The Bamberger rearrangement is the chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

 of N-phenylhydroxylamines with strong aqueous acid

Acid

An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

, which will rearrange

Rearrangement reaction

A rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another atom in the same molecule...

 to give 4-aminophenols. It is named for the German chemist Eugen Bamberger

Eugen Bamberger

Eugen Bamberger was a German chemist and discoverer of the Bamberger rearrangement.-Life and achievements:Bamberger started studying medicine in 1875 at the University of Berlin, but changed subjects and university after one year, starting his studies of science at the University of Heidelberg in...

 (1857–1932).
N-Phenylhydroxylamines are typically synthesized from nitrobenzene

Nitrobenzene

Nitrobenzene is an organic compound with the chemical formula C6H5NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale as a precursor to aniline. Although occasionally used as a flavoring or perfume...

s by reduction

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 using rhodium

Rhodium

Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...

 or zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

.

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

Nitrenium ion

A nitrenium ion in organic chemistry is a reactive intermediate based on nitrogen with both an electron lone pair and a positive charge and with two substituents . Nitrenium ions are isoelectronic to carbenes, and can exist in either a singlet or a triplet state...

 4, which can react with nucleophiles (H₂O) to form the desired 4-aminophenol 5.