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.
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.