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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]
N-(1-Naphthyl)ethylenediamine dihydrochloride is widely used in the quantitative analysis of nitrate and nitrite in water samples by colorimetry.It readily undergoes a diazonium coupling reaction in the presence of nitrite to give a strongly colored azo compound.
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 ...
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.
Pigment Yellow 74 is an azo dye and classified as an arylide yellow. It is an intensely yellow-green solid. [1] It is prepared by azo coupling of the diazonium derivative of 2-methoxy-4-nitroaniline with 2-methoxyacetoacetanilide. [2] It is a flat molecule, enforced by the hydrogen-bonding via the ketohydrazide group. [3]
The compound is obtained by azo coupling of aniline and acetoacetanilide or their derivatives. The class of compounds was discovered in Germany in 1909. The initially formed diazo compound tautomerizes to give a ketohydrazone, which features extended pi-conjugation.
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