Electrophilic Substitution Reaction - Azo Coupling Reaction

Chemistry | Organic Chemistry

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General Aim of Electrophilic Substitution Reaction-Azo Coupling

Diazotization of phenolic and aromatic amines to study the electrophilic aromatic substitution mechanism and understand how electrophilic aromatic substitution effects influence reaction outcomes.

Method of Electrophilic Substitution Reaction-Azo Coupling

Azo coupling reactions are used for the diazotization of phenols and aromatic amines to produce azo dyes, and some sulfa drugs.

Learning Objectives (ILOs)

  •  Become proficient at running organic chemical reactions through electrophilic aromatic substitution experiment.

  • Learning basics of organic synthesis procedures and understanding the detailed electrophilic aromatic substitution mechanism.
  • Understand the mechanism of Azo coupling reaction and how it exemplifies electrophilic aromatic substitution effects in organic synthesis.
  • Learn the function of the Azo coupling reaction process.
  • Get trained on how the reaction is used during the electrophilic substitution reaction. 

Theoretical Background / Context

  • Azo coupling reactions are a major class of organic chemical reactions that are utilized to prepare several organic molecules, especially organic dyes such as methyl orange. 
  • Azo compounds are characterized by their colors due to possessing electronically conjugated systems within their chemical structure. 
  • They have a broad range of colors that depend on the structure of each dye. 
  • Azo coupling reactions occur through the electrophilic attack of diazonium ions on electron rich aromatic rings containing compounds such as phenols and aromatic amines. 
  • Electrophilic diazonium ions should be freshly prepared just prior to use in azo coupling reactions as they are unstable. 
  • Moreover, their stability can be increased through their keeping in an ice bath. 
  • Diazonium ions can be prepared through the reaction between sodium nitrite and primary aromatic amines in the  acidic medium at low temperature as shown in the below scheme.

                             

                                Figure 1. Diazonium ion formation.

Principle of Work

In the electrophilic substitution reaction experiment: 

  • Azo coupling reaction is carried out through diazotization of some phenolic and aromatic amines compounds such as 1-naphthol, 2-naphthol & N,N-dimethylaniline to prepare some colored dyes such as methyl orange.

        

1-Naphthol                   2-Naphthol                N,N-dimethylaniline          

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