8.6.1.5 N-Arylhydroxylamines (Bamberger Rearrangement)

Arylhydroxyamines with acid undergoes rearrangement to give aminophenols. Mechanism of this reaction is different from those described above. In this rearrangement, the conjugate acid of the hydroxylamine undergoes nucleophilic attack by the solvent.

Examples:

8.6.2 Fries Rearrangement

Aryl esters with Lewis acid undergo rearrangement to give phenols having keto substituent at ortho and para positions. The complex between the ester and Lewis acid gives an acylium ion which reacts at the ortho and para positions as in Friedel-Crafts acylation.

Mechanism

In general, low temperature favors the formation of para- product (kinetic control) and high temperature lead to the formation ortho -product (thermodynamic control).