The Glaser coupling is a type of

coupling reaction In organic chemistry, a coupling reaction is a type of reaction in which two reactant molecules are bonded together. Such reactions often require the aid of a metal catalyst. In one important reaction type, a main group organometallic compound o ...

. It is by far one of the oldest coupling reactions and is based on copper compounds 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 gr ...

copper(I) bromide Copper(I) bromide is the chemical compound with the formula CuBr. This white 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 ...

and an additional oxidant like air. The base used in the original research paper is

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

and the solvent is water or an alcohol. The reaction was first reported by in 1869. He suggested the following process on his way to

diphenylbutadiyne Diphenylbutadiyne is the hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, ...

: :CuCl + PhC₂H + NH₃ → PhC₂Cu + NH₄Cl :4PhC₂Cu + O₂ → 2PhC₂C₂Ph + 2Cu₂O

Modifications

Eglinton reaction

In the related Eglinton reaction two terminal alkynes are coupled by a copper(II) salt such as cupric acetate. :2R-\!\!-H -> overset\ce\ce] R-\!\!-\!\!-R The oxidative coupling of alkynes has been used to synthesize a number of

natural product A natural product is a natural compound or substance produced by a living organism—that is, found in nature. In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by chemical s ...

s. The stoichiometry is represented by this highly simplified scheme: : Such reactions proceed via 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

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 In ...

Hay coupling

The Hay coupling is variant of the Glaser coupling. It relies on the

TMEDA Tetramethylethylenediamine (TMEDA or TEMED) is a chemical compound with the formula (CH3)2NCH2CH2N(CH3)2. This species is derived from ethylenediamine by replacement of the four amine hydrogens with four methyl groups. It is a colorless liquid, ...

complex of

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 anion 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 dye, indigo and developed a Von Baeyer nomenclature, nomenclature for cyclic compounds (that was subsequently extended a ...

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 indigo, blue color. Indigo is a natural dye obtained from the leaves of some plants of the Indigofera#Uses, ''Indigofera'' genus, in particular ''Indigofera tinctoria''. Dye-bearing ''Indigofer ...

. Shortly afterwards, Baeyer reported a different route to indigo, now known as the Baeyer–Drewson indigo synthesis.

References

{{Alkynes Carbon-carbon bond forming reactions Name reactions

Modifications

Eglinton reaction

Hay coupling

Scope

See also

References