SolutionsReaction of Organometallic Compounds with Nitriles
1. From nitrile to ketone
Give the products of: a) propanenitrile with phenylmagnesium bromide and then H3O+; b) benzonitrile with tert-butyllithium and then H3O+.
- Propiophenone (1-phenyl-1-propanone).
- 2,2-Dimethyl-1-phenyl-1-propanone (tert-butyl phenyl ketone).
The organometallic adds to the nitrile carbon and gives the salt of an imine; acid hydrolysis of the imine releases ammonia (as NH4+) and gives the ketone.
2. Why is no tertiary alcohol formed?
With esters, Grignard reagents give tertiary alcohols. Why does the reaction with nitriles stop at the ketone?
After the first addition an imide anion (R2C=N−, bonded to magnesium) forms; it is negatively charged and not electrophilic, so it cannot undergo a second attack. The ketone only appears on hydrolysis during the workup, when no organometallic reagent is left.