Azo group

Azo compound with the blue marked azo group

( E ) -isomer, more stable

( Z ) -isomer, less stable

In chemistry, the azo group is a functional group consisting of two nitrogen atoms linked by a double bond (–N = N–).

Organic compounds with azo group are called azo compounds. Azo compounds with aromatic radicals are azo dyes . The relatively unstable aliphatic azo compounds, such as. B. azoisobutyronitrile (AIBN) are used as polymerization initiators .

The name Azo is derived from the French word azote for nitrogen .

properties

The simplest inorganic compound with an azo group is the bright yellow diimine (H – N = N – H, diazen, diimide, azo hydrogen). It is unstable at room temperature, but can be synthesized at very low temperatures.

The simplest aliphatic azo compound is azomethane (H ₃ C – N = N – CH ₃ ), a yellowish, explosive gas that breaks down into methyl radicals and nitrogen at 60–100 ° C.

Among the aromatic azo compounds, the red azobenzene (H ₅ C ₆ –N = N – C ₆ H ₅ ) is the parent compound. In general, aromatic azo compounds are more stable than aliphatic ones. While the aliphatic azo compounds are usually colorless, the aromatic azo compounds are dyes . The more the π electrons are delocalized , the greater the wavelength of the maximum absorption .

With suitable substitution, azo-hydrazo-tautomerism is present in the case of azo compounds .

Manufacturing

Azo compounds are typically made by:

• Azo coupling , in which a diazonium salt reacts with a nucleophilic coupling component - usually an aromatic or a CH-acidic compound - in the sense of an electrophilic aromatic substitution .
• The oxidation of 1,2-alkyl or 1,2-aryl hydrazines with mercury (II) oxide, sodium hypobromite or atmospheric oxygen yields azo compounds.

See also

• Azo pigment

literature

• Organikum . Organic-chemical basic internship. 18th corrected edition. VEB Deutscher Verlag der Wissenschaften, Berlin 1990, ISBN 3-326-00076-6 .
• Ludwig Gattermann , Heinrich Wieland: The practice of the organic chemist. 43rd edition. de Gruyter, Berlin et al. 1982, ISBN 3-11-006654-8 .

Individual evidence

1. ^ Siegfried Hauptmann : Organic Chemistry , 2nd Edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985, p. 524, ISBN 3-342-00280-8 .
2. ^ ^{A b} Hans Beyer, Wolfgang Walter: Textbook of organic chemistry . 18th edition. S. Hirzel Verlag, Stuttgart 1978, ISBN 3-7776-0342-2 .
3. ^ Specialty Chemicals. Fujifilm WAKO Pure Chemical corporation, accessed December 17, 2018 . 
4. ^ Siegfried Hauptmann : Organic Chemistry , 2nd revised edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 524, ISBN 3-342-00280-8 .