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Author: Subject: sodium iodide from KI
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[*] posted on 21-5-2014 at 08:23
sodium iodide from KI


One of my friends has been asking me about a way to produce sodium iodide from potassium iodide. An idea was raised over reacting sodium bromide with potassium iodide resulting in sodium iodide and potassium bromide. I have doubts as to whether this would even work. Does anyone know more on this?
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[*] posted on 21-5-2014 at 10:24


You could make CH3I (KI, MeOH, H3PO4) and then decompose it with aqueous NaOH, it would have ~20% loss of iodide though.

Also you could oxidize it to I2 then react it with aqueous NaOH to form a mixture of NaI and NaIO3, the latter can be crystallized out due to its relatively low solubility (~17% loss of iodide to the iodate).
3I2 + 6NaOH → NaIO3 + 5NaI + 3 H2O

I2 can also be reacted with H2O2/NH3 to form NH4I which can be treated with NaOH to give NaI.
I2 + 2NH3 +H2O2 → 2NH4I + O2
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[*] posted on 21-5-2014 at 13:07


Quote: Originally posted by Scr0t  
You could make CH3I (KI, MeOH, H3PO4) and then decompose it with aqueous NaOH, it would have ~20% loss of iodide though.

Or you could skip the methanol, terrible losses and pointless use of highly toxic and carcinogenic methylating agents, and just make HI, which will react sodium hydroxide or carbonate to give NaI after evaporation of water.




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[*] posted on 21-5-2014 at 14:06


Why not oxidize it to iodine and react it with sodium hydroxide? I think this will produce the iodate as well. [edit] Oh, wait, Scr0t already posted this. From what I've read, I think the iodate can be heated to convert it into the iodide.

What is your intended application for the sodium iodide?

[Edited on 21.5.2014 by Brain&Force]




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[*] posted on 22-5-2014 at 05:04


Thanks for all the input on this, the application was initially for the elephant toothpaste demonstration, (I later learned that both would work) but the method of going from potassium iodide to sodium iodide proved trickier than anticipated and I started trying to simply learn how it would be done.
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[*] posted on 22-5-2014 at 11:22


Of course both would work since the alkali ion plays no role in the elephant toothpaste reaction. You could use any soluble iodide.



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[*] posted on 22-5-2014 at 17:25


I once read an interesting source that claimed passing water vapor (steam?) over heated KI reacted as follows:

KI (s) + H2O (hot vapor) ---) KOH (s) + HI (g)

If correct, this would be an acid free path to HI gas, which then could be directed to react with NaOH to form the required Sodium iodide:

HI + NaOH ---) NaI + H2O

the KOH is also a valuable side product.
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[*] posted on 22-5-2014 at 19:21


That's very interesting, if it indeed does work. I would have expected the reveres reaction to occur at all but quite high temperatures. Do you have a reference?
The hydroxide would probably be very wet though, but still hydroxide, which is useful. If I did do this, it would certainly be for the HI and produce Na/KOH as a byproduct. I think HI's affinity for water would also keep the reaction from going to completion, except at very high temperatures.
Of course this is all assuming that the reaction occurs at all, I'll look for some info...
[EDIT] Couldn't find a thing:( I might try this tomorrow if time permits, and if I have any NaI or KI, I forget these things...

[Edited on 23-5-2014 by Zyklonb]




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[*] posted on 23-5-2014 at 04:17


OK, I suspect the action of water vapor on KI may be similar to the observed action of CO2 rich air on the salt, to quote from Wikipedia ( http://en.m.wikipedia.org/wiki/Potassium_iodide#/search ):

"Aged and impure samples are yellow because of the slow oxidation of the salt to potassium carbonate and elemental iodine.[3]

4 KI + 2 CO2 + O2 → 2 K2CO3 + 2 I2 "

and, as again per Wikipedia on Iodine ( http://en.m.wikipedia.org/wiki/Iodine) to quote:

"Iodine is reduced to hydroiodic acid by hydrogen sulfide and hydrazine:[14]

8 I2 + 8 H2S → 16 HI + S8 "

So not so clean air and water vapor can form some HI, but these, at times, slow reactions provide only limited support for the questioned preparatory route.

[EDIT] Interestingly, Atomistry.com on KI (link: http://potassium.atomistry.com/potassium_iodide.html ) apparentlty disputes the description of the action of CO2 and air on Potassium iodide as "slow". To quote:

"The salt dissolves in water to form a neutral solution, readily decomposed by atmospheric oxygen and carbon dioxide with separation of iodine."

[Edited on 23-5-2014 by AJKOER]
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[*] posted on 23-5-2014 at 04:54


Quote: Originally posted by AJKOER  
I once read an interesting source that claimed passing water vapor (steam?) over heated KI reacted as follows:

KI (s) + H2O (hot vapor) ---) KOH (s) + HI (g)



I'm deeply sceptical about that.

Your KI would immediately become a soggy mess (unless perhaps very hot steam was used), as it's highly water soluble.

HI is a very strong acid and iodides do not hydrolyse appreciably.

Of course HI is a gas and its removal by the steam would drive the equilibrium to the right.

I don't think this is a remotely practical way of preparing HI, even less so at the hobbyist level.




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[*] posted on 23-5-2014 at 05:50



Quote:

I'm deeply sceptical about that.

Your KI would immediately become a soggy mess (unless perhaps very hot steam was used), as it's highly water soluble.

Yep, my thoughts exactly, perhaps it could be used to make hydroiodic acid. Just distill the gasses (H2O • x HI).



Quote:

I don't think this is a remotely practical way of preparing HI, even less so at the hobbyist level.

I can see it being used by home chemists. Depending on what temperatures are required. I Cannot see it being used on an industrial scale. It would be more expensive then the current methods to produce both of those reagents.


[EDIT] I wonder if this would work with KBr or NaBr? Of course the reaction would require much higher temps and would go even less to completion than the iodide version.
I know even if it does work it would be very unpractical and energy consuming.
I wonder this because it's a different sort of reaction then what I would think could happen, and because I have lots of NaBr and KBr.

[Edited on 23-5-2014 by Zyklonb]




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