Diazonium salts
Diazonium salts (selection) |
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Phenyldiazonium chloride ( aromatic diazonium salt) is somewhat stable in water at 0 ° C |
Methanediazonium chloride ( aliphatic diazonium salt) very unstable |
Diazonium salts are a class of organic-chemical compounds with the general structural formula Ar – N 2 + X - . Ar stands for an organic , aromatic aryl group and X - stands for an unspecified anion . The simplest representatives of this group of substances are the phenyldiazonium salts, which are reasonably stable at low temperatures. Aliphatic diazonium salts are unstable. When heated ( thermolysis ) or when irradiated ( photolysis ), carbenes are formed with the elimination of nitrogen (N 2 ) .
presentation
Aromatic diazonium salts can be prepared by diazotizing primary aromatic amines with nitrite in an acidic medium at low temperature.
properties
Pure diazonium salts are unstable, sometimes explosive and can only be handled in an aqueous solution (at temperatures <5 ° C). When trying to keep the salts anhydrous, they break down explosively, but can be stabilized with sterically demanding anions and then isolated.
Aromatic diazonium salts (here the phenyldiazonium cation) are significantly more stable than aliphatic diazonium salts because of the possible mesomeric stabilization of the positive charge:
use
- Aromatic diazonium salts are intermediates in the synthesis of aromatic compounds by attack by nucleophiles , e.g. B. in the so-called overcooking , in which phenols are formed, or in the Sandmeyer reaction , which leads to halogenated aromatics or aromatic nitriles .
- As weakly electrophilic reagents, aromatic diazonium cations attack other aromatics at electron-rich positions. During this reaction, the so-called azo coupling , azo dyes are then formed.
- In the diazotization of chiral α- amino acids , diazonium salts occur as intermediates, which react stereoselectively in aqueous solution to α- hydroxycarboxylic acids of the same configuration .
Individual evidence
- ^ Siegfried Hauptmann : Organische Chemie , Verlag Harri Deutsch, 1985, p. 531, ISBN 3-87144-902-4 .