Question

Show how to prepare the following aromatic amines by aromatic nitration, followed by reduction. You may use benzene and toluene as your aromatic starting materials.

1. Aniline
2. p-bromoaniline
3. m-bromoaniline
4. m-aminobenzoic acid

Short answer

(a)

(b)

(c)

(d)

Step-by-step solution

Step-1. Explanation of part (a):

Nitration happens when one (or more) of the hydrogen atoms on the benzene ring is replaced by a nitro group. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at high temperature. During nitration, a nitronium ion is formed when nitric acid undergoes a reaction with sulfuric acid. Nitronium serves as an electrophile which is attacked by the nucleophilic benzene ring. Resulting product of nitration is nitrobenzene.

In part (a), nitration of benzene gives nitrobenzene which on reduction with tin and hydrogen chloride mixture gives aniline.

Formation of the required product

Step-2. Explanation of part (b):

Nitration happens when one (or more) of the hydrogen atoms on the benzene ring is replaced by a nitro group. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at high temperature. During nitration, a nitronium ion is formed when nitric acid undergoes a reaction with sulfuric acid. Nitronium serves as an electrophile which is attacked by the nucleophilic benzene ring. Resulting product of nitration is nitrobenzene.

In part (b), bromination of benzene gives bromobenzene which on nitration gives mixture of para and ortho-nitro bromobenzene. Halogens are ortho and para directing. Para product on reduction with iron and hydrogen chloride mixture gives the required product.

Formation of the required product

Step-3. Explanation of part (c):

Nitration happens when one (or more) of the hydrogen atoms on the benzene ring is replaced by a nitro group. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at high temperature. During nitration, a nitronium ion is formed when nitric acid undergoes a reaction with sulfuric acid. Nitronium serves as an electrophile which is attacked by the nucleophilic benzene ring. Resulting product of nitration is nitrobenzene.

In part (c), nitrobenzene on bromination results in product in which bromo group is at meta to nitro group due to directive influence of nitro group. Further, on reduction with tin and hydrogen chloride mixture, required product is obtained.

Formation of the required product

Step-4. Explanation of part (d):

Nitration happens when one (or more) of the hydrogen atoms on the benzene ring is replaced by a nitro group. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at high temperature. During nitration, a nitronium ion is formed when nitric acid undergoes a reaction with sulfuric acid. Nitronium serves as an electrophile which is attacked by the nucleophilic benzene ring. Resulting product of nitration is nitrobenzene.

In part (d), toluene on reaction with potassium permanganate gives benzoic acid which on nitration results in product in which nitro group is at meta position to the carboxylic group due to directive influence of carboxylic group. Further, on reduction with iron and hydrogen chloride, required product is obtained.

Formation of the required product