Question

How do you convert Acetonitrile to Acetone ?

Hint:

Important conversion: \[ R-CN \xrightarrow{R'MgX} R-C(=N-MgX)-R' \xrightarrow{H_3O^+} R-CO-R' \] Thus, \[ CH_3CN \xrightarrow{CH_3MgBr} CH_3COCH_3 \] Nitriles + Grignard reagent + Hydrolysis \(\rightarrow\) Ketones.

Answer 1

Step 1: Choose the method.
Reacting a nitrile with a Grignard reagent and then hydrolyzing builds a new C-C bond and introduces a $C=O$ group. To get acetone ($CH_3COCH_3$) from acetonitrile ($CH_3CN$), use $CH_3MgBr$.
Step 2: Grignard reaction with nitrile.
$CH_3MgBr$ attacks the electrophilic nitrile carbon, forming an imine magnesium salt: \[ CH_3CN + CH_3MgBr \rightarrow CH_3C(=NMgBr)CH_3 \]
Step 3: Acid hydrolysis gives acetone.
Treatment with $H_3O^+$ converts the $C=N$ bond to $C=O$: \[ CH_3C(=NMgBr)CH_3 \xrightarrow{H_3O^+} CH_3COCH_3 \] \[ \boxed{CH_3CN \xrightarrow{(i)\;CH_3MgBr;\;(ii)\;H_3O^+} CH_3COCH_3} \]