Sciencemadness Discussion Board - Drying Iodine

Drying Iodine

Nickbb - 10-12-2012 at 13:52

How can you dry iodine without losing any product? I typically synthesize it by adding H₂O₂ and HCL to colorless iodine tincture (simply a solution of iodine salts). The iodine is wet after doing this, and if you sit it out to fully dry most of it would have evaporated. Would sublimating it work?

bahamuth - 10-12-2012 at 15:01

Best way is to melt the iodine under concentrated sulfuric acid, and let cool.

That way you can just flush off the remaining sulfuric acid when you remove the now solid iodine chunk without retaining much if any water water.

I believe the yields would be more or less quantitative.

I've actually done this and it is by far the best way I've found.

Also worth mentioning is that this information is in several of the threads contained in this forum, but I didn't bother an extensive search.

Endimion17 - 10-12-2012 at 15:04

You don't synthesize iodine. You isolate it. It's an element, not a compound.

Work on a larger scale. Wash it with some cold water to remove the acid and press dry the isolated sample using a filter paper, pack into a small bottle (to avoid sublimation loss) which fits both the sample and a vial of solid sodium hydroxide. Keep replacing the vial with fresh NaOH until after 24 hours it doesn't show signs of deliquescence. Poke the iodine sample now and then to ensure there are no trapped bubbles of water. NaOH will trap the water and hydrogen chloride leftovers.

You get crude iodine which is enough pure for most amateur applications. Further purification steps are intimate mixing with freshly fused quicklime and sublimation on a cold finger or less complicated apparatus.

Larger amounts and small glassware, remember.

Nickbb - 10-12-2012 at 16:20

Alright thanks guys. I'll try both methods and see how they work the next time I isolate iodine.

mr.crow - 11-12-2012 at 11:03

I think the word synthesize can still be used. The compound is I2 and an oxidation reaction is happening from iodide. But anyways that's besides the point.

Yes melt it under H2SO4, it forms an unreal looking solid chunk. Easy!

Then put it in a beaker on a hotplate and sublime/boil it onto a flask with cold water. Not as easy but incredibly beautiful to watch.

Subliming wet iodine doesn't work, the water condenses too.

Endimion17 - 12-12-2012 at 04:17

Quote: Originally posted by mr.crow

I think the word synthesize can still be used. The compound is I2 and an oxidation reaction is happening from iodide. But anyways that's besides the point.

Yes melt it under H2SO4, it forms an unreal looking solid chunk. Easy!

Then put it in a beaker on a hotplate and sublime/boil it onto a flask with cold water. Not as easy but incredibly beautiful to watch.

Subliming wet iodine doesn't work, the water condenses too.

No, it can not. I<sub>2</sub> is an element. Elements can not be chemically synthesized, but can be synthesized using nuclear processes.
It's one of the staples in chemisty, and before YouTube started spreading this bad "synthesize elements" meme via amateur chemistry videos, nobody officially talked about synthetizing chemical elements.

The thing with the beaker and flask filled with hot water is a school demo experiment used to show how iodine vapors can directly deposit (also teachers stubbornly spread disinformation that iodine doesn't melt, which is incorrect).
If one wants to purify iodine, and yields are important (because it's valuable and hard to get), beakers and flasks are not sufficient because losses are substantial, and the deposited crystals are so thin and have such large surface they sublime easily.

This is needed. Actual ground glass joint apparatus is quite expensive, but you can do it using regular test tubes of different sizes and some glass tubing. I've purified naphtalene in a similar apparatus.
The smaller the available volume is, the larger the yields become.

vmelkon - 13-12-2012 at 09:38

How about using anhydrous CaCl2? Mix the CaCl2 and iodine as best you can and then distill off the iodine.

neptunium - 16-12-2013 at 14:04

also worth trying , I mixed the slushy I2 with conc sulfuric acid and DCM (di chloro methane) separate with a sep funnel and let air dry (with a fan)
the remaining solution of DCM and I2, I2 remain as dry crystals . never had to heat anything!

thebean - 16-12-2013 at 15:13

Quote: Originally posted by bahamuth

Best way is to melt the iodine under concentrated sulfuric acid, and let cool.

Do you have a video or picture of this, I'd be quite interested in seeing it and possibly trying it myself.

elementcollector1 - 16-12-2013 at 15:35

Curiously, when I placed some of the 'wet' iodine under sulfuric acid, it dissolved to a black sludge that I couldn't separate the iodine out of.

Pyro - 16-12-2013 at 16:23

first the wet I2 slush is put into conc. H2SO4 (this can spatter and make I2 vapor depending on how wet it is)

then it is heated until it melts

The beaker is held at around 45* for the I2 to cool

The H2SO4 is drained off and the lump of I2 is removed from the beaker with a dissection needle (force it between the I2 chunk and the beaker wall)

the I2 is surprisingly dense, that piece weighs in it 53.9g

It was later re-sublimed using small beaker and a flask of cold water to give little chunks (if you leave the flask on long enough the fine crystals will become a thick (1-2mm) layer which can then be broken up and stored)

(this was from more than one batch)

[Edited on 17-12-2013 by Pyro]

elementcollector1 - 16-12-2013 at 16:49

Nice. I actually prefer the lump form - it seems so odd that iodine can look like that.

Pyro - 16-12-2013 at 16:51

well yes, it is pretty, but re-sublimation makes it purer. i think its like 99,9+% if you re-sublime it once.

MrHomeScientist - 17-12-2013 at 09:48

I tried to sublime iodine once but kept getting water condensation on my cold flask that kept everything wet. Does this get eliminated with the sulfuric acid drying step? My iodine wasn't damp at all, but I do live in a humid climate.

thebean - 17-12-2013 at 13:41

Pyro, when you say 45* do you mean Celsius or Fahrenheit? This looks like a very interesting procedure, but does the it really dry the iodine?

Pyro - 17-12-2013 at 13:53

when I say 45* I mean an angle, when I say 45*C I mean temperature. you want the I2 to form a lump, not a layer on the bottom of the beaker (I made this mistake, it never comes out

)

I had to remove the flask of ice every now and again to get the I2 cake off, when I did that I wiped it with a paper towel just in case.

unless you dried your I2 in a dessicator or under H2SO4 it will always be a little bit moist

thebean - 17-12-2013 at 14:47

Quote: Originally posted by Pyro

when I say 45* I mean an angle, when I say 45*C I mean temperature. you want the I2 to form a lump, not a layer on the bottom of the beaker (I made this mistake, it never comes out

Is this because H2SO4 "picks up" the water? Like in a nitration mix?

Pyro - 17-12-2013 at 16:23

yep, and when you melt it it fuses into one solid block that you can dry manually

zenosx - 17-12-2013 at 17:32

I will have to try the H2SO4 method. I have always used a filter paper full of dessicant sealed around the top of a beaker full of I2 to dry, then sublimed it twice using a cold finger made from a test-tube and some glass tubing that works very well.

I am sure I lose much more than the H2SO4 method, I still have about 3 bottles to do an extraction from, will do this next time.

Fantasma4500 - 18-12-2013 at 04:55

i was just about to imply that you should wetten it with acetone so that it would evaporate off at low temperature but then i recalled that.. acetone and iodine is not a good idea

keep that in mind, please (:

neptunium - 18-12-2013 at 06:03

Quote: Originally posted by Antiswat

i was just about to imply that you should wetten it with acetone so that it would evaporate off at low temperature but then i recalled that.. acetone and iodine is not a good idea

keep that in mind, please (:

especially mixed with sulfuric acid!! no I used DCM and it work great !

neptunium - 25-12-2013 at 17:53

I tried the sulfuric methode and did get the lump of I2 shown on your picture ... however, how do you get rid of the sulfuric acid the lump is still wet with it!
i put it in paper towel and it did dry it somewhat but the inside is still very much wet with H2SO4....

Pyro - 26-12-2013 at 14:50

You pour out the H2SO4, dislodge the chunk of I2 and wash it with water. Then you can dry the surface with a paper towel. Or you can let it dry on air. I left my chunk out for 4 days and only lost 0,1g

agent_entropy - 16-4-2015 at 06:13

I just tried the sulfuric acid method and had the same problem as neptunium (2 posts up) where I can easily dry the outside of the lump of I2 but the inside is porous and the pores are filled with H2SO4. Does anyone have any suggestions on how to prevent this porosity or how to remove the H2SO4?

I was thinking about grinding up the lump into coarse granules and blotting them dry with a paper towel before re-sublimating. Anyone have a better idea?

[Edited on 16-4-2015 by agent_entropy]

agent_entropy - 20-4-2015 at 12:10

I found a way to get rid of the remaining H2SO4:

The lump of I2 was ground into coarse chunks and blotted as dry as possible. Then the I2 was melted in a loosely stoppered flask without the H2SO4 blanket and the molten I2 was poured into a shallow glass tray. The rapid cooling appeared to have excluded all of the remaining H2SO4 from and the acid was rinsed off of the cooled I2 film.

An improvised sublimator was fashioned using a test tube through a hole in a rubber stopper as a coldfinger and suspending it in the middle of a flask. The flask was heated on a hotplate while coolant was supplied to the coldfinger. However, this produced small needle-like crystals of iodine (not the best form due to the high surface area).

The remaining remaining I2 was placed in a sealed jar and placed atop a laboratory oven that is always on (in order to provide a small temperature gradient), and there are now nice granular crystals slowly growing on the upper walls of the jar.

agent_entropy - 15-5-2015 at 07:48

Now that I have finished, I thought I would share my whole experience with isolating I₂.

A few months ago when I was cleaning out a laboratory I found 2 bottles of KI solution that had expired a LONG time ago and were VERY yellow in color. Check out the expiration dates.

I decided to precipitate the iodine by adding nitric acid as I have a ready supply and it would not form any insoluble salts with potential impurities (also it acts as both the acid and the oxidizer). After rinsing with DI water, a cake of very small, very wet I₂ crystals was left.

The iodine was then dried by fusion under concentrated sulfuric acid to yield a solid lump (as described by others above). However, this lump had channels and pockets full of sulfuric acid inside it.

I did my best to get the majority of the acid out by picking away at the channels and rinsing out the acid, but when I broke the chunk in half I found a bunch of acid pockets still inside.

I crushed the chunk into granules and blotted them as dry as possible. Then melted the chunk into liquid without the sulfuric acid blanket and poured the iodine into a cool shallow pan. This seemed to exclude the remaining sulfuric from the bulk iodine film. I then scraped the film out of the dish and proceeded to sublimate it.

At first I tried a makeshift sublimator, as described in a previous post, but this produced very small needle-like crystals with high surface area and high susceptibility to static electric charge. This made them very difficult to handle and was unsatisfying.

I now know that if you want to isolate iodine as high-quality, large-granule, easy to handle crystals AND you want to incur as little loss as possible, then the name of the game is low heat and PATIENCE.

I placed the iodine in a jar and sat it on the top of a laboratory oven near the vent.

As crystals collected on the slightly cooler upper surfaces within the jar I scraped them away and collected them. After about a month of doing this I collected the last of the iodine crystals.

I also collected a small amount of brown powdery material from the bottom of the sublimation jar consisting of the impurities that the sublimation process removed. I think it’s probably either a sulfate or some organic contaminants from blotting away the sulfuric acid.

A final piece of advice: Use plastic tools to scrape the iodine or handle it in any way, because, as I discovered, iodine attacks stainless steel. In the picture you can see how the iodine has damaged the finish and whatever iodide salts formed by reaction with the stainless are absorbing moisture from the atmosphere and becoming liquid (thus, the smeared appearance). http://cdn.intechopen.com/pdfs-wm/46242.pdf

agent_entropy - 5-6-2015 at 07:10

Neptunium's comment about drying a solution of I2 in DCM over sulfuric acid and letting the DCM evaporate got me thinking about other solvents that I2 might be soluble in. So I tried dissolving I2 in liquid butane. It didn't dissolve very well since the butane was very cold as it was boiling away. This made me want to produce a saturated solution of iodine in butane (actually isobutane, from a lighter refill). I managed to make a saturated room temperature solution of I2 in liquid butane under pressure inside a small soda bottle. The solution is definitely saturated because there are a few small crystals of I2 in the bottom that will not dissolve.

After storing the solution for about a week the bottle was looking pretty rough.

So I did some experiments with the solution... First, some of the solution was poured onto a watch glass to see what would happen. Predictably, the butane started boiling away and small I2 crystals began forming and depositing on the glass. The watchglass was left until any material that could boil away or sublimate was gone. What was left was a very small amount of brownish residue, likely iodinated products of impurities in the butane.

Since halogens tend to inhibit fire, a small sample was ingnited on a watchglass. As is clear from the picture, not enough I2 vapor was rising to inhibit combustion. After the butane had burned away, I2 crystals remained on the glass.

The rest of the solution was allowed to evaporate in a flask.

I wonder what other solvents with a boiling point below room temperature might be interesting or useful for dissolving iodine. Certain freons? Carbon dioxide? Even though liquid nitrogen is non-polar I suspect that it would be too cold to dissolve any appreciable amount of iodine, and I don't know of any way to keep it liquid at room temperature since the pressure would be insanely high.

AJKOER - 7-6-2015 at 11:46

Would simply treating a thin layer of moist iodine in a vessel with frigid air and stirring periodically, effectively dry the iodine? Note, the iodine is in a container to capture any sublimated I2 as per Wikipedia http://en.m.wikipedia.org/wiki/Portable_water_purification, to quote:

"Iodine crystals will sublimate if exposed to air for long periods of time".

If feasible, one could avoid adding organic contaminants (or, for that matter, other drying agents).

My logic is that the reaction of I2 and water, namely:

I2 + H2O = HI + HIO

is moved more to the left for neutral water (and more so, by adding, say CO2) as the temperature is lowered forming solid ice, which hopefully sublimes and is successfully removed from the vessel in the blast of cold dry air. To quote from a reference ( https://www.google.com/url?sa=t&source=web&rct=j&... ):

"The air is so dry that when it hits a snowpack, the frozen water evaporates, going directly from the ice to vapor and bypassing the liquid phase entirely. This is called sublimation, and it's a common way for snow to disappear in the arid West."

Note, if one instead opts for heating, would not more moist iodine be lost in the form of HI and HIO3 ?(the latter from the disproportionation of 3 HIO to HIO3 + 2 HI and possible subsequent reaction with 2 more HIO resulting in HIO3 + 2 I2 + 2 H2O from 5 HIO). However, I should add that the iodine sublimation process (which occurs at about 180 C) itself can result in a high purity product, although thermal decomposition of HIO3/I2O5 at higher temperatures (over 300C ) can produce some iodine oxides as well (see https://docs.google.com/viewer?url=patentimages.storage.goog... ).

Interestingly, my curious suggestion is a complete turn around from the normal suggestion of employing warm iodine sublimation with the primary focus on the sublimation of the ice instead!

The good news is that if this methods does not work, little product is lost and, upon warming to RT, you are where you started, the same purity moist iodine.

Unfortunately, I do not have sufficient iodine on hand to test my curious hypothesis. In any event, I would not argue that the proposed process is the most economical, rapid, highest purity or scalable, but does obviate the need for other reagents.

[Edited on 8-6-2015 by AJKOER]

agent_entropy - 8-6-2015 at 04:13

An interesting reversal of the paradigm, AJKOER. Sounds like freeze drying (lyophilization) could work, provided that the water is more volatile than the iodine under whatever conditions are employed.

All of the freeze drying I have done in the past involved freezing with liquid nitrogen followed by gentle warming (<60 C) under vacuum, but I like the idea of a dried gas stream to drive the sublimation of water. Such a stream could remove the need for heating and vacuum if it is sufficiently dry to avoid depositing more moisture by condensation on the chilled sample.

Molecular Manipulations - 8-6-2015 at 09:36

Nitrogen has a critical temperature of -147 degree's C, no amount of pressure will mantain it as a liquid above that temp.
Sublimating iodine using boiling water as a heat source is how I purify it - never had a problem before.

confused - 8-6-2015 at 18:21

Quote: Originally posted by MrHomeScientist

I tried to sublime iodine once but kept getting water condensation on my cold flask that kept everything wet. Does this get eliminated with the sulfuric acid drying step? My iodine wasn't damp at all, but I do live in a humid climate.

Same thing happened to me, when i tried that, does sulfuric acid prevent that from happening?

agent_entropy - 9-6-2015 at 05:31

@Molecular Manipulations: Right! I forgot about the critical point. Silly me!

@confused: Sulfuric acid drying will probably not prevent the water condensation, the water is probably condensing from the atmosphere. You can try to prevent it by doing the sublimation on a cool, dry day (low humidity), or by doing the sublimation under vacuum, or by sublimating at low temp inside a sealed jar.