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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.
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]
An example is Disperse Orange 1. Some azo compounds, e.g., methyl orange, are used as acid-base indicators. ... Most azo dyes are prepared by azo coupling, ...
When the coupling partners are arenes such as anilines and phenols, the process is an example of electrophilic aromatic substitution: [ArN 2] + + Ar'H → ArN 2 Ar' + H + The deep colors of the dyes reflects their extended conjugation. A popular azo dye is aniline yellow, produced from aniline. [14]
The compound is a precursor to several cationic azo dyes via reaction of the chloroethyl group with tertiary amines or pyridine followed by azo coupling. Examples of derived dyes include C. I. Basic Red 18, Maxilon Red 2GL, and Yoracryl Red 2G. [1]
The dye is simple to prepare because the diamine serves both as a source of the diazonium cation and as the coupling partner in the azo coupling reaction. The synthesis is thought to start with double diazotization of 1,3-phenylenediamine: (H 2 N) 2 C 6 H 4 + 2 H + + 2 HNO 2 → [C 6 H 4 (N 2) 2] 2+ + 2 H 2 O
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Azobenzene is a photoswitchable chemical compound composed of two phenyl rings linked by a N=N double bond.It is the simplest example of an aryl azo compound.The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of similar compounds.