Chapter 23, Problem 23.71P

Interpretation Introduction

Interpretation:

The structures of the arenediazonium ion and the separate aromatic compound that would react to form the azo dye tartrazine are to be drawn. The complete mechanism for the reaction is to be drawn.

Concept introduction:

Arenediazonium ion has a positively charged nitrogen as a part of the ${\text{-N}}_{\text{2}}{}^{\text{+}}$ substituent. This makes it an electrophile that can add to another aromatic ring in an electrophilic aromatic substitution reaction. The reaction is an electrophilic addition-substitution reaction. The $\text{π}$ electron pair of the activated aromatic ring attacks the electrophilic diazo group of the arenediazonium ion, forming an arenium ion intermediate with an azo coupling, $-\text{N}=\text{N}-$. In the next step, the hydrogen from the carbon that formed the bond with the diazo group is extracted by a base. The $\text{C}-\text{H}$ bond pair moves to the other atom of the substrate to reform the aromatic ring and the final product.