Diazotization is the reaction of primary amine and nitrite at low temperature to produce diazonium salt. The reaction of aromatic amine and nitrite to produce diazonium is diazotized. Aromatic amine is often used as a heavy nitrogen component and nitric acid is a diazo. Nitrous acid, which is usually produced by sodium nitrite and hydrochloric acid or sulfuric acid, reacts with the aromatic amine immediately to avoid the decomposition of nitrite. The diazonium salt is generated after diazotization due to the unstable nitrous acid.
The primary amine of aliphatic, aromatic and heterocyclic can undergo diazotization.
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group R−N2+X− where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halogen. Diazonium salts, especially those where R is an aryl group, are important intermediates in the organic synthesis of azo dyes.
The mechanism of diazotization is firstly by combining primary amine with diazotized reagent, then by a series of proton transfer, and finally the diazonium salt is generated. The form of diazotized reagent is related to the inorganic acid used. When weak acid is used, nitrite is balanced with nitric oxide in solution, and the effective diazotized reagent is nitrogen trioxide. When strong acid is used, the diazotized reagent is protonated nitrite and nitrosyl cation. Therefore, it is important to control the appropriate pH value in the diazo reaction. Aromatic primary amine is relatively weak and needs stronger nitrite reagent, so it usually reacts under strong acidity.
Azo coupling is the most widely practiced reaction of diazonium salts. In this process, the diazonium compound is attacked by, i.e., coupled to, electron-rich substrates. When the coupling partners are arenes such as anilines and phenols, the process is an example of electrophilic aromatic substitution:
Diazonium salt is widely used, and the reaction can be divided into two categories. One is that diazo base - H, - OH, -, - CN, X - NO2 groups are treated with appropriate reagents to generate the corresponding direction compounds, and aromatic diazonium salt was so called "Grignard reagent of aromatic". The other is to keep nitrogen reaction, that is, with the corresponding aromatic amine or phenol coupling reaction to generate azo dye (or indicator), such as ph indicator of commonly used methyl orange, red, Congo red, commonly used solid red dye A, trypan blue and so on.
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