Farbstoffverknüpfung

Farbstoffverknüpfung, also known as dye coupling, is a chemical reaction used in the synthesis of azo dyes. This process involves the electrophilic substitution of a diazonium salt onto an activated aromatic ring, typically a phenol or an amine. The diazonium salt is formed by the diazotization of a primary aromatic amine, which involves reacting the amine with nitrous acid at low temperatures. The resulting diazonium salt is then coupled with a coupling component, which contains an electron-donating group such as a hydroxyl or amino group, making the aromatic ring electron-rich and susceptible to electrophilic attack.

The reaction typically occurs in aqueous solution, often under slightly alkaline or acidic conditions depending on the specific reactants. The position of coupling is usually ortho or para to the activating group on the coupling component. The resulting azo compounds are characterized by the presence of an azo group (-N=N-) that links two aromatic rings. This azo group is responsible for the intense color of these dyes, as it forms part of a conjugated system that absorbs visible light. Farbstoffverknüpfung is a versatile and widely used method for producing a vast array of colors, making azo dyes the largest class of synthetic dyes. The specific color and properties of the dye can be finely tuned by altering the substituents on the aromatic rings of both the diazonium salt and the coupling component.