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In organic chemistry, an azo coupling is an reaction between a diazonium compound (R−N≡N +) and another aromatic compound that produces an azo compound (R−N=N−R’).In this electrophilic aromatic substitution reaction, the aryldiazonium cation is the electrophile, and the activated carbon (usually from an arene, which is called coupling agent), serves as a nucleophile.
The first and still main use of diazonium salts is azo coupling, which is exploited in the production of azo dyes. [12] [13] In some cases water-fast dyed fabrics are simply immersed in an aqueous solution of the diazonium compound, followed by immersion in a solution of the coupler (the electron-rich ring that undergoes electrophilic ...
To illustrate the mechanism, the Japp-Klingemann ester variation will be considered. The first step is the deprotonation of the β-keto-ester. The nucleophilic addition of the enolate anion 2 to the diazonium salt produces the azo compound 3. Intermediate 3 has been isolated in rare cases.
Most azo dyes are prepared by azo coupling, which entails an electrophilic substitution reaction of an aryl diazonium cation with another compound, the coupling partner. Generally, coupling partners are other aromatic compounds with electron-donating groups: [ 7 ]
Since diazonium salts are often unstable near room temperature, the azo coupling reactions are typically conducted near 0 °C. The oxidation of hydrazines (R−NH−NH−R′) also gives azo compounds. [5] Azo dyes are also prepared by the condensation of nitroaromatics with anilines followed by reduction of the resulting azoxy intermediate:
Alizarine Yellow R is a yellow colored azo dye made by the diazo coupling reaction. It is usually commercially available as a sodium salt. In its pure form, it is a rust-colored solid. [2] It is mainly used as a pH indicator.
[8] [9] The diazotization reaction can be affected with nitrosonium salts such as [NO]SbF 6 without isolation of the diazonium intermediate. [2] As a practical matter, the traditional Balz–Schiemann reaction consumes relatively expensive BF 4 − as a source of fluoride. An alternative methodology produces the fluoride salt of the diazonium ...
The Griess test involves two subsequent reactions. When sulfanilamide is added, the nitrite ion reacts with it in the Griess diazotization reaction to form a diazonium salt, which then reacts with N-(1-naphthyl)ethylenediamine in an azo coupling reaction, forming a pink-red azo dye.