A ketone can be prepared from the reaction of a nitrile with a Grignard reagent. Describe the intermediate formed in this reaction, and show how it can be converted to a ketone.

Nitriles are compounds containing a nitrogen atom directly bonded to a carbon atom.

The carbon atom and nitrogen atom have a triple bond with one sigma bond and two pi bonds. Nitriles are electrophiles with an electron-deficient carbon atom.

These compounds are named by adding a suffix –nitrile to the alkane name. The nitriles have similar properties to a carboxylic acid as both these compounds have carbon atoms attached to the electronegative atom by three covalent bonds.

Compounds of the form RMgX where R is an alkyl chain and X is a halogen are called Grignard reagents. The carbon attached to the magnesium atom is nucleophilic and bears a partial negative charge.

These compounds are important in organic synthesis as they can produce a carbanion. These carbanions can react with electrophilic carbon atoms forming a direct C-C bond. The Grignard reagent reacts with ketones, esters, nitriles, etc. to form carbon-carbon bonds.

The carbon attached to the electronegative nitrogen atom in a nitrile has low electron density and therefore is electrophilic. Therefore, The carbanion formed from the Grignard reagent attacks the electrophilic carbon forming an imine anion.

The imine anion has a negatively charged nitrogen atom which can abstract a proton from an acid forming an imine. This imine is the intermediate for the Grignard reaction of nitriles.

The imines can be converted to ketones by the reaction of an acid followed by hydrolysis.

The reaction can be given as:

Reaction of nitriles with Grignard reagent