Cyanohydrin reaction

In organic chemistry, a cyanohydrin reaction is an organic reaction in which an aldehyde (−CH=O) or ketone (>C=O) reacts with a cyanide anion (N≡C⁻) or a nitrile (−C≡N) to form a cyanohydrin (>C(OH)C≡N). For example:

$${\displaystyle {\ce {R}}{\color {red}{\ce {CH=O}}}+{\ce {R}}{\color {purple}{\ce {C#N}}}\longrightarrow {\ce {R2}}{\color {red}{\ce {C(OH)}}}{\color {purple}{\ce {C#N}}}}$$

This nucleophilic addition is a reversible reaction but with aliphatic carbonyl compounds equilibrium is in favor of the reaction products. The cyanide source can be potassium cyanide (KCN), sodium cyanide (NaCN) or trimethylsilyl cyanide ((CH₃)₃SiCN). With aromatic aldehydes such as benzaldehyde, the benzoin condensation is a competing reaction. The reaction is used in carbohydrate chemistry as a chain extension method for example that of D-xylose.