Elbs reaction
Encyclopedia
The Elbs reaction is an organic reaction
describing the pyrolysis
of an ortho methyl substituted benzophenone
to condensed polyaromatic. The reaction is named after its inventor, the German chemist Karl Elbs
also responsible for the Elbs oxidation. The reaction was published in 1884
Elbs however did not correctly interpret the reaction product due to a lack of knowledge about naphthalene
structure.
through dehydration
. Larger aromatic systems like pentacene
are also feasible. This reaction does not take place in a single step but leads first to dihydropentacene that is dehydrogenated in a second step with copper
as a catalyst.
The acyl
compounds required for this reaction can be obtained through a Friedel-Crafts acylation with aluminum chloride.
s via the Elbs reaction. In 1956 an Elbs reaction of a thiophene
derivative was published. The expected linear product was not obtained due to a change in reaction mechanism
after formation of the first intermediate which caused multiple free radical reaction steps.
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,...
describing the pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
of an ortho methyl substituted benzophenone
Benzophenone
Benzophenone is the organic compound with the formula 2CO, generally abbreviated Ph2CO. Benzophenone is a widely used building block in organic chemistry, being the parent diarylketone.-Uses:...
to condensed polyaromatic. The reaction is named after its inventor, the German chemist Karl Elbs
Karl Elbs
Karl Elbs , 13 September 1858 in Alt-Breisach, Baden, Germany – 24 August 1933) was a German chemist. He is credited with developing the Elbs reaction for the synthesis of anthracene. He is also responsible for the Elbs persulfate oxidation.-References:...
also responsible for the Elbs oxidation. The reaction was published in 1884
Elbs however did not correctly interpret the reaction product due to a lack of knowledge about naphthalene
Naphthalene
Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...
structure.
Scope
The Elbs reaction enables the synthesis of condensed aromatic systems. As already demonstrated by Elbs in 1884 it is possible to obtain anthraceneAnthracene
Anthracene is a solid polycyclic aromatic hydrocarbon consisting of three fused benzene rings. It is a component of coal-tar. Anthracene is used in the production of the red dye alizarin and other dyes...
through dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
. Larger aromatic systems like pentacene
Pentacene
Pentacene is a polycyclic aromatic hydrocarbon consisting of five linearly-fused benzene rings. This highly conjugated compound is an organic semiconductor. The compound generates excitons upon absorption of ultra-violet or visible light; this makes it very sensitive to oxidation...
are also feasible. This reaction does not take place in a single step but leads first to dihydropentacene that is dehydrogenated in a second step with copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
as a catalyst.
The acyl
Acyl
An acyl group is a functional group derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids.In organic chemistry, the acyl group is usually derived from a carboxylic acid . Therefore, it has the formula RCO-, where R represents an alkyl group that is...
compounds required for this reaction can be obtained through a Friedel-Crafts acylation with aluminum chloride.
Variations
It is also possible to synthesise heterocyclic compoundHeterocyclic compound
A heterocyclic compound is a cyclic compound which has atoms of at least two different elements as members of its ring. The counterparts of heterocyclic compounds are homocyclic compounds, the rings of which are made of a single element....
s via the Elbs reaction. In 1956 an Elbs reaction of a thiophene
Thiophene
Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromatic as indicated by its extensive substitution reactions. Related to thiophene are benzothiophene and dibenzothiophene, containing the thiophene ring fused with one and two benzene...
derivative was published. The expected linear product was not obtained due to a change in reaction mechanism
Reaction mechanism
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...
after formation of the first intermediate which caused multiple free radical reaction steps.