How are azo dyes formed?
Most azo dyes are synthesized by diazotization of an aromatic primary amine, followed by coupling with one or more electron-rich nucleophiles such as amino and hydroxy [2]. The azo group may be bonded to benzene rings, naphthalenes, aromatic heterocycles or to enolizable aliphatic groups [12].
What are azo dyes with example?
The azo dyes, also called aryl azo compounds, are a large group of chemical compounds with vivid colors that share a similar molecular structure. The group includes, for example, congo red, aniline yellow, and Ci direct black.
How do azo dyes work?
They are synthetic compounds characterized by one (monoazo) or several intramolecular NQN bonds. Azo dyes, if they are systemically absorbed, can be metabolized via azoreductases of intestinal microflora by liver cells and skin surface bacteria. This metabolism leads to aromatic amines that can be hazardous.
What is azo dyes textile?
Azo dyes are the largest group of synthetic aromatic dye used in the textile industry for dyeing purpose and are highly water soluble in nature. It consist of one or more azo (−N=N−) groups and sulfonic (SO3−) groups and are of huge commercial interest [2, 9].
Why are azo dyes colored?
Azo dyes are coloured because they contain alternating single and double bonds, known as a conjugated system. This creates and areas of delocalisation above and below the plane of the molecule.
Who invented azo dye?
Peter Greiss
Azo chromophores were first discovered in 1863 when Martius and Lightfoot coupled diazonium ions and amines. Within the year, Peter Greiss prepared Bismarck brown, the first azo dye. By the 1880s numerous other azo dyes, such as para red and primuline red, were developed.
How is azo dye prepared from phenol?
Phenol is dissolved in sodium hydroxide solution to give a solution of sodium phenoxide. The solution is cooled in ice, and cold benzenediazonium chloride solution is added. There is a reaction between the diazonium ion and the phenoxide ion and a yellow-orange solution or precipitate is formed.
What chemicals are in azo dyes?
Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl. They are a commercially important family of azo compounds, i.e. compounds containing the linkage C-N=N-C. Azo dyes are widely used to treat textiles, leather articles, and some foods.
What is colorant made of?
Dyes are soluble coloured organic compounds that are usually applied to textiles from a solution in water. They are designed to bond strongly to the polymer molecules that make up the textile fibre….Classification of colorants by methods of application.
| Dye | Fibre |
|---|---|
| Sulfur | Cotton, linen |
What structural feature of an azo dye is responsible for its intensive color?
The azo dyes constitute the largest chemical class, containing at least 66% of all colorants. The characteristic feature is the presence in the structures of one or more azo groups, together with hydroxyl groups, amine and substituted amine groups as auxochromes.