Question

To synthesize m-ethylbenzenesulfonic acid, a student attempted the Friedel–Crafts alkylation of benzenesulfonic acid with bromoethane. Do you predict that this reaction was successful? If not, propose an alternative synthesis.

m-ethylbenzenesulfonic acid

Short answer

A chemical reaction in which alkyl halide (RX) is added to the benzene to produce alkyl benzene through an electrophilic attack is known as the Friedel-crafts alkylation reaction. Here an aromatic proton is replaced with an alkyl group.

Step-by-step solution

Friedel-Crafts Alkylation

A chemical reaction in which alkyl halide (RX) is added to the benzene to produce alkyl benzene through an electrophilic attack is known as the Friedel-crafts alkylation reaction. Here an aromatic proton is replaced with an alkyl group.

Alternative synthesis of m-ethylbenzenesulfonic acid

Friedel-crafts alkylation does not work on deactivated rings so it’s not possible to synthesize m-ethylbenzenesulfonic acid by Friedel-crafts alkylation of benzenesulfonic acid with bromoethane.

The alternative way to synthesize m-ethylbenzenesulfonic acid is shown below.

Here, firstly the alkylation of the benzene ring goes which adds the acetyl group to it. Later, the sulphonation of compound B goes which adds the sulhpo-group at the meta position of the deactivating ring. The carbonyl group extracts electron density (-R) from ortho/para position and not from meta.

In the end, the reduction of the carbonyl group with the help of Clemmensen reduction forms the final product.