Question

1. What function does a sulonic acid group serve in food coloring and other azo dyes

2.How can a sulfonic acid group be introduced in an aromatic ring. illustrate answer using reaction mechanism

Answer 1

Solution:

1) The food colorant is known as chromogen. Sulfonic group (-SO3H) intensify the color of food because it works as an auxochrome. Thus, it attached with coloring chromogen in foods and intensity the color due to bathocromic shift. In other dyes, it attached easily with chromophoric groups and intensify the color.

2) SO3H group is introduced in aromatic ring by using concentrated or fuming H2SO4.

When benzene is reacted with H2SO4, then it SO3H group is attached to benzene ring by electrophilic substitution reaction.

Mechanism:

H2SO4 === SO3H+ (electrophile) + OH-

C6H6 + (+SO3H) === C6H5SO3H