Cyanohydrin reaction
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2008-04-18T17:18:22Z
Benjah-bmm27
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mechanism added
A '''Cyanohydrin reaction''' is an [[organic reaction|organic chemical reaction]] by an [[aldehyde]] or [[ketone]] with a [[cyanide]] [[anion]] or a [[nitrile]] to form a [[cyanohydrin]]. 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, [[sodium cyanide]] 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]].
== Examples ==
<center>[[Image:Cyanohydrin acetone reaction.gif|center|Reaction of [[acetone]] with [[sodium cyanide]] to hydroxyacetonitrile]]</center>
<center><small>Reaction of [[acetone]] with [[sodium cyanide]] to hydroxyacetonitrile</small></center>
<center>[[Image:Benzoquinone cyanohydrin reaction.gif|none|center|Reaction of [[benzoquinone]] with trimethylsilylcyanide, catalyst KCN is introduced as a 1:1 complex with the [[Crown ether]] 18-crown-6]]</center>
<center><small>Reaction of [[benzoquinone]] with trimethylsilylcyanide in [[tetrachloromethane]], catalyst KCN is introduced as a 1:1 complex with the [[Crown ether]] 18-crown-6</small></center>
<center>[[Image:Xylose cyanohydrin reaction.gif|none|center|chain extension of D-[[xylose]] in equilibrium with its [[hemiacetal]] with KCN to the cyclic [[ester]]]]</center>
<center><small>chain extension of D-[[xylose]] in equilibrium with its [[hemiacetal]] with KCN to the cyclic [[ester]]</small></center>
== Reaction mechanism ==
<center>[[Image:Cyanohydrin-mechanism-2D.png|400px|Mechanism of the cyanohydrin reaction]]</center>
== Asymmetric synthesis ==
The [[asymmetric synthesis|asymmetric]] cyanohydrin reaction of [[benzaldehyde]] with trimethylsilylcyanide is made possible by employment of (R)-[[Binol]] <ref>''Chiral Lithium Binaphtholate Aqua Complex as a Highly Effective Asymmetric Catalyst for Cyanohydrin Synthesis'' Manabu Hatano, Takumi Ikeno, Takashi Miyamoto, and Kazuaki Ishihara [[J. Am. Chem. Soc.]]; '''2005'''; 127(31) pp 10776 - 10777 [http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/2005/127/i31/abs/ja051125c.html Abstract] [http://pubs.acs.org/subscribe/journals/jacsat/suppinfo/ja051125c/ja051125csi20050627_072816.pdf Support info plus proposed transition state]</ref> at 1 to 10% [[catalyst]] loading. This [[ligand]] firsts reacts with a lithium alkoxy compound to form a lithium binaphtholate Complex.
[[Image:Asymetric cyanohydrin reaction.gif|center|Asymmetric reaction of benzaldehyde with (R)-[[Binol]]-lithium(i-propyloxy) gives (S)-cyanohydrin with 98% [[Enantiomer|ee]]]]
<center><small>Asymmetric reaction of benzaldehyde with (R)-[[Binol]]-lithium(i-propyloxy) gives (S)-cyanohydrin with 98% [[Enantiomer|ee]] </small> </center>
The chemist Urech in 1872 was the first to synthesize cyanohydrins from ketones with alkali cyanides and acetic acid <ref>Urech, Ann. 164, 256 ('''1872''')</ref> 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 [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[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 [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 [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 [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 [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv7p0517 Article]
== References ==
<div class="references-small"><references/></div>
[[Category:Addition reactions]]