Azobisisobutyronitrile

Azobisisobutyronitrile (abbreviated AIBN) is an organic compound with the formula [(CH3)2C(CN)]2N2. This white powder is soluble in alcohols and common organic solvents but is insoluble in water. It is often used as a foamer in plastics and rubber and as a radical initiator.

Azobisisobutyronitrile
Names
IUPAC name
2,2′-Azobis(2-methylpropionitrile), 2-(azo(1-cyano-1-methylethyl))-2-methylpropane nitrile
Other names
Azobisisobutyronitrile
Azobisisobutylonitrile
AIBN
Identifiers
3D model (JSmol)
Abbreviations AIBN
ChemSpider
ECHA InfoCard 100.001.030
EC Number
  • 201-132-3
RTECS number
  • UG0800000
UNII
UN number 3234 1325
Properties
C8H12N4
Molar mass 164.21 g/mol
Appearance white crystals
Density 1.1 g cm−3
Melting point 103 to 105 °C (217 to 221 °F; 376 to 378 K)
poor
Hazards
GHS pictograms
GHS Signal word Warning
H242, H302, H332, H412
P210, P220, P234, P261, P264, P270, P271, P273, P280, P301+312, P304+312, P304+340, P312, P330, P370+378, P403+235, P411, P420, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

As an azo initiator, radicals resulting from AIBN have multiple benefits[1] over common organic peroxides. For example, they do not have oxygenated byproducts or much yellow discoloration. Additionally, they do not cause too much grafting and therefore are often used when making adhesives, acrylic fibers, detergents, etc.

Mechanism of Decomposition

In its most characteristic reaction, AIBN decomposes, eliminating a molecule of nitrogen gas to form two 2-cyanoprop-2-yl radicals:

Because azobisisobutyronitrile readily gives off free radicals, it is often used as a radical initiator. This happens at temperatures above 40°C,[2] but in experiments is more commonly done at temperatures between 66-72°C.[3] This decomposition has a ΔG‡ of 131 kJ mol-1[4] and results in two 2-cyano-2-propyl (carbon) radicals and a molecule of nitrogen gas. The release of nitrogen gas pushes this decomposition forward due to the increase in entropy. And the 2-cyano-2-propyl radical is stabilized by the -CN group.

Chemical Reactions

These radicals formed by the decomposition of AIBN can initiate free-radical polymerizations and other radical-induced reactions. For instance, a mixture of styrene and maleic anhydride in toluene will react if heated, forming the copolymer upon addition of AIBN. Another example of a radical reaction that can be initiated by AIBN is the anti-Markovnikov hydrohalogenation of alkenes.

Benzylic Bromination

AIBN can be used as the radical initiator for Wohl–Ziegler bromination.

Reaction:

AIBN decomposes to create the 2-cyano-2-propyl radical, which then abstracts the hydrogen off of tributyltin hydride. This results in a tributyltin radical, which can be used in numerous reactions. For example, this radical could be used to remove a bromine from an alkene.

Mechanism:

Reaction:

This reaction starts out with AIBN decomposing into 2-cyano-2-propyl radicals that abstract a hydrogen from HBr to leave a bromine radical. This bromine radical adds to the alkene. In the hydrohalogenation of an alkene using AIBN, the halogen’s regioselectivity is anti-Markovnikov.

Mechanism:

Production and analogues

AIBN is produced from acetone cyanohydrin and hydrazine, then followed by oxidation:[5]

2 (CH3)2C(CN)OH + N2H4 → [(CH3)2C(CN)]2N2H2 + 2 H2O
[(CH3)2C(CN)]2N2H2 + Cl2 → [(CH3)2C(CN)]2N2 + 2 HCl

Related azo compounds behave similarly, such as 1,1′-azobis(cyclohexanecarbonitrile). Water-soluble azo initiators are also available.[6][7]

Another possible way to produce AIBN:

AIBN can also be produced by the reaction shown below.[8]

Safety

AIBN is safer to use than benzoyl peroxide (another radical initiator) because the risk of explosion is far less. However, it is still considered as an explosive compound, decomposing above 65 °C. A respirator dust mask, protective gloves and safety glasses are recommended. Pyrolysis of AIBN without a trap for the formed 2-cyanopropyl radicals results in the formation of tetramethylsuccinonitrile, which is highly toxic.

References
  1. AIBN initiator and other azo initiators. (n.d.). Retrieved from https://polymerchemistry.nouryon.com/products-applications/acrylic-polymer-initiators/aibn/
  2. 2,2′-Azobis(2-methylpropionitrile) 441090. (n.d.). Retrieved from https://www.sigmaaldrich.com/catalog/product/aldrich/441090?lang=en®ion=US
  3. Clayden, J., Greeves, N., & Warren, S. (2017). Organic chemistry. MTM.
  4. Clayden, J., Greeves, N., & Warren, S. (2017). Organic chemistry. MTM.
  5. Schirmann, Jean-Pierre; Bourdauducq, Paul. "Hydrazine". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_177.
  6. "Vazo Product Grades". www2.dupont.com.
  7. Water soluble Azo initiators
  8. Overberger, C. G., O'shaughnessy, M. T., & Shalit, H. (1949). The Preparation of Some Aliphatic Azo Nitriles and their Decomposition in Solution. Journal of the American Chemical Society, 71(8), 2661-2666. doi:10.1021/ja01176a018
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