Wolff rearrangement
Encyclopedia
The Wolff rearrangement is a rearrangement reaction
converting a α-diazo
-ketone
into a ketene
. This reaction was first reported by Ludwig Wolff
in 1912.
The rearrangement is catalyzed by light, heat, or a transition metal
catalyst such as silver oxide. Nitrogen gas is expelled forming a carbenic
intermediate which rearranges. This 1,2-rearrangement
is the key step in the Arndt-Eistert synthesis
.
The reaction may or may not proceed in a concerted mechanism. A carbene intermediate is avoided if the reaction proceeds through the concerted mechanism. Mechanistic studies have been aimed at determining if migration is concerted with loss of nitrogen. The conclusion that has emerged is that a carbene is generated in photochemical reactions but the reaction can be concerted under the thermal conditions.
In one application, the Wolff rearrangement is performed in an electrochemical
setup in which the catalyst silver oxide is reduced
to elemental silver in the shape of monodisperse nanoparticles
(2-4 nm diameter) which trigger the decomposition of the diazoketone by the formation of a radical cation.
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...
converting a α-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...
-ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
into a ketene
Ketene
A ketene is an organic compound of the form R'RC=C=O. The term is also used specifically to mean ethenone, the simplest ketene, where R' and R are hydrogen atoms.Ketenes were first studied as a class by Hermann Staudinger.-Formation:...
. This reaction was first reported by Ludwig Wolff
Ludwig Wolff
Ludwig Wolff was a German chemist.He studied chemistry at the University of Strasbourg, where he received his Ph.D. from Rudolph Fittig in 1882. He became Professor at the University of Jena in 1891 and held this position till his death in 1919. In 1912 he published a new reaction now known as the...
in 1912.
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
catalyst such as silver oxide. Nitrogen gas is expelled forming a carbenic
Carbene
In chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called...
intermediate which rearranges. This 1,2-rearrangement
1,2-rearrangement
A 1,2-rearrangement or 1,2-migration or 1,2-shift or Whitmore 1,2-shift is an organic reaction where a substituent moves from one atom to another atom in a chemical compound. In a 1,2 shift the movement involves two adjacent atoms but moves over larger distances are possible...
is the key step in the Arndt-Eistert synthesis
Arndt-Eistert synthesis
The Arndt-Eistert synthesis is a series of chemical reactions designed to convert a carboxylic acid to a higher carboxylic acid homologue and is considered a homologation process...
.
The reaction may or may not proceed in a concerted mechanism. A carbene intermediate is avoided if the reaction proceeds through the concerted mechanism. Mechanistic studies have been aimed at determining if migration is concerted with loss of nitrogen. The conclusion that has emerged is that a carbene is generated in photochemical reactions but the reaction can be concerted under the thermal conditions.
In one application, the Wolff rearrangement is performed in an electrochemical
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
setup in which the catalyst silver oxide is reduced
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
to elemental silver in the shape of monodisperse nanoparticles
Nanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
(2-4 nm diameter) which trigger the decomposition of the diazoketone by the formation of a radical cation.