xfusion44
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H2O2 + KI + HCl = unexpected reaction
Hi!
I was trying to make some iodine, so I've mixed conc. solution of KI with 30% HCl. After a few minutes, there was a slight colour change (the mixture
became a bit brownish), so I assumed that some iodine has already formed. Then I added 30% H2O2 and the iodine immediately precipitated. After a
minute, the mixture was quite hot and it looked like it boiled, but it was just the oxygen from H2O2 coming out as a result of mixture heating up.
Temperature was maybe a little above 40°C. All of the iodine settled at the bottom pretty quickly and I could smell some chlorine gas... However,
when I tried to filter out the iodine I added some distilled water (to help wash out all of the iodine), but the mixture became almost dark orange (I
thought it was just the iodine crystals that were giving the orange colour, since I added a lot of water), but it seemed like there was no iodine left
(it should at least precipitate out of solution, right?). I waited some time and there was no precipitation, so I just filtered the mixture and there
was no iodine on the filter paper! (except some small pieces that this weird reaction mixture didn't consume). All went right through the filter
paper. There was still exactly the same colour after filtration. I'm really wondering where all of my iodine went? It seems like some soluble iodine
compound was formed, which is giving that orange colour in water. Otherwise I don't know where the iodine would be. If you need some pictures, just
say...
Thanks!
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chemplayer..
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A few things could be getting in the way of your desired reaction:
1. Iodine dissolves fairly readily in KI solution to form a brown (can appear dark orange) soluble KI3 addition compound. Addition of more oxidising
agent to convert all the KI to iodine should cause the iodine to be precipitated out as the KI and KI3 are oxidised and can't dissolve the iodine.
2. KI is quite a good catalyst for decomposing hydrogen peroxide to oxygen and water (which is quite an exothermic process), so this will be using up
some of the H2O2 you are adding.
3. Concentrated or close-to-concentrated aqueous HCl is pretty prone to oxidation to chlorine gas by strong oxidising agents (e.g. spontaneous
vigorous reaction with MnO2, permanganate etc.). Hot 30% hydrogen peroxide is probably going to do this to some extent as a side-reaction. Diluting
the mixture a bit more from the start will help to stop this from happening.
Did you try adding more peroxide to the filtrate to see if this re-precipitated the iodine?
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xfusion44
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Quote: Originally posted by chemplayer..  | A few things could be getting in the way of your desired reaction:
1. Iodine dissolves fairly readily in KI solution to form a brown (can appear dark orange) soluble KI3 addition compound. Addition of more oxidising
agent to convert all the KI to iodine should cause the iodine to be precipitated out as the KI and KI3 are oxidised and can't dissolve the iodine.
2. KI is quite a good catalyst for decomposing hydrogen peroxide to oxygen and water (which is quite an exothermic process), so this will be using up
some of the H2O2 you are adding.
3. Concentrated or close-to-concentrated aqueous HCl is pretty prone to oxidation to chlorine gas by strong oxidising agents (e.g. spontaneous
vigorous reaction with MnO2, permanganate etc.). Hot 30% hydrogen peroxide is probably going to do this to some extent as a side-reaction. Diluting
the mixture a bit more from the start will help to stop this from happening.
Did you try adding more peroxide to the filtrate to see if this re-precipitated the iodine? |
I've tried to add more H2O2, but nothing happens (maybe it's a bit darker now, but even adding alot of it doesn't make the difference).
I'll add the picture...
PS: What if I'd try to boil off the water?
[Edited on 27-2-2016 by xfusion44]
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xfusion44
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If I add more HCl it becomes brighter orange...
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byko3y
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What is pH of the final solution? How does it react to addition of bleach+acid?
I don't think filtering of iodine through the paper is a good idea as far as iodine forms complex with cellulose.
Dichloromethane or similar solvent can be used to extract the iodine.
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xfusion44
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| Quote: Originally posted by byko3y | What is pH of the final solution? How does it react to addition of bleach+acid?
I don't think filtering of iodine through the paper is a good idea as far as iodine forms complex with cellulose.
Dichloromethane or similar solvent can be used to extract the iodine. |
pH looks to be pretty much 0.
What do you mean by "bleach+acid"? If I'd mix bleach+acid, I'd make chlorine gas or did you mean adding them separatly?
The one about filtering paper seems to be true, since all of the small pieces of iodine that I left on the paper disappeared 
Unfortunatly I don't have DCM, but I have toluene, acetone, benzene, ethanol, isopropanol, ethyl acetate, butyl acetate, chloroform and acetonitrile.
Would any of these work?
Thanks!
[Edited on 27-2-2016 by xfusion44]
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byko3y
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Okay, I think now I know what actually happenned. https://www.youtube.com/watch?v=ZFP7fYGrFRI - here's your procedure, http://www.sciencemadness.org/talk/viewthread.php?tid=24862 - and here's a precise description of the result you had and a possible solution to
it.
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S.C. Wack
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Focus on the last post in that thread, where it says the product would be oxidized. There have been calculators on the internet for meth cooks for
some years, for the correct amounts, because excess is bad. If the solution is neutralized, evaporated, and cooled, salt that is not KCl may or may
not precipitate.
Brauer, preparation of KICl4:
Concentrated KI solution is acidified with hydrochloric acid and chlorine is introduced. The weight increase should be controlled so as to avoid an
excess of chlorine. The yield is 70%.
[Edited on 27-2-2016 by S.C. Wack]
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Boffis
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Is it possible that you have produced iodine chloride or trichloride?
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xfusion44
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Hmm, but I've used H2O2, not NaClO... So, the iodine should not dissolve, or did I miss something?
I tried mixing the resulting mixture with ethyl acetate. Two layers formed. The bottom layer is probably water, hcl and h2o2 if I'm correct. And the
top, dark violet/red layer is ethyl acetate with iodine or some iodine compound, dissolved in it, I'd say... Could you confirm that?
Here's the picture:
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xfusion44
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| Quote: Originally posted by S.C. Wack | Focus on the last post in that thread, where it says the product would be oxidized. There have been calculators on the internet for meth cooks for
some years, for the correct amounts, because excess is bad. If the solution is neutralized, evaporated, and cooled, salt that is not KCl may or may
not precipitate.
[Edited on 27-2-2016 by S.C. Wack] |
What salt did you mean?
@Boffis
I've been wondering about that...
[Edited on 27-2-2016 by xfusion44]
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S.C. Wack
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Who knows? Maybe the whole mixture can be separated into pure products that can be identified, or not.
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xfusion44
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So, should I just try to heat the top layer to evaporate EtOAc, to see if there's iodine in it?
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xfusion44
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I think I've got the iodine monochloride. After evaporating EtOAc, there was reddish brown liquid, which slowly evaporated and smelled like chlorine
(and maybe even a bit like vinegar)
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S.C. Wack
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Is ICl possible in water with HCl, Cl2, and H2O2? This is what woelen addressed in the other thread. Weird chloroiodo things apparently may not be
entirely stable.
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byko3y
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I told you! It looks like you've ignored my link, while it was the correct answer - you've got iodine monochloride via I2 + Cl2 -> ICl. Iodine
monochloride is somewhat soluble in water, while better also soluble in ethyl acetate.
In water iodine mnochloride disproportianates ICl + H2O -> HCl + HOI. That's why bicarbonate is needed - to neutralize HCl (bicarbonate does not
form hypochlorite-hypoiodite, only carbonate does). However, I'm not sure whether this reaction is correct or if there's some tricks in measuring
reagent amounts..
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xfusion44
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| Quote: Originally posted by byko3y | I told you! It looks like you've ignored my link, while it was the correct answer - you've got iodine monochloride via I2 + Cl2 -> ICl. Iodine
monochloride is somewhat soluble in water, while better also soluble in ethyl acetate.
In water iodine mnochloride disproportianates ICl + H2O -> HCl + HOI. That's why bicarbonate is needed - to neutralize HCl (bicarbonate does not
form hypochlorite-hypoiodite, only carbonate does). However, I'm not sure whether this reaction is correct or if there's some tricks in measuring
reagent amounts.. |
I didn't ignore it, I just didn't know what to look for, since I didn't use NaClO, as "APO" did.
I added some NaHCO3 to the EtOAc/ICl solution and it totally worked! Iodine precipitated out. But when I added NaHCO3 to the crude reaction mixture
(without extracting ICl) it went completely clear! There was no iodine... Does anybody know what happened?
Actually, does anybody even know how this reaction even work? I mean H2O2 + HCl + KI
Thanks! Best regards
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byko3y
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Hydrogen peroxide generates radicals, which in the end oxidizes iodide, chloride, oxide to iodine, chlorine and oxygen respectively. Cl2 + 2KI ->
2KCl + I2, but when all the iodide is converted into iodine, next reactins comes into play Cl2 + I2 -> 2ICl. In the solution ICl + H2O -> HCl +
IOH. When you add sodium bicarbonate HCl + IOH + NaHCO3 -> NaCl + H2O + CO2 + IOH; IOH in acidic conditions decomposes 4IOH -> 2I2 + O2 + 2H2O,
this last reaction is at least second order in [IOH], thus the solution needs to be concentrated, or longer reaction time is required, or maybe
heating will do the job. Also, your solution might had some kind of salt that could influence the reaction.
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woelen
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You used way too concentrated reagents. What happens is that excess H2O2 oxidizes HCl to Cl2 and water, the Cl2 in turn reacts with iodine, producing
IO3(-) and ICl4(-) ions and you lose all of your iodine to highly oxidized species.
Try again with 3% H2O2 and 10% HCl. Dissolve your KI in 10% HCl.
The reaction you want is 2I(-) + 2H(+) + H2O2 --> I2 + 2H2O
In practice, assure that you have quite some excess of acid. E.g. 2 molecules of HCl for each KI is OK and non-critical. A little more or a little
less HCl is no problem.
Also, use some excess H2O2. At these low concentrations, the H2O2 does not oxidize the HCl (or very slowly), while it immediately oxidizes the iodine.
By using excess H2O2 you assure that all iodide is converted to iodine. Without any iodide ions present, the solubility of iodine is very low and
nearly 100% of the iodine precipitates.
[Edited on 28-2-16 by woelen]
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xfusion44
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Hi!
I've tried again, with 30% HCl and 3% H2O2 and it worked!
Thank you all 
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