Cyanohydrin reaction explained

In organic chemistry, a cyanohydrin reaction is an organic reaction in which an aldehyde or ketone reacts with a cyanide anion or a nitrile to form a cyanohydrin . For example:

$$\backslash ce\; +\; \backslash ce\; \backslash longrightarrow\; \backslash ce$$

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 . 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.

Asymmetric synthesis

The asymmetric cyanohydrin reaction of benzaldehyde with trimethylsilylcyanide is made possible by employment of (R)-Binol^[1] at 1–10% catalyst loading. This ligand firsts reacts with a lithium alkoxy compound to form a lithium binaphtholate Complex.

The chemist Urech in 1872 was the first to synthesize cyanohydrins from ketones with alkali cyanides and acetic acid^[2] and therefore this reaction also goes by the name of Urech cyanohydrin method.

External links

• Cyanohydrin reaction of formaldehyde to hydroxyacetonitrile or glycolonitrile with sodium cyanide in Organic Syntheses Coll. Vol. 2, p. 387; Vol. 13, p. 56 Article
• Cyanohydrin reaction of formaldehyde with potassium cyanide Organic Syntheses Coll. Vol. 3, p. 436; Vol. 27, p. 41 Article
• Cyanohydrin reaction of acetophenone with potassium cyanide Organic Syntheses Coll. Vol. 4, p. 58; Vol. 33, p. 7 Article
• Cyanohydrin reaction of D-xylose with potassium cyanide Organic Syntheses Coll. Vol. 4, p. 506; Vol. 36, p. 38 Article
• Cyanohydrin reaction of acetone with potassium cyanide Organic Syntheses Coll. Vol. 2, p. 7; Vol. 15, p. 1 Article
• Cyanohydrin reaction of benzoquinone with trimethylsilylcyanide Organic Syntheses Coll. Vol. 7, p. 517; Vol. 60, p. 126 Article

Notes and References

1. Chiral Lithium Binaphtholate Aqua Complex as a Highly Effective Asymmetric Catalyst for Cyanohydrin Synthesis . Manabu . Hatano . Takumi . Ikeno . Takashi . Miyamoto . Kazuaki . Ishihara . . 2005 . 127 . 31 . 10776–77 . 10.1021/ja051125c. 16076152 .
2. Urech . Friedrich . Ueber einige Cyanderivate des Acetons . . 164 . 255 . 1872 . 2 . 10.1002/jlac.18721640207.