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.

Friedel–Crafts alkylation is a key reaction in organic chemistry that involves the introduction of an alkyl group into an aromatic ring using a Lewis acid catalyst. This reaction typically requires a strong electrophile and can lead to polysubstitution or rearrangement of the alkyl group, which may complicate the desired product formation. The presence of electron-withdrawing groups, such as sulfonic acid, can deactivate the aromatic ring, making it less reactive towards alkylation.

Electron-withdrawing groups (EWGs) are substituents that pull electron density away from the aromatic ring, decreasing its nucleophilicity and reactivity in electrophilic aromatic substitution reactions. In the case of benzenesulfonic acid, the sulfonic acid group (-SO3H) is a strong EWG, which significantly reduces the ring's ability to undergo Friedel–Crafts alkylation. This makes the alkylation of benzenesulfonic acid with bromoethane unlikely to succeed.

When a direct synthesis route is hindered, alternative strategies must be considered. For synthesizing m-ethylbenzenesulfonic acid, one could first perform a Friedel–Crafts acylation to introduce an acyl group, followed by a reduction to form the desired alkyl group. This two-step process can help bypass the limitations imposed by the sulfonic acid group, allowing for successful synthesis of the target compound.