Azobisisobutyronitrile (abbreviated AIBN) is an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
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 betwee ...
3)2C(CN)">CH3)2C(CN)sub>2N
2. 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 polymers, synthetic or semi-synthetic materials that use polymers as a main ingredient. Their Plasticity (physics), plasticity makes it possible for plastics to be Injection moulding, moulded, Extrusion, e ...
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. Thailand, Malaysia, and ...
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 ini ...
.
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 the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
gas to form two 2-cyanoprop-2-yl radicals:
:
Because azobisisobutyronitrile readily gives off free radicals, it is often used 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 ini ...
. 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, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
. 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
Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
and
maleic anhydride
Maleic anhydride is an organic compound with the formula C2H2(CO)2O. 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 poly ...
in
toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) at ...
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 some ...
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
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 tetr ...
.
AIBN and tributyltin hydride (HSnBu3) reaction
Reaction
AIBN decomposes to create the 2-cyano-2-propyl radical, which then abstracts the hydrogen off of
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 ...
. 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
:
Hydrohalogenation of alkenes
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 organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
. In the
hydrohalogenation of an alkene using AIBN, the halogen's regioselectivity is anti-Markovnikov.
:
Mechanism
:
Poly(acrylic acid) production
It's in production of
poly(acrylic acid).
Production and analogues
AIBN is produced 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 ...
and
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 toxic unless handled in solution as, for example, hydrazine ...
, then followed by oxidation:
:2 (CH
3)
2C(CN)OH + N
2H
4 →
3)2C(CN)">CH3)2C(CN)sub>2N
2H
2 + 2 H
2O
:
3)2C(CN)">CH3)2C(CN)sub>2N
2H
2 + Cl
2 →
3)2C(CN)">CH3)2C(CN)sub>2N
2 + 2 HCl
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.
Another possible way to produce AIBN
AIBN can also be produced by the reaction shown below.
[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]
:
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
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 ini ...
) 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 di nitrile. It is a colorless and odorless solid. TMSN is the byproduct from the use of some radical initiators used in polymer manufacture.
T ...
, which is highly toxic.
References
External links
*{{SIDS, name=2,2′-Azobis(2-methylpropionitrile), id =78671
Azo compounds
Radical initiators