Diazotization

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The diazotization is a reaction of organic chemistry and describes the reaction of aromatic amines with cold dilute nitrous acid (HNO 2 ) to aryldiazonium salts .

Overview of diazotization

The diazotization of bifunctional aromatic amines is also known as tetrazotization (e.g. p- phenylenediamine or benzidine ).

Reaction mechanism

First the nitrous acid 1 is protonated. The electrophilic nitrosyl cation 3 is formed with the elimination of water .

Formation of a nitrosyl cation

In practice, nitrous acid (HNO 2 ) is often only formed in the reaction mixture of sodium nitrite (NaNO 2 ) and the mineral acid.

Then the lone pair of electrons on the nitrogen atom on arylamine 4 attacks the positively charged nitrogen atom of the nitrosyl cation. A diazo hydroxide 7 is formed with deprotonation and rearrangement . This compound is protonated at the oxygen atom and an aryldiazonium cation 9 is formed when a water molecule is split off .

Mechanism of diazotization

Aryldiazonium salts are very reactive and have many uses in synthesis, in particular for the preparation of azo dyes by azo coupling . Diazotization is a standard method for determining the content of primary aromatic amines. The synthesis of aryldiazonium salts is carried out at temperatures below 5 ° C. The highly reactive diazonium salts would decompose quickly at higher temperatures. The reaction is therefore continued in situ , i.e. without isolating the intermediate products. Aryldiazonium chlorides are highly explosive in the solid, dry state. The tetrafluoroborates [BF 4 ] - or hexafluorophosphates [PF 6 ] - are more stable and can be handled as solids.

Reactions of aryldiazonium salts

literature

Individual evidence

  1. ↑ T. Laue, A. Plagens: Name and catchword reactions of organic chemistry . Teubner Verlag, 2006, ISBN 3-8351-0091-2 , p. 94 .