In general, the reduction of carbonyl groups (in aldehydes and ketones) to methylene groups with zinc amalgam and hydrochloric acid is known as the reduction reaction of Clemmensen. It has been concluded that alcohol is not the intermediate of the Clemmensen reduction and carbonium is involved in this Clemmensen reduction. Benzylic and allylic alcohols can be reduced under the Clemmensen reduction conditions. In particular, the Clemmensen reduction conditions are reactive to the reduction of aryl-alkyl ketones, such as those produced in the Friedel-Crafts acylation reaction, and these alcohols are firstly converted into the respective benzyl and allylic chlorides reacted by the HCL and then react with the zinc amalgam.