Author Topic: Bromination with NaBr and Oxone  (Read 2041 times)

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Vibrating_Lights

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Bromination with NaBr and Oxone
« on: August 23, 2002, 10:54:00 AM »
Recently Rhodium posted about para Clorinations with NaCl and Oxone i believe.  Will oxone Convert NaBr into Br2 or is it nescesary to first produce HBr Like with an I2 extraction with HCl/H2O2.. would it be wise to try a 2 phase bromination by dissolving 2CH freebase in DCM and addin (aq)  Oxone to an (Aq) solution of NaBr???  or even better collect Br2 In DCm wash with Bicarb the combine with 2CH.???

So much game I could sell a hooker some pussy
Vl_

Chromic

  • Guest
Best way
« Reply #1 on: August 23, 2002, 04:09:00 PM »
The best way to brominate aromatic rings with KBr (or an equivilant of NaBr) as the source is via a reference that Osmium gave to brominate vanillin. What are you planning to brominate?

Here's the general idea:

Prepare 120ml of GAA, 40ml H2O, 11.8g H2SO4 (120mmol), 14.3g KBr (120mmol) and 5.8g 35% H2O2 (60mmol) in a container. Stir and watch as the solution turns orange-red as the bromine is formed, and it starts to smell like bleach.

Dissolve 100mmol of freebase (or hydrochloride, shouldn't matter either way) into 50ml GAA in a flask. Cool this in an icebath. Then drip in the Br2 solution from the container. Once this is done, slowly drip in 5.8g 35% H2O2 (60mmol). Basify the whole thing, extract and work up as usual.

The overall reaction goes as follows:
A + H2O2 + KBr + H+ ==> Br-A + 2 H2O + K+

Of course, there's a few separate reactions going on:

in the container:
1) H2O2 + 2 KBr + H+ ==> Br2 + H2O + K+
in the flask:
2) A + Br2 ==> Br-A + Br-
3) H2O2 + 2 Br- + H+ ==> Br2 + H2O (then back to rxn 2 with the Br2, until most all the Br- is used up)

I've done this on PMA, and I'm unsure if it works exactly as stated as the Br-PMA seemed to have pretty much the same effect as the starting material, so caveat emptor.

Vibrating_Lights

  • Guest
chromic
« Reply #2 on: August 23, 2002, 10:42:00 PM »
2CH

So much game I could sell a hooker some pussy
Vl_

Chromic

  • Guest
Yeah, I read that.
« Reply #3 on: August 23, 2002, 11:55:00 PM »
Yeah, I read that.

The above procedure is for 100mmol of aromatic you want to brominate. DMMDA-2, PMA, MDA, 2C-H, vanillin, whatever... it will work for any of it, and making bromine in situ is a blessing compared to handling liquid bromine.

Good luck!

slothrop

  • Guest
Bromination with NaBr and Oxone
« Reply #4 on: August 24, 2002, 02:20:00 AM »

Recently Rhodium posted about para Clorinations with NaCl and Oxone i believe.  Will oxone Convert NaBr into Br2 or is it nescesary to first produce HBr Like with an I2 extraction with HCl/H2O2.. would it be wise to try a 2 phase bromination by dissolving 2CH freebase in DCM and addin (aq)  Oxone to an (Aq) solution of NaBr???  or even better collect Br2 In DCm wash with Bicarb the combine with 2CH.???




SYNTHETIC COMMUNICATIONS
Vol.32,No.15,pp.2313 –2318,2002

AN EFFICIENT AND REGIOSELECTIVE
OXYBROMINATION OF AROMATIC
COMPOUNDS USING POTASSIUM
BROMIDE AND OXONE


General Procedure for the Bromination of Aromatic Compounds:
Oxone (2.2 mmol) was added to a well stirred solution of KBr
(2.2 mmol) and substrate (2.0 mmol) in methanol (10 mL) and the reaction
mixture was allowed to stir at room temperature. The reaction was
monitored by thin layer chromatography (TLC).After the completion of
the reaction.The mixture was ?ltered and solvent evaporated under reduced
pressure.The products were puri ?ed by column chromatography over silica
gel and confirmed by HNMR and Mass spectra.

Parasubsts are dominating and generally > 70 %

//Tyrone Slothrop


Mindflux

  • Guest
nice!
« Reply #5 on: August 24, 2002, 03:26:00 AM »
This is the greatest thing since sliced bread  ;D

Chromic

  • Guest
What?
« Reply #6 on: August 24, 2002, 03:39:00 AM »
Why is oxone better than H2O2/H2SO4? But... if the above reference is correct, there's no need for brominations to be done in acetic acid, and methanol will suffice. (that's good news!)

Any opinions?

Vibrating_Lights

  • Guest
everything
« Reply #7 on: August 24, 2002, 11:05:00 AM »
I bet this will also work with KCl And KI too.  We will call this the easy analog maker.
VL_

So much game I could sell a hooker some pussy
Vl_

cilliersb

  • Guest
Maybe
« Reply #8 on: August 26, 2002, 02:27:00 PM »
It cill work for KCl, but not for KI.

H2SO4 can not form HI when reacting with KI, but will form HCl when reacted with NaCl. H2O2 will produce free I2 from HI and free Cl2 from HCl, but getting to HI from NaI or KI is the problem.

Rather use NIS for your Iodinations, elemental I2 will not work anyway.

Osmium

  • Guest
> H2SO4 can not form HI when reacting with KI ...
« Reply #9 on: August 26, 2002, 06:26:00 PM »
> H2SO4 can not form HI when reacting with KI

It should work as long as the concentrations aren't too high.

I'm not fat just horizontally disproportionate.

moo

  • Guest
Iodinations
« Reply #10 on: August 26, 2002, 08:15:00 PM »
What has HI got to do with the subject? Isn't the H2SO4 supposed to catalyze the oxidation (H2O2 + 2H+ + 2e- --> 2H2O)? Furthermore, there are many examples of I2 + oxidising agent aromatic iodinations, including H2O2, peracetic acid, HNO3 and its salts, NO2 and KMnO4. (Goddamn, if there were no subscript tags it would take a lot less time to write a post! ;D )

Mindflux

  • Guest

lugh

  • Guest
Following Paper
« Reply #12 on: August 31, 2002, 11:55:00 PM »

I bet this will also work with KCl And KI too.  We will call this the easy analog maker.




Since the following paper the paper cited by slothrop by the Narender group is on iodination using KI and oxone, you are definitely correct  ;D


Rhodium

  • Guest
Aromatic iodination
« Reply #13 on: September 03, 2002, 12:37:00 AM »

Rhodium

  • Guest
Aromatic Bromination: Ammonium bromide + Oxone
« Reply #14 on: October 05, 2004, 03:52:00 AM »
Mild and regioselective oxidative bromination of aromatic compounds using ammonium bromide and oxone
N. Narender, K.V.V. Krishna Mohan, S.J. Kulkarni and K.V. Raghavan

J. Chem. Research (S), 597-598 (2003)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/aromatic.bromination.oxone.nh4br.pdf)

Abstract
The selective mono-bromination of various activated aromatic compounds is reported using in situ generated bromine from NH4Br as a bromine source and oxone as an oxidant for the first time.