frogfot
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Iodoform
On my recent search for some easy experiment with iodine i found synthesis of iodoform. It required easy to get things..
Reactions:
CH3-CO-CH3 + I2 ==> CI3-CO-CH3 + 3HI
CI3-CO-CH3 + NaOH ==> CHI3 + CH3COONa
Preparation
4 g of KI are dissolved in 7,5 ml of destilled water and 2 g of I2 is added. 17,5 ml of water is added, followed by 5ml of acetone.
While stirring, a 10% solution of NaOH is dropped into reaction mixture from a dropping funnel until reddish color dissapears (approx. 4,5 ml).
Iodoform precipitates as yellow crystalls, those are filtered after 30 minutes, washed with small ammount of water and air dryed.
Yield is 0,93g (90%). In presence of light its hydrolised fast with strong bases, therefore excess of NaOH should be avoided.
Preparation was taken from "Practicum of organic chemistry" by S.S. Gitis, A. I. Glaz, A.V. Ivanov 1991
So, now I get to the point of this post, and point why I woke up 3:00 at the morning... Since I wanna survive the synthesis and after, happily sit and
observe the mysterious product behind tightly sealed glass jar, I wanna ask, how nasty is this stuff?
Heres MSDS of substance:
http://physchem.ox.ac.uk/MSDS/IO/iodoform.html
Heres its inhalation lethal concentration:
IHL-RAT LC50 165 ppm/7h
I wanned to carry out synthesis outside, then bring it in for quick vacuum filtration and after dry it outside and seal. Am I safe? or do I concern to
much?
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frogfot
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I guess I have to try this and see how it goes... treating it as gently as death.. 
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chemoleo
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Well, having made some iodoform recently, I have to say it's an extremely easy prep (the one above, only 3x the amount) - and upon NaOH addition
the red/brown colour of the KI/I2 disappears completely, leaving you with beautiful lemmon-yellow crystals. It looks like a dye, that's how
intensely yellow it is.
I checked some MSDS's, but it's not THAT toxic - it takes an adult about 80 g to ingest to die from it. Also it was used as an antiseptic. Inhalation is termed 'irritant'. On
that note, it's not just irritant, it is a frigging lachrymator! I was crying my eyes out when I poured the supernatant into the sink. Flushing
down the supernatant with lots of water seemed to help. I am not quite sure how to get this dry, considering this lachrymatory property. The smell,
other than that, is not very strong, just slightly of iodine - weird stuff.
On second thoughts - it looks like the properly washed iodoform is not as lachrymatory - instead this property was probably caused by intial reaction
products that were present in the supernatant - I imagine iodoacetone, a close relative to the well-known lachrymator chloroacetone, was formed as a
byproduct.
Also, the smell of acetaldehyde was there.
Further, it sticks to plastic (and glass somewhat) when in an aqueous suspension, and it forms a thin layer on top of water (surfactant properties). I
wouldn't recommend centrifugation therefore, filtration (fumehood or outside) is probably better.
It dissolves nicely in ethanol.
Anyway, it's a nice & easy prep.
[Edited on 22-12-2004 by chemoleo]
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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S.C. Wack
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It is wasteful of I (expensive here due to meth cooks) though. Of the 15 grams of I in, you poured 12.3 down the sink, using frogfot's reference
numbers 3X. Use of EtOH instead of acetone will keep you from flushing!
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chemoleo
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I know, it seems incredibly wasteful.
Why will ethanol be better though? I don't see how, the equation is still the same?
I figure the KI doesn't really participate in the reaction though, I think it's only there to solubilise the I2 in water (which it did).
Hmm... I think I should work out the reaction proper. Will be back on this.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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S.C. Wack
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EtOH is better because there isn't any iodoacetone or other lachrymator being produced making you pour your stuff down the drain, so you can
recover your iodide. Acetaldehyde and ethyl alcohol are exceptions to the methyl ketone rule. Stepwise:
CH3CH2OH + KOI ->CH3CHO + KI + H2O
CH3CHO + 3 KOI -> CI3CHO + 3 KOH
CI3CHO + KOH -> CHI3 + HCOOK.
or
CH3COCH3 + 3 KOI -> CH3COCI3 + 3 KOH
CH3COCI3 + KOH -> CH3COOK + CHI3
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woelen
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I made iodoform in a way, which is somewhat less wasteful on (expensive) iodine and no elemental iodine is needed.
Dissolve some KI in water and add excess mix of H2O2(3%) and HCl(10%). This causes iodine to precipitate out of the liquid as a heavy and
compact precipitate which very quickly settles at the bottom. The liquid above it only remains light brown and recovering any iodine from this is not
worth the effort (it is less than 1% of the initial amount in the KI).
Decant the liquid carefully.
Add quite some water and shake. Hardly any iodine dissolves.
Within just a few seconds the iodine has settled again.
Decant the liquid carefully again and do another rinse with water.
Do a final decant and then add new water.
Also add some acetone, use an excess amount.
Now carefully add a concentrated solution of NaOH drop by drop and shake after each drop. Do this, until all brown/black iodine has disappeared.
You are left with a beautiful bright yellow precipitate, which can easily be filtered and rinsed with a little distilled water. Dry this at air in a
dark and (preferrably) warm place.
As you see, there is no need to work with dissolved iodine. The precipitate from the KI/H2O2/HCl liquid is sufficiently porous. In this way, you do
not flush away 2 out of three parts of iodine, but 1 out of 2 parts of iodine and you do not need I2, but the easier to obtain KI.
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Douchermann
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Is it neccesary to have the potassium Iodide for this reaction. Could I just sub in the ammount of elemental iodine that is in the KI (so about 5.3
grams of iodine total)? Or is it needed.
It\'s better to be pissed off than to be pissed on
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woelen
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If you really want to use iodine instead of potassium iodide, then you can proceed as follows:
1) Dissolve all iodine in some acetone. For 5 grams of iodine I think that 10 ml of acetone will do.
2) Then add quite some water. Amount is not critical, a good starting point may be ten times the volume of acetone used. The iodine will precipitate
out as a heavy and coarse precipitate. The liquid above it is brown and consists of a small amount of iodine, dissolved in a water/acetone mix.
3) Next, add solution of NaOH dropwise, until no iodine can be seen anymore.
So, this method essentially is the same as mine, I just first transformed the iodide to iodine before making iodoform.
I, however, strongly prefer using potassium iodide, because that is MUCH easier to obtain and also quite a lot cheaper. I don't want to spoil my
precious iodine for a reaction, which also can be done with an iodide.
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FPMAGEL
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This is type of the same as above with different ratios.
Make a solution with 1g of potassium iodide in 5ml of water. Add iodine crystals to get a brown colour. Add 5ml of ethanol.Add some 10%NaOH solution
until the color disappears. Heat gently for two minutes. Allow to cool. The yellow precipitate is iodoform(CHI3)
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woelen
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What's the difference of this recipe with the ones, given at the start of this thread? Even the alcohol-variation is mentioned already.
The main difference between my recipe and the others is that no iodide is needed for keeping the iodine in solution. It works with a suspension of
iodine without dissolved iodide. This makes the process 33% more economic in terms of loosing iodine/iodide in the process. The cost of the process is
mainly determined by the iodine content, all other chems are dirt-cheap.
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