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Converting bromobenzene to 1‐bromo‐3‐methylbenzene

Chemistry Asked by Rover on December 23, 2020

bromobenzene to 1‐bromo‐3‐methylbenzene

I started by taking $ce{FeCl3}$ to reduce electron-giving capacity of $ce{Br}.$ Then we need a methyl at meta, so I thought about Friedel–Crafts acylation, but then also methyl will come at para.

One Answer

This is one of those pointless paper exercises that you would never do in the real world. I would not start from bromobenzene as $ce{Br}$ directs ortho/para, so this is going to take several steps.

You could make the phenyl Grignard or phenyllithium from bromobenzene quenching with DMF followed by aqueous acid workup to give benzaldehyde. Brominate this with $ce{BrCl}/ce{AlCl3}$ described here to give 3-bromobenzaldehyde then do a Wolff–Kishner reduction $(ce{H2NNH2}/ce{KOH})$ on the aldehyde to give 3-bromotoluene. I would not risk a Clemmensen $(ce{Zn}/ce{Hg}$ & conc. $ce{HCl})$ here as I think there is a danger of reducing the $ce{Ar-Br}$ to $ce{Ar-H}.$

Correct answer by Waylander on December 23, 2020

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