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Adiponitrile is the organic compound with the formula (CH2)4(CN)2. This dinitrile, a viscous, colourless liquid, is an important precursor to the polymer nylon-6,6. In 2005, about one billion kilograms were produced.

Other names

Adipic acid dinitrile
Adipic acid nitrile
Adipyldinitrile
1,4-Dicyanobutane
Hexanedioic acid dinitrile
Nitrile adipico
Tetramethylene cyanide
Tetramethylene dicyanide

Production

Early routes

Because of the industrial value of adiponitrile, many methods have been developed for its synthesis. Early industrial routes started from furfural and later by the chlorination of butadiene to give 1,4-dichloro-2-butene, which with sodium cyanide, converts to 3-hexenedinitrile, which in turn can be hydrogenated to adiponitrile:

ClCH2CH=CHCH2Cl + 2 NaCN → NCCH2CH=CHCH2CN + 2 NaCl
NCCH2CH=CHCH2CN + H2 → NC(CH2)4CN

Adiponitrile has also been produced from adipic acid, by dehydration of the diamide, but this route is rarely employed.

Modern routes

The majority of adiponitrile is prepared by the nickel-catalysed hydrocyanation of butadiene, as discovered at DuPont, pioneered by Drinkard. The net reaction is:

CH2=CHCH=CH2 + 2 HCN → NCCH2CH2CH2CH2CN
ButadieneHydrocyanation.svg

The process involves several stages, the first of which involves monohydrocyanation (addition of one molecule of HCN), affording isomers of pentenenitriles as well as 2- and 3-methylbutenenitriles. These unsaturated nitriles are subsequently isomerized to the 3-and 4-pentenenitriles. In the final stage, these pentenenitriles are subjected to a second hydrocyanation, in an anti-Markovnikov sense, to produce adiponitrile.

Research has shown that the 3-pentenenitrile, formed in the first hydrocyanation, can undergo alkene metathesis to give dicyanobutenes, which are readily hydrogenated as described above.

The other major industrial route involves electrosynthesis, starting from acrylonitrile, which is dimerized:

2 CH2=CHCN + 2 e− + 2 H+ → NCCH2CH2CH2CH2CN

The electrolytic coupling of acrylonitrile was discovered at Monsanto Company.

Applications

Almost all adiponitrile is hydrogenated to 1,6-diaminohexane for the production of nylon:

NC(CH2)4CN + 4 H2 → H2N(CH2)6NH2

Like other nitriles, adiponitrile is susceptible to hydrolysis. The resulting adipic acid however is more cheaply prepared by other routes.