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Author: Subject: Aromatic iodinations
solo
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[*] posted on 5-12-2008 at 07:19


Reference Information


Iodination of various unprotected amines with iodine and silver sulfate
Wing-Wah Sy
Tet. Lett. 1993, Vol. 34, No. 39, pp. 6223-6224


Abstract
Iodination of methoxyamphetamines with iodine / silver sulfate at room temperature gives iodomethoxyamphetamines in good yield.



[Edited on 5-12-2008 by solo]

Attachment: Iodination of methoxyamphetamines with iodine and silver sulfate..pdf (129kB)
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chemrox
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[*] posted on 5-12-2008 at 09:50


Br. was Br radical which happens easily in the presence of elemental Fe. Also, I did not mean to imply that I get my scientific information here. I think you know from my posts in refs that I research the literature as often as I can. I was referring to the advantages in having frequent discussions with other chemists that you have and I only get here. I hope this clears up two misunderstandings. The best I can do to type a radical mark is a period (.).



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UnintentionalChaos
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[*] posted on 5-12-2008 at 10:25


I dislike posting useless naggy things, but wouldn't Br* be more appropriate chemrox? Your keyboard does have an asterisk key, doesn't it?



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stoichiometric_steve
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[*] posted on 5-12-2008 at 13:18


Quote:
Originally posted by solo
Reference Information


Iodination of various unprotected amines with iodine and silver sulfate
Wing-Wah Sy
Tet. Lett. 1993, Vol. 34, No. 39, pp. 6223-6224


That paper was of course the first one i consulted on this particular matter, although Tet. Lett. not being a peer reviewed journal, it happens to have a relevant number articles which are outright bullshit. And the amines in this article are all on a secondary carbon, not sure if this might put some steric hindrance to the N-iodination.




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Nicodem
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[*] posted on 6-12-2008 at 06:37


Quote:
Originally posted by chemrox
Br. was Br radical which happens easily in the presence of elemental Fe. Also, I did not mean to imply that I get my scientific information here.

I thought you just confused something. Just about every undergraduate schoolbook about organic chemistry describes the electrophilic bromination of benzene with Br2 using iron as precatalyst and explains why so. Iron reacts with Br2 to give FeBr3, an acid which catalyses the electrophilic bromination. You can not have a radical bromination in the presence of elemental iron because it is a reducent, thus reducing any potentially occurring Br* radical to bromide.

See:
http://mason.gmu.edu/~bbishop1/chem318/Chem318%20020607.pdf
http://www.scribd.com/doc/7757435/Aromatic-Rxns-for-Beginers
http://www.chem.ualberta.ca/~fenniri/CHM-263/Chapter15.pdf
http://en.wikipedia.org/wiki/Electrophilic_halogenation
http://www.chem.umd.edu/courses/fall05/chem231fribush/pdfs/C...
...and about hundreds of other random sites
Quote:
Originally posted by stoichiometric_steve
That paper was of course the first one i consulted on this particular matter, although Tet. Lett. not being a peer reviewed journal, it happens to have a relevant number articles which are outright bullshit. And the amines in this article are all on a secondary carbon, not sure if this might put some steric hindrance to the N-iodination.

Actually, Tetrahedron letters is a peer reviewed journal with a relatively high impact factor (not that this guarantees its quality). Even though it is true that a lot of bullshit nevertheless passes through (the reviewers are just the same researchers who publish there anyway), I would not claim this paper bullshit before trying that method. On the other hand, the only organic journal/series that publish checked procedures is Organic syntheses, so you might (and you should) as well consider all the rest as potential bullshit anyway.
The amine being on a secondary or primary carbon is more or less irrelevant stericaly. Actually, I would tend to believe the iodoamine on a secondary carbon would tend to decompose even faster than the one on a primary.




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S.C. Wack
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[*] posted on 1-8-2009 at 16:09


Comparison of Iodination of Methoxylated Benzaldehydes and Related Compounds using Iodine/Silver Nitrate and Iodine/Periodic Acid

I/AgNO3 works OK for certain aldehydes of interest here.

Attachment: synth_comm_37_3855_2007.pdf (74kB)
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JohnWW
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[*] posted on 1-8-2009 at 21:01


That iodination procedure sounds as if it would be an important step in the total synthesis of the thyroid hormone thyroxine and related compounds; see http://en.wikipedia.org/wiki/Thyroxine for its structure and properties. It is administered to patients suffering thyroid deficiency, who would otherwise become cretins. (These are the subnormal people who squeal to Rapidshare, alleging "breach of copyright" and demanding that uploads be deleted, in spite of not even being the authors).
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Sandmeyer
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[*] posted on 2-8-2009 at 08:48


Quote: Originally posted by stoichiometric_steve  
Quote:
Originally posted by solo
Reference Information


Iodination of various unprotected amines with iodine and silver sulfate
Wing-Wah Sy
Tet. Lett. 1993, Vol. 34, No. 39, pp. 6223-6224


That paper was of course the first one i consulted on this particular matter, although Tet. Lett. not being a peer reviewed journal, it happens to have a relevant number articles which are outright bullshit. And the amines in this article are all on a secondary carbon, not sure if this might put some steric hindrance to the N-iodination.


The method isn't bullsit. Some russian members have even used silver nitrate instead of sulfate and it has worked too.




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[*] posted on 15-8-2009 at 10:22


I can safely say that NaOCl + KI iodination of Vanillin works nicely.
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[*] posted on 5-9-2009 at 19:15


I don't think this method has been discussed previously. Found it a while back but lost the link:
http://www.erowid.org/archive/rhodium/chemistry/aromatic.iod...

Formula409.
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[*] posted on 8-9-2009 at 06:46


Quote: Originally posted by Sandmeyer  
Quote: Originally posted by stoichiometric_steve  
Quote:
Originally posted by solo
Reference Information


Iodination of various unprotected amines with iodine and silver sulfate
Wing-Wah Sy
Tet. Lett. 1993, Vol. 34, No. 39, pp. 6223-6224


That paper was of course the first one i consulted on this particular matter, although Tet. Lett. not being a peer reviewed journal, it happens to have a relevant number articles which are outright bullshit. And the amines in this article are all on a secondary carbon, not sure if this might put some steric hindrance to the N-iodination.


The method isn't bullsit. Some russian members have even used silver nitrate instead of sulfate and it has worked too.


Have anything about it?
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[*] posted on 29-3-2019 at 15:31
Iodine-Iodic acid 5-minute-iodination proof-test


Month ago I tested this easy iodination procedure with I2-HIO3 system from the paper given below, using vanillin as substrate.
It worked, but the yield is very bad.


Avinash T. Shinde, Sainath B. Zangade, Shivaji B. Chavan, Archana Y. Vibhute, Yogesh S. Nalwar, Yeshwant B. Vibhute
A Practical Iodination of Aromatic Compounds by Using Iodine and Iodic Acid
Synth. Commun., 2010, 40 (16), 3506-3513
DOI: 10.1080/00397910903457332

pdf attachted (I did UTFSE and didn't find this paper posted before)

Attachment: shinde2010.pdf (336kB)
This file has been downloaded 470 times


Authors claim good to excellent yields on all kinds of substrates and provide very easy procedure (only 5 minutes reaction time!)

Quote: Originally posted by PROCEDURE FROM THE PAPER  
General Procedures for Iodination of Aromatic Amines, Hydroxy Aromatic Aldehydes, Hydroxy Acetophenones, and Phenols

Aromatic Compounds (50 mmol), iodine (20 mmol) dissolved in ethanol (20 ml) by warming, iodic acid (10 mmol) dissolved in water (1 ml) was added with shaking and refluxed on boiling water bath for 5 min. on cooling solid separated out. Obtained solid product was filtered and crystallized from ethanol.



Experiment:

Iodic acid solution was prepared by dissolving I2O5 (0.34 g, 1 mmol) in ~0.3 mL of hot water.

I2O5 + H2O = 2HIO3

In a RBF, equipped with a reflux condenser, was prepared solution of iodine (1 g, 4 mmol) in 95% EtOH (4 mL) by heating it to slight boiling.
Then this solution was chilled to ~RT° and there was added vanillin (1.52 g, 10 mmol). Obtained mixture was stirred for half a minute and there was added previously prepared iodic acid solution (exothermic reaction occures). Reaction flask was set in a boiling water bath and heating with stirring was applied for 5 minutes. After that, the reaction flask was cooled for 10 minutes on a cold water bath. Then, the reaction mixture was diluted with 5 mL of 95% EtOH, filtered and solids on the filter was thoroughly washed with EtOH (2 x 5 mL).
Product was recrystallized from 25 mL IPA, filtered, washed with 5 mL of fresh cold IPA and dried at 50°.
There was obtained 0.8 g (only 28.7% yield) of 5-iodovanilin as beige colored crystalline powder with very subtle smell (which indicates impurity since pure 5-iodovanillin doesn't have any smell). Mp. 178-180° (- slightly depressed even after recrystallization).


Authors of the paper give their yield for ethyl-vanillin as high as 75%. Unfortunately, there is no regular vanillin in the paper.


Then I repeated this procedure on the same scale, but heating was continued for 30 instead of 5 minutes (but also I used a little bit more of the solvent).
This time the yield was significantly less (0.6 g, 21.5% - and this is yield without recrystallization).



So, since increased reaction time has led to lower yield of the product, I can conlude that this reaction takes place at, indeed, very high rate (at least with this substrate).
Resulting 5-iodovanillin seems to be relatively stable in the reaction conditions (only ~7% yield loss after 25 min), so it seems that most of the initial vanillin simply doesn't have time to iodinate - side reactions are happening much faster.
Well, that's how I see it anyway.


Maybe this procedure will work as it should (with good yields as given in the paper) for some other, more 'inert' compounds, but I am kinda skeptical about that.



[Edited on 30-3-2019 by bipolar]
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