Cyanohydrin
In organic chemistry, a cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is Template:Chem2, where R is H, alkyl, or aryl. Cyanohydrins are industrially important precursors to carboxylic acids and 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 excess amounts of sodium cyanide (NaCN) as a catalyst:<ref name=CR>Template:Cite journal</ref>
In this reaction, the nucleophilic Template:Chem2 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:<ref name=Corson>Template:OrgSynth</ref>
Cyanohydrins are intermediates in the Strecker amino acid synthesis. In aqueous acid, they are hydrolyzed to the α-hydroxy acid.
Preparative methodsEdit
Cyanohydrins are traditionally prepared by the addition of HCN to the corresponding carbonyl. The reaction is typically catalyzed by base or an enzyme.<ref name=CR1>Template:Cite journal</ref><ref name=CR2>Template:Cite journal</ref> Because of the hazards with HCN, other less dangerous cyanation reagents are often used.<ref>Template:Cite journal</ref>
- Trimethylsilyl cyanide, affording the silyl ether derivative of the cyanohydrin
- Diethylaluminium cyanide, especially for less reactive carbonyls
- Diethyl phosphorocyanidate (DEPC) and lithium cyanide
- Acyl cyanides (RC(O)CN)
TranshydrocyanationEdit
Acetone cyanohydrin, (CH3)2C(OH)CN is the cyanohydrin of acetone. It is generated as an intermediate in the industrial production of methyl methacrylate.<ref>William Bauer, Jr. "Methacrylic Acid and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. {{#invoke:doi|main}}. Article Online Posting Date: June 15, 2000</ref> In the laboratory, this liquid serves as a source of HCN. The process is called transhydrocyanation, where acetone cyanohydrin, is used as a source of HCN.<ref name=CR1/><ref name=CR2/><ref>Haroutounian, S. A. "Acetone Cyanohydrin" Encyclopedia of Reagents for Organic Synthesis 2001, John Wiley & Sons. {{#invoke:doi|main}}</ref> Thus, acetone cyanohydrin can be used for the preparation of other cyanohydrins, for the transformation of HCN to Michael acceptors, and for the formylation of arenes. Treatment of this cyanohydrin with lithium hydride affords anhydrous lithium cyanide:
Asymmetric cyanohydrin formationEdit
Formation of cyanohydrins introduces a chiral center for aldehydes and for unsymmetrical ketones. The enantioselective hydrocyanation has attracted some attention for the preparation of 2-chloromandelic acid, a drug precursor.<ref name=CR1/>
- Some Prominent Cyanohydrins
- Glyconitrile Structural FormulaV1.svg
glycolonitrile, also called hydroxyacetonitrile or formaldehyde cyanohydrin, is the simplest cyanohydrin.<ref>Template:OrgSynth</ref>
- Acetone cyanohydrin.svg
acetone cyanohydrin
- Mandelonitrile-2D-skeletal.svg
mandelonitrile, occurs in small amounts in the pits of some fruits.<ref name=Corson/>
- Amygdalin structure.svg
Amygdalin, a naturally occurring cyanogenic glycoside