Why do you use acetanilide rather than aniline in the synthesis of 4-acetamidobenzenesulfonyl chloride?

Answer 1

Sulfanilamide has two groups on the benzene ring in para- positions to each other. The amino group is a highly activating ortho-directing group and the sulfonamide group is a meta-directing group.

Consequently, the amino group must be introduced first followed by the introduction of the sulfonamide group. To introduce the sulfonamide group one must first use chlorosulfonic acid then ammonium hydroxide.

Unfortunately, amino groups react with chlorosulfonic acid leading to undesired products and the direct chlorosulfonation of aniline would not lead to the desired intermediate product. However, if the amino group is converted to an amide, the undesired side reaction with chlorosulfonic acid is avoided. The acetyl group in this

case serves as a "protecting group" for the amine that allows a smooth chlorosulfonation of the benzene ring.

The amide nitrogen does not activate the ring towards substitution as much as the free amino group, but it can still exert its ortho/para- directing influence. In this case the steric hindrance provided by the acetyl group results in the substitution occurring predominantly at the para- substitution. The protecting acetyl group is removed later to give the desired "free" amino group. The protection of groups that would interfere with a given step in a synthesis is not uncommon, but I it is necessary for the "protecting group" to be introduced and removed readily by reactions that will not adversely affect other groups in the molecule.

REFERENCE: http://www.uwf.edu/chemistry/faculty/Gurst/SULFANIL.pdf Sulfanilamide has two groups on the benzene ring in para- positions to each other. The amino group is a highly activating ortho-directing group and the sulfonamide group is a meta-directing group.

Consequently, the amino group must be introduced first followed by the introduction of the sulfonamide group. To introduce the sulfonamide group one must first use chlorosulfonic acid then ammonium hydroxide.

Unfortunately, amino groups react with chlorosulfonic acid leading to undesired products and the direct chlorosulfonation of aniline would not lead to the desired intermediate product. However, if the amino group is converted to an amide, the undesired side reaction with chlorosulfonic acid is avoided. The acetyl group in this

case serves as a "protecting group" for the amine that allows a smooth chlorosulfonation of the benzene ring.

The amide nitrogen does not activate the ring towards substitution as much as the free amino group, but it can still exert its ortho/para- directing influence. In this case the steric hindrance provided by the acetyl group results in the substitution occurring predominantly at the para- substitution. The protecting acetyl group is removed later to give the desired "free" amino group. The protection of groups that would interfere with a given step in a synthesis is not uncommon, but I it is necessary for the "protecting group" to be introduced and removed readily by reactions that will not adversely affect other groups in the molecule.

REFERENCE: http://www.uwf.edu/chemistry/faculty/Gurst/SULFANIL.pdf Sulfanilamide has two groups on the benzene ring in para- positions to each other. The amino

group is a highly activating ortho-directing group and the sulfonamide group is a meta-directing group.

Consequently, the amino group must be introduced first followed by the introduction of the sulfonamide

group. To introduce the sulfonamide group one must first use chlorosulfonic acid then ammonium hydroxide.

Unfortunately, amino groups react with chlorosulfonic acid leading to undesired products and the direct

chlorosulfonation of aniline would not lead to the desired intermediate product. However, if the amino group is

converted to an amide, the undesired side reaction with chlorosulfonic acid is avoided. The acetyl group in this

case serves as a "protecting group" for the amine that allows a smooth chlorosulfonation of the benzene ring.

The amide nitrogen does not activate the ring towards substitution as much as the free amino group, but it can

still exert its ortho/para- directing influence. In this case the steric hindrance provided by the acetyl group

results in the substitution occurring predominantly at the para- substitution. The protecting acetyl group is

removed later to give the desired "free" amino group. The protection of groups that would interfere with a

given step in a synthesis is not uncommon, but I it is necessary for the "protecting group" to be introduced and

removed readily by reactions that will not adversely affect other groups in the molecule.

From: http://www.uwf.edu/chemistry/faculty/Gurst/SULFANIL.pdf