14.28: Nitriles to Amines: LiAlH4 Reduction
Nitriles are reduced to amines in the presence of strong reducing agents like lithium aluminum hydride through a typical nucleophilic acyl substitution. The reaction requires two equivalents of the reducing agent. The reducing agent acts as a source of hydride ions.
As shown below, the mechanism involves three steps. Firstly, the hydride ion acting as a nucleophile attacks the nitrile carbon to form an anion. In the second step, a second equivalent of the hydride ion attacks the anion to generate a dianion. A final protonation of the dianion with water yields a primary amine as the final product.
A milder reducing agent like diisobutylaluminum hydride reduces nitriles to aldehydes. In this reaction, nitrile reacts with one equivalent of the reducing agent. This is followed by hydrolysis to yield aldehyde.