Author Topic: one-pot iodine synthesis and aromatic iodides  (Read 132 times)

poisoninthestain

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one-pot iodine synthesis and aromatic iodides
« on: April 06, 2009, 03:07:35 PM »
Iodine is an extremely useful reagent in organic synthesis.

A simple preparation of iodine crystals of fairly pure quality can be easily obtained from the rxn between a metal salt of iodine and CuSO4 in water.

This will form CuI2 and a metal sulfate salt in situ. The CuI2 readily decomposes into I2 and the water insoluable CuI. The resulting iodine can then be collected through condensation.

Prepare an equimolar ratio of CuSO4 and DH2O in a rxn vessel with a coldfinger/condenser attached or just use a plate with ice on top of it sitting on a jar if needed.

Quickly add the iodide salt and reattach your condenser. The solution will quickly change color and a purple-ish gas resulting from the rapidly sublimated iodine will condense on the condenser.

Scrape or wash the condenser with water(iodine is only slightly soluble in water). Tada. Elemental iodine all OTC.

Iodine is very tough to add directly across double bonds such as 2C-I but a iodine cation will work just fine. For this we can form iodine monochloride.

This is easily accomplished by gassing I2 with Cl2 and collecting the resulting, extremely pure, brown ICl liquid. However, most of us don't like working with Cl2 so in situ chlorination with calcium hypochlorite works dandy.

Prepare a saturated solution of calcium hypochlorite in DH2O and chill it to freezing cold. Attach a condenser and titrate in con. HCl very slowly, being careful not to let the temp. rise to anything above warm. Stop adding HCl when the solution remains a red/brown. Allow the mixture to cool if warm, pour into a sep. funnel, collect the brown bottom layer, decant the brown liquid into another container while trying to make sure no precipitates follow. Done.

ICl is great for adding across the bond for 2C-H to 2C-I and other compounds.

I'll post pics in the future.
« Last Edit: April 06, 2009, 03:09:52 PM by poisoninthestain »

zzhuchila_clocker

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Re: one-pot iodine synthesis and aromatic iodides
« Reply #1 on: April 25, 2009, 08:14:26 AM »
Very nice!
Do you mean, iodine is chlorinated with chlorine in situ - generated from calcium hypochlorite? That is fine, because (afaik) NaOCl in alkaline medium oxidizes I2 into IO4- . Is the same reaction avoided in case of calcium hypochlorite? Oh yes, thats probably because high pH is required to break iodine into I- and IO- that are then oxidized, and if there is no base the reaction is slow.
Can the ICl be used for iodination of non activated aromatic compounds like benzene and toluene? Does it require lewis acid catalyst? I want to experiment with phenyl iodosoacetate, but the main problem for me was aryliodide, now i think it can be solved
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poisoninthestain

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Re: one-pot iodine synthesis and aromatic iodides
« Reply #2 on: July 11, 2009, 01:30:39 AM »
"Do you mean, iodine is chlorinated with chlorine in situ - generated from calcium hypochlorite?"

Yep.

"Can the ICl be used for iodination of non activated aromatic compounds like benzene and toluene?"

Should work.

"Does it require lewis acid catalyst?"

Usually not.


Douchermann

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Re: one-pot iodine synthesis and aromatic iodides
« Reply #3 on: July 11, 2009, 06:12:50 AM »
It might be easier to prepare iodine from iodides with the iodide, hydrogen peroxide, and hydrochloric acid. 

KI + HCl <====> HI + KCl

2HI + H2O2 -----> I2 + 2H2O

Or something like that.  Normally I would say that HCl can't form HI, but there is clearly a reaction that goes on, more than just dissolution of HCl.  With this, no sublimation is necessary as the only impurity would be the highly water soluble by-products and reactants, and of course water.  Just filter and use directly in the insitu chlorination.