19.16:
Preparation of Amines: Reduction of Amides and Nitriles
Reduction of nitriles gives primary amines, while reduction of amides can give primary, secondary, and tertiary amines.
Nitriles are formed from alkyl halides through an SN2 reaction involving an attack of the cyanide nucleophile. A further reduction by LiAlH4 or catalytic hydrogenation forms the amine.
Since the reaction follows an SN2 mechanism in the first step, primary alkyl halides are the preferred substrates, and the reaction gives primary amines.
The overall reaction replaces the halide with an amino group while also introducing an additional carbon atom.
Amides are prepared from carboxylic acid derivatives through condensation reactions with ammonia. They are further reduced to give amines.
Amide reduction only introduces the amino group without an extra carbon in the skeleton, while nitrile reduction installs an amino group and extends the carbon chain.
During amide reduction, the class of amine formed depends on the degree of alkylation at the amide nitrogen.
19.16:
Preparation of Amines: Reduction of Amides and Nitriles
Nitriles can be reduced to primary amines using reducing agents like lithium aluminum hydride or catalytic hydrogenation. The reduction introduces an amino group with an extra carbon in the skeleton. Nitriles are formed from the reaction between alkyl halides and sodium cyanide through the SN2 mechanism. Primary alkyl halides are the preferred substrates to prepare nitriles.
Amides can be reduced to primary, secondary, and tertiary amines using catalytic hydrogenation, active metals like Fe, Zn, Ni, and strong reducing agents like lithium aluminum hydride. The reaction introduces only the amino group without extending the carbon skeleton.
Amide reduction is useful in the last step of monoalkylation of arylamines.
