# The Reduction of Nitriles

This page looks at the reduction of nitriles to primary amines using either lithium tetrahydridoaluminate(III) (lithium aluminium hydride) or hydrogen and a metal catalyst.

## The reduction of nitriles using LiAlH4

Despite its name, the structure of the reducing agent is very simple. There are four hydrogens ("tetrahydido") around the aluminium in a negative ion (shown by the "ate" ending). The "(III)" shows the oxidation state of the aluminium, and is often left out because aluminium only ever shows the +3 oxidation state in its compounds. To make the name shorter, that's what I shall do for the rest of this page.

The structure of LiAlH4 is:

In the negative ion, one of the bonds is a co-ordinate covalent (dative covalent) bond using the lone pair on a hydride ion (H-) to form a bond with an empty orbital on the aluminum.

## The overall reaction

The nitrile reacts with the lithium tetrahydridoaluminate in solution in ethoxyethane (diethyl ether, or just "ether") followed by treatment of the product of that reaction with a dilute acid. Overall, the carbon-nitrogen triple bond is reduced to give a primary amine. Primary amines contain the $$-NH_2$$ group. For example, with ethanenitrile you get ethylamine:

$\ce{CH_3CN + 4[H] \longrightarrow CH_3CH_2NH_2}$

## The reduction of nitriles using hydrogen and a metal catalyst

The carbon-nitrogen triple bond in a nitrile can also be reduced by reaction with hydrogen gas in the presence of a variety of metal catalysts. Commonly used catalysts are palladium, platinum or nickel. The reaction will take place at a raised temperature and pressure, but the exact details vary from catalyst to catalyst.

For example, ethanenitrile can be reduced to ethylamine by reaction with hydrogen in the presence of a palladium catalyst.

$\ce{CH_3CN + 2H_2 ->[Pd] CH3CH2NH2}$