Sciencemadness Discussion Board

Solid Phosphorus Triiodide

artemov - 27-10-2018 at 22:28

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]

unionised - 28-10-2018 at 01:52

I don't know, but I'd use something more volatile than toluene- maybe hexane.

Heptylene - 28-10-2018 at 03:45

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?

Sulaiman - 28-10-2018 at 04:23

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 ?

unionised - 28-10-2018 at 04:40

Red phosphorus isn't soluble.
However it's possible that it will react with a solution of I2 in CS2

wg48 - 28-10-2018 at 04:59

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 466 times

Sulaiman - 28-10-2018 at 05:13

nice pdf ... back later ...

[Edited on 28-10-2018 by Sulaiman]

artemov - 28-10-2018 at 06:00

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.

S.C. Wack - 28-10-2018 at 08:28

Relevant pages from Gmelin's (1965)

Attachment: GmelinPI3.pdf (132kB)
This file has been downloaded 436 times

wg48 - 28-10-2018 at 11:38

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.

woelen - 28-10-2018 at 11:59

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.

oops ! ... suggestions for help please

Sulaiman - 28-10-2018 at 12:39

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]

DavidJR - 28-10-2018 at 13:04

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.

unionised - 28-10-2018 at 13:34

Quote: Originally posted by woelen  
PI3 probably also is insoluble (or only marginally soluble)


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).

Melgar - 28-10-2018 at 15:25

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.

S.C. Wack - 28-10-2018 at 16:16

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.

artemov - 28-10-2018 at 17:10

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 ...

Sulaiman - 29-10-2018 at 06:22

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]

DavidJR - 29-10-2018 at 09:31

Quote: Originally posted by Sulaiman  

plenty of fumes but I can't be sure that the fumes are not just P4O10 and I2 ...


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.

Good idea

Sulaiman - 29-10-2018 at 11:45

Here is the setup
BubblerPI3.jpg - 161kB
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.

wg48 - 29-10-2018 at 11:47

Quote: Originally posted by DavidJR  
Quote: Originally posted by Sulaiman  

plenty of fumes but I can't be sure that the fumes are not just P4O10 and I2 ...


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]

Sulaiman - 30-10-2018 at 13:34

I guess you were typing while I was posting.
I'm quite confident that some PI3 formed,
how much formed is the question now.

S.C. Wack - 30-10-2018 at 16:35

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.

Sulaiman - 30-10-2018 at 17:57

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 :)

DavidJR - 31-10-2018 at 02:40

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.

Sulaiman - 31-10-2018 at 05:59

CS2 is rather pricey;
http://onyxmet.com/?route=product/product&filter_name=ca...

If someone could point me to a competitive source that ships to UK amateurs I'd be grateful.

DavidJR - 31-10-2018 at 06:12

Quote: Originally posted by Sulaiman  
CS2 is rather pricey;
http://onyxmet.com/?route=product/product&filter_name=ca...

If someone could point me to a competitive source that ships to UK amateurs I'd be grateful.


You could maybe try Rathburn Chemicals as they list CS2 on their site: http://rathburn.co.uk/product-list/

You'll have to email them to get a quote and order. They specialise in very high purity solvents so it might not be cheap but it's worth asking. I've ordered HPLC-grade solvents from them before and they are friendly and helpful and willing to sell to individuals/sole traders.

Thank You !

Sulaiman - 31-10-2018 at 06:45

I just telephoned Rathburn Chemicals,
RG2027 glass-distilled Carbon Disulphide, 500ml £20 ++
I am in the process of registration now.
Not only a competitive source but a new source that ships to amateurs,
with 30-day credit.
Shipping is £14 for up to one pallet of chems...
Thanks so much.

Herr Haber - 31-10-2018 at 07:25

I've got enough CS2 to pick up where your bottle left you.
Trouble is, I have to distill enough HNO3 by the end of the weekend to dissolve 1.5kg of silverware...

I might give it a try as I also have red P and a few miligrams of impure white P.

Sulaiman - 31-10-2018 at 11:31

Quote: Originally posted by Herr Haber  
I've got enough CS2 to pick up where your bottle left you.


Excellent,
because I'm not going to buy any chemicals for a while due to lack of spare cash :(


UPDATE:
Rathburn chemicals have replied ... I can order as soon as funds permit :)

[Edited on 1-11-2018 by Sulaiman]

artemov - 1-11-2018 at 03:14

I have chemicals envy of all of you ... :(

minor PI3 update

Sulaiman - 17-11-2018 at 04:16

I just examined the 250ml bottle with c60ml mixture as described earlier above;
. the blue plastic GL45 cap is very discoloured and bulging a little :(
. there is very little sediment :D

the volume of sediment is visibly less than the starting volume of the redP alone ...
either all of the iodine and some of the redP has dissolved in the CS2
or there has been a significant quantity of redP consumed,
and as I have been reminded a few times above ... 'redP is not soluble in CS2'
... something good must be happening.

After getting 'dressed-up' for the unexpected,
with the camera rolling I carefully opened the bottle cap and
... absolutely nothing dramatic happened.
Very little internal pressure (Ta<<20oC) but some 'smoke'.
I re-capped the bottle and I'll check it sometime later - nearer to Xmas.

So it appears that although redP is 'insoluble' in CS2,
the minute solubility that it does have enables the reaction to proceed, very slowly, hopefully to completion.
Other than glimpses of sediment I really can not determine what is happening by any noticeable visible change.

Considering that the reactants and product and solvent each have their own safety hazards,
so far, this has been one of the gentlest reactions that I've ever done.

My main concern now is;
what the heck am I going to do with the PI3 ?
and how do I recover my CS2 ?
... t.b.d.

artemov - 17-11-2018 at 06:21

Quote: Originally posted by Sulaiman  
I just examined the 250ml bottle with c60ml mixture as described earlier above;
. the blue plastic GL45 cap is very discoloured and bulging a little :(
. there is very little sediment :D

the volume of sediment is visibly less than the starting volume of the redP alone ...
either all of the iodine and some of the redP has dissolved in the CS2
or there has been a significant quantity of redP consumed,
and as I have been reminded a few times above ... 'redP is not soluble in CS2'
... something good must be happening.

After getting 'dressed-up' for the unexpected,
with the camera rolling I carefully opened the bottle cap and
... absolutely nothing dramatic happened.
Very little internal pressure (Ta<<20oC) but some 'smoke'.
I re-capped the bottle and I'll check it sometime later - nearer to Xmas.

So it appears that although redP is 'insoluble' in CS2,
the minute solubility that it does have enables the reaction to proceed, very slowly, hopefully to completion.
Other than glimpses of sediment I really can not determine what is happening by any noticeable visible change.

Considering that the reactants and product and solvent each have their own safety hazards,
so far, this has been one of the gentlest reactions that I've ever done.

My main concern now is;
what the heck am I going to do with the PI3 ?
and how do I recover my CS2 ?
... t.b.d.


Fantastic!!! I dun have CS2, so I'll probably try it with toluene (or hexane).

What's the color of the solution? Any pics? :D
Are you able to dry a few drops of the clear solution and obtain dry red PI3?

Sulaiman - 17-11-2018 at 08:06

A quick video of the appearance, nothing interesting. https://www.youtube.com/watch?v=WngVdTs9DME

artemov - 17-11-2018 at 17:13

Wow thanks! Nice dark red, and nice weather!

Sulaiman - 20-11-2018 at 10:22

Quote: Originally posted by Herr Haber  
I've got enough CS2 to pick up where your bottle left you.
Trouble is, I have to distill enough HNO3 by the end of the weekend to dissolve 1.5kg of silverware...

I might give it a try as I also have red P and a few milligrams of impure white P.

Unless you need PI3 please do not waste your time and reagents,
it is just a simple combination synthesis.
(SM Wiki: http://www.sciencemadness.org/smwiki/index.php/Phosphorus_tr... )
I guess that refluxing would have the job done in minutes.
Just about all of the redP has now 'gone'.
Pouring the liquid from the 250ml bottle into a 100ml bottle I could smell/taste :
. the CS2 (impurities),
. hints of both iodine and phosphorus,
. an unfamiliar strong nasty smell.
Even in cold dry air there was 'smoke'

Today I completed the construction of my upgraded water cooler/chiller module
(now 4x TEC@c6V, was 2x TEC@c12V)
so soon I hope to recover the CS2 and PI3.

[Edited on 21-11-2018 by Sulaiman]

Herr Haber - 21-11-2018 at 04:57

Thanks Sulaiman,

No need for it but I'm following the thread because it's interesting.
3 weeks later finally the last of my silver is dissolved. Spent the last week watching a 300 grams ingot go into solution...

Thanks for sharing your results and congratulations of your water cooler ;)

... update ...

Sulaiman - 20-4-2019 at 06:27

I have not yet tried to recover the CS2 from my (assumed) PI3,
the mixture was stored with a cork covered in many layers of cling film plastic.
(I did not expect such a long storage period)
Here is the result, on the right;

IodineInWater_and_PT3inCS2.jpg - 371kB

On the left are a few iodine prills in distilled water as a colour reference for saturated iodine solution,
the stopper seems to have absorbed more iodine than the water :)
(The stopper was white and never in contact with the liquid,
only iodine vapour that passed through, then evaporated from, the water, could be responsible).
i.e. water does not reduce the evaporation rate to zero.

P.S. My water cooler is now two similar modules,
each module has two fan/heatsink/TEC and one 40x40 mm water tank.
At high water flow rate it makes little difference if the two modules are plumbed in series or parallel.
Progress suspended until probably next year due to relocation with expected ambient temperature 'upgraded' to 22 to 32 oC :)

[Edited on 20-4-2019 by Sulaiman]