Cyanohydrin

  A cyanohydrin is a functional group in organic compounds. Cyanohydrins have the formula R₂C(OH)CN, where R is H, alkyl, or aryl. Cyanohydrins are industrially important precursors to carboxylic acids including some amino acids. Cyanohydrins can be formed by the cyanohydrin reaction, which involves treating a ketone or an aldehyde with hydrogen cyanide (HCN) in the presence of an excess amounts of sodium cyanide (NaCN) as a catalyst:

RR’C=O + HCN → RR’C(OH)CN

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In this reaction, the nucleophilic CN⁻ ion attacks the electrophilic carbonyl carbon in the ketone, followed by protonation by HCN, thereby regenerating the cyanide anion. Cyanohydrins are also prepared by displacement of sulfite by cyanide salts.^[1]

Cyanohydrins are intermediates in the Strecker amino acid synthesis.

Illustrative cyanohydrins

Acetone cyanohydrin (CAS# 75-86-5, b.p. 95 °C, also known as α-hydroxyisobutyronitrile), (CH₃)₂C(OH)CN is the cyanohydrin of acetone. This liquid serves as a source of HCN (which is a gas).^[2] Thus, acetone cyanohydrin can be used for the preparation other cyanohydrins, for of HCN to Michael acceptors, and for the formylation of arenes. Treatment of this cyanohydrin with lithium hydride affords anhydrous lithium cyanide.

(CH₃)₂C(OH)CN + LiH → LiCN + (CH₃)₂CO + H₂

Mandelonitrile (CAS# 532-28-5, b.p. 170 °C) is the chemical compound with the formula C₆H₅CH(OH)CN.^[1] Small amounts of this cyanohydrin occur in the pits of some fruits.

Glycolonitrile, also called hydroxyacetonitrile or formaldehyde cyanohydrin (CAS#107-16-4), is the chemical compound with the formula HOCH₂CN. It is the simplest cyanohydrin, being derived from formaldehyde.^[3]

References

1. ^ ^{a b} Corson, B. B.; Dodge, R. A.; Harris, S. A.; Yeaw, J. S. “Mandelic Acid” Organic Syntheses, Collected Volume 1, p.336 (1941). http://www.orgsyn.org/orgsyn/pdfs/CV1P0336.pdf. This paper describes the synthesis of mandelonitrile.
2. ^ Haroutounian, S. A. ”Acetone Cyanohydrin” Encyclopedia of Reagents for Organic Synthesis 2001, John Wiley & Sons. DOI: 10.1002/047084289X.ra014
3. ^ Gaudry, R. “Glycolonitrile” Organic Syntheses, Collected Volume 3, p.436 (1955). http://www.orgsyn.org/orgsyn/pdfs/CV3P0436.pdf