The Hive > Methods Discourse

Bromination with NaBr and Oxone

(1/3) > >>

Vibrating_Lights:
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:
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:
2CH
So much game I could sell a hooker some pussy
Vl_

Chromic:
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:
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.???
--- End quote ---


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

Navigation

[0] Message Index

[#] Next page