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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 Gomberg–Bachmann reaction, named for the Russian-American chemist Moses Gomberg and the American chemist Werner Emmanuel Bachmann, is an aryl-aryl coupling reaction via a diazonium salt. [1] [2] [3] The arene compound (here benzene) is reacted with a diazonium salt in the presence of a base to provide the biaryl through an intermediate ...
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group [R−N + ≡N]X − 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. The parent compound where R is hydrogen, is diazenylium.
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] ArN + 2 + Ar′H → ArN=NAr′ + H +
Azo compounds are organic compounds bearing the functional group diazenyl (R−N=N−R′, in which R and R′ can be either aryl or alkyl groups).. IUPAC defines azo compounds as: "Derivatives of diazene (diimide), HN=NH, wherein both hydrogens are substituted by hydrocarbyl groups, e.g. PhN=NPh azobenzene or diphenyldiazene.", where Ph stands for phenyl group. [1]
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. However, in most cases, the hydrolysis of intermediate 3 produces a tetrahedral intermediate 4 , which quickly decomposes to release the carboxylic acid 6 .
Anthranilic acid can be diazotized to give the diazonium cation [C 6 H 4 (CO 2 H)(N 2)] +. This cation can be used to generate benzyne, [20] dimerized to give diphenic acid, [21] or undergo diazonium coupling reactions such as in the synthesis of methyl red. [22] It reacts with phosgene to give isatoic anhydride, a versatile reagent. [23]
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.