Question

How do you convert the following? Propanone to Propan-2-ol

Hint:

Ketones always reduce to $2^\circ$ alcohols; Aldehydes always reduce to $1^\circ$ alcohols.

Answer 1

Step 1: Identify what is needed.
Propanone ($CH_3COCH_3$, a ketone) must be converted to propan-2-ol ($CH_3CH(OH)CH_3$, a secondary alcohol). This requires adding $H_2$ across the $C=O$ double bond (reduction).
Step 2: Choose a reducing method.
Catalytic hydrogenation can be used: passing $H_2$ gas over the ketone in the presence of Ni, Pt, or Pd catalyst at moderate temperature and pressure reduces the carbonyl group to a secondary alcohol.
Step 3: Alternative reducing agent.
A mild reducing agent such as sodium borohydride ($NaBH_4$) or lithium aluminium hydride ($LiAlH_4$) delivers a hydride ion ($H^-$) to the carbonyl carbon; the resulting alkoxide is then protonated on workup to give the alcohol.
Step 4: Write the equation.
$CH_3COCH_3 \xrightarrow{NaBH_4 \text{ or } H_2/Ni} CH_3CH(OH)CH_3$ (propan-2-ol).