Diazonium Reduction To Arene

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Benzenediazonium chloride is warmed with hypophosphorous acid in water, and nitrogen gas is evolved; what is the principal aromatic product of this transformation?

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A diazonium group can be removed entirely from an aromatic ring and replaced by hydrogen, a process used to delete an amino-derived substituent after it has served as a directing or blocking group. Treating benzenediazonium chloride with hypophosphorous acid (H3PO2) in water reduces the diazonium ion, replacing the –N2+ group with –H and liberating nitrogen gas, so the product is simply benzene. The phenol option is wrong because that arises only when the salt is hydrolysed by warm water in the absence of a reducing agent. Chlorobenzene would require a Sandmeyer reaction with cuprous chloride, which is not present here. Nitrobenzene cannot form because no nitration occurs; the reaction is reductive, not oxidative. This deamination route is the standard NCERT method for using and then removing an amino group in aromatic synthesis. As a plausibility check, the loss of nitrogen gas and the formation of an unsubstituted ring confirm that the diazonium group has been cleanly replaced by hydrogen rather than by any nucleophile.

Diazonium Reduction To Arene

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