Jor
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easy iodine/hydroiodic acid from iodoform
I was just doing a iodoform synthesis, and I started heating the material. As seen on woelen's website, heating of iodoform gives I2, HI and C.
Now, for me I2 is not hard to acquire (about 20 EUR for 250g, I still have 100g and get new 250g in 2 weeks), but for many of us it is.
I heard people trying to make I2 in aquous environment and having difficulty drying it, etc.
How about making I2 from iodoform. Making iodoform from KI or NaI only requires acetone and bleach, all very cheap materials. The yield is good and a
very easy preparation.
Remaining iodides in solution can be recovered by just boiling down the solution, leaving a mixture of iodides and acetates (if started from acetone).
Now this iodoform van easily be dried, and then be strongly heated. It readily decomposes. The I2 can be sublimed on a cool surface, and the HI can be
absorbed in water.
Seems to me that you get easy, dry I2.
Also easy hydroiodic acid. No messing with H2S, or using expensive H3PO4.
Only problem is the carbon. it ruins your flasks. But using cheap glass and working on a larger scale should compensate for the costs.
Ideas?
[Edited on 2-9-2008 by Jor]
[Edited on 2-9-2008 by Jor]
[Edited on 2-9-2008 by Jor]
[Edited on 2-9-2008 by Jor]
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Jor
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Vogel gives a 3,5g yield of iodoform from 6g of KI.
Not all the absolute mass of iodine in the KI is in the iodoform. The reaming mass is in solution as I-. This can be recovered.
35g of iodoform can give about 22,5g iodine and 11,25g hydrogen iodide.
So per run of 60g KI one can obtain 22,5g iodine and 11,25g HI, wich is about 11,5mL 57% HI. This is not much iodine, but at least it's easy and dry.
And ofcourse the Iodides remaning in solution can be recovered.
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ScienceSquirrel
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You can easily prepare iodine from an iodide salt, eg potassium or sodium iodide, by dissolving it in water adding the calculated quantity of
sulphuric acid and then adding 35% hydrogen peroxide.
The iodine separates out as purple / black crystals, it can be filtered, sucked dry and then dried over calcium chloride.
The iodine will be at least reagent grade, if you want to get 'cheffy', you can sublime it.
A lot of people have problems with iodine because they are starting from povidone iodine, tincture of iodine etc. The other things in there make a
mess of the preparation.
The other thing is that you must oxidise all of the iodide to iodine, iodine is a lot more soluble in water in the presence of iodide due to the
formation of the triodide anion.
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Jor
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But still, Im thinking this can be an easy way to prepare hydroiodic acid, with iodine as a bonus. This is, assuming that CHI3 actually decomposes to
HI. (???)
HI can very hardly prepared by H3PO4, and H2So4 method does not work (oxidation of iodide, formation of I2,H2S,SO2,etc), and H2S method is very
dangerous.
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ScienceSquirrel
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| Quote: | Originally posted by Jor
But still, Im thinking this can be an easy way to prepare hydroiodic acid, with iodine as a bonus. This is, assuming that CHI3 actually decomposes to
HI. (???)
HI can very hardly prepared by H3PO4, and H2So4 method does not work (oxidation of iodide, formation of I2,H2S,SO2,etc), and H2S method is very
dangerous. |
Good point.
An easy way of making hydroiodic acid would be nice.
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Ketone
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| Quote: | Originally posted by ScienceSquirrel
You can easily prepare iodine from an iodide salt, eg potassium or sodium iodide, by dissolving it in water adding the calculated quantity of
sulphuric acid and then adding 35% hydrogen peroxide. |
IMO, that seems a bit wasteful, especially as 35% hydrogen peroxide can be hard to get in many places.
I'm thinking more like a "halogen replacement" reaction.. (Probably not the correct name in english.)
But in short: To oxidize the iodide with a more electronegative halogen.
I've done this with bromides and it's really easy.
And I can't think of anything that should prevent it from working on iodides.
(On the contrary, since iodine is less electronegative than bromine.)
Another benefit is that Cl2 is quite easy to generate with cheap and easily available chemicals.
Cl2(aq) + 2KI(aq) -> 2KCl + I2
Only problem I can see would be the formation of triiodide, but if you use a slight excess of chlorine, it shouldn't be a real problem.
As for HI, I read somewhere that you can actually make it (and H2SO4 at the same time) from I2, SO2, and H2O.. I don't put too much faith in that
reaction though..
Guess it could be theoretically possible but it sounds a bit too good to be true. And I might have read it on wikipedia even..
But I intend to try it all the same (as I'm going to make sulfur oxides for H2SO4 production anyways) when I've finally raised enough money to buy
some new glassware. Don't hold your breath though, considering my income (almost zero), that might be a looong time.
[Edited on 3-9-2008 by Ketone]
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Klute
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The probem withthe Cl2 method is the production of mixed halogens, ICl in the case of iodides IIRC. This can or cannot be a problem depending on what
you plan on using your iodine. ICl is a nasty toxic volatil solid, not something nice to handle.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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not_important
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That is the Bunsen Reaction
2H2O + SO2 + I2 <=> H2SO4 + 2HI
an equilibrium that doesn't allow the making of concentrated HI without a large excess of at least one of the left hand reactants, meaning I2 and SO2
(under pressure) as excess water dilutes the products. As the concentration of the acids goes up, the sulfuric acid begins to oxidise the hydroiodic
acid, so with ordinary lab methods you'll not get high concentrations. however the mixture is useful for converting alcohols to iodides
Another reaction used is
I2 + H2S => 2 HI + S
the sulfur being filtered out using fritted glass or glass wool filters, then the acid distilled to get constant boiling hydroiodic acid. See Vogel,
Practical Organic Chemistry 3rd edition; Inorganic Synthesis Volume 1 page 157.
As for using chlorine, as Klute said you'll get some ICl in your product, it will need to be mixed with additional NaI or KI and then sublimed to
remove the chlorine.
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ScienceSquirrel
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35% hydrogen peroxide is cheap as chips and readily available around here so it is my oxidising agent of first choice.
Easy work up with no byproducts except water and a bit of oxygen, luverly 
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panziandi
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Klute, You can purify the iodine from ICl if you mix with KI and sublime the I2 out.
Reaction:
ICl + KI => I2 + KCl
It also removes other pseudohalogens such as ICN etc from crude iodine. This is standard method of purifying iodine it's given in text books on
analytical chemistry for obtaining high-purity iodine.
Interestingly if iodoform is mixed with silver powder and distilled you obtain acetylene HC#CH which can be interesting preparation from a small scale
preparative point of view...
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Klute
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Thank you for pointing that out!
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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Ketone
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| Quote: | Originally posted by ScienceSquirrel
35% hydrogen peroxide is cheap as chips and readily available around here so it is my oxidising agent of first choice.
Easy work up with no byproducts except water and a bit of oxygen, luverly
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Yeah, judging from what I've read on the forums here alot of people seems to like it alot..
But over here, far as I know, it (35% that is) can only be bought from a chemical supplier, and not without raising suspicions that you're going to
make Acetone peroxide. I try to avoid chemical suppliers as much as possible, don't fancy big brother's attention..
Plus- I think it's just way cooler to try and use chemicals that can be bought almost anywhere as much as possible. 
| Quote: | Originally posted by not_important
That is the Bunsen Reaction
2H2O + SO2 + I2 <=> H2SO4 + 2HI
an equilibrium that doesn't allow the making of concentrated HI without a large excess of at least one of the left hand reactants, meaning I2 and SO2
(under pressure) as excess water dilutes the products. As the concentration of the acids goes up, the sulfuric acid begins to oxidise the hydroiodic
acid, so with ordinary lab methods you'll not get high concentrations. however the mixture is useful for converting alcohols to iodides
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In other words.. I shouldn't bother trying to make just HI like that. Thanks for saving me some chemicals.
| Quote: | Another reaction used is
I2 + H2S => 2 HI + S
the sulfur being filtered out using fritted glass or glass wool filters, then the acid distilled to get constant boiling hydroiodic acid. See Vogel,
Practical Organic Chemistry 3rd edition; Inorganic Synthesis Volume 1 page 157. |
Yeah, that reaction would have been my first choice too, if H2S wasn't so nasty..
Don't even have a fume hood and I don't think I'm the only one who doesn't have one.
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ScienceSquirrel
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I buy my peroxide from a lentil and dried bean shop.
The alternative therapy crowd have taken on hydrogen peroxide in a big way.
It is also a good place to meet natural ladies 
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Ketone
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| Quote: | Originally posted by ScienceSquirrel
I buy my peroxide from a lentil and dried bean shop.
The alternative therapy crowd have taken on hydrogen peroxide in a big way.
It is also a good place to meet natural ladies |
Hehe..
And thanks for the tips, ehh on where to find peroxide that is..
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