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

Concept: Nitriles react with Grignard reagents to form ketones after hydrolysis. This reaction is one of the most important methods for the preparation of ketones. The carbon atom of the nitrile group \((-C \equiv N)\) is electrophilic and is attacked by the nucleophilic carbon of the Grignard reagent. The intermediate formed is an imine magnesium complex which on acidic hydrolysis gives the corresponding ketone.

Step 1: Writing the structure of acetonitrile. Acetonitrile has the formula \[ CH_3CN \] or \[ CH_3-C \equiv N \] It contains the nitrile functional group.

Step 2: Reaction with Grignard reagent. To obtain acetone \((CH_3COCH_3)\), the required Grignard reagent is methyl magnesium bromide. \[ CH_3MgBr \] The methyl group of the Grignard reagent attacks the carbon atom of the nitrile group. The reaction produces an imine magnesium salt. \[ CH_3CN + CH_3MgBr \longrightarrow CH_3C(=N-MgBr)CH_3 \]

Step 3: Hydrolysis of the intermediate. The imine magnesium salt formed in the previous step is hydrolysed using dilute acid. \[ H_3O^+ \] Acidic hydrolysis converts the imine group into a carbonyl group. Thus, \[ CH_3C(=N-MgBr)CH_3 \xrightarrow{H_3O^+} CH_3COCH_3 \]

Step 4: Identification of the product. The compound obtained is \[ CH_3COCH_3 \] which is acetone (propanone). Therefore, \[ \boxed{\text{Acetonitrile} \rightarrow \text{Acetone}} \]

Step 5: Writing the complete conversion. \[ \boxed{ CH_3CN \xrightarrow{CH_3MgBr} CH_3C(=N-MgBr)CH_3 \xrightarrow{H_3O^+} CH_3COCH_3 } \] or simply, \[ \boxed{ CH_3CN \xrightarrow[\text{Hydrolysis}]{CH_3MgBr} CH_3COCH_3 } \]

Final Answer: Acetonitrile is converted into acetone by treatment with methyl magnesium bromide followed by acidic hydrolysis. \[ \boxed{ CH_3CN \xrightarrow{CH_3MgBr} \text{Imine Magnesium Salt} \xrightarrow{H_3O^+} CH_3COCH_3 } \]