loki_tiwaz
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KI + HCl --> Lugol's iodine??
Ok, the topic heading is not that informative.
This subject is specifically about the idea of substituting plain I2 for KI/HCl. Now, I know, before anyone else jumps in and points this out, that
KCl is less soluble than KI, and thus on the basis of this equilibrium, the likelihood of HI being available for reaction in any given reaction
involving hydriodic acid.
But I realised something today. Lugol's solution. Yes, I couldn't find an ancient text I posted to the hive explaining the stochiometry so I was
rather lost as to what to do about a hypothetical quantity of KI with regards to transforming it into HI. But then I realised... oh wait, KI makes I2
more soluble. To be precise, every mole of KI = 1 mol of I2 soluble. A la Lugol's Iodine. Put HCl and Ki together in equimolar amounts and you too
will see what is clearly dissolved aqueous iodine. Dark red solution.
I'd seen it before but I think this was the first time I'd seen equimolar HCl and KI. It occurs to me that this mixture and a little phosphorus will
create a potential iodinating/de-iodinating reaction system. I have heard tell of this being used as a reaction mechanism and I can verify that it
defintely works. You have to run it a bit cooler, ie, simmer temperature, ie 70 degrees C, and run it longer, but it produces the goods, reacts in the
way one wants.
I'd seen it before but for a change, in a calculated equimolar ratio, and ... omg ... red it goes. Anyone familiar with iodine chemistry knows that
red is a very good sign for the indication of the presence of I2.
Anyway, I just wanted to put this forth since this is the only place on the web where discussions of this sort of reaction chemistry occurs. I
searched quite a bit and could not find a single clear mechanism of oxidising iodides (via iodates) to iodine, so I decided to just do the first step
I knew, which is to add an equimolar amount of HCl to the KI. The red colour reminded me... oh yes, there is I2 already formed there.
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loki_tiwaz
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i miss the hive ever so badly... but i just wanted to add, i figured out what pink means in product. polymerised p2p. it seems pretty obvious but when
you realise it is so obvious. thank goodness like dissolves like.
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loki_tiwaz
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[edit: oh deary me... i am repeating myself in this post but i think i more got to the point more rapidly. sorry for the repetition.]
oh, i forgot the point of this post.
reading about lugol's iodine solution, which is basically that KI makes equimolar amounts of I2 soluble - KI and HCl mixed equimolar, to be precise,
300g/L HCl solution and pure KI, produces a situation where some I- is floating around. It is probable this reaction requires UV but in this situation
the briefly free I- forms I2.
It is obvious if you test this for yourself, a small amount of KI and some HCl in equimolar proportions. The solution turns quite red. That is almost
certainly lugols iodine going on.
Add some phosphites, hypophosphites or P4 and you have the conditions for iodination.
I wanted to share this so I could get some feedback from knowledgable chemists. I know it works, I have numerous experiences verifying this but it is
not widely known.
[Edited on 25-2-2007 by loki_tiwaz]
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Nicodem
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You might want to read about reduction&oxidation and oxidation numbers in inorganic chemistry before cluttering the forum with nonsense.
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unionised
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"oh, i forgot the point of this post."
No kidding?
With HCl and KI you will get some HI (not a lot) and it might work as a reducing/ iodinating agent. If that's what you meant, why not just say so?
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loki_tiwaz
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it works awesomely is the reason for posting this.
and yes I know that there is not a lot of HI produced (doesn't even have the smell particularly) BUT it turns quite dark red, indicating that, as one
would expect, that HI as minimal as it is, is binding into iodine which remains in solution because of the presence of the very soluble KI. In doing
this inevitably some of the HCl is displaced onto the K and because the whole solution is so near to or beyond saturated the kinetics eventually
result in precipitated KCl (it forms a solid salt and thus ceases to participate in the system) and just add some P and lots of very smelly and lovely
HI forms.
i'm not sure if an excess of this reagent mixture is required to get adequate usability but it certainly performs as well as HI/Rp or Rp/I2 given a
gentle reaction temperature (about 70-75) for 2-3 days. excess reagents probably just ensures it happens more completely.
if you don't think it has any validity find someone to replicate. the reaction proportions was approximately equimolar HCl and KI. i'm not sure how
critical the right ratio is, i would assume one would desire to make it equimolar so nearly no excess HCl exists in the solution which would of course
promote oxidation.
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Nicodem
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Your knowledge of chemistry is awesome! I'm left speechless.
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loki_tiwaz
Just for the record, HI is colourless.
What you are getting is traces of I2 from oxidation of iodide by the oxygen in the air. The rest of your ideas are, therfore, complete nonsense.
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loki_tiwaz
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i'm not sure what happens with this reaction. it works and produces a noticably more potent material than goes in. i am trying to figure out why and
what.
[Edited on 4-3-2007 by loki_tiwaz]
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