BASF
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Iodination of organic compounds
I still have 10g elemental iodine.
Does anybody know how i could use that for halogenations?
I know that the introduction of iodine is not a very fast reaction, so the decision on the solvent is a critical one, i think.
However, i had the idea of using a small amount of AP to get the radical-chain reaction running, instead of UV.
Any feedback, ideas or experiences?
Thanks in advance...
HLR
[Edited on 26-6-2003 by BASF]
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vulture
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It really depends whether you inted to iodate (is that a word?) olefines, aromatics, alkanes....
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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ziqquratu
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I apologise if this appears twice... I tried to post, and it said it went through, but apparently not...
Anyways, basic idea - if you're trying to iodinate an aromatic compound, you could use the iodine to make N-iodosuccinimide (analagous to
N-bromosuccinimide). Or you could use a Lewis acid to perform the task - and I dont think it matters which halogens are on the Lewis acid - that is,
I think you could use, say, Aluminium trichloride or Aluminium tri-iodide with equal success. Finally, you could use the iodine with nitric acid
(or, i assume, some other oxidant) to give I+ which is (obviously) an electrophile which should be happy to add to an aromatic ring. Which of these
you want to use depends on what chemicals you have available and also to which position on the ring you want to add the iodine relative to any other
substituents. And I think the UV or peroxide route should work - I'm not sure, but using simple hydrogen peroxide may work.
If you were planning on adding to an alkene, it should (at least in theory) happen quite readily without any for help. In practice, however, I think
that di-iodide compounds have a low equilibrium constant, so you'd be better off adding bromine to a double bond in many cases.
Hope this is useful!!
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Organikum
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Finkelstein swap
The iodation is either interesting for giving a better leaving group or something I don´t know probably something energetic.
Anyways, don´t hassle but chlorinate whats to halogenate - UV and heat and Cl2 or some other chlorination agent of choice and then do it! Yes just do
it! Finkelstein rulez!
Convert I2 to NaI or KI (depends on compounds addressed, mostly NaI is the best choice) and swap Cl with I by dissolving an stochiometric amount of
NaI together with the organic chlorocompound in acetone and gentle boil it. I and Cl get funny and start changing places but NaCl is not real soluble
in acetone so it falls out, equilibrium shifts and here we go to final iodation in near theorethical yields.
From my head - don´t nail me on details but it works and is much better yielding and easier as direct iodation wherefore PI3 or such would be needed,
shit.
attached it is the Finkelstein!
Attachment: finkelstein97.pdf (285kB)
This file has been downloaded 1036 times
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Organikum
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Hey Polverone!
I didn´t look it up, but:
trichloroacetic acid -> trifluoroacetic acid
by Finkelstein?
would be to good to be true.....
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vulture
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I don't think that will work considering the high electronegativity of fluorine.
As it occurs to me, finkelstein works when swapping less electronegative on the organic compound by removal of the more electronegative one.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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BASF
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Thanks for your thoughts so far!
It seems that the Finkelstein-reaction would be useful...i´ve already found it in my Vollhardt, and maybe i can also find a procedure in the
"Organikum".
I was trying to think practical about iodination of RDX recently, this could be a new project for the summer vacances.
Finkelstein-reaction would be no choice for this task, because it would be SN2, the backside attack.
I think the ring is too much of a steric hindrance...
I´ve then thought of halogenation of DPT(intermediate in RDX-synth), but the same problem occurs, since this is a bicyclic-5-ring, so even more
steric hindrance.
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BASF
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Bromination using KBR
Hmm.
Well, let´s explain another problem.
I´d also like to try bromination of RDX, but i only have KBr to realize this.
1st) dissolving RDX in aqueous acetone(radical bromination is faster in polar solvents, i think), then bubbling a thin stream of Br2 into it, made by
KBr + H2SO4 + H2O2.
Then add a little bit AP to start the radical chain...
If the reaction is successful, the bromine-solution decolourizes(i don´t know if i would have to use big excess, which would make recognizing a
colour-change more difficult).
Finally: weighing the solid product, eventually testing the filtrate on NO2- with Fe3+ and H2SO4(did the bromine attack the aza-function, therefor
generate NO2- ?).
2nd) the electrolysis of KBr in aqueous solution has been proposed(by a forum-member ).
I have experienced that ionic salt- impurities(like KBr) often make mixtures of organic solvents(here acetone) with protic solvents(here water)
seperate.
(Ausserdem passiert dasselbe glaube ich beim Aussalzen, beispielsweise kann man ja 50% ethanol durch zugabe von K2CO3 bis auf nahezu 100%
aufkonzentrieren, die ethanol-phase schwimmt dann auf der sole obenauf.)
I´m grateful for any feedback, new or even better ideas !
 
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vulture
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(Ausserdem passiert dasselbe glaube ich beim Aussalzen, beispielsweise kann man ja 50% ethanol durch zugabe von K2CO3 bis auf nahezu 100%
aufkonzentrieren, die ethanol-phase schwimmt dann auf der sole obenauf.)
I don't know why you posted this in german but I'll try my best at translating this:
IIRC the same thing happens when "outsalting" , one can concentrate 50% ethanol up to nearly 100% using K2CO3 for example, the ethanol
containing phase will swim on the mother liquid.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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ziqquratu
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Not relevant to RDX, but for future reference - a Finkelstein swap will only work for aliphatic halides (ie. don't even bother trying it on an
aromatic one - the mechanism is nucleophilic, and an aromatic ring is electron-dense so it doesn't substitute). Secondly, the only thing that a
Finkelstein can actually do (as far as I know) is convert and aliphatic chloride or bromide into an iodide. I don't think you can even
substitute bromine for chlorine (although it may be possible to substitute, say, bromine for fluorine - of course, if you manage to get an
organo-fluorine compound, it's probably because you want the F atom there anyway!). And even if I'm wrong about that, you certainly
can't substitute to get a fluorine atom on there (and I don't think working with elemental fluorine would be that much fun in the best of
labs...)
I assume you're trying to add three halogen atoms to the molecule, one at each of the methylene (-CH2-) groups in the ring?
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Organikum
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not true ziqquratu !
Where are your references? Here are mine. (what I gathered in three minutes, more to come..)
| Quote: |
Copper-Catalyzed Halogen Exchange in Aryl Halides: An Aromatic Finkelstein Reaction
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named here:
http://www.cas.org/spotlight/rlist1q03j/200304j4.html
Maybe you were thinking of halogenes attached directly to an aromatic ring and also here I am not sure if this would be true. Finkelstein works well
on the chain of aromatics and is worth a closer look before telling it is not applicable, in special regarding variations developed over the times.
And BASF wrote he has 10grams of iodine left.......
It doesn´t work for the trifluoroacetic acid - but this was just a idea as told.
article is attached
[Edited on 27-6-2003 by Organikum]
Attachment: finkelstein_variation_ja028865v.pdf (125kB)
This file has been downloaded 3356 times
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ziqquratu
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Organikum, you've just officially made my day! Until right now, I had never heard or read of a Finkelstein on an aromatic halide anywhere! This
is a very intersting article - thank you!
Yes, I was referring to halogens directly attached to the ring - it is, of course, quite simple to do a swap of a halogen on an aliphatic chain
attached to an aromatic ring.
Also, I wasn't criticizing your idea for trifluoroacetic acid (I wish that one would work - don't suppose you've got any more exciting
articles tucked up your sleeve?), merely commenting on why it wouldn't happen like that.
I'm also thinking, since it is generally far easier to obtain NaI or KI than to get elemental iodine, would it not be a more attractive option to
either find a method using elemental iodine or to buy the salt and save the iodine for another day, rather than convert it? Of course, in BASF's
case, obtaining the salts may not be an option, but I know I would certainly rather save my iodine if I could... depends on your situation, I suppose.
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Organikum
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Puhhh, read the first sentence and thought I had offended you ziqquratu! Glad that not as wasn´t intended anyways.
I had no problem with the critics on the trifluoroacetic acid - you are absolute right on this.
Love to learn.
I admit the article was surprising as it contains more as I thought on first sight.
The page I found it is worth a look:
Look in "Bücher" and "pdf" !
Grap the "test4.pdf"! Solventfree organic synthesis - book. Fresh and free.
In my eyes a treasurebox.
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vulture
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If you can get iodine salts you can easily make iodine yourself either by reacting with H2O2 and H2SO4 or concentrated H2SO4 in dry condition.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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