Diazoniumsalze

Diazoniumsalze are a class of organic compounds containing the functional group R−N₂⁺X⁻, where R is an organic group, N₂⁺ is the diazonium group, and X⁻ is an anion. They are typically formed by the reaction of a primary aromatic amine with nitrous acid (generated in situ from sodium nitrite and a strong acid) at low temperatures. This process is known as diazotization.

Diazoniumsalze are highly reactive and serve as important intermediates in organic synthesis. The diazonium group is an excellent leaving group, which facilitates a variety of substitution reactions. A well-known reaction is the Sandmeyer reaction, where the diazonium group is replaced by a halogen (Cl, Br) or a cyanide group (CN) using copper(I) salts. The Schiemann reaction allows for the introduction of a fluorine atom by heating the diazonium tetrafluoroborate salt.

Another significant application is in the synthesis of azo dyes. Diazoniumsalze readily couple with electron-rich aromatic compounds, such as phenols or anilines, to form azo compounds, which are characterized by the −N=N− functional group. These azo compounds are often intensely colored and are widely used as dyes and pigments.

Due to their instability, diazoniumsalze are usually prepared and used immediately in situ. They can be explosive when dry, especially those derived from aliphatic amines, which are generally much less stable than their aromatic counterparts. Aromatic diazoniumsalze, while more stable, are still typically handled at low temperatures (0-5 °C) to prevent decomposition.