The Glaser coupling is a type of
coupling reaction A coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R = ...
. It is by far the oldest acetylenic coupling and is based on cuprous salts like
copper(I) chloride
Copper(I) chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid. Impure samples appear gre ...
or
copper(I) bromide
Copper(I) bromide is the chemical compound with the formula CuBr. This diamagnetic solid adopts a polymeric structure akin to that for zinc sulfide. The compound is widely used in the synthesis of organic compounds and as a lasing medium in c ...
and an additional oxidant like oxygen. The base in its original scope is
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
. The solvent is water or an alcohol.
The reaction was first reported by in 1869. He suggested the following process for his way to diphenylbutadiyne:
:CuCl + PhC
2H + NH
3 → PhC
2Cu + NH
4Cl
:2PhC
2Cu + O → PhC
2C
2Ph + Cu
2O
Modifications
Eglinton reaction
In the related Eglinton reaction two terminal alkynes are coupled by a copper(II) salt such as
cupric acetate.
:
2R-\!\!-H -> ce\ce] R-\!\!-\!\!-R
The oxidative coupling of alkynes has been used to synthesize a number of fungal antibiotics. The stoichiometry is represented by this highly simplified scheme:
:
Such reactions proceed via
metal-alkyne complex, copper(I)-alkyne complexes.
This methodology was used in the synthesis of
cyclooctadecanonaene
Cyclooctadecanonaene or 8nnulene is an organic compound with chemical formula . It belongs to the class of highly conjugated compounds known as annulenes and is aromatic. The usual isomer that 8nnulene refers to is the most stable one, containi ...
. Another example is the synthesis of
diphenylbutadiyne
Diphenylbutadiyne is the organic compound with the formula (C6H5C2)2. It is a common diyne. It is the product of the coupling of phenylacetylene
Phenylacetylene is an alkyne hydrocarbon containing a phenyl group. It exists as a colorless, vi ...
from
phenylacetylene
Phenylacetylene is an alkyne hydrocarbon containing a phenyl group. It exists as a colorless, viscous liquid. In research, it is sometimes used as an analog for acetylene; being a liquid, it is easier to handle than acetylene gas.
Preparation
I ...
.
Hay coupling
The Hay coupling is variant of the Glaser coupling. It relies on the
TMEDA complex of
copper(I) chloride
Copper(I) chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid. Impure samples appear gre ...
to activate the terminal alkyne. Oxygen (air) is used in the Hay variant to oxidize catalytic amounts of Cu(I) to Cu(II) throughout the reaction, as opposed to a stoichiometric amount of Cu(II) used in the Eglington variant. The Hay coupling of
trimethylsilylacetylene
Trimethylsilylacetylene is the organosilicon compound with the formula . A colorless liquid, "tms acetylene", as it is also called, is used as a source of "HC2−" in organic synthesis.
Use
Trimethylsilylacetylene is used in Sonogashira couplin ...
gives the butadiyne derivative.
Scope
In 1882
Adolf von Baeyer
Johann Friedrich Wilhelm Adolf von Baeyer (; 31 October 1835 – 20 August 1917) was a German chemist who synthesised indigo and developed a nomenclature for cyclic compounds (that was subsequently extended and adopted as part of the IUPAC org ...
used the method to prepare 1,4-bis(2-nitrophenyl)butadiyne, en route to
indigo dye
Indigo dye is an organic compound with a distinctive blue color. Historically, indigo was a natural dye extracted from the leaves of some plants of the ''Indigofera'' genus, in particular ''Indigofera tinctoria''; dye-bearing ''Indigofera'' pla ...
.
Shortly afterwards, Baeyer reported a different route to indigo, now known as the
Baeyer–Drewson indigo synthesis
The Baeyer–Drewson indigo synthesis (1882) is an organic reaction in which indigo is prepared from 2-nitrobenzaldehyde and acetone The reaction was developed by von Baeyer in 1880 to produce the first synthetic indigo at laboratory ...
.
See also
*
Cadiot–Chodkiewicz coupling
The Cadiot–Chodkiewicz coupling in organic chemistry is a coupling reaction between a terminal alkyne and a haloalkyne catalyzed by a copper(I) salt such as copper(I) bromide and an amine base.Cadiot,
P.; Chodkiewicz, W. In Chemistry of Acety ...
- Another alkyne coupling reaction catalysed by copper(I).
*
Sonogashira coupling
The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon–carbon bonds. It employs a palladium catalyst as well as copper co-catalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or v ...
- Pd/Cu catalysed coupling of an alkyne and an aryl or vinyl halide
*
Castro–Stephens coupling - A cross-coupling reaction between a
copper(I) acetylide
Copper(I) acetylide, or cuprous acetylide, is a chemical compound with the formula Cu2 C2. Although never characterized by X-ray crystallography, the material has been claimed at least since 1856. One form is claimed to be a monohydrate with for ...
and an aryl halide
*
Fritsch–Buttenberg–Wiechell rearrangement
The Fritsch–Buttenberg–Wiechell rearrangement, named for Paul Ernst Moritz Fritsch (1859–1913), Wilhelm Paul Buttenberg, and Heinrich G. Wiechell, is a chemical reaction whereby a 1,1-diaryl-2-bromo-alkene rearranges to a 1,2-diaryl- alkyne ...
- can also form diynes
References
{{Alkynes
Carbon-carbon bond forming reactions