Addition of CN - Cyanohydrins

Aldehydes and ketones are converted to cyanohydrins upon treatment with HCN (hydrogen cyanide). 

HCN is weakly acidic (pKa=9.2), so it does not significantly protonate a carbonyl.  Note a protonated ketone has a pKa=-7.  The reaction can be catalyzed by the addition of small amounts of NaCN.

Working with HCN is problematic because it is a highly toxic gas.  An alternative procedure is to use NaCN in DMSO and then a dilute acid work up.


This mechanism is analogous to hydration under basic conditions.  Cyanide ions are an excellent nucleophile attacking the elertophilic carbonyl C atom.  An alkoxide intermediate is formed which is subsequently protonated in a mildly acid water work up.

Reactions of Cyanohydrins

Cyanohydrins are useful precursors to α-hydroxy acids and α-hydroxy amines.

Reduction of cyanohydrin to amine

When the nitrile (CN) of a cyanohydrin is reduced a primary amine is produced.

Hydrolysis of cyanohydrin to carboxylic acid

The heating of cyanohydrins with very acid water, results in the hydrolysis of the nitrile group, producing a carboxylic acid.