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artemov
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Solid Phosphorus Triiodide
Just wondering if it's possible to obtain solid phosphorus triiodide ...
According to https://en.wikipedia.org/wiki/Phosphorus_triiodide, "(it) is an unstable red solid which reacts violently with water. It is a common
misconception[1] that PI3 is too unstable to be stored; it is, in fact, commercially available."
Perhaps dissolve iodine in toluene, slowly add red P powder (with an ice bath), then let the toluene evaporate away while keeping everything dry?
[Edited on 28-10-2018 by artemov]
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unionised
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I don't know, but I'd use something more volatile than toluene- maybe hexane.
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Heptylene
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I've wondered about that too. If you do try it, please make sure to post your results. Maybe DCM can be used as the solvent?
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Sulaiman
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As I have red P, Iodine and CS2 I just went to my lab and put
1.1g red P in 10 ml CS2 intending to mix two solutions,
expecting it to dissolve easily like white P.
WRONG ! ... maybe it is too cold so I'll leave it for a few days.
I noticed that artemov mentioned an ice bath,
is the reaction expected to be significantly exothermic ?
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unionised
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Red phosphorus isn't soluble.
However it's possible that it will react with a solution of I2 in CS2
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wg48
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Here are some PI3 preps:
"The simplest phosphorus iodide—phosphorus triiodide—was initially
obtained in 1850, but its chemical properties were not fully investigated till
1959, since it was virtually inaccessible being synthesized from the pure2ed
phosphorus or white phosphorus in the purest sulphur—hydrocarbon solution3'4'
.
P white C.P. + 31 C.P. CS2CP
We succeeded in making phosphorus triiodide quite accessibl9, having
realized the same synthesis, but from ordinary red phosphorus and iodine
without solvents with further crystallization from phenyl chloride or dichioroethane6.
crystallized from P red + 31 —÷ P13 P13 CP 6 5 or 2 4 2
Phosphorus triiodide is also obtained in quite pure condition from
phosphorus trichloride and alkali-metal iodides in benzol- or dichloroethane
solution7.
Pd3 + 3MI C2H4Cl2 3MC1 + PT3
M: Li, Na, K"
The above is from an interesting paper on CHEMISTRY OF PHOSPHORUS IOD1DES:
Attachment: PIx-4402x0125 (1).pdf (318kB)
This file has been downloaded 465 times
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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Sulaiman
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nice pdf ... back later ...
[Edited on 28-10-2018 by Sulaiman]
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artemov
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I have read that paper too ... I only have access to toluene and maybe xylene or hexane here ... definitely no CS2 or DCM or CCl4 ...
I reckon most reactions directly involving a halogen to be exothermic ... without a solvent I would expect a puff of iodine vapor lol
Anyway, I dun expect the red P to be soluble in anything ... hence I'm thinking of dissolving iodine in an inert solvent first, then add red P slowly
with strong stirring ... similar to the synthesis of methyl iodide with Red P, I2 and MeOH (which is also exothermic?). In this case, the PI3 formed
won't react further (with methanol to form methyl iodide and phosphorous acid) and will probably stay in solution with the inert solvent, hopefully
lol.
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S.C. Wack
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Relevant pages from Gmelin's (1965)
Attachment: GmelinPI3.pdf (132kB)
This file has been downloaded 435 times
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wg48
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Quote: Originally posted by artemov  | I have read that paper too ... I only have access to toluene and maybe xylene or hexane here ... definitely no CS2 or DCM or CCl4 ...
I reckon most reactions directly involving a halogen to be exothermic ... without a solvent I would expect a puff of iodine vapor lol
Anyway, I dun expect the red P to be soluble in anything ... hence I'm thinking of dissolving iodine in an inert solvent first, then add red P slowly
with strong stirring ... similar to the synthesis of methyl iodide with Red P, I2 and MeOH (which is also exothermic?). In this case, the PI3 formed
won't react further (with methanol to form methyl iodide and phosphorous acid) and will probably stay in solution with the inert solvent, hopefully
lol. |
If you can find ref 6 from that PDF it should contain the details of the direct synthesis of PI3 from the elements or as PI3 decomposes at 200C it
suggests its not strongly bound together so I doubt the direct reaction between red P and I will be very exothermic. You could try grinding a small
(sub gram) stoichiometric mixture of red P and I together or warming (100C) the mixture in a test tube.
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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woelen
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I expect severe difficulties in making PI3 from red P and I2. Red P is insoluble, there is no known solvent for this compound (at least not one, which
does not react with the red P). PI3 probably also is insoluble (or only marginally soluble), so you will get a layer of PI3 around unreacted red P.
If you use white P, dissolved in CS2 or toluene and you add a solution of I2, then the reaction can take place in solution and a precipitate of PI3
can be formed. This will be much ieasier to isolate and clean.
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Sulaiman
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oops ! ... suggestions for help please
despite having plenty of planned experiments, I was impulsive this morning,
I now have a 250 ml bottle containing;
c60 ml carbon disulphide
c1.1 g red phosphorous
c13.52 g iodine prills
or the reaction product(s) of the mixture.
I over estimated the solubility of iodine and red P in carbon disulphide,
so used my entire remaining stock of c60 ml, not enough.
All of the measurements were accurate when I started, (near stoichiometric P & I)
but some of each was lost when I needed to transfer to a larger vessel.
So I seem to be in a mess, the suspension is totally opaque but swirling leaves particles on the wall of the bottle.
I have no more CS2 but I have other solvents such as toluene, ether, chloroform, and a larger quantity of DCM.
I noticed no change in temperature on mixing.
I can see a difference between the red of redP and of iodine in solution,
but will I be able to distinguish them from the red of PI3 ?
Assuming that PI3 precipitate is preferred over Pn and In ...... (I'm an optimist)
would the reaction proceed to completion,
even though the rate would be determined by the rates of dissolution and precipitation ?
Any suggestions for my next step ?
Should I make a different thread ?
[Edited on 28-10-2018 by Sulaiman]
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DavidJR
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Just tried this:
0.31g (0.01 gram atoms) of red phosphorus and 3.8g (0.03 gram atoms) of iodine were added to a porcelain mortar. On grinding, the mixture began to
smoke profusely - indicating that PI3 was formed and reacted with the humid atmosphere. The fumes turn moistened universal indicator paper
red, as expected.
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unionised
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Are you sure?
The stuff has a low melting point indicating that the molecules are not stuck together well. PBr3 is soluble in CS2
https://pubchem.ncbi.nlm.nih.gov/compound/phosphorus_tribrom...
If PI3 is soluble in CS2 then the reaction should go slowly to completion.
(and the fact that the red P dissolves will show that the reaction has taken place in spite of it being the reaction of red stuff with a red solution
to make red stuff).
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Melgar
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PI3 is sort of orangeish-brown. Dissolved iodine will appear anywhere from yellow to purple depending on how polar the solvent is that it's dissolved
in. If you want to be able to notice the two elements reacting with each other, use hexane or heptane or something. Not only would a color change
from purple to orange/brown be really noticeable, but you also are going to want to exclude water as much as possible.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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S.C. Wack
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Needless to say Gmelin's indicates it has allegedly been made without solvent or with only the I dissolved in the CS2, I is less soluble in CS2 than
PI3, excess P is fine to get all the I to react, as long as not all the P reacts....filter and evap...I don't see the problem except PI3 not liking
air.
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artemov
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According to the Gmelin's article, Sulaiman, your method should work ... (I'm relying on Google translate here)
Perhaps you can let the undissolved solids (red P, iodine, PI3???) settle down to the bottom, take a few drops of the solution from the top and let it
evaporate to dryness on a watch glass. If the residue fumes in the moist air, like what DavidJR observed, you probably have PI3. But you will probably
have iodine mix in too ...
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Sulaiman
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The mixture is still opaque, some sediment present.
I transferred about 1ml of the liquid into a small beaker,
which I put at the focus of a 5" shaving (concave) mirror to heat with sunlight,
(the mirror is off to the left of the video)
plenty of fumes but I can't be sure that the fumes are not just P4O10 and I2 ...
A short video https://www.youtube.com/watch?v=rhOLoSuuyAM&t=5s
After taking the video I added a further 0.1g redP to the mixture
as I think that not all of the iodine had reacted.
____________________________________________________
Could someone please point me in the direction of the solubility in CS2 of I2, redP and PI3 ?
[Edited on 29-10-2018 by Sulaiman]
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DavidJR
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I wouldn't have thought you'd get P4O10 unless dissolving (if that's even possible to any extent) red phosphorus in
CS2 and evaporating the solution can produce white phosphorus. I suppose if you had any more CS2 left you could try it without
the iodine.
Or, transfer a small amount of the mixture to a flask, add a drop or two of water, and connect a tube to bubble the fumes through a small volume of
distilled water (warming may be necessary). The HI should dissolve in the water producing a strongly acidic solution. Add some silver nitrate solution
and see if you get a precipitate of silver iodide.
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Sulaiman
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Good idea
Here is the setup
1ml of the mixture in a side arm test tube,
disposable pipette with water in one-hole bung,
plastic and glass tubing bubbling into
distilled water with a piece of pH 1-14 indicator paper.
Short version ...
suck-back, then most of the distilled water exited the experiment 
So at least a little HI must have been formed 
Silver nitrate solution caused a little cloudiness in the remaining contaminated water.
I'll try something different tomorrow.
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wg48
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| Quote: Originally posted by DavidJR |
I wouldn't have thought you'd get P4O10 unless dissolving (if that's even possible to any extent) red phosphorus in
CS2 and evaporating the solution can produce white phosphorus. I suppose if you had any more CS2 left you could try it without
the iodine.
Or, transfer a small amount of the mixture to a flask, add a drop or two of water, and connect a tube to bubble the fumes through a small volume of
distilled water (warming may be necessary). The HI should dissolve in the water producing a strongly acidic solution. Add some silver nitrate solution
and see if you get a precipitate of silver iodide. |
Its already been said that red phosphorous does not dissolve in any solvents including CS2 that do not react with it. As red P is inert to air and
moisture the fuming strongly suggest that a reaction has occurred between the P and I to produce a P iodide which is reacting with air and or the
water vapour it contains. But its always good to confirm theory with tests, theory can be wrong.
According to wiki PI3 is soluble in CS2 but it does not give a value.
[Edited on 29-10-2018 by wg48]
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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Sulaiman
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I guess you were typing while I was posting.
I'm quite confident that some PI3 formed,
how much formed is the question now.
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S.C. Wack
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BTW the CRC says v sol for PI3, obviously if CS2 is the recrystallization solvent of record, one proceeds accordingly. No doubt many references give
figures for I and CS2 but I checked Mellor first which indicates low solubility at -100C, going up significantly with heat. enough that one would
think it's not hard to dissolve or recrystallize in that solvent.
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Sulaiman
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Due to using my entire stock of CS2 in one not-thought-out experiment,
and my only known supplier being temporarily out of stock,
I'm going to leave the mixture aside for a while
- allowing time for equilibrium to be achieved.
or maybe one impulsive day I'll try other solvents that I have
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DavidJR
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| Quote: Originally posted by Sulaiman | Due to using my entire stock of CS2 in one not-thought-out experiment,
and my only known supplier being temporarily out of stock,
I'm going to leave the mixture aside for a while
- allowing time for equilibrium to be achieved.
or maybe one impulsive day I'll try other solvents that I have
|
Where are you getting your CS2? Limac sells it but it's pretty pricey.
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