COCl)2 -> P2O3 + 6 HCl + 3 CO + 3 CO2
P2O3 + 3 (COCl)2 -> 2 PCl3 + 3 CO + 3 CO2
Oxalyl chloride is expensive, but I don't care too much about that.
This ought to work.
----------------
How about H3PO3 + PCl5?
This would shift the problem back to getting red P.
Let me think about this. The analogous reaction for H3PO4 is well known. Looks like H3PO3 + PCl5 would produce a mixture of PCl3 and POCl3.
H3PO3 + 3 PCl5 -> PCl3 + 3 POCl3 + 3 HCl
In the reaction of H3PO4 with PCl5 this does not arise since both the hydrolysis of the PCl5 and the chlorination of the acid produce POCl3.
Anyway oxalyl chloride is clealy better.
Yes I am well aware that H3PO3 commercially contains a little water. No that is not built into any of the above.
[Edited on 2-11-2008 by Sauron]not_important - 1-11-2008 at 21:02
Most ferrophosphorus seems to come from China these days, and in large lots as they are targeting industrial users. I believe the usual types are 1/4
and 1/3 phosphorous, purity over a wide range depending on needs.
But unless you get lucky it appears to be mainly an industrial produce, and you don't seem to want to buy 1000 kg so it's likely not practical.Sauron - 1-11-2008 at 22:22
No luck so far, tomorrow I will put my importer to work on it.
With the rodenticide type (P-rich) phosphides there may well be import problems even if I can source them anywhere.
And I note with chagrin that the cretin who wrote the Wiki piece on Ca3P3 stresses, from the start, purported applications to incendiary bombs. This
is alarmist, it is ancient history, no one uses Ca phosphide this way now, it's an agro-pesticide nothing more. But that's just the sort of thing that
would get Thai Customs very upset. What rubbish!
Ferrophosphorus by the way is mostly Fe2P ferrous phosphide, although that is 21% P and ferrophosphorus goes up to 27%.
It's a byproduct of WP manufacture. By far the most mass produced phosphide.
Phosphor bronze is about 1% P as Cu3P with a little tin.Sauron - 1-11-2008 at 23:00
Pardon the double post but I would like to summarize:
Some time back I made the observation that Roger Adams' prep-1920 paper in JACS pointed out that oxalyl chloride reacts with certain inorganic acid
anhydrides (i.e., oxides) to produce the corresponding acid chlorides. The examples he demonstrated were AsCl3 from As2O3, chromyl chloride from CrO3
and one other, I forget which. My observation was that this reaction will work with P2O5 to produce POCl3.
Well now we have a cheaper way to produce POCl2 from P2O5 and NaCl.
So I turned my attention to PCl3. The requisite P2O3 is unavailable but we can buy H3PO3 (P(OH)3) and simply throw enough oxalyl chloride at it to
effectively make P2O3 in situ.
I am sure I need not point out that phosgene would act just like oxalyl chloride does.
So the problem is solved, albeit expensively. I can achieve some economy by making my own oxalyl chloride using TCT and anhydrous oxalic acid.
The phosphide route is uncertain of supply, unsure of importability, and iffy as to result.
So I am for the time being, satisfied.Sauron - 3-11-2008 at 18:56
From this point on this thread is a continuation of discussions in the Acetic Anhydride thread on making POCl3 and/or PCl3
In particular the chemistries of H3PO3 and P2O3/P4O6
To recap:
Just as P2O5 (P4O10) is the acid anhydride of H3PO4, the familiar orthophosphoric acid, P2O3 is the anhydride of H3PO3 the less familiar phosphorous
acid sometimes called phosphonic acid.
H3PO3 exists in tautomerism between P(OH)3 and HP(=O)(OH)2
POCl3 is the acid chloride of H3PO4 and PCl3 is the acid chloride of H3PO3.
We have a number of ways to prepare POCl3 but only one for PCl3 which is unavailable to us because it requires WP.
We can obtain PBr3, H3PO3, and P2O5 without any trouble.
One prep of POCl3 from P2O5 and NaCl produced 10-25% PCl3 by wt of POCl3 formed so if we make enough POCl3 by this methos we will obtain a decent
amount of PCl3 and maybe our problem is solved.
We know that oxalyl chloride according to Roger Adams, reacts with some inorganic oxides that are anhydrides of mineral acids, to produce the acid
chlorides. Adams demonstrated this with As2O3 to obtain AsCl3 in excellent yield. We have long theorized therefore that oxalyl chloride will react
with P2O5 to give POCl3 and with P2O3 if available to yield PCl3.
Thorpe and Tutton in JCS Trans., 1890 57 545 prepared P2O3 from WP and limited O2 in CO2 and reacted it with Cl2. He obtained POCl3 and a glassy
metaphosphoryl chloride.
It turned out however that Prof.Thorpe's P2O3 contained appreciable amounts of WP which helps explain the violence of the chlorination and so perhaps
PCl3 was formed but under those conditions, may have scavenged enough O2 from the reaction vessel's atmosphere to be oxidized to POCl3.
On the other handP2O3 is a very odd compound as can be seen from its reactions with cold water and especially hot water. A review in Inorg.Chem. 5
(1966) documents the chemistry of P2O3/P4O6 which sometimes eacts very energetically and can undergoe simultaneous oxidation-reduction.
For example with hot water, P2O3 almost explosively decomposes to red P, PH3 and H3PO4. Huh? That's simultaneousreduction ( -> P and PH3) and
oxidation (to P2O5 which hydrolyzes to H3PO4 with water.
Go figure.
Therefore I am not prepared to say what P2O3 will do with oxalyl chloride. It might smoorhtly be chlorinated to PCl3 as I wish, or it might do
something unexpected.
I probably will not find out in absence of WP.
But I can get H3PO3 and try that. Again there is a large uncertainty factor.
I have some papers to read.
P2O3 can be prepared from PCl3. According to a paper in Ber. in 77 (the citation is incorrect in Merck, they got the right volume only. They have page
as 689 when it is 698 and year 1944 when in fact it is 1945 as the volume straddles both years.) Anyway PCl3 is reacted with trimethylammonium sulfite
in liquid SO2 as solvent. I love learning new reagents.
To me, the transformation PCl3 -> P2O4 is a hopeful omen, as it implies that P2O3 -> PCl3 ought to be possible. Better, maybe the available PBr3
might work instead of PCl3 our target.
I am awaiting these papers. Will post them here asap.
[Edited on 4-11-2008 by Sauron]
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Sauron - 3-11-2008 at 23:05
The upshot of that review in Inorg.Chem posted in post just above is that most of the "violent" reactions of P2O3 in solid or liquid phase can be
controlled by proper technique. This includes the hydrolysis with cold water which when conducted properly gives exclusively the normal
(orthophosphorus acid) product as one would expect from an anhydride.
About the only reaction which was not amenable to mederation was that with methanol.
Isn't that sweet? And I see no reason why the available PBr3 should not work just as well.
If so we can get P2O3 without recourse to elemental P at all.
Scaleup may be a bit of a problem.
For joy for joy!
[Edited on 4-11-2008 by Sauron]
[Edited on 4-11-2008 by Sauron]
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Sauron - 4-11-2008 at 05:24
Here is a German review article from Z.Anorg.Allgem.Chem. covering three preps of P2O3 including the one from PCl3 above. The others are from the
elements with the air diluted with N2O or N2 and run at diminished pressure so the liquid P2O3 distills off.
The prep from PCl3 in liquid SO2 works best at 80-100 mmols per 250 ml SO2 with yields up to 85% So a prep run in a liter of SO2 would yield about 15
g P2O3.
[Edited on 4-11-2008 by Sauron]
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Klute - 4-11-2008 at 05:58
How do they form tetramethylammonium sulfate? Heating dimethylsulfate with excess trimethylamine? Wouldn't that form the hydrogenosulfate?Sauron - 4-11-2008 at 13:21
Sulfite not sulfate.
I do not know ywt, I have two German papers to translate and about a dozen ACS articles and some googling results that will reveal the answer. However
TMA-sulfite appears to be a relatively populat CTH agent, reducing agent, etc. When I have the details of prep I will post.
Were I to speculate I would say that passing SO2 into a solution of tetramethylammonium quaternary salt would suffice.
Tetramethylammonium chloride is rather cheap - $35 for 250 g (Acros) so if this is starting material, no worries.
[(Me4)N+]2[SO2]-2 sorry this does not support superscript or subscript text
This is a n ionic compound (quaternary ammonium salt)
whereas dimethyl sulfite is an ester (MeO)2SO2
and Me2SO2 would be dimethylsulfone.
[Edited on 5-11-2008 by Sauron]Klute - 4-11-2008 at 16:06
Maybe methylating trimethylamine with dimethylsulfite? Or using SO2Cl2 in a way or an other (although Cl2 might oxidize the sulfite to sulfate?)
have you got any indication for it's use in CTH? Seems quite interesting..
EDIT: apparently tetramethylammonium sulfite solution are prepared by bubbling SO2 in a solution of tetramethylammonium hydroxide... Seems pretty
easy. Drying the salt might be another story though.
I guess you could use the hydroxide with a little % of water, enough to form H2SO2 in-situ, and then remove the formed water under vacuum or by
azeotropic removal , and complete drying over P2O5 or by adding SOCl2?
[Edited on 5-11-2008 by Klute]Sauron - 4-11-2008 at 16:12
Yes there is mention in one of the ACS articles I found using their SE of CTH use of this compound. I searched all journals, all dates, using OR
boolean switchs, on title and full text keywords tetramethylammonium sulfite and with page set to 100 responses I got 25 hits. I pulled up the ones
from J Org Chem to read first (from my archive) rather than having to go through References.
--------------
An interesting article from Ber. 34 (1901) by Krafft et al. This reports that transformations are possible between oxides or chlorides (and I assume
other halides) and the elements of same group (P, As, Sb).
Thus 4 PCl3 + Sb4 -> 4 SbCl3 + P4
I already posted the Brauer prep of red P from PBr3 and Hg metal. The Krafft reactions are similar.
_________________________
I just received another paper by Wolff from Berichte in 1929, this one related to the last mentioned, but one reaction looks even sweeter for
extracting the elemental P content of PX3 halides,
4 H3PO3 + PCl3 -> 3 H3PO4 + 2 P + 3 HCl
The 2 P there is really 0.5 mol P4 = 62 g from 1 mol PX3 and 4 mols orthophosphorous acid. I have 1 Kg of the tribromide, which is a little more than
4 mols. So this requires 16 mols H3PO3 if I want to reduce it all to red P, which would be if I got the arithmetic right almost 250 g.
If and when I figure out how to take that to PCl3 it would be about 600 g. That would make me happy, especially augmented with more from the P2O5/NaCl
reaction.
Because of the uncertainty of getting from red P directly to PCl3, I might opt to wait. To be certain of PCl3 I'd have to convert the red P to white P
and that is a task neither easy nor without hazard.
Anyway this line of inquiry is so far unusually productive.
[Edited on 5-11-2008 by Sauron]
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Sauron - 5-11-2008 at 00:27
The paper referred to in last post by Wolf and coworkers is attached. The reaction I highlighted, between phosphorous acid (phosphonic acid) and PCl3
was reported by Michaelis, in J.Prakt.Chem 8, 359 (1873) I am seeking the paper in References, all I know so far is thet reaction proceeds at 150 C.
The attached paper (Wolf et al) was an attempt to extend the work of Krafft to prepare P2O3 from PCl3 and H3PO3 It ended in failure. But it pointed me
at the Michaelis paper in next post, from Annalen 325 p365 (1902) which looks very useful.
[Edited on 5-11-2008 by Sauron]
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Sauron - 5-11-2008 at 03:19
This paper by the famous A.Michaelis describes the reaction of H3PO3 with PCl3 to produce elemental P and H3PO4 along with HCl.
12 g H3PO3 and 5 g PCl3 are heated 12 hours at 150 C in an autoclave. The red powder obtained is washed successively with H2O, alcohol and ether,
affording 1.15 g red powder which analyzed as 93% P, balance mostly Cl.
By using 12 g PCl3 and 12 g H3PO3, the powder analyzed as 97.83% P.
(My comment: halide contamination is not an issue since I will chlorinate this anyway to PCl3 or PCl5 so the original stoichiometry is better.)
The yield is 50% of the theoretical.
Yhe significance is that while PCl3 may be hard to obtain if not impossible, PBr3 is not, I can buy it and some of you may be able to as well. The
stoichiometry ought to be same, HBr will be produced rather than HCl.
I will ferret out the rest of the details.
If yield is 50% of theory I would only get c.125 g red P out of 1 Kg PBr3 this way.
The reduction with Hg in Brauer is better, almost qiantitative.
[Edited on 6-11-2008 by Sauron]
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Sauron - 6-11-2008 at 09:34
I revisited that Brauer prep and I may have spoken too soon. It also produces a highly impure red P contaminated by bromine as Hg bromides, and
although the % yield may be better, the actual amount of isolated P from a mol of PBr3 is the same as in the Michaelis prep.Sauron - 18-2-2009 at 20:06
As of 2/09 most of my goals in this area have now been achieved, at least on paper.
I set out some years ago to find ways to prepare a variety of phosphorus compounds useful as reagents for organic synthesis which for various reasons
I cannot purchase. The chief difficulty was thst I also cannot purchase red phosphorus where I am.
I wanted to be able to prepare PCl3, PCl5, POCl3, PSCl3, and some derivatives of these such as triethyl phosphite and diethyl chlorophosphite which at
first glance is rather daynting without elemental phosphorus.
But I am happy to report that this is now all feasible and that all that remains is experimental verification of the known methods.
There are two entry points.
P2O5 (P4O10) reacts at temperature with NaCl to yield POCl3, and a little PCl3.
PBr3 is available unrestricted and can be converted to PCl3 with Hg2Cl2. PBr3 can also be converted to red P with Hg metal but that process is
inefficient and gives a product contaminated with Br2.
With these points of entry, the whole panoply opens up.
POCl3 -> PCl3 ->PCl5 POCl5 is reduced with tin to PCl3 which can be chlorinated further to PCl5 as needed.
