AZO COMPOUNDS

The name azo comes from azote, an old name of nitrogen that originates in French and is derived from the Greek a (not) + zoe (to live).

Azo compounds refer to chemical compound bearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl The N=N group is called an azo or diamide. Many of the more stable derivatives contain two aryl groups due to the electron delocalization. Because of this delocalization, many azo compounds are colored and in fact many are used as dyes.

Aromatic azo compounds (R = R' = aromatic) are usually stable and have vivid colors such as red, orange, and yellow. Therefore, they are used as dyes which are called azo dyes. Some azo compounds, eg. Methyl orange, can also be used as acid-base indicators, due to their ability to function as weak acids, and the different colors of the acid and salt forms. Azobenzene is another typical aromatic azo compound. Their color originates from absorbance in the visible region of the spectrum due to the delocalization of electrons in the benzene and azo groups forming a conjugated system, whereby the N=N group is the chromophore.

Aliphatic azo compounds (R and/or R' = aliphatic) are less common. One example is diethyldiazene
Synthesized Aromatic azo compounds can be synthesized by using an azo coupling reaction, that is, an electrophonic substitution reaction.on aromatic rings with diazonim salts. Diazonium salts decompose at temperatures warmer than about 5 degrees Celsius, so the reaction must take place in solution under freezing conditions

Diazonium salt synthesis

The most important method for the preparation of diazonium salts is treatment of aromatic amines such anline with sodium nitrate in the presence of mineral acid In aqueous solution these salts are unstable at temperatures higher than +5 °C. One can isolate diazonium compounds as the tetrafluoroborate salt, which is stable at room temperature, but typically diazonium compounds are not isolated and once prepared, used immediately in further reactions. The process of forming diazonium compound is called diazotation or diazotization.

Applications

The first use of diazonium salts was to produce water-fast dyed fabrics by immersing the fabric in an aqueous solution of the diazonium compound, then a solution of the coupler. Diazonium salts are light sensitive and break down under near UV or violet light. This