organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...

, an azo coupling is an

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, Mechanistic Organ ...

between a

diazonium compound Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide. General propert ...

() and another aromatic compound that produces an azo compound (). In this electrophilic aromatic substitution reaction, the aryldiazonium cation is the electrophile and the activated arene is a

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

. In most cases, including the examples below, the diazonium compound is also aromatic.

Diazotization

The process of conversion of primary aromatic amines into its diazonium salt is called diazotization. Diazonium salts are important synthetic intermediates that can undergo coupling reactions to form

azo dyes Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C-N=N ...

and electrophilic substitution reactions to introduce functional groups.

Uses of the reaction

Aromatic azo compounds tend to be brightly colored due to the extended conjugated systems. Many are used as dyes (see

azo dye Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C-N=N ...

). Important azo dyes include methyl red and pigment red 170. Azo printing exploits this reaction as well. Azo coupling is also used to produce prontosil and other

sulfa drugs Sulfonamide is a functional group (a part of a molecule) that is the basis of several groups of drugs, which are called sulphonamides, sulfa drugs or sulpha drugs. The original antibacterial sulfonamides are synthetic (nonantibiotic) antim ...

Examples of azo C-coupling reactions

Many procedures have been described. Phenol reacts with benzenediazonium chloride to give a Solvent Yellow 7, a yellow-orange azo compound. The reaction is base-catalysed. : The related dye called aniline yellow is produced from the reaction of aniline and the diazonium salt. Naphthols are popular acceptors. One example is the synthesis of the dye "organol brown" from aniline and

1-naphthol 1-Naphthol, or α-naphthol, is a fluorescent organic compound with the formula . It is a white solid. It is an isomer of 2-naphthol differing by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues ...

: :

Similarly β-naphthol couples with

phenyldiazonium Benzenediazonium tetrafluoroborate is an organic compound with the formula 6H5N2F4. It is a salt of a diazonium cation and tetrafluoroborate. It exists as a colourless solid that is soluble in polar solvents. It is the parent member of the ary ...

electrophile to produce an intense orange-red dye.

Examples of azo N-coupling reactions

In alkaline media, diazonium salt can react with most primary and secondary amines that exist as a free base and produce triazene. This chemical reaction is called azo N-coupling or the synthesis of azoamines. PigmentYellow12corrected

References

{{DEFAULTSORT:Azo Coupling Substitution reactions Carbon-heteroatom bond forming reactions