The Azo Group

Azo compound refers to those compounds that have within them the azo group i.e the molecular structure —N=N—. They have the functional group diazenyl in them. The term azo is derived from the French word azote meaning nitrogen, which itself is derived from a Greek word.

Azo compounds are derivatives of diazine, in which both hydrogens are substituted with hydrocarbyl groups. Azo compounds are used to make a number of azo dyes and pigments which are used in a variety of industries.

These commercial dyes have the benzene group or its derivatives attached instead of the usual nitrogen. The attachment of the benzene groups gives the azo compound an aroma and is referred to as the aromatic azo compound.

Some samples of popular azo dyes are- methyl orange azo dye- widely used in textiles, dimethylamino azobenzene- which is the name of the red azo dye, benzene azo beta naphthol, etc.

Preparation of Azo Dye

Azo dyes are prepared using a simple process of diazotization and coupling. Their importance has been growing massively. Azo dyes today make up for more than half of the commercial dyes and dominate the printing press market.

  1. Generally, azo dyes are prepared by diazotization of a primary aromatic amine, then followed by coupling with one or more than one electron-rich nucleophile. Examples of electron-rich nucleophiles include- amino and hydroxy.

  2. Another method of preparing azo dyes is by first reducing nitroaromatic derivatives in an alkaline medium. 

  3. It can also be prepared by the oxidation of primary amines by potassium permanganate.

  4. Reduction of nitroso compounds by lithium aluminium hydride.

  5. Condensation of primary amines with nitroso derivatives.

Conclusively, azo dyes have a chemical structure in which there is a dominant auxochrome group, followed by the chromophoric group and then the solubilizing groups.

The color of the dye is dependent on the azo bond and the associated chromophores and auxochromes. Azo dyes are widely used in textile, print, and other industries. They make up for 70% of the world’s commercial dyes.

Azo dyes are characterized by chemical groups having the ability to form covalent bonds with textile substrates. The most common method of production is the diazotization of a primary amine aromatic and the coupling with a diazonium salt.

Use of Azo Dyes

Azo dyes have a variety of uses and this is the reason that they comprise on an average- 70% of the world’s commercial dyes. It is believed that around 2000 azo dyes are currently in the market. They are widely used in textile industries, printing market, biomedical industry, cosmetic, leather, paint, and other industries.

They Have the Characteristic Features of Being: 

  • Coloring functions

  • Antibacterial

  • Antiviral

  • Antifungal

  • Cytotoxic 


Within the biomedical field, the name of red azo dye is used as drug carriers, either by acting as a cargo that carries therapeutic agents or with the use of a prodrug approach.

They are also used in cellular staining to better view cellular compounds and metabolic processes. Researchers are also working on finding more possible uses of azo dyes in other biomedical fields, especially cancer diagnosis and chemotherapy, where its role is still in the early stages.


Azo dyes are present in cosmetic and skincare products such as hair dyes, face masks, make-up, conditioners, skincare lotions, nail paints, lipsticks, bath products such as scrubs, soaps, etc. and also in personal hygiene products such as sanitary napkins.

Manufacturing Industry

Azo dyes are a popular choice in the manufacturing industry because of the easy availability, cheap price point as well as easy usage. Azo dyes are widely used in the textile industry because they easily dye most fabrics like- silk, wool, viscose, and even synthetic ones.

Azo dyes are also used in tattoos, inks for printers, insecticides, pesticides, paints, varnishes, lacquers, and personal care products. 

Harmful Effects of Azo Compounds

Unfortunately, the harmful effects of azo compounds are not as well known as their usage is. Research studies have shown that these compounds can be carcinogenic, reproductive toxins, have cellular and neurological toxicants, irritants, allergens, environmental hazards, and developmental toxicants.

There are two types of azo dyes namely azo direct dyes and azo reactive dyes. The former has been found to be carcinogenic, mutagenic, and to have negative reproductive effects. The latter has been linked to increasingly active allergy risk.

Both of these types of diet are non-biodegradable, harmful to the environment as they accumulate in the oceans and affect the marine food chain. 

The Swedish chemicals agency said that these dyes can cause allergy on the skin, irritation to the eyes, and can also be toxic if swallowed or inhaled for a long period of time.

Another aspect of these dyes is that they can be absorbed by the skin and accumulate in the body, leading to a variety of problems.

These dyes are especially detrimental to the health of children and infants and their exposure causes various problems for them. Some samples of harmful azo dyes are:

  1. Congo Red- it has been classified as a substance of very high concern. It can cause cancer, damage to the unborn child, and even be toxic for reproduction.

  2. Aniline Yellow or Para Amino Azo Benzene– can cause cancer, be harmful to aquatic life, cause allergy reactions, and have long-term effects if swallowed.

  3. Pigment Red 4- It is a color that is restricted for use in Canada due to its potential detrimental health concerns.

  4. C.I Acid Red 114- It is again on the red list in Canada and can be carcinogenic.

FAQs (Frequently Asked Questions)

1. What is the Chemical Structure of Azo Compounds?

Answer. Azo compounds are characterized by being derivatives of diazine, wherein both hydrogens (HN=NH) are substituted with hydrocarbyl groups (PhN=NPh). 

They have the functional group diazenyl R-N=N-R’. They are vividly colorful and are thus used as dyes in multiple industries. Azo compounds can be Aryl azo or Alkyl azo. 

Aryl azo compounds are stable and crystalline. Azo benzene is used as the aromatic azo compound. The oxidation of hydrazine creates azo compounds (R-NH-NH-R).

Alkyl azo compounds are less commonly used. For example, diethyl diazene is an alkyl azo compound. In it, a racial initiator is used for the preparation of polymers.

2. Where are Azo Compounds Used?

Answer. It is no secret that azo compounds are widely used in almost all areas of life. As is mentioned above, they are widely used in feminine care products, dyeing clothes, in leather industries, and textile industries, in making payments and varnishes etc.

They are even used in everyday makeup products such as lipstick and bath products like shampoos and conditioners, scented body lotions, and more. The main reason behind their excessive use is easy availability, ease of use, cheap price, and the generalized mode of production.