Question

What happens when: Propanenitrile is treated with phenyl magnesium bromide followed by hydrolysis?

Hint:

Nitriles + Grignard \( \rightarrow \) Ketones.
Nitriles + Grignard followed by excessive hydrolysis is one of the best ways to prepare aryl alkyl ketones.

Answer 1

Step 1: See the nitrile carbon as the target.
A nitrile carbon, $CH_3CH_2-C\equiv N$, is electron poor because nitrogen pulls the shared electrons towards itself. A Grignard reagent like $C_6H_5MgBr$ carries a carbanion-like phenyl group that is drawn straight to this electrophilic carbon.
Step 2: Let the phenyl group add across the triple bond.
The phenyl group bonds to the nitrile carbon while the magnesium bromide settles on the nitrogen, giving an intermediate imine-magnesium salt, $CH_3CH_2-C(C_6H_5)=N-MgBr$.
Step 3: Hydrolyse to reveal the carbonyl.
Adding water (with acid) breaks this imine salt apart. The nitrogen leaves as an ammonium species while the carbon becomes a proper carbonyl carbon, giving a ketone.
\[ CH_3CH_2CN \xrightarrow{(i)\ C_6H_5MgBr} \xrightarrow{(ii)\ H_2O/H^+} CH_3CH_2COC_6H_5 \]
\[ \boxed{\text{Propiophenone (1-phenylpropan-1-one)}} \]