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Topic: Free radical benzylic bromination  (Read 3051 times)

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Offline meshohel

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Free radical benzylic bromination
« on: November 20, 2012, 10:35:42 AM »
I would like to do bromination of 2-methyl-pyridine on methyl group. My condition is AIBN, NBS, DCM, substrate, heat (50 C). The reaction did not work. May be due to low temp. I recovered the substrate only. My substrate is not soluble in CCl4. What are the good solvents and initiation processes to perform this reaction.

Thanks
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Offline discodermolide

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Re: Free radical benzylic bromination
« Reply #1 on: November 20, 2012, 10:55:33 AM »
You may have a problem with the pyridine nitrogen.
AIBN really needs a bit higher temp. to keep the radicals coming, try benzoyl peroxide.
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Offline orgopete

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Re: Free radical benzylic bromination
« Reply #2 on: November 20, 2012, 06:27:43 PM »
I would look up your desired compound. Does it polymerize? I think it is known, but may require special treatment.

Secondly, AIBN has a lower decomposition temperature than benzoyl peroxide. However, I don't think much decomposes at 50°C.

I think you need to make the pyridine N-oxide and can rearrange it to a chloride or bromide.
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Offline discodermolide

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Re: Free radical benzylic bromination
« Reply #3 on: November 20, 2012, 08:34:33 PM »
I have a table of radical generators and their half-lives etc somewhere here in my mess. I seem to remember that  AIBN was better with a strong light source.
I'll try and find the table.
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