- Azo Dye Synthesis. Illustrate your essay with specific exa...
Azo Dye Synthesis. Illustrate your essay with specific examples.
Azo dyes form a class of compounds that are widely used as food
additives as well as coloring agents in textile industry (Gordon
and Gregory, 1983; Fierz-David and Blangey, 1949). They constitute
sixty to seventy percent of the dyes used for industrial purposes.
The term "Azo" comes from the French term "Azote" which denotes
nitrogen. The general formula of azo dye is R-N=N-R', where N
stands for Nitrogen and R stands for an alkyl (groups containing
methyl, ethyl, propyl or other similar moieties) or aryl (aromatic
moieties especially benzene) groups. The group -N=N- is called the
Azo group. Azo dyes may have more than one azo group. Azo dyes come
in a number of hues; however, the yellow and red ones are in
preponderance. The different colors are generated by using
different compounds for the reaction.
Azo dye synthesis using a two step reaction:
Experiment for Azo-coupling
In the following example, 2, 6 dibromo-4-methyl diazonium
chloride generated in the previous experiment is used to react with
para-cresol (also known as 4- methyl phenol) to produce azo dye and
hydrochloric acid. In this case since phenol is acidic, it is
dissolved in 1 molar sodium hydroxide, cooled and diazonium salt
added to it to produce the azo dye.
Figure 2: Step 2 for Azo dye synthesis (Azo-coupling).
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