It is well-established that a Lewis acid catalyst (popularly $\ce{ZnCl2})$ is necessary to form an alkyl chloride when reacting $\ce{HCl}$ with a primary alcohol. This actually changes the mechanism: the Lewis acid complexes with the alcohol and the resulting leaving group is $\ce{[Zn(OH)Cl2]-}$ instead of water. For $\ce{HBr}$ and $\ce{HI}$ this is technically not necessary.

However, practically speaking $\ce{HBr}$ alone is also insufficient as its azeotrope is insufficiently concentrated. Generally one adds conc. sulfuric acid to increase the acidity.

I am curious as to whether the addition of a Lewis acid could be used instead. Bromide is a stronger nucleophile (in protic solvents) than chloride, so I expect that it would. Has anyone ever tried this?



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