Question

Explain Clemmensen reduction giving example.

Hint:

Clemmensen = \(\mathrm{Zn(Hg)/HCl}\) (acidic)\,; Wolff–Kishner = \(\mathrm{NH_2NH_2/KOH}\) (basic). Both reduce \(>\!C{=}O\) to \(-\!CH_2-\).

Answer 1

Definition: Clemmensen reduction converts aldehydes and ketones to the corresponding methylene compounds using zinc amalgam and concentrated hydrochloric acid.
\[ \mathrm{R{-}CO{-}R'} \xrightarrow[\ \text{reflux}\ ]{\mathrm{Zn(Hg)},\ \mathrm{conc.\ HCl}} \mathrm{R{-}CH_2{-}R'} \] Example: Acetophenone to ethylbenzene
\[ \mathrm{C_6H_5COCH_3} \xrightarrow{\mathrm{Zn(Hg)},\ \mathrm{HCl}} \mathrm{C_6H_5CH_2CH_3} \] Note: Works best for acid-stable substrates; for base-sensitive substrates use Wolff–Kishner instead.