Sciencemadness Discussion Board

Preparing solid iodine.

Tengo - 8-10-2002 at 13:41

I need some suggestions about this method...
From a water solution containing 5% iodine and 15% acetic acid (store bought), I'm aiming to prepare solide iodine.
I presume that the brown solution contains an equilibrium between I- + I2 <-> I3-, shifted to right.
I extract I2 with toluene, making the organic phase purple. Thus leaving I- in the water phase, making it yellow (probably because of the acetic acid).
Am I correct this far?
So I removed the organic phase.
Now I want to oxidize the remaining I- to I2, so I bubble some Cl2 thru the water phase and repeat the procedure as above...
Can I now let the toluene evaporate, leaving cristallized I2? Or would I2 evaporate along with the toluene?

Now an idea hit me... Could I start by bubbling Cl2 thru the original solution, forcing I2 to precipitate?
Adding MnO4- to the original solution.
Any other ideas? Coldfinger?

Thankful for any inputs /Tengo

IodineForLunch - 8-10-2002 at 17:52


Iodine can be prepared from iodides, mineral acid, and hydrogen peroxide.

As an example:

H2SO4 + H2O2 + 2NaI ----> I2 + Na2SO4 + 2H2O

Iodine will precipitate.

Someone is currently selling 500 g of sodium iodide on ebay for $15. Do an ebay search for it.

David Hansen

madscientist - 8-10-2002 at 19:24

Actually, it's not possible to prepare I2 by action of H2SO4 and H2O2 on NaI. Iodine is oxidized by the sulfuric acid.

Polverone - 8-10-2002 at 20:05

Actually, I do think IodineForLunch's method will work, though I have always used HCl, not H2SO4, for this procedure. In any case, mixing concentrated H2SO4 and H2O2 is asking for trouble, unless you really know what you're getting into. I know that heating an iodide with a mixture of sodium hydrogen sulfate and manganese dioxide will form iodine vapor, which can then be condensed on a cold surface. I have also prepared iodine from KI, HCl, and H2O2. Be aware that the form the iodine precipitates in (if using this last method) is very fluffy, with a high surface area. It will rapidly sublime at room temperature. You must therefore keep it in an airtight container. The iodine vapor will penetrate thin plastic, so you can't keep it in (say) a plastic bag. A glass bottle with a screw-on lid works well.

If some e-bay guy is selling 500 g NaI for $15, that's a real bargain.

I wouldn't have extracted the iodine with toluene, although it was a decent idea. Toluene evaporates relatively slowly, and your iodine will sublime as the toluene disappears. Condensing the vapors on a coldfinger (as you considered) may allow you to salvage the iodine.

Chlorine will indeed oxidize iodides to iodine, but it's kind of an extreme method for such a simple problem, and iodine can also form compounds with chlorine.

Overall, I think the mineral acid + H2O2 oxidation is the best idea. You might evaporate your iodide-containing fluid first so you don't have so much diluting liquid.

a_bab - 9-10-2002 at 00:06

Yeah, and besides, toluene doesn't disolve that much iodine after all. The best way is like Polverone said (H2O2, HCl and a iodine salt) AND the fluffy iodine must be sublimated and recondensed in order to get bigger crystals.

Tengo - 9-10-2002 at 02:16

How much water can I evaporate from the original solution (what is the solubiltity of I3-) before the iodine starts evaporating?
What would be a resonable temperature?

Cl gassing an iodide

pROcon - 11-10-2002 at 04:34

Polve: You say that compunds can be forned when oxidizing an iodide with chlorine, what compounds mate?

I'm going to use a Cl gas produced from a hypochlorite and HCl, then bubbled through H2O [to wash off any excess HCl] and passed through calcium chloride, then a tube leading to a KI solution, would this be alright?
Can the KI solution be over gassed or will it just cease precipitating I2?

I know it's probably overdoing it but it'll be awesome fun - what this is all about to me!

See for chlorine gas with bleach and HCl:-

pRO :)

Tengo - 11-10-2002 at 08:36

Too much Cl2 => ICl then ICl3
So you have to stop at I2...

pROcon - 11-10-2002 at 09:23

Tengo: Thanks!

So is it the typical nature of gassings of this sort that thare will be a composite mixture of I2, and ICl*. Or will all the I2 available in the solution precipitate

i.e does it rely on uncontrollable conditions like Cl atoms colliding with KI atoms, or will the Cl gas cause the KI solution to contain a certain conc% of Cl to oxidize to I2, then a certain conc% to make steps?

(The second would be preferable thats why I'm asking)

Tengo - 11-10-2002 at 14:17

Use a two-phase system!
Follow this link...

vulture - 12-10-2002 at 09:10

Oxidation with NaClO or KMnO4 might be worth a try also.

Nick F - 12-10-2002 at 12:35

Last time I did it I used NaOCl (5% bleach) and HCl (15% brick cleaner), although the large volume of water was compensated for by using a more concentrated solution of NaI (no extra water was added, it was dissolved in the HCl). It worked pretty well, it ppted the I2 as crystals that were less than 1mm in all dimensions. I purified and recrystalised it using a quickfit leibig condensor with a slightly modified stopper in one end - the stopper was hollow, and I ground off the front, forming a small cup that fits exactly into the end of the condensor. This was filled with iodine and heated in an oil bath, while cold water was running through the condensor jacket. This produced angular plates, around 5mm wide, that were easily scraped out and collected. This simple apparatus seems to work quite well for batches of a few grams, and is easily attached to a vaccuum pump for sublimating less volatile compounds which could be broken down by heat (I've used it with caffeine, for example).

Thanks Tengo

pROcon - 14-10-2002 at 07:57

I went the electrolysis route, awesome fun.

The carbon electrodes dissolved, which surprised me. I got some foam too. Reduced the voltage, seemed to help.

I used 14 grams of KI dissolved in 105ml of spring water (hehe!).

I piped the H2 out window with PVC.

I filtered out the carbon that had dissolved, and now have a bright red solution. But I added a bit more H2O so it's not quite as bright, just in case it was over saturated.

So I now have a conc. solution of H2O(l), KOH(aq) and I2(aq) I think.

How much HCl (300grams/litre) should I use to acid-base help on this anyone?

This is the balanced equation if that helps (youll find all this at site Tengo offered):

2I--->(aq) I2(s) + 2e-2H2O(l) + 2e- --> 2OH-(aq) + H2(g)

net reaction: 2I-(aq) + 2H2O(l) -->I2(s) + 2OH-(aq) + H2(g)

madscientist - 14-10-2002 at 09:13

The bright red color is due to I3- ions.

I- + I2 ----> I3-

Tengo - 14-10-2002 at 10:00

I went the H2O2/HCl route...
But I ran into some problems...
To the original (deep brown) solution (500 ml) containing 5% iodine and 15% Acetic acid, I added 20ml HCl (30% conc.) and 100 ml H2O2 (20% conc.).
The solution is still deep brown and nothing has precipitated...
What have I done wrong and how do I salvage the I2?

Tengo - 14-10-2002 at 15:40

Now I know why the iodine didn't precipitate. The solution I had was a iodophor. Is there some way now I can salvage the I2?
I tried toluene and it seemed to work (the organic phase turned purple), but the water phase turned milky white...
When I tried to extract the I2 earlier (before adding H2O2 and HCl) the water phase turned orange.
Now I don't really know what the H2O2 has done, and having respect to peroxides, I wonder if I dare to extract the I2 with toluene.
Thankful for any ideas...

pROcon - 15-10-2002 at 01:07

MS, damn thanks for that. so it's most likely a solution of OH-, I3- and H2O?
It's still a definete red colour after more H2O is added so I'm guessing your right with the I3.

Well for starters, no I2(s) formed in the solution through the electrolysis process, so I must have done something wrong.

If theres I2 and I3 then it'll probably be messy to try recover most of it, should I keep it for anything or toss it?

I think ill try potassium monopersulfate compund (oxone) on a KI solution, hopefully that will be straight forward, safe and quick. The results are supposed to be quantitative too, but ill probably end up over oxidizing that too. Because I measured accurately for the electrolysis with a volumetric cyllender and scales.

Another method of recovering iodine

trinitrotoluene - 17-12-2002 at 18:59

For those people who live near the ocean you can collect some sea weed dry it and maybe extract the iodine by heating it and recrystalizering the iodine crystals. But i'm not sure how much you will get though.Lucky for my I live next to the San Fransico Bay and i live like maybe 1/6th of a mile from the beach.But i've been only seeing lots of green seaweed washing onto the shore.It says that brown or purple seaweed have the most iodine. But soon i will do some experenments to try to extrace the iodine out og the sea weed. Any suggestions about extracting it out of seaweed?

madscientist - 17-12-2002 at 20:15

The iodine in the seaweed is probably in the form of sodium iodide. So, this is my suggestion: add the seaweed to some hydrochloric acid; filter, and then add H2O2, which likely would precipitate some elemental iodide. Of course, this is all assuming that the iodine in the seaweed is in the form of NaI, and is easily converted into HI and dissolved in water by the action of HCl on the seaweed.

Marvin - 18-12-2002 at 09:35

You arnt thinking big enough unfortunatly, exactly the same mistake I made when I tried to extract iodine from seaweed duriing a holiday.

The seaweed needs to be washed with clean water and then burned to ash at a low temp, then the ash is extracted with water, the soluable material is treated with sulphuric acid, in excess as a lot of carbonates are present at this stage, an oxidising agent is added and the iodine distilled off.

Approx 4 kilograms of iodine can be recovered from 1 ton of ash. To make 1 ton of ash you require about 22 tons of moist seaweed.

I used a bag of seaweed which is why I only ended up with a brown coloured solution for my troubles. Anyone wanting actual solid iodine, in *gasp*, visible amounts would do well to look up a tried and tested process for this before starting work.

Iodine from tincture and soloutions

trinitrotoluene - 17-2-2003 at 21:07

Just a week ago I had successfully extracted I2 out of tincture.Its 30ml of soloution. 2% I2 2.4% NaI 47% alcohol and the rest is purified water.I took the 30ml of soloution and added 5ml of HCl to it, then poured it into 150ml of 3% H2O2 soloution, the I2 precipated. IT was filtered with a coffee filter , washed with distilled water, then dried in a container filled with NH4NO3. After that I had gotten 1 gram of I2. Seeing how its expensive because the cheapest I can find 30ml of tincture was $1.19 a bottle. So I decided to extract out of those larger bottles in a bottle of Betadine it has 237ml of soloution I can get it for $4.99. It contains 10% povidone Iodine which is equivalent to 1% avaliable iodine. I'm not sure if its 1% I2 or 10%I2. But the other stuff that was in it is citric acid,disodium phosphate,glycerin,nonoxynol-9,sodium hydroxide, and pruified water.So I took 30ml and did what I exactly did with the tincture treatment with HCl then precipitate with H2O2. But the soloution remained the same. After adding the HCl the mixture because thick. But after adding to the H2O2 nothing happand.I poured out the soloution and no I2 crystals just found a few slimy golbs. I beleave thats more concentrated I2. But I beleave the golbs are the nonoxynol-9 which is glycols. Next time I will try to extract the I2 with a reflex condenser when I build one.