Azo derivative

An azo group is a functional group of the type R-N=N-R', where R and R' are groups that contain carbon atoms, and the nitrogen atoms are linked by a double bond. Compounds containing the bond -N=N- are called azo derivatives, azo compounds, or azo compounds.

When the azo group is conjugated with two aromatic rings, the compound that contains it absorbs electromagnetic radiation in the visible spectrum, which is why it presents coloration and, moreover, it is intense. For this reason they are used as dyes in the textile, paper, food industry, etc. For example, p-dimethylaminoazobenzene was used as a colorant in margarine.

The presence of other groups in the compound can cause it to absorb at different wavelengths (so different compounds with different colors are obtained). They can also cause the compound to absorb light with more or less intensity. Likewise, some groups (for example sulfonic groups) serve to make the compound soluble in the medium in which it is going to be applied.

In 1884, Congo Red was synthesized, an azo dye that was used to dye cotton, and azo dyes are currently the most widely used in the textile industry.

Methyl orange

These compounds are also used as indicators in acid-base titrations. For example, methyl orange (or methyl orange). Depending on the pH, methyl orange can have the azo group protonated or not, thus presenting different colors depending on the pH.

There has been talk of their danger as carcinogenic agents

Organic Chemistry

Aryl or Allyl Azo Compounds

Aryl azo compounds are usually stable, crystalline species. Azobenzene is the prototypical azo aromatic compound. It exists primarily as the trans isomer, but through photolysis, it is converted to the cis isomer. Aromatic azo compounds can be synthesized using the diazo coupling reaction, which involves an electrophilic aromatic substitution reaction, where an aryl diazonium cation attacks another aryl ring, especially those that have electron-releasing groups. Since aryl diazonium salts Diazonium are usually unstable near room temperature, diazo coupling reactions are usually carried out at low temperatures (around 0 °C). Oxidation of hydrazines also produces azo compounds.

Alkyl Azo Compounds

Aliphatic azo compounds ((R and/or R' = aliphatic) are less common than aryl azo compounds. An example is diethyldiazene, EtN=NEt. At elevated temperatures or irradiation, carbon bonds -nitrogen (C-N) in certain alkyl azo compounds cleave on loss of nitrogen gas to generate free radicals. Due to this process, some aliphatic azo compounds are used as radical initiators. A representative example is azobisisobutylonitrile (AIBN), which is widely used as an initiator in polymerization.Because of its instability, especially for aliphatics, care must be taken when handling azo compounds, or an explosion may occur.