zooligan
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Aromatic Bromination w/Oxone
I originally posted this in the 'Zinc reduction for 2C-H from nytrostirene' thread, but thought it may start more discussion as a stand-alone thread.
Anyone familiar with this reaction?
Originally posted by zooligan
Hmm... NBS seems to be eluding me. KBr and Oxone are readily had, however.
In http://www.erowid.org/archive/rhodium/chemistry/oxone.aromat... the reagent proportions are 2.2 mmol Oxone, 2.2 mmol KBr, and 2 mmol substrate in
10ml MeOH.
Is the substrate they are referring to the HCL salt or the freebase form of the compound (2C-H in this case)?
In converting the result of the above reaction from an HBr salt to an HCL salt, is it really necessary to basify, extract w/DCM, evap the DCM,
dissolve the residual oil in dH2O/GAA, and form the salt w/HCl? Can one simply basify, extract w/toluene or xylene, and form the salt w/HCl or is
there some kind of solubility issue that requires the dH2O/GAA?
Thanks,
-z
[Edited on 20-1-2006 by zooligan]
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xwinorb
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I was thinking about using this bromination for 2C-H --> 2C-B initially. I asked for advice, some guys who know more chemistry that I do said I
better brominate in an acidic environment.
I tried first ammonium bromide in AcOH, that one does not work for 2C-H. I was able to recover 3.2 g of initial 5 g 2C-H that went trough the
bromination procedure unchanged.
Next I tried KBR + H2SO4 + H2O2 in acetic acid ( Chromic method, using as little water as possible. My reason for this is, then it is close to having
pure Br2 in AcOH with a bit water and a bit NaHSO4, that hopefully are not going to mess up things too much.
This indeed works. I am not sure if using less water helps or no. In my first bromination, I was lucky, got nice, clean 2C-B xtals, in the subsequent
ones ( total five, usually 5 g 2C-H or less ) some byproducts noticed but overall OK.
I have combined all the 2C-B I was able to make less a little bit, distilled it all, got water clear 2C-B, then re-xtalized it.
I also got the overbromination problem ( 2C-B getting darker after a few months ) but I fixed it by basifying with NaOH, extracting with toluene and
re-xtalizing from HCl dripped in toluene + 2C-B freebase. BTW, I think this is a better way to xtalize the 2C-B than Shulgin's technique, cleaner,
simple, good yields. Have tried both.
If the Oxone + MeOH works, please post. I would like to know if it works or not.
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niobium
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Zooligan,
1. KHalo/oxone halogenation on the said compound does not
work as stated on the hive. check -
https://sciencemadness.org/talk/viewthread.php?tid=4665#pid5...
Bees have reported 0 success rates with this kind of
method. This method does work for anisole but not for ur
amine.
Best bet would be either to brominate with Br2 (insitu or
bought) or to use NBS. Trying the Khalo/oxone method is a
waste of amine.
2. the said brominated compound (as far as swin know, swin
did not try to make this salt) can be simply made by
basifiying extraction with non-polar and titration with
concentrated HCl since the salt is supposed to be very
hydrophobic. bee sure to wash ur non polar with brine
solution and dH2O and to dry it before u acidify.
Also VERY important to xtalize ur salt.
Hope this helps 
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xwinorb
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Chromic bromination
This is cut and paste from an old post from The Hive. I had downloaded it to my PC.
I have changed the procedure slightly, using the minimum ammount of water and also experimenting with 1.5 X and 2 X the ammount of H2SO4 and NaBr. It
works, but have to do it carefully to avoid byproducts. My best yield was I guess close to 75 %.
Chromic
(Synaptic Self-Mutilator)
08-23-02 07:09
No 348105
Best way Bookmark Reply
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.
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