Azo coupling

Source: Wikipedia, the free encyclopedia.
Not to be confused with
chromogenic photographic film
development.

In

arene, which is called coupling agent), serves as a nucleophile. Classical coupling agents are phenols and naphhthols.[1]
Usually the diazonium reagent attacks at the para position of the coupling agent. When the para position is occupied, coupling occurs at a ortho position, albeit at a slower rate.

Uses of the reaction

Aromatic azo compounds tend to be brightly colored due to their extended

pigment red 170
.

Azo printing exploits this reaction as well. In this case, the diazonium ion is degraded by light, leaving a latent image in undegraded diazonium salt which is made to react with a phenol, producing a colored image: the blueprint.[3]

sulfa drug
, was once produced by azo coupling. The azo compound is a prodrug that is activated in-vivo to produce the sufanilamide.

The reaction is also used in the Pauly reaction test to detect tyrosine or histidine residues in proteins.

Additionally, through the azo coupling reaction between the aromatic diazonium ion and aromatic amino acid residues, this reaction also be used to form or to modify proteins such as tRNA synthetase.[4]

Examples of azo C-coupling reactions

Illustrative is the reaction of

benzenediazonium chloride to give a Solvent Yellow 7, a yellow-orange azo compound. The reaction is faster at high pH.[2] Many other azo dyes have been prepared by similarly. Several procedures have been described in detail.[5][6] [7]

Naphthols are popular coupling agents. One example is the synthesis of the dye "organol brown" from aniline and 1-naphthol:

Synthesis of organol brown from aniline and 1-naphthol
Synthesis of organol brown from aniline and 1-naphthol

Similarly,

phenyldiazonium electrophile
to produce an intense orange-red dye.

Besides activated aromatic coupling agents, other nucleophilic carbons could also be coupled with diazonium salt:

Synthesis of C.I. Pigment Yellow 12, a diarylide pigment.

Examples of azo N-coupling reactions

Azo N-coupling under basic condition

In alkaline media, diazonium salt can react with most primary and secondary amines, which exist as a free base to produce triazene.[8] This chemical reaction is called azo N-coupling,[9] or the synthesis of azoamines.[10]

The dye called aniline yellow is produced by the reaction of aniline and a diazonium salt. In this case the C- and N-coupling compete.[2]


References

  1. ISBN 978-0-471-72091-1
  2. ^
    ISBN 978-3527306732
    .
  3. ISBN 978-3527306732
    .
  4. PMID 28787141
    .
  5. doi:10.15227/orgsyn.016.0012
    .
  6. doi:10.15227/orgsyn.002.0047
    .
  7. doi:10.15227/orgsyn.003.0007
    .
  8. S2CID 196805424
    .
  9. doi:10.1002/app.39069
    .
  10. ^ Serge Ratton, Bernard Botannet (1981). "Preparation of aromatic azoamines by diazotization/coupling/rearrangement of aromatic amines". US Patent 4275003A.
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