Adiponitrile

Adiponitrile
IUPAC name Hexanedinitrile
Other names 1,4-Dicyanobutane, Adipic acid dinitrile, Adipic acid nitrile, Hexanedioic acid dinitrile, Adipyldinitrile, Nitrile adipico, Tetramethylene cyanide, Tetramethylene dicyanide, UN 2205
Identifiers
CAS number	111-69-3 Y
ChemSpider	13876621 Y
UNII	VK98I9YW5M Y
Jmol-3D images	Image 1
SMILES N#CCCCCC#N
InChI InChI=1S/C6H8N2/c7-5-3-1-2-4-6-8/h1-4H2 Y Key: BTGRAWJCKBQKAO-UHFFFAOYSA-N Y InChI=1/C6H8N2/c7-5-3-1-2-4-6-8/h1-4H2 Key: BTGRAWJCKBQKAO-UHFFFAOYAW
Properties
Molecular formula	C6H8N2
Molar mass	108.14 g mol−1
Appearance	Colourless oil
Density	0.97 g/cm3
Melting point	1 °C
Boiling point	295 °C
Solubility in water	50 g/L (20 °C)
Vapor pressure	0.003 hPa (20 °C)
Hazards
R-phrases	R23, R25, R36, R38
S-phrases	S26, S37, S45
Main hazards	Toxic, irritant
NFPA 704	2 4 1
Flash point	93 °C (decomposition)
Autoignition temperature	460 °C
Explosive limits	1.7 - 4.9 %V
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 66. In 2005, about one billion kilograms were produced annually.^[1]

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:^[1]

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. The net reaction is:

CH₂=CHCH=CH₂ + 2 HCN → NCCH₂CH₂CH₂CH₂CN

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.^[1]

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:^[2]

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.

Safety

The LD₅₀ for adiponitrile is 300 mg/kg for oral ingestion by rats.^[1]

In 1990, ACGIH adopted a time weighted average Threshold Limit Value of 2ppm for work related skin exposure. ^[3]

The NIOSH recommended skin exposure limit for a work related time weighted average concentration is 4ppm (18mg/m3). ^[4]

References

1. ^ ^{a b c d} M. T. Musser, "Adipic Acid" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a01 269
2. ^ Robert A. Smiley "Hexamethylenediamine" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a12 629
3. ^ 2009 TLVs and BEIs, American Conference of Governmental Industrial Hygienists, Signature Publications, page 11 of 254.
4. ^ NIOSH Pocket Guide NIOSH Publication 2005-149; September 2005

External links

• International Chemical Safety Card 0211
• NIOSH Pocket Guide to Chemical Hazards 0015
• www.chemicalland.com
• www.nist.gov