lagerdale
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Unknown green solid
Today I was preparing a solution of HI in DMSO, by dissolving NaI in DMSO and adding phosphoric acid to it. I know this is not the "right" way of
doing this, maybe I should have just made the HI separately and bubbled it in DMSO, but whatever.
Anyway, things gone strange, and not exactly as I expected. First, the milky white solution of NaI in DMSO turned reddish as phosphoric acid was
added, like if iodine was being formed, what shouldn't happen since phosphoric acid does not oxidize iodide salts. It immediately came to my mind:
'Iodine? Wtf!'.
During the addition, a green solid started to form aswell, which by the end of the addition had turned the solution into a green mud. I expected to
see white sodium phosphate precipitating, but not these green stuff.
Anyone knows what is that?
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AJKOER
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No idea, but if I have to list one possibility:
(CH3)2SO + NaI → [Na(CH3)2SO]I
which is perhaps Sodium-dimethylsulfoxonium iodide (?). Then on adding H3PO4:
[Na(CH3)2SO]I + H3PO4 → [Na(CH3)2CH2SO]H2PO4 + HI
which is, if it exists, would be monosodium-dimethylsulfoxonium phosphate(?).
Support for my logic, the compound Tetra methyl ammonium hydroxide exists. So replacing one (CH3) with Na and another with SO, and the hydroxide with
an iodide, we're done.
If anyone has better/alternate candidates, please post.
[Edited on 19-5-2012 by AJKOER]
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Nicodem
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DMSO is not only a reducing reagent, it can act as an oxidant as well, so that I find it hard to believe an anhydrous solution of HI in DMSO would be
stable. It is known that DMSO reacts with hydrogen halides. The main reaction pathway initially occur via reactions analogous to the Pummerer
rearrangement in the case of HCl and HBr. Don't remember ever reading what decomposition pathway prevails upon the reaction with HI. I would guess the
major end product would be trimethylsulfonium iodide.
See the Gaylord chemical DMSO bulletins for more details and references (the company is a major producer of this solvent).
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BromicAcid
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Where is your phosphoric acid from... a major impurity in phosphoric acid produced by the wet process, even some that you buy, is iron. That would be
my first thought.
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simba
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Funningly, this also happened to me some time ago. After adding phosphoric acid to a solution of NaI in anhydrous DMSO, the solution turns reddish
with these green solids filling up the flask. It came to me as a surprise also, but I didn't bother look what it was. I just assumed some bizarre
complex had formed.
What Nicodem said makes a lot of sense aswell. When I added phosphoric acid to a solution of NaI in water/DMSO, everything went as expected, the
solution remained clear with white sodium phosphate falling to the bottom of the flask. The idea of adding water to the mixture was originally to help
NaI to dissolve, since it rocks up like nothing, and these rocks dissolve only slowly in pure DMSO.
This green solid is quite beautiful also, having a deep emerald green color.
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Arthur Dent
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http://www.youtube.com/watch?v=TkZFuKHXa7w
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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Eddygp
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[Na(CH3)2SO]I
or
[NaHCCH3S]I·H2O
there may be bugs in gfind
[ˌɛdidʒiˈpiː] IPA pronunciation for my Username |
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Nicodem
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Thread Moved
19-5-2012 at 11:39 |
lagerdale
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Quote: Originally posted by Nicodem  | DMSO is not only a reducing reagent, it can act as an oxidant as well, so that I find it hard to believe an anhydrous solution of HI in DMSO would be
stable. It is known that DMSO reacts with hydrogen halides. The main reaction pathway initially occur via reactions analogous to the Pummerer
rearrangement in the case of HCl and HBr. Don't remember ever reading what decomposition pathway prevails upon the reaction with HI. I would guess the
major end product would be trimethylsulfonium iodide.
See the Gaylord chemical DMSO bulletins for more details and references (the company is a major producer of this solvent). |
I did a quick search here and found that trimethylsulfonium iodide is a "white to yellowish" powder, so I don't think this is the case.
The crystals are needle like with a deep emerald green color as simba said. I think I will just filter the green crystals and post in the 'pretty
pictures' topic. But I'm still curious to find out what this really is, all we have are hypothesis.
I will do more search later to see if I can get a name for this. Thanks for the responses. 
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woelen
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You could try with sulphuric acid as well. You also get this green solid with H2SO4? If so, then the green is not specific to phosphate.
If you use H2SO4, then you need to dilute the acid before adding, otherwise it oxidizes iodide to iodine. Make 85% acid by adding a little water and
then adding this acid slowly to some DMSO and then add this to the solution of NaI in DMSO.
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Adas
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It is probably the iron impurity, some iron compounds can have green color, IIRC.
Rest In Pieces!
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barley81
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Surely there is not enough iron to cause a "green mud" to form! It is probably from something else.
[Edited on 23-5-2012 by barley81]
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lagerdale
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I took some photos of the "green mud", hope it helps solving this little mystery.
http://imageshack.us/photo/my-images/717/0000001w.jpg/
http://imageshack.us/photo/my-images/209/0000004p.jpg/
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simba
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I was thinking, could DMSO somehow oxidize HI all the way into I5+? Because I5+ ion is said to be green, just like I2+ is blue. Maybe what we have
here is a I5+ complex?
Another thing, is that this green crystals apparently decompose in solution, giving a red liquid which stains everything, just like a common iodine
solution.
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