Clemmensen Reduction

If 4-hydroxy-3-methoxybenzaldehyde undergoes Clemmensen reduction, will the hydroxyl group (OH) be converted to a chloro group (Cl)?


I know that it happens in cyclohexanes, and I am not sure if this is true for aromatic compounds as well.




You're right about the side reaction (hydroxy-halogen exchange) in the case of cyclohexanols. It is nucleophilic substitution on a (secondary) alkanol under acidic conditions.


In the case of vanillin, your starting material, the situation is different. Under the conditions of the *Clemmensen* reaction, that is in the presence of (amalgamated) zinc and hydrochloric acid, a nucleophilic **aromatic** substitution can be ruled out.


 2