Innitrile reductionanitrileisreduced to either an amine or an aldehyde with a suitable chemical reagent.[1][2]
The catalytic hydrogenation of nitriles is often the most economical route available for the production of primary amines.[3] Catalysts for the reaction often include group 10 metals such as Raney nickel,[4][5][6] palladium black, or platinum dioxide.[1] However, other catalysts, such as cobalt boride, also can be regioselective for primary amine production:
A commercial application of this technology includes the production of hexamethylenediamine from adiponitrile, a precursortoNylon 66.[7]
Depending on reaction conditions, reactive intermediate imines can also undergo attack by amine products to afford secondary and tertiary amines:
Such reactions proceed via enamine intermediates.[8] The most important reaction condition for selective primary amine production is catalyst choice.[1] Other important factors include solvent choice, solution pH, steric effects, temperature, and the pressure of hydrogen.
Reducing agents for the non-catalytic conversion to amines include lithium aluminium hydride, lithium borohydride,[9] diborane,[10] or elemental sodiuminalcohol solvents.[11]
Nitriles can also be converted to aldehydes by reduction and hydrolysis. The Stephen aldehyde synthesis uses Tin(II) chloride and hydrochloric acid to yield an aldehyde via the hydrolysis of a resulting iminium salt. Aldehydes can also form using a hydrogen donor followed by in-situ hydrolysis of an imine. Useful reagents for this reaction include formic acid with a hydrogenation catalysis[12] or metal hydrides, which are used to add one mol of hydrogen to the nitrile. For example, sodium borohydride reduces nitriles in alcoholic solvents with a CoCl2 catalyst or Raney nickel.[13]
The hydride reagent Diisobutylaluminium hydride, or DIBAL-H, is commonly used to convert nitriles to the aldehyde.[14] Regarding the proposed mechanism, DIBAL forms a Lewis acid-base adduct with the nitrile by formation of an N-Al bond. The hydride is then transferred to the carbon of the nitrile. Aqueous workup produce the desired aldehyde and ammonia.[15]
Benzyl nitriles can also be reduced electrochemically.[16][17]