CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.6.5 Azo Compounds

Azo Compounds

  • Azo (or diazonium) compounds are organic compounds that have an R1-N=N-R2 group
  • They are often used as dyes and are formed in a coupling reaction between the diazonium ion and an alkaline solution of phenol

 

Nitrogen Compounds - Azo Compounds, downloadable AS & A Level Chemistry revision notes

Azo compounds are characterized by the presence of an R1-N=N-R2 group

Coupling of benzenediazonium chloride with phenol in NaOH

  • Azo compounds can be formed from the coupling reaction of a benzenediazonium chloride salt with alkaline phenol
  • Making an azo dye is a multi-step process

Formation of azo compounds table

Nitrogen Compounds - Formation of azo compounds table, downloadable AS & A Level Chemistry revision notes

Nitrogen Compounds - Formation Azo Compounds (1), downloadable AS & A Level Chemistry revision notes Nitrogen Compounds - Formation Azo Compounds (2), downloadable AS & A Level Chemistry revision notes

Reaction mechanism of the formation of azo compounds

  • The delocalised electrons in the π bonding systems of the two benzene rings are extended through the -N=N- which acts as a bridge between the two rings
  • As a result of the delocalisation of electrons throughout the compound, azo compounds are very stable

Making other azo dyes

  • Other dyes can be formed via a similar route as described above
  • For example, the yellow dye can be formed from the coupling reaction between benzenediazonium chloride and C6H5N(CH3)2 instead of phenol (C6H5OH)

 

Nitrogen Compounds - Forming Yellow Dye, downloadable AS & A Level Chemistry revision notes

The yellow azo dye is formed via a coupling reaction between benzenediazonium chloride and C6H5N(CH3)2

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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