Reduction of nitriles to primary amines with LiAlH4
Description: Lithium aluminum hydride [but NOT sodium borohydride (NaBH4)] can reduce nitriles to primary amines.
The purpose of acid at the end is to protonate the nitrogen in order to give the amine.
Note that 2 or more equivalents of LiAlH4 is best for this reaction.
Notes: Note that the last example is a cyanohydrin, which also works in this reaction.
Addition of hydride ion (H–) from LiAlH4 to the carbon of the nitrile in a 1,2-addition (Step 1, arrows A and B) followed by addition of a second equivalent of hydride (Step 2, arrows C and D) gives an amine anion. When acid is added, the nitrogen is protonated twice to give the neutral amine.
Notes: The choice of Cl as the counter-ion for H3O(+) here is completely arbitrary – it’s just a spectator ion, anyway. Note that it could also be reasonable to use an equivalent of AlH3 formed after Step 1 as the reducing agent in Step 2.