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Mardec
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Well
In the first year of my studies we had an experiment involving redox reactions.
We made Cl2 with KMnO4 and HCl and putted that chlorine in CHCl3 (testtube amounts).
Then we added too a bit of this Cl2 in CHCl3 (just to keep it from flowing away, Cl2 gas..) some NaBr Solution, the whole became red/brow.
Cl2 replaces Br because it is a stronger oxidiser then Br2. Same with Cl2 to I- or Br2 to I-
So I was kinda hoping this would work to with PBr3. PBr3 after al is notting more but with Br2 oxidized phosphorus. So wouldn't Cl2 wanna replace Br2
on the phosphorus just because of the redox potential?
Sorry if I am wrong, I was just trying to apply the things I know to the unknow. It is called experimenting after all 
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Fleaker
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I can give this a shot as well, but I'll have to get PBr3. I think there might be a small equilibrium quantity of PCl3 produced which maybe would be
enough that an efficient distillation setup might make this direct chlorination worthwhile. My experience working with Cl2 and Br2 in non aqueous
systems is that the Cl and Br like to hook up with each other, often resulting in various compounds. Brauer's has a good bit (I think  ) on how things like BrCl are formed... As Sauron said, there are many competing
reactions and usually you won't chlorinate something fully. It may be higher up on the electron negativity scale, but it won't necessarily displace
all of your other Br atoms.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Sauron
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Sorry, but it's just not that simple.
You were dealing with ionic NaBr, while PBr3 is covalent P-Br bonds.
Furthermore the three in PBr3 are not equivalent; you might replace one and then find that replacing the second is a LOT harder and the third even
harder than that. You must appreciate that PX3 (any trivalent P halide) is an acid halide of phosphorous acid, H3PO3 and that acid exists in two
tautomeric forms
P(OH)3 trivalent
HP(=O)(OH)2 pentavalent
with the latter predominating.
So a simple redox model simply does not fly.
This is what makes the lower oxyacids of P so "interesting" in the Chinese-curse sense. "May you live in interesting times!"
Look up the alcoholysis of PCl3 and PBr3. The Wiki level of understanding will tell you that PCl3 makes trialkyl esters while PBr3 makes only alkyl
halides. And Wiki will show you all sorts of nice mechanistic diagrams to explain this as a sN2 reaction yada yada.
Actually what goes on is that the reaction of 3 mols of ROH with one mol PCl3 releases HCl while forming P(OR)3 and HCl is quite slow to attach the
O-C bond. In the case of PBr3 however, HBr is much better at the same job so you will get some R-Br and normally at best dialkyl hydrogen phosphite
H-P(O)(OR)2
That pesky tautomerism at work again!
If you allow the process to continue (but it gets slower at each consecutive stage) you will end up with 3 RBr and phosphorous acid and that is why
PBr3, or red P and Br2, are a method for making alkyl halides. The red P/Br2 makes PBr3 in situ.
HOWEVER if you run this same reaction in the cold and employ three mols of a tertiary amine to trap the HBr you CAN make triesters of phosphorus from
PBr3. No matter what crap Wiki puts out to the contrary.
With PI3 or red P/I2, same story only even worse. But even here under the right conditions trialkyl esters can be made, it is just more difficult.
(And absurd economically.)
Note that the dialkyl hydrogen phoshite is pentavalent. You can easily halogenate that -P-H bond and make a chlorophosphite diester. You can then
react that with alcohol and a tertiary amine and what do you have? a trialkyl PHOSPHATE not a phosphite at all. Just as if you have started with H3PO4
or POCl3 or P2O5. Got a headache yet? Eyes glazed over?
That last method is actually used to prepare mixed phosphate esters P9O)(OR)2(OR1) etc.
I wish it were so easy to replace Br with Cl on P(III) as you suggest.
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Mardec
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Yes of course, how foolish of me to presume all PBr3 would become PCl3 :-).
Btw PBr3 is collourless liquid right? So make some Cl2 and put it in some CHCl3, add some PBr3 and if it becomes red/brown we know..
Btw Sauron if you need red P, I know a webstore that sells it in 0,5 kg quantities.
EDIT,
I now read saurons post to... Yes, I shouldn't confuse anorganic with P chemistry.. :-)
I Get a good Idea of what you say, but it is still difficult to comprehend.. I am all new to P chemixtry.
So a triester of phophorus woud be like : (R1O)(R2O)(R3O)P right? But if it goes wrong you get crap like this : (R1O)(R2O)(R3O)P(=O) right?
And yeah, wikipedia is a nice fictional site with some real life elements.
[Edited on 28-9-2007 by Mardec]
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Sauron
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Well normally you make a triester with all three R the same, and if all goes well and you use tertiary amine and you stir well so no hydrogen halide
builds uplocally...you don't get any contamination with dialkyl hydrogen phosphite. Which is undesirable because sometimes this is very hard to
remove, as in the case of the ethyl esters.
My point was that normally once P(III) goes to P(V) it is bloody hard to reverse that.
Because P(III) WANTS to be P(V) or to put it in chemical terms, it is favored, kinetically, thermodynamically or both.
I could try your idea and might at some point, but I am hoarding my 1 Kg PBr3 (which not very much in molar terms not in volume as it is bloody dense)
while continuing the paper chase.
I would happily buy from that website if I thought there was a chance in hell of getting it in through Thai Customs. Red P requires a special import
license from the Defense Ministry, Office of the Permanent Secretary, hard to get. As you might imagine I would not care to have a package addressed
to me or mine, confiscated, quite apart from the loss of $$ this could have repercussions. So alas...I will stick to what I am allowed to buy.
But thanks for the tip.
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Mardec
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Oh yeah live in Thailand. Well, then I don't think I can help you. You could try to look for a factory that makes novelty fireworks. And try to buy
some red P from them.
But it seems like you manage :-).
And something I noticed. Red P with Br2, does that give PBr5 of PBr3?
Edit, PBr3 of course, my mind was sleeping..
[Edited on 28-9-2007 by Mardec]
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Sauron
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RedP with Br5 can give either PBr3 or PBr5 depending on proportions. Normally you would make these in an inert medium (red P does not dissolve in
anything I can think of.) See Brauser and IS for details.
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Sauron
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Here's a relatively clear-cut reaction of P4S10 with an ortho-ester, specifically triethyl orthoformate
Heating the two gives a 92.5% yield of triethyl dithiophosphate
P(=S)(OEt)2(SEt) or P(=S)(SEt)2(Oet) - the authors were not certain which.
I would not really care as I would want to cleave the ester to PSCl3 with Cl2 and then continue the chlorination. According to Gmelin, 2 PSCl3 + Cl2
-> 2 PCl3 + S2Cl2, isn't that nice? I found this reference in a Knotz patent, US 2765561 p.2 end of example 6:
Gmelin Kraut, Handbuch der Anorganischen Chemie I, 2, Seite 192, 7.Auflage (1909)
This could be a solution for those who can't buy or make oxalyl chloride, but want to start with P4S10 to get to PSCl3 and PCl3.
The ethyl orthoformate is not hard to make. Also can be bought. Here is the Org.Syn prep from abs ethanol, chloroform and sodium metal. It is also
possible to employ commercial or preformed sodium ethoxide (dry or in solution) or ethanolic NaOH - see references at end of the monograph.
Procedure:
146 g triethyl orthoformate and 61 g P4O10 are heated in a 500 ml RB flask equipped for vacuum distillation and fitted with a thermometer at the still
head, the temperature being raised to 95 C over ten minutes, At this point an exothermic reaction set in and heating was stopped. In 15 minutes the
reaction abated and heating was resumed. The temperature was raised to 150 C over 30 minutes; during this time 56.5 g of ethyl formate and ethyl
thionoformate distilled over at 760 mm and were condensed. The pressure was then reduced to 10mm and a further 12,3 g of ethyl formate and ethyl
thioformate were condensed in the dry ice-cooled cold trap, and 5.5 g of unchanged ethyl orthoformate distilled at 40-42 C.
The pressure was then reduced to 0.65 mm and 109.2 g of crude triethyl dithiophosphate distilled between 66 and 74 C(92.5%). This product was
redistilled and 94 g of pure triethyl dithiophosphate boiling sharply at 115-115.5 C/10mm. Density and refractive index are given in the text.
[Edited on 29-9-2007 by Sauron]
Attachment: CV1P0258.pdf (125kB)
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Mardec
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2 PSCl3 + Cl2 -> 2 PCl3 + S2Cl2
Sounds nice, but to obvious.
But wouldn't PCl3 react with the Cl2 gas too?
PCl3 + Cl3 -> PCl5
or
PSCl3 + Cl2 -> PCl5 + S
So special conditions should be follow to avoid these reaction I guess.
-Snip-
EDIT: Stupid idea, but would PCl5 + (2)S -> PCl3 + S(2)Cl2 work?!
[Edited on 29-9-2007 by Mardec]
[Edited on 29-9-2007 by Mardec]
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Sauron
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Complain to Gmelin not to me.
Gmelin is the inorganic Bible (even more than Mellor.)
It is the inorganic equivalent of Beilstein.
So, I would suppose that Cl2 will cleave the S faster than it might add to P. If you continue chlorination beyond the amount needed, as determined by
mass gain, then you would maybe start to convert some PCl3 to PCl5 - unless the S2Cl2 absorbed it first.
(Thanks for the edit.)
SCl2 is not stable. S2Cl2 is stable. If you overchlorinate S2Cl2, any SCl2 you make will slowly disproportionate to S2Cl2 and Cl2. Once again see
Brauer.
As to the mix of PCl3 and S2Cl2, along maybe with some unreacted PSCl3 and some overchlorinated PSCl3 now PCl5, and SCl2, trick will be to examine the
bp's and see how tricky the fractionation might get.
[Edited on 29-9-2007 by Sauron]
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Mardec
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| Quote: | Originally posted by Sauron
Complain to Gmelin not to me.
Gmelin is the inorganic Bible (even more than Mellor.)
It is the inorganic equivalent of Beilstein.
[Edited on 29-9-2007 by Sauron] |
I was not complaining ;-)
And I didn't know Gmelin, so I didn't know it was such a good book. I am looking to download it right now.
And I deleted the mustard joke..
I am going to look for my first year books, I just remembered there was a page about PCl3 in that.
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Sauron
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Not to worry.
Gmelin is not a book but a massive mult-shelf collection of books, so good luck on downloading. Also, it is entirely in German. (Unlike Mellor.)
Like Beilstein, Gmelin is usually to be found only in libraries. Although about the first half of the Beilstein Haupwerk is available in pdf. That
covers all the alicyclic and single ring hydrocarbon lit. through 1910. The first supplement (likewise, about 30 volumes) goes to 1920, the 2nd
supplement to 1930. The 3rd and fourth supplements (combined) to 1959 and the fifth supplement, only one in both German and English, to 1979.
Plus the huge indexes, particularly the centennial index.
But it is worth it to try to buy these up on used market even though it will run a couple thousand at least.
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JohnWW
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Has Gmelin been scanned and uploaded anywhere? It certainly should be, especially as nearly all of it is now out of copyright.
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Mardec
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German is not such a big problem, I am a native dutch speaker. Dutch and Deutsch are familie.
Still though I prefer english.
After Christmas I will be working (stage) in a chemical research and devellopment facility for a huge international. They have a huge chemical library
(Chemicals and books). I am looking forward to it!!
So maybe I will have acces to gmelin there :-).
[Edited on 29-9-2007 by Mardec]
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Sauron
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The reaction of P4O10 wurh benzene under autogenous pressure in an autoclave (275 C, 24 hrs) is interesting and when done under the right conditions
quite high yielding.
However it requires a massive molar excess of benzene to P4O10, and since the working capacity of the autoclave is 2/3 nominal capacity, and
especially since benzene expands in volume threefold at the temperature involved, which is near its critical temperature, these factors conspire to
demand a rather large capacity autoclave for a reaction that will produce a relatively small amount of product.
I have a 1 liter autoclave and the most I could get out of a batch I could run in that is 5-10 g phenylphosphonic acid.
Autoclaves being expensive, unless you have a big one on hand, this looks like a non-starter.
Too bad, because otherwise it looks like fun.
My target anyway is phenylphospnous dichloride. To get there from the phenylphosphonic acid is possible but extra work.
PhP(O)(OH)2 -> PhP(O)Cl2 by means of a large excess (6 fold) PCl5 in POCl3. The byproduct is POCl3 but as PCl5 is scarce, the alternative SOCl2
suggests itself even though the reaction is described as sluggish and lower yielding.
I would try oxalyl chloride instead of SOCl2.
So I just pulled up yet another Chem.Rev. article, this time on the phosphonic acids instead of the phosphonous acids, and we will see what we will
see.
[Edited on 1-10-2007 by Sauron]
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Sauron
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Traditionally the routes into the R-phosphonic acids
R-P(O)(OH)2
have been few. In the late 19th century Michaelis modified the Friedel-Crafts alkylation reaction to condense alkyl halides with PCl3 (or PBr3) with
the help of AlCl3.
Grignard and co workers however found that the reaction of alkyl and aryl magnesium halides to PCl3 gives exclusively tertiary phosphines. It was not
until the 1950s that methods were developed that allow the use of Grignard and lithium reagents to prepare RP(O)(OH)2 and R2P(O)OH.
Generally we would not regard these techniques as familiar protecting hroup strategies.
Classical diazonium salts have failed to react with phosphorus halides, but again in the 50s, it was found that diazonium fluoborates and
fluosilicates react in organic solvents with PCl3 using copper chloride as catalyst. This is an extension or special case of the Bart reaction. Yields
are no better than fair but the reaction has been widely used because is has more scope than the more usual techniques and many phosphonic acids and
derivatives have been prepared this way that have not been easy, or even possible, by other means.
The diazonium complexes can be worked up as either phsphonic acids or phosphonous dichlorides.
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Sauron
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Back to P4S10 electrophilic substitution reaction with anisole.
It seems that the 24 hr reaction in an autoclave is now passe. Org.Syn. has an 82% yield prep of same compound, now known as Lawesson's Reagent, done
in glass under reflux, 10:1 excess of anisole, neat.
Attached.
Product is a useful and stable thiating reagent.
[Edited on 2-10-2007 by Sauron]
Attachment: CV7P0372.pdf (167kB)
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Sauron
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Some basics
Hydrolysis of P4S10
This is instructive because it is the simplest case of the thiation effect of this reagent.
Quite in accordance with my contention that P4S10 ought to be regarded as the anhydride of the real but unstable thiophosphoric acid, phosphorus
pentasulfide reacts with water according to the equation
P4S10 + 16 H2O -> 4 H3PO4 + 10 H2S
In effect P4O10 thated the water.
If thiophosphoric acid were stable then
P4S10 + 12 H2O -> 4 H3PSO3 + 6 H2S
but it isn't, so an additional four mols water are required
4 H3PSO3 + 4 H2O -> 4 H3PO4 + 4 H2S
If you combine these equations you get the overall reaction.
Kekule described the hydrolysis and the alcoholysis of P4O10 in his classic paper, attached.
P4S10 + 10 EtOH -> 10 EtSH + P4O10
But in fact the interaction of P4S10 and ethanol gives rather a mess, principal products being triethyl O.O,S-thiophosphate and triethyl
O,S,S-thiophosphate. So P4S10 is behaving in this instance very much like an anhydride of thiophosphoric acid.
[Edited on 3-10-2007 by Sauron]
Attachment: kekule.pdf (309kB)
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Sauron
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As the attached paper demonstrates, the crude neutral fraction of the reaction product of alcoholysis of P4S10 with ethanol is a complex mixture.
However a 50% yield of P(S)(OEt)2Cl can be isolated in pure form after chlorination with a single equivalent of Cl2 in MeCl2 (DCM).
My conclusion is that further stepwise chlorination would likely yield
P(S)(OEt)Cl2, then PSCl3, and if Gmelin got it right, exhaustive chlorination would proceed to PCl3 + S2Cl2.
This may be worth a try. I will have a closer look at this paper and its antecedents.
Well the yields suck (16%) so the way to go with P4S10 is definitely ethyl orthoformate not alcohol.
Ethyl orthoformate reacts in minutes not hours or days, gives a 90+% yield of same product, and is both readily purchasable and readily preparable if
you can get Na and CHCl3. Or even just NaOH and EtOH if you can wait a few days for them to react.
[Edited on 4-10-2007 by Sauron]
Attachment: jo01340a028.pdf (423kB)
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