The Kolbe nitrile synthesis is a method for the preparation of
alkyl nitriles by reaction of the corresponding
alkyl halide
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
with a metal
cyanide
Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms.
In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
. A side product for this reaction is the formation of an
isonitrile
An isocyanide (also called isonitrile or carbylamine) is an organic compound with the functional group –. It is the isomer of the related nitrile (–C≡N), hence the prefix is ''isocyano''.IUPAC Goldboo''isocyanides''/ref> The organic fragme ...
because the cyanide ion is an
ambident nucleophile
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 are ...
and according to
Kornblum's rule
HSAB concept is a jargon for "hard and soft (Lewis) acids and bases". HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways. It assigns the terms 'hard' or 'soft', and 'acid' or 'base' to chemic ...
is capable of reacting with either carbon or nitrogen. The reaction is named after
Hermann Kolbe.
:
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The ratio in which both
isomers form depends on the
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
and the
reaction mechanism. With the application of alkali cyanides such as
sodium cyanide
Sodium cyanide is a poisonous compound with the formula Na C N. 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 exploits its hi ...
and polar solvents the reaction type is an
SN2 reaction whereby the alkylhalide is attacked by the more nucleophilic carbon atom of the cyanide ion. This type of reaction together with
dimethyl sulfoxide as a solvent is a convenient method for the synthesis of nitriles.
The use of DMSO was a major advancement in the development of this reaction, as it works for more
sterically hindered electrophilies (secondary and neopentyl halides) without rearrangement side-reactions.
See also
*
Rosenmund–von Braun reaction, a similar reaction for the synthesis of aromatic nitriles
References
{{DEFAULTSORT:Kolbe Nitrile Synthesis
Substitution reactions
Name reactions