Why is the extensive multi-step synthesis of aryl halides via benzenediazonium salt intermediates consistently preferred over simple, single-step direct electrophilic halogenation for targeting comple

Question

Why is the extensive multi-step synthesis of aryl halides via benzenediazonium salt intermediates consistently preferred over simple, single-step direct electrophilic halogenation for targeting complex, specifically substituted aromatic isomers?

Prashant Kotian · Accepted Answer

Correct answer: B. Direct halogenation of an arene (e.g., toluene) typically yields an inseparable mixture of ortho and para isomers due to the directing effects of existing substituents. In contrast, synthesizing via a diazonium salt involves nitration (often isomerically separable), reduction to an amine, and diazotization. The group is an exceptional leaving group that is replaced exclusively at its exact location. This guarantees absolute positional control, allowing chemists to synthesize a pure ortho, meta, or para isomer without contamination from regional byproducts.

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