Question

Organic Synthesis Tutorial: Azo-Coupling

Answer 1

\({\bf{Overall~Mechanism:}}\)

HNO2 is prepared in situ from HCl and NaOH (HNO2 is too unstable to be stored as a reagent by itself, so it must be prepared during the experiment in which it is to be used)

Then the HNO2 reacts with the aniline to create the diazonium intermediate, which is the stepping stone for synthesizing other dyes. The diazonium intermediate then undergoes addition with another compound (in this example, hydroxybenzene) to synthesize the dye.

Answer 2

to determine the final product structure, consider the ortho/para directing groups on the compound to be added. for example, -OH is a strong ortho/para director so substitution will preferentially occur at either the ortho/para position (with respect to the OH). Generally para is preferred over ortho due to the lack of steric hindrance.

Answer 3

\({\bf{Safety-Information:}}\)
> the reagents during the in situ synthesis of HNO2 are corrosive/otherwise harmful to skin/eyes
> the reagents during the in situ synthesis of HNO2 go into the aqueous waste container
> the reaction is vigorous and requires an ice bath

> filtrate from the azo coupling step also goes into aqueous waste

> dye solid and dye solution will be given their own waste disposal containers