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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).

COSSH data and precautions:

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