Cyanohydrins
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In
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, a cyanohydrin or hydroxynitrile is a
functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
found in
organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
s in which a
cyano In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...
and a
hydroxy group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
are attached to the same carbon atom. The general formula is , where R is H,
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...
, or
aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...
. Cyanohydrins are industrially important precursors to
carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
s and some
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
s. Cyanohydrins can be formed by the
cyanohydrin reaction 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: \ce + \ce \longrightarrow \ce This nucleophilic ad ...
, which involves treating a
ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
or an
aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
with
hydrogen cyanide Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the chemical formula, formula HCN and structural formula . It is a highly toxic and flammable liquid that boiling, boils slightly above room temperature, at . HCN is ...
(HCN) in the presence of excess amounts of
sodium cyanide Sodium cyanide is a compound with the formula Na C N and the structure . It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also expl ...
(NaCN) as a catalyst: : In this reaction, the
nucleophilic In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they a ...
ion attacks the
electrophilic In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carr ...
carbonyl carbon in the ketone, followed by protonation by HCN, thereby regenerating the
cyanide anion In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This an ...
. Cyanohydrins are also prepared by displacement of
sulfite Sulfites or sulphites are compounds that contain the sulfite ion (systematic name: sulfate(IV) ion), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widely used. Sulfites are ...
by cyanide salts: : Cyanohydrins are intermediates in the
Strecker amino acid synthesis The Strecker amino acid synthesis, also known simply as the Strecker synthesis, is a method for the synthesis of amino acids by the reaction of an aldehyde with cyanide in the presence of ammonia. The condensation reaction yields an α-aminonitri ...
. In aqueous acid, they are hydrolyzed to the α-hydroxy acid.


Preparative methods

Cyanohydrins are traditionally prepared by the addition of HCN to the corresponding carbonyl. The reaction is typically catalyzed by base or an enzyme. Because of the hazards with HCN, other less dangerous cyanation reagents are often used. *
Trimethylsilyl cyanide Trimethylsilyl cyanide is the chemical compound with the chemical formula, formula . This volatile liquid consists of a cyanide group, that is CN, attached to a trimethylsilyl group. The molecule is used in organic synthesis as the equivalent of h ...
, 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)


Transhydrocyanation

Acetone cyanohydrin Acetone cyanohydrin (ACH) is an organic compound used in the production of methyl methacrylate, the monomer of the transparent plastic polymethyl methacrylate (PMMA), also known as acrylic. It liberates hydrogen cyanide easily, so it is used as a ...
, (CH3)2C(OH)CN is the cyanohydrin of
acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...
. It is generated as an intermediate in the industrial production of
methyl methacrylate Methyl methacrylate (MMA) is an organic compound with the formula . This colorless liquid, the methyl ester of methacrylic acid (MAA), is a monomer produced on a large scale for the production of poly(methyl methacrylate) (PMMA). History MMA ...
. 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. Thus, acetone cyanohydrin can be used for the preparation of other cyanohydrins, for the transformation of HCN to
Michael acceptor In organic chemistry, the Michael reaction or Michael 1,4 addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a c ...
s, and for the
formylation Formylation refers to any chemical processes in which a compound is functionalized with a formyl group (-CH=O). In organic chemistry, the term is most commonly used with regards to aromatic compounds (for example the conversion of benzene to benz ...
of
arene Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...
s. Treatment of this cyanohydrin with
lithium hydride Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not solub ...
affords
anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
lithium cyanide: :


Asymmetric cyanohydrin formation

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. File:Glyconitrile Structural FormulaV1.svg, glycolonitrile, also called hydroxyacetonitrile or formaldehyde cyanohydrin, is the simplest cyanohydrin. File:Acetone cyanohydrin.svg, acetone cyanohydrin File:Mandelonitrile-2D-skeletal.svg, mandelonitrile, occurs in small amounts in the pits of some fruits. File:Amygdalin structure.svg,
Amygdalin Amygdalin (from Ancient Greek: ' 'almond') is a naturally occurring chemical compound found in many plants, most notably in the seeds (kernels, pips or stones) of apricots, bitter almonds, apples, peaches, cherries and plums, and in the roots ...
, a naturally occurring cyanogenic glycoside


See also

*
Halohydrin In organic chemistry a halohydrin (also a haloalcohol or β-halo alcohol) is a functional group in which a halogen and a hydroxyl are bonded to adjacent carbon atoms, which otherwise bear only hydrogen or hydrocarbyl groups (e.g. 2-chloroethanol ...
*
Benzoin condensation In organic chemistry, the benzoin addition is an addition reaction involving two aldehydes (). The reaction generally occurs between aromatic compound, aromatic aldehydes or glyoxals (), and results in formation of an acyloin (). In the classic ex ...


References

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External links

*
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
s
Gold Book The International Union of Pure and Applied Chemistry (IUPAC) publishes many books which contain its complete list of definitions. The definitions are divided initially into seven IUPAC Colour Books: Gold, Green, Blue, Purple, Orange, White, and R ...
definition of cyanohydrin

Functional groups