cyanohydrin reaction
{{Short description|Addition reaction of carbonyl compounds and cyanide}}
{{Use dmy dates|date=January 2024}}
{{Reactionbox
| Name = Cyanohydrin reaction
| Type = Addition reaction
| NamedAfter = Friedrich Urech
}}
In organic chemistry, a cyanohydrin reaction is an organic reaction in which an aldehyde ({{chem2|\sCH\dO}}) or ketone ({{chem2|>C\dO}}) reacts with a cyanide anion ({{chem2|N\tC-}}) or a nitrile ({{chem2|\sC\tN}}) to form a cyanohydrin ({{chem2|>C(OH)C\tN}}). For example:
\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 ({{chem2|(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.
Examples
Image:Cyanohydrin_acetone_reaction.svg with sodium cyanide to hydroxyacetonitrile]]
Image:Benzoquinone cyanohydrin reaction.svg with trimethylsilylcyanide, catalyst KCN is introduced as a 1:1 complex with the Crown ether 18-crown-6]]
Reaction mechanism
Asymmetric synthesis
The asymmetric cyanohydrin reaction of benzaldehyde with trimethylsilylcyanide is made possible by employment of (R)-Binol{{cite journal |title=Chiral Lithium Binaphtholate Aqua Complex as a Highly Effective Asymmetric Catalyst for Cyanohydrin Synthesis |first1=Manabu |last1=Hatano |first2=Takumi |last2=Ikeno |first3=Takashi |last3=Miyamoto |first4=Kazuaki |last4=Ishihara |journal=J. Am. Chem. Soc. |year=2005 |volume=127 |issue=31 |pages=10776–77 |doi=10.1021/ja051125c|pmid=16076152 }} at 1–10% catalyst loading. This ligand firsts reacts with a lithium alkoxy compound to form a lithium binaphtholate Complex.
Image:Asym cyanohydrin reaction.svg–lithium(i-propyloxy) gives (S)-acetonitrile with 98% ee]]
{{center|Asymmetric reaction of benzaldehyde with (R)–Binol–lithium(i-propyloxy) gives (S)-acetonitrile with 98% ee }}
The chemist Urech in 1872 was the first to synthesize cyanohydrins from ketones with alkali cyanides and acetic acid{{ cite journal| last1=Urech |first1=Friedrich |title=Ueber einige Cyanderivate des Acetons |journal=Liebigs Ann. |volume=164 |page=255 |year=1872 |issue=2 |doi=10.1002/jlac.18721640207|url=https://zenodo.org/record/1427311 }} and therefore this reaction also goes by the name of Urech cyanohydrin method.
References
{{reflist}}
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 [https://web.archive.org/web/20120329051302/http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0387 Article]
- Cyanohydrin reaction of formaldehyde with potassium cyanide Organic Syntheses Coll. Vol. 3, p. 436; Vol. 27, p. 41 [https://web.archive.org/web/20120329051307/http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0436 Article]
- Cyanohydrin reaction of acetophenone with potassium cyanide Organic Syntheses Coll. Vol. 4, p. 58; Vol. 33, p. 7 [https://web.archive.org/web/20120329051310/http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0058 Article]
- Cyanohydrin reaction of D-xylose with potassium cyanide Organic Syntheses Coll. Vol. 4, p. 506; Vol. 36, p. 38 [https://web.archive.org/web/20120329051316/http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0506 Article]
- Cyanohydrin reaction of acetone with potassium cyanide Organic Syntheses Coll. Vol. 2, p. 7; Vol. 15, p. 1 [https://web.archive.org/web/20121022154058/http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0007 Article]
- Cyanohydrin reaction of benzoquinone with trimethylsilylcyanide Organic Syntheses Coll. Vol. 7, p. 517; Vol. 60, p. 126 [https://web.archive.org/web/20120329051335/http://www.orgsyn.org/orgsyn/prep.asp?prep=cv7p0517 Article]
{{Organic reactions}}
Category:Nucleophilic addition reactions