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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: meshohel on November 20, 2012, 10:35:42 AM

Title: Free radical benzylic bromination
Post by: meshohel 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
MD

Title: Re: Free radical benzylic bromination
Post by: discodermolide 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.

Title: Re: Free radical benzylic bromination
Post by: orgopete 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.

Title: Re: Free radical benzylic bromination
Post by: discodermolide 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.