The Dimroth rearrangement is a rearrangement reaction

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...

 taking place with certain 1,2,3-triazole

1,2,3-Triazole

1,2,3-Triazole is one of a pair of isomeric chemical compounds with molecular formula C2H3N3, called triazoles, which have a five-membered ring of two carbon atoms and three nitrogen atoms...

s where endocyclic and exocyclic nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 atoms switch place . This organic reaction

Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis,...

 was discovered in 1909 by Otto Dimroth

Otto Dimroth

Otto Dimroth was a German chemist. He is known for the Dimroth rearrangement, as well as a type of condenser with an internal double spiral, the Dimroth condenser....

  .

With R a phenyl group the reaction takes place in boiling pyridine

Pyridine

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...

 for 24 hours

This type of triazole has a amino group in the 5 position. After ring-opening to a diazo

Diazo

Diazo refers to a type of organic compound called diazo compound that has two linked nitrogen atoms as a terminal functional group. The general formula is R2C=N2. The simplest example of a diazo compound is diazomethane...

 intermediate, C-C bond rotation is possible with 1,3-migration of a proton.

Certain 1-alkyl-2-iminopyrimidine

Pyrimidine

Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring...

s also display this type of rearrangement.

In the first step is an addition reaction

Addition reaction

An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one....

 of water followed by ring-opening of the hemiaminal

Hemiaminal

A hemiaminal is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: -C-. R can be hydrogen or an alkyl group...

to the aminoaldehyde followed by ring closure.