Azobisisobutyronitrile (abbreviated AIBN) is an

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 ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

. 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 Plastics are a wide range of synthetic or semisynthetic materials composed primarily of polymers. Their defining characteristic, plasticity, allows them to be molded, extruded, or pressed into a diverse range of solid forms. This adaptab ...

and

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Types of polyisoprene ...

and as a

radical initiator In chemistry, radical initiators are substances that can produce radical species under mild conditions and promote radical reactions. These substances generally possess weak bonds—bonds that have small bond dissociation energies. Radical in ...

. As an azo initiator, radicals resulting from AIBN have multiple benefits over common

organic peroxide In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group (). If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily b ...

s. 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 Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

gas to form two 2-cyanoprop-2-yl radicals: Because azobisisobutyronitrile readily gives off free radicals, it is often used as a

. This happens at temperatures above 40 °C, but in experiments is more commonly done at temperatures between 66 °C and 72 °C.Clayden, J., Greeves, N., & Warren, S. (2017). Organic chemistry. MTM. This decomposition has a Δ''G''^‡ of 131 kJ/mol 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 Entropy is a scientific concept, most commonly associated with states of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics, where it was first recognized, to the micros ...

. 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 polymerization In polymer chemistry, radical polymerization (RP) is a method of polymerization by which a polymer forms by the successive addition of a radical to building blocks (repeat units). Radicals can be formed by a number of different mechanisms, usuall ...

s and other radical-induced reactions. For instance, a mixture of

styrene Styrene is an organic compound with the chemical formula C6H5CH=CH2. Its structure consists of a vinyl group as substituent on benzene. Styrene is a colorless, oily liquid, although aged samples can appear yellowish. The compound evaporates easi ...

and

maleic anhydride Maleic anhydride is an organic compound with the formula . It is the acid anhydride of maleic acid. It is a colorless or white solid with an acrid odor. It is produced industrially on a large scale for applications in coatings and polymers. Str ...

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

will react if heated, forming the

copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...

upon addition of AIBN. Another example of a radical reaction that can be initiated by AIBN is the anti-Markovnikov hydrohalogenation of alkenes. AIBN has also been used as the radical initiator for

Wohl–Ziegler bromination The Wohl–Ziegler reaction is a chemical reaction that involves the allylic or benzylic bromination of hydrocarbons using an ''N''-bromosuccinimide and a radical initiator. : Best yields are achieved with ''N''-bromosuccinimide in carbon tet ...

. The AIBN-derived 2-cyano-2-propyl radical abstracts the hydrogen from

tributyltin hydride Tributyltin hydride is an organotin compound with the formula (C4H9)3SnH. It is a colorless liquid that is soluble in organic solvents. The compound is used as a source of hydrogen atoms in organic synthesis. Synthesis and characterization The c ...

. The resulting tributyltin radical can be used for removal of a bromine atom. AIBN-derived radicals abstract a hydrogen from HBr to give a bromine radical, which can add to

alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

s. This type of

hydrohalogenation A hydrohalogenation reaction is the electrophilic addition of hydrogen halides like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes. : If the two carbon atoms at the double bond are linked to a different ...

of an alkene proceeds with anti-Markovnikov selectivity. : Hydrohalogenation of Alkene Reaction

Production and analogues

AIBN is produced in two steps from

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 ...

. Reaction with

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydraz ...

gives the substituted dialkylhydrazine. In the second step, the hydrazine is oxidized to the azo derivative: : : Related

azo compound Azo compounds are organic compounds bearing the functional group diazenyl (, in which R and R′ can be either aryl or alkyl groups). IUPAC defines azo compounds as: "Derivatives of diazene (diimide), , wherein both hydrogens are substituted ...

s behave similarly, such as 1,1′-azobis(cyclohexanecarbonitrile). Water-soluble azo initiators are also available.Water-soluble Azo initiators
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Safety

AIBN is safer to use than

benzoyl peroxide Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide ...

(another

) 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 Tetramethylsuccinonitrile or TMSN is an organic compound with the formula (C(CH3)2CN)2, classified as a dinitrile, and a colorless and odorless solid derived from 2,2'-azobis-isobutyronitrile, a common radical initiator in the manufacture of PVC: ...

, which is highly toxic.

References

External links

*{{SIDS, name=2,2′-Azobis(2-methylpropionitrile), id =78671 Azo compounds Radical initiators Nitriles