Sciencemadness Discussion Board

Iodine drying

thesmug - 15-3-2014 at 12:13

I was making some iodine earlier today (via KI + HCl) and after filtering it, it was still really wet. I know it's insoluble in water, so drying should be easy, but it's taking forever. Is there any way of drying it (not with sulfuric acid) that would take less time, but also wouldn't risk subliming too much of it?

HgDinis25 - 15-3-2014 at 12:24

You could use a dessicator chamber or, much easier, one of nurdrage's dessicator bag:
http://www.youtube.com/watch?v=XJFfS_YbbYI
He explains very well how it works.

Texium - 15-3-2014 at 12:52

It doesn't seem like a desiccator would exactly fit the taking less time parameter, as it may take many days.
The best and fastest method for drying the iodine is probably still by using concentrated sulfuric acid, as described in this thread:
http://www.sciencemadness.org/talk/viewthread.php?tid=22658

thesmug - 15-3-2014 at 12:53

Thanks! How long would about 5g of I2 take to dry in a desiccator with NaOH?

Texium - 15-3-2014 at 12:59

Well, it depends on how wet the iodine is. I guess since iodine is not water soluble, if you got enough of the water off of it, it may not take too long. Ambient humidity can also play a role when you first place the sample in the desiccator, so keep that in mind if it doesn't seem to be drying at first. It may still take hours.

thesmug - 15-3-2014 at 13:08

Quote: Originally posted by zts16  
Well, it depends on how wet the iodine is. I guess since iodine is not water soluble, if you got enough of the water off of it, it may not take too long. Ambient humidity can also play a role when you first place the sample in the desiccator, so keep that in mind if it doesn't seem to be drying at first. It may still take hours.

Is there risk of loss by sublimation when letting it sit so long? I ask because my iodine was subliming as soon as I removed it from the water.

Texium - 15-3-2014 at 13:38

That is definitely a risk, which is why I originally suggested not using a desiccator. If you had no other options though, it may finish drying before you lose too much through sublimation. It depends on how much iodine you are willing to lose.
You could also possibly cool it down a bit, which would decrease the rate of sublimation, although it would also probably decrease the rate of desiccation.

HgDinis25 - 15-3-2014 at 13:57

You will always lose more iodine when you let it sit than using a dessicator bag. If you use, for example, 3 cups of powdered NaOH (to increase surface area and increase location of the NaOH inside the bag) it could take you less than 12 hours.
You could also try to wash it with pure methanol or pure ethanol. The alcohol would drive away the water and would be a lot easier to evaporate at room temp.

Texium - 15-3-2014 at 15:53

Oh yeah, I didn't even think about alcohol washing. That's probably your best bet.

BromicAcid - 15-3-2014 at 16:41

Hopefully you didn't think of alcohols because of how soluble iodine is in alcohols. For example, 19.35 wt% in EtOH. And drying in a desiccator, most people that have dealt with iodine know how much it loves to sublime, there will be losses, possibly significant depending on how long you dry, some to the NaOH and some to the inside of the lid of the dissector. Question is, do you need dry iodine? You could sublime it yourself to try to dry it, patting with a paper towel will remove the bulk of the water, but sulfuric acid is still your best way to go.

HgDinis25 - 15-3-2014 at 16:45

Quote: Originally posted by BromicAcid  
Hopefully you didn't think of alcohols because of how soluble iodine is in alcohols. For example, 19.35 wt% in EtOH. And drying in a desiccator, most people that have dealt with iodine know how much it loves to sublime, there will be losses, possibly significant depending on how long you dry, some to the NaOH and some to the inside of the lid of the dissector. Question is, do you need dry iodine? You could sublime it yourself to try to dry it, patting with a paper towel will remove the bulk of the water, but sulfuric acid is still your best way to go.


I've dried iodine my making a quick wash with chilled methanol, in a vacuum filtration apparatus. It worked like a charm, but yes, iodine is soluble in the simplest alcohols.

thesmug - 15-3-2014 at 16:58

Thank you all for your suggestions. I have also dried it for a while now and (sadly) lost most of it in my filter paper and by sublimation. I will retain your suggestions for when I do it again later. I also know that I2 is soluble in toluene, so wouldn't you be able to dissolve it and let the toluene evaporate?

HgDinis25 - 15-3-2014 at 17:17

Quote: Originally posted by thesmug  
Thank you all for your suggestions. I have also dried it for a while now and (sadly) lost most of it in my filter paper and by sublimation. I will retain your suggestions for when I do it again later. I also know that I2 is soluble in toluene, so wouldn't you be able to dissolve it and let the toluene evaporate?


Why not dissolve it in methanol instead? It evaporets quicker. But if you don't have it, toluene should work too. Or use toluene to do a wash like I described before. Also, I wonder if it's soluble in glycerin. If it is, then heating a solution of iodine in glycerin should leave water behind and sublime iodine directly out of the glycerin solution (is this mere speculation and nonsense, or can it happen)?

BromicAcid - 15-3-2014 at 18:16

Dissolving in toluene would let you phase off the water....

thesmug - 15-3-2014 at 18:49

Quote: Originally posted by BromicAcid  
Dissolving in toluene would let you phase off the water....

I knew that, which is why I suggested toluene as opposed to an alcohol.
[EDIT] Is there any solvent that you would be able to recrystallize iodine with?

[Edited on 3/16/14 by thesmug]

Mercedesbenzene - 15-3-2014 at 19:42

What I do, and it seems to work fairly well, is that I take the wet iodine and put it into a sealed bottle for storage with 4A molecular sieves. The 4-8 mesh sieves are quite easy to remove as well due to their size.

thesmug - 15-3-2014 at 19:45

Quote: Originally posted by Mercedesbenzene  
What I do, and it seems to work fairly well, is that I take the wet iodine and put it into a sealed bottle for storage with 4A molecular sieves. The 4-8 mesh sieves are quite easy to remove as well due to their size.

All you have to do is put them in the same container? I will try that!

Bezaleel - 19-3-2014 at 09:57

Yet something else you may try, but this is definitely NOT a quick method, is to add some powdered CaCl2, and put that in a well closing vial. When you place the vial in a warm environment, and cool one side of it, then iodine will crystallise on the cooled side of your vial over time, while the wetted CaCl2 will remain on the bottom of your vial.

The setup is primitive, but does work (to my own astonishment). You'll have an almost 100% yield and shiny crystals. My setup was to put the bottle next to a cold water pipe in the room where the boiler is (that heats the room). After a few months, the separation was complete.

I guess you could speed up the method, if you put the mixtue in a long tube that is closed on one side. Putting in the mixture and very gentle heating at the closed end, may sublime your iodine which will crystallise in the cold region of the tube. Keep the tube horizontal.

Texium - 19-3-2014 at 14:18

Quote: Originally posted by Bezaleel  
Yet something else you may try, but this is definitely NOT a quick method, is to add some powdered CaCl2, and put that in a well closing vial. When you place the vial in a warm environment, and cool one side of it, then iodine will crystallise on the cooled side of your vial over time, while the wetted CaCl2 will remain on the bottom of your vial.

The setup is primitive, but does work (to my own astonishment). You'll have an almost 100% yield and shiny crystals. My setup was to put the bottle next to a cold water pipe in the room where the boiler is (that heats the room). After a few months, the separation was complete.

I guess you could speed up the method, if you put the mixtue in a long tube that is closed on one side. Putting in the mixture and very gentle heating at the closed end, may sublime your iodine which will crystallise in the cold region of the tube. Keep the tube horizontal.



Wow, that sounds like a really cool method to use. I'll definitely try that when I isolate some iodine.

Fantasma4500 - 20-3-2014 at 05:44

dont use acetone on it tho..

you can take the filter paper and fold it in half, then dub cotton or tissue paper on the sides of it to remove water quite effectively, this will reduce drying time alot

also if you use dessicator bag dont dump plastic into it, it will take several months and may never even become perfectly clear again.. ~~speaking of experience~~

CaCl2 + iodine inside one flask is a quite interesting idea tho, simplicity is underrated