Azo compound
In
chemistry, azo compounds generally have a
molecular formula of the form R-N=N-R', in which R and R' can be either
aromatic or aliphatic. The N=N group is called an azo or diimide
functional group. This helps to stabilise the N=N group by making it part of an extended delocalised system. This also has the effect of making many azo compounds coloured, as delocalised or
conjugated systems often absorb visible frequencies of light.
The name azo comes from
azote, an old name of
nitrogen that originates in French and is derived from the Greek
a +
zoe .
Encyclopedia
In
chemistry,
azo compounds generally have a
molecular formula of the form R-N=N-R', in which R and R' can be either
aromatic or aliphatic. The N=N group is called an
azo or
diimide functional group. This helps to stabilise the N=N group by making it part of an extended delocalised system. This also has the effect of making many azo compounds coloured, as delocalised or
conjugated systems often absorb visible frequencies of light.
The name azo comes from
azote, an old name of
nitrogen that originates in French and is derived from the Greek
a +
zoe .
Aromatic azo compounds 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 colours of the acid and salt forms.
Azobenzene is another typical aromatic azo compound. Their colour 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 are rather unstable. At an elevated temperature or by irradiation, two
carbon-nitrogen bonds are cleaved simultaneously with the loss of nitrogen gas to generate carbon-centered
radicals. Owing to this process, some aliphatic azo compounds are utilized as radical initiators.
Azobisisobutylonitrile is a typical one and is widely used in industrial processes and in laboratory experiments.
Aromatic azo compounds can be synthesized by using an azocoupling reaction, that is, an
electrophilic substitution reaction on aromatic rings with
diazonium salts. Diazonium salts decompose at temperatures warmer than about 5 degrees Celsius, so the reaction must take place in solution under freezing conditions:
An
oxidation reaction of
hydrazine also gives an azo compound.
Because of their instability, especially for aliphatic ones, care should be taken with the handling of azo compounds or an
explosion may occur.
