My plan is to chlorinate the methyl groups of the p-xylene using chlorine gas and uv light. Could the chlorination take place along the benzene ring,
or is it restricted to first the methyl groups? Has anyone else done this with success?
Also, do I need to reflux the p-xylene, or could this be done in liquid phase because ClCH2C6H4CH3 melts at 4C and the (ClCH2)C6H4 is a solid at room
temperature, so it would just precipitate out?Metacelsus - 11-11-2016 at 16:03
I'd expect that you wouldn't get much ring chlorination, especially if you kept the temperature low. Do not reflux the xylene, as heat will tend to
lower your selectivity.
Bromination would be more selective. Also, bromine, being a liquid, is easier to handle than chlorine gas. I've brominated toluene to benzyl bromide
using strong sunlight as a UV source. If you just need a xylyl halide (and don't care whether it's a chloride or bromide), then I would recommend
bromination.
If you do use chlorine gas, make sure to stay safe. If you don't have a fume hood, I'd recommend doing it outside. Also, have a plan to deal with the
hydrogen chloride that will be produced.
[Edited on 11-12-2016 by Metacelsus]Meltonium - 11-11-2016 at 18:20
If you just need a xylyl halide (and don't care whether it's a chloride or bromide), then I would recommend bromination.
If I do decide to use bromine, I'm guessing that a future Sn1 reaction on the bromines would require a bromine-based catalyst? (For example AlBr3)Metacelsus - 11-11-2016 at 20:06
Benzylic halides usually do SN2 reactions (due to electronic effects stabilizing the transition state). What nucleophile are you planning to use? You
probably won't need a catalyst. In any case, it's fine to use a chloride-based Lewis acid. Assuming you'll have no halide in your end product, a
little scrambling won't hurt things.Meltonium - 12-11-2016 at 05:20
First, I was going to substitute one of the bromines with propionic acid in the secondary position, then I was going to substitute the other bromine
with propane, also in the secondary position. Not sure if my plan will work though.
