Bamberger rearrangement

The Bamberger rearrangement is the chemical reaction of phenylhydroxylamines with strong aqueous acid, which will rearrange to give 4-aminophenols. It is named for the German chemist Eugen Bamberger (1857–1932).



The starting phenylhydroxylamines are typically synthesized by the transfer hydrogenation of nitrobenzenes using rhodium or zinc catalysts.

One application is in the synthesis of fenhexamid.

Reaction mechanism
The mechanism of the Bamberger rearrangement proceeds from the monoprotonation of N-phenylhydroxylamine 1. N-protonation 2 is favored, but unproductive. O-protonation 3 can form the nitrenium ion 4, which can react with nucleophiles (H2O) to form the desired 4-aminophenol 5.